AOS Spine Manual book sample by AO Foundation

Volume 1 presents basic scientific and technical principles—it provides the reader with the scientific background to understand spine surgery and it teaches how to apply these surgical principles using the instrumentation necessary in a step-by-step manner with exceptional illustrations; some critical steps are explained using sequences from AOSpine teaching videos. PRINCIPLES AND TECHNIQUES (VOL 1) relates to the teaching of basic surgical knowledge and surgical techniques at AOSpine courses and acts as a foundation for the application of these principles in clinical practice.

www.aospine.org

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The Americas

Rest of World

ISBN 978-1-58890-557-4 (TPN)

ISBN 978-3-13-144481-3 (TPS)

(2-volume set)

Aebi | Arlet | Webb

Continuous systematic learning is essential for all spine surgeons endeavoring to improve their daily practice and enhance patient outcome. The mission of AOSpine is to share knowledge and expertise through accessible quality education.

AOSPINE MANUAL PRINCIPLES AND TECHNIQUES (VOL 1)

AOSPINE MANUAL—PRINCIPLES AND TECHNIQUES (VOL 1)

Max Aebi | Vincent Arlet | John K Webb

AOSPINE MANUAL PRINCIPLES AND TECHNIQUES (VOL 1)

Practical exercise video clips on DVD-ROM included

16.1.2007 17:06:53 Uhr

TABLE OF CONTENTS 1

PREFACE—AO EDUCATION AND TEACHING CONCEPT

INTRODUCTION—AO PRINCIPLES APPLIED TO THE SPINE

HISTORY OF SPINE SURGERY WITHIN AO

BIOMECHANICS OF THE SPINE THOMAS STEFFEN …………………………………………………………… Introduction ……………………………………………………………………………………………………… General biomechanics of the spinal motion segment and the spinal organ THOMAS STEFFEN ………… Biomechanics of spinal stabilization STEPHEN J FERGUSON, THOMAS STEFFEN ……………………………………

4.1 4.2

5 5.1 5.2 5.3 5.4

6 6.1 6.2 6.3 6.4 6.5 6.6 6.7

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……………

MA X AEBI ……………………………………

MA X AEBI, VINCENT ARLET, JOHN K WEBB

THOMAS SCHLICH, MA X AEBI

…………………………………… 15

29 31 33 53

BIOLOGY OF THE SPINE NORBERT BOOS ……………………………………………………………………… 71 Introduction ……………………………………………………………………………………………………… 73 Biology of the motion segment NORBERT BOOS ……………………………………………………………… 77 Aging and pathological degeneration MAURO ALINI, KEITA ITO, ANDREAS G NERLICH, NORBERT BOOS ……………… 87 Biology of the osteoporotic spine MA XIMILIAN A DAMBACHER, NORBERT BOOS ………………………………… 103 Biology of fusion with bone and bone substitutes DANTE G MARCHESI …………………………………… 117

SURGICAL ANATOMY OF THE SPINE SERGE NAZARIAN …………………………………………………… Introduction …………………………………………………………………………………………………… Upper cervical spine SERGE NAZARIAN, CYRIL SOLARI …………………………………………………………… Lower cervical spine SERGE NAZARIAN, CYRIL SOLARI …………………………………………………………… Cervicothoracic junction SERGE NAZARIAN, CYRIL SOLARI ……………………………………………………… Thoracic spine SERGE NAZARIAN, CYRIL SOLARI …………………………………………………………………… Thoracolumbar junction SERGE NAZARIAN, CYRIL SOLARI ……………………………………………………… Lumbar spine and lumbosacral junction SERGE NAZARIAN, CYRIL SOLARI …………………………………… Sacrum SERGE NAZARIAN, CYRIL SOLARI ……………………………………………………………………………

129 131 135 147 161 173 193 205 235

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Table of contents

7 7.1 7.2 7.2.1 7.2.2 7.2.3 7.2.4 7.2.5 7.2.6 7.3 7.3.1 7.3.2

SPINAL INSTRUMENTATION VINCENT ARLET ……………………………………………………………… 241 Introduction …………………………………………………………………………………………………… 243 Modularity of spinal instruments (systems) MA X AEBI …………………………………………………… 247 Cervical spine Modularity and evolution of instrumentation for the cervical spine MICHAEL E JANSSEN, JASON C DATTA, VINCENT ARLET ……………………………………………………………………… Upper cervical spine VINCENT ARLET, JASON C DATTA …………………………………………………………… Middle and lower cervical spine JASON C DATTA, MICHAEL E JANSSEN ………………………………………… Craniocervical junction MICHAEL E JANSSEN …………………………………………………………………… Cervicothoracic junction BRIAN JC FREEMAN, FRANK KANDZIORA ………………………………………………… Cervical laminoplasty CHRISTOPHER I SHAFFREY …………………………………………………………………

253 265 289 305 315 329

7.3.3 7.3.4 7.3.5

Thoracolumbar and sacropelvic spine Modularity of the universal spine system CHRISTOPHER CAIN ……………………………………………… Stabilization and reconstruction techniques for the thoracolumbar spine (fractures, tumors, degenerative) DANTE G MARCHESI …………………………… Universal spinal instrumentation for deformity CHRISTOPHER CAIN ……………………………………… Instrumentation for the degenerative thoracolumbar spine DANTE G MARCHESI ……………………… Fixation of the sacrum and pelvis TRAVIS HUNT, VINCENT ARLET ………………………………………………

357 391 423 457

7.4 7.4.1 7.4.2 7.4.3 7.4.4 7.4.5

Special techniques and instrumentation Concept of MISS/LISS MA X AEBI ……………………………………………………………………………… Bone harvesting tool MA X AEBI ……………………………………………………………………………… Vertebroplasty PAUL HEINI ……………………………………………………………………………………… Fixation technology in osteoporosis PAUL HEINI …………………………………………………………… Spondylolysis, spondylolisthesis—reduction and stabilization VINCENT ARLET, MARTIN KRISMER …………

467 485 491 507 519

7.5 7.5.1 7.5.2

Motion-preserving technology Arthroplasty in cervical spine surgery Arthroplasty in lumbar spine surgery

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…………………………………… 543 …………………………………………………… 555

JOCHEN MEISSNER, MICHAEL OGON H MICHAEL MAYER

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COMPUTER-ASSISTED SURGERY

ANESTHESIA FOR SPINE SURGERY

FRANK LANGLOTZ, LUTZ-PETER NOLTE

JUAN FRANCISCO ASENJO

……………………………………… 571

……………………………………………… 589

GLOSSARY ……………………………………………………………………………………………………………… 617 INDEX

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TABLE OF CONTENTS 1

SPINAL TRAUMA MICHAEL BLAUTH ……………………………………………………………………………… Introduction ………………………………………………………………………………………………………

1.1 1.1.1 1.1.2 1.1.3 1.1.4

Classification Classification of injuries of the upper cervical spine BERNARD JEANNERET ………………………………… 9 Classification of injuries of the subaxial cervical spine MICHAEL BLAUTH, ANTON KATHREIN, GEORG MAIR, RENÉ SCHMID, MA X REINHOLD, MICHAEL RIEGER ………………………………………………………………… 21 Classification of injuries of the thoracic and lumbar spine MA X AEBI, FRIEDRICH P MAGERL ………………… 41 Classification of fractures of the sacrum TIM POHLEMANN, UTA LANGE, ULF CULEMANN ………………………… 77

1.2 1.2.1 1.2.2 1.2.3

Cervical spinal trauma Upper cervical spine STEFAN SCHAEREN, ALEXIS FALICOV, CHARLES FISHER, MARCEL DVORAK …………………………… 85 Middle and lower cervical spine BARTOLOMÉ MARRÉ, MA X AEBI ……………………………………………… 117 Cervicothoracic junction HELTON DEFINO, MA X AEBI …………………………………………………………… 137

1.3 1.3.1 1.3.2

Thoracic and lumbar spinal trauma Thoracic spine LUIZ R VIALLE, EMILIANO VIALLE …………………………………………………………………… 149 Thoracolumbar and lumbar spine BARTOLOMÉ MARRÉ ……………………………………………………… 165

1.4

Sacral spinal fractures

SPINAL TUMORS DANTE MARCHESI …………………………………………………………………………… 209 Introduction …………………………………………………………………………………………………… 211

2.1 2.2

Primary spinal tumors CARLOS A BAGLEY, ZIYA L GOKASLAN ……………………………………………………… 215 Secondary spinal tumors (metastases) DANTE G MARCHESI, ZDENEK KLEZL …………………………………… 235

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1 3

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INFECTIONS OF THE SPINE GERMÁN OCHOA………………………………………………………………… 257 Introduction …………………………………………………………………………………………………… 259

3.1 3.2 3.3

Tuberculosis GERMÁN OCHOA …………………………………………………………………………………… 263 Bacterial and other nonspecific infections NORBERT BOOS ……………………………………………… 279 Fungal infections GERMÁN OCHOA ……………………………………………………………………………… 291

INFLAMMATORY PROCESSES MAX AEBI …………………………………………………………………… 301 Introduction …………………………………………………………………………………………………… 303

4.1 4.2

Rheumatoid arthritis and other inflammatory conditions DIETER GROB ……………………………… 305 Ankylosing spondylitis JOHN K WEBB ………………………………………………………………………… 319

DEFORMITIES OF THE SPINE VINCENT ARLET ……………………………………………………………… 329 Introduction …………………………………………………………………………………………………… 331

5.1 5.1.1 5.1.1.1 5.1.1.2 5.1.1.3 5.1.2 5.1.3

Scoliosis Idiopathic scoliosis Early onset idiopathic scoliosis JOHN K WEBB, VINCENT ARLET ………………………………………………… 335 Late onset idiopathic scoliosis JOHN K WEBB ………………………………………………………………… 345 Adult idiopathic scoliosis MA X AEBI ………………………………………………………………………… 367 Congenital scoliosis VINCENT ARLET …………………………………………………………………………… 383 Neuromuscular scoliosis JEAN OUELLET, VINCENT ARLET ……………………………………………………………411

5.2 5.2.1 5.2.2

Kyphosis Scheuermann disease DIETRICH SCHLENZKA …………………………………………………………………… 437 Congenital kyphosis and kyphoscoliosis VINCENT ARLET, JEAN OUELLET …………………………………… 455

5.3

Spinal deformities due to bone dysplasia, bone dystrophies, and metabolic bone disease VINCENT ARLET ………………………………………………………………… 469 Posttraumatic deformity of the spine RUDY REINDL, VINCENT ARLET ………………………………………… 495

5.4

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SPONDYLOLYSIS, SPONDYLOLISTHESIS, AND SPONDYLOPTOSIS RÜDIGER KRAUSPE ……………… 509 Introduction …………………………………………………………………………………………………… 511

6.1 6.2 6.3

Spondylolysis KONRAD SELLER, RÜDIGER KRAUSPE ………………………………………………………………… 516 Spondylolisthesis CLAUDIO LAMARTINA ………………………………………………………………………… 531 Spondyloptosis KONRAD SELLER, JOHN K WEBB, ALEXANDER WILD …………………………………………………… 545

DEGENERATIVE SPINAL DISEASES PAUL W PAVLOV ……………………………………………………… 555 Introduction …………………………………………………………………………………………………… 557

7.1 7.1.1 7.1.2 7.1.3 7.1.4 7.1.5 7.1.6

Lumbar spine Black disc syndrome MAARTEN SPRUIT ………………………………………………………………………… Disc herniation ANDREAS KRÖDEL ……………………………………………………………………………… Lumbar degenerative spondylolisthesis JASON C DATTA, PAUL W PAVLOV …………………………………… Acquired lumbar spinal stenosis MARINUS DE KLEUVER, ERIC C KRAANEVELD …………………………………… Degenerative scoliosis MA X AEBI …………………………………………………………………………… Degenerative disease of the lumbar spine—treatment by motion-sparing technology MICHAEL E JANSSEN, JASON C DATTA …………………………………………………

7.2 7.2.1 7.2.2 7.2.3 7.2.4

Cervical spine Cervical spondylosis and neck pain JASON C DATTA, PAUL W PAVLOV ………………………………………… Radiculopathy PAUL W PAVLOV ………………………………………………………………………………… Myelopathy PAUL W PAVLOV …………………………………………………………………………………… Degenerative disease of the cervical spine —treatment by disc arthroplasty MICHAEL E JANSSEN, JASON C DATTA …………………………………………………………

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561 569 579 587 599 617 627 635 645 655

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METABOLIC BONE DISEASE OF THE SPINE—OSTEOPOROSIS

PAUL HEINI ……………………………

663

COMPLICATIONS IN SPINE SURGERY JOHN K O’DOWD …………………………………………………… 683 Introduction …………………………………………………………………………………………………… 685

9.1 9.2 9.3 9.4 9.5 9.6 9.7

Management of perioperative spinal cord injury HENRY AHN, MICHAEL G FEHLINGS ……………………… Management of incidental durotomies and CSF leaks RANDALL M CHESNUT …………………………… Management of early and late infections JAMES WILSON-MCDONALD, IONA COLLINS ………………………… Pseudarthrosis JOHN K O’DOWD, JAN SIMCIK ……………………………………………………………………… Early and late implant revision VINCENT ARLET ……………………………………………………………… Crankshaft phenomenon FRANCIS H SHEN, VINCENT ARLET ……………………………………………………… Complications of lumbar total disc arthroplasty MARINUS DE KLEUVER, PAUL M ARNOLD, MICHAEL E JANSSEN …

DOCUMENTATION, EVALUATION, AND OUTCOME IN SPINE SURGERY MAX AEBI ………………… 751 Introduction …………………………………………………………………………………………………… 753

10.1 10.2 10.3

Outcome questionnaires and tools MATHIAS HAEFELI, NORBERT BOOS ………………………………………… 755 AOSpine international registry CHRISTOPH RÖDER, TONY AMBROSE, MA X AEBI …………………………………… 769 Controlled studies ANDRÉ BUSATO …………………………………………………………………………… 779

687 695 705 715 723 733 739

GLOSSARY ……………………………………………………………………………………………………………… 787 INDEX

…………………………………………………………………………………………………………………… 812

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573

Frank Langlotz, Lutz-Peter Nolte

COMPUTER-ASSISTED SURGERY

INTRODUCTION

The term computer-assisted surgery (CAS) or computer-aided surgery (CAS) summarizes approaches that aim to improve visibility of the surgical field and to increase geometrical accuracy by means of robotic devices or so-called navigation systems when carrying out surgical procedures. These aims are achieved by virtually linking the operated bony anatomy with a radiological representation, such as a CT scan or a fluoroscopic image. The principles of both approaches were fi rst elaborated by neurosurgeons. While surgical robots were not widely used in spine surgery, the technology of navigation has been successfully applied to several types of intervention since the mid 1990s, eg, neurosurgical stereotaxic devices were used on the cervical spine. However, their frame-based approach was impractical for exploration of the lower levels of the vertebral column.

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Today, approximately eight to ten companies offer surgical navigation systems for various types of intervention along the spine that involve the placement of screws. Although their products differ in expandability toward other orthopedic applications as well as in ergonomic and technical details, there are equivalent underlying principles that enable surgical navigation. The purpose of this chapter is to give an overview of these principles; it is not intended as a replacement for the user manuals and instructional material provided with each navigation system. In addition, potential future trends in the area of computer-assisted spine surgery are elucidated within the most recent research results that have emerged from the integration of novel enabling technologies into the field of CAS.

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574

PRINCIPLES OF SURGICAL NAVIGATION

The idea of surgical navigation is to replay on a computer monitor in real time the surgical action performed with different instruments. The display presents computer-generated models of surgical instruments in relation to radiological images of the operated anatomy ( Fig 8-1 )1. This concept is comparable to a GPS satellite navigation system installed in a car that constantly displays the car’s location on a street map. In order to generate such feedback, three tasks have to be fulfi lled by a spinal navigation system: • An image or a set of images of the spine has to be provided serving as the “map” of the patient. • The spatial location of all important instruments has to be measured constantly in three dimensions and in relation to the operated bone. • The relative instrument position has to be transferred into image space to enable visualization at the correct location.

2.1

IMAGE OF THE SPINE

Theoretically, any kind of patient-specific image could serve as the basis for surgical navigation. However, the need to display bone clearly and to process the image digitally by a computer currently limits surgical navigation to the use of preoperative CT scans and intraoperative fluoroscopic images. Preoperative imaging allows for detailed planning of the intended intervention and may be advisable in difficult cases in which high precision and the additional third dimension are required. Moreover, patients who are scheduled for spine surgery have often had one or even several diagnostic CT scans already. Therefore, a 3-D image of the spine may be available to be used for intraoperative navigation.

Fig 8-1 Several sections through the CT data along and parallel to the instrument’s axis give a detailed insight into the pedicular area. A 3-D view shows an overview of the scene.

The screen shots provided in this chapter were taken from the VectorVision applications (BrainLAB, Heimstetten, Germany). Other companies’ products provide comparable features.

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However, CT data always represent the preoperative situation and are thus not able to reflect intraoperative changes to the bony geometry of an individual vertebra that may occur in cases of fracture reduction or tumor removal. These changes can be identified by intraoperative fluoroscopic images. This advantage, together with the obsoleteness of manual registration (see below), often outweigh the disadvantage of having neither a preoperative dataset nor any detailed computer-assisted planning prior to the intervention. Another disadvantage of fluoroscopy-based navigation (the missing third dimension in conventional 2-D projective fluoroscopic images) has recently been overcome by the introduction of a new 3-D fluoroscope (see below). So far, MRI datasets are infrequently used as a navigational image in computer-assisted spine surgery due to the inherent geometric distortions together with the difficulty in creating 3-D representations. Research groups have looked into the fusion of preoperative CT and MRI scans to enable the simultaneous use of information from both modalities during CAS application. Again, remaining questions and difficulties have hindered wide-spread usage of these approaches so far.

2.2

MEASURING INSTRUMENT POSITION

To determine the position and orientation of surgical instruments in relation to a vertebra requires the contactless tracking of both bone and tool. Surgical navigation systems follow the principle of rigid bodies, ie, vertebra and instruments are assumed to be nondeformable and of known shape. The tracking of such an object can then be simplified by the tracking of at least three noncollinear points that are rigidly attached to it. This theoretical principle is realized by means

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of infrared light emitting diodes (IREDs) or infrared light reflecting markers that are observed by a camera system. IREDs need external power to actively emit light, most active navigation systems therefore require instruments to be connected via cables. In contrast, passive markers reflect light that is sent out from an infrared light source within the tracking camera. In both cases, direct line-of-sight between the camera system and the observed IREDs/markers is required. Another principle of tracking is based on electromagnetic sensors. This technology does not call for direct line-of-sight, ie, objects in between the instrument and the tracker do not interfere with the tracking process. Spinal navigation based on electromagnetic tracking was not successful in the past due to a high degree of inaccuracy [1]. However, a new system initially developed for endonasal navigation has recently been adapted for spinal applications [2]. To date, there does not appear to be any data available about the performance of this product. Fig 8-2 A DRB allows the navigation system to track the vertebra that the surgeon is operating on. This DRB is usually attached to the spinous process with the help of a clamping mechanism. It is essential that it remains rigidly fixed during the entire use of the CAS system on that vertebra.

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576

2.3

DISPLAYING INSTRUMENT POSITION

In order to display the measured instrument position at its correct location within the CT scan or fluoroscopic image, it is also necessary to track the location of the operated vertebra. For this purpose, a so-called dynamic reference base (DRB) [3] is attached to the spinous process ( Fig 8-2 ). A clamping mechanism secured with a screw allows for a stable, nondestructive fi xation. Technically, the DRB establishes a local coordinate system that enables measuring of the instrument’s position with respect to the operated bone. In order to provide navigational feedback, the acquired coordinates need to be transferred into the image space. The necessary transformation matrix is determined differently for CT-based as compared to fluoroscopy-based spinal navigation, and the applied methods will be described in the associated sections. Once the position information of the tracked instrument is known in relation to the image data, there are a number of alternative ways of how it can be most efficiently presented to the surgeon. The example shown in Fig 8-3 uses a set of multiplanar CT reconstructions at different magnification levels. In each of the six 2-D windows, the current location of a digitizing pointer is displayed and updated in real time.

Fig 8-3 Several sections through the CT data intersecting with the pointer’s tip allow for the qualitative assessment of tracking accuracy. With the tracked pointer placed in arbitary locations on the vertebra, the surgeon can verify that the corresponding location presented by the navigation system is sufficiently precise.

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Fig 8-4 Alternatively, the navigation system can present the planned screw trajectory (red) and the current orientation of the instrument (green). The window in the top right corner displays an abstract view along the trajectory providing a tunnel-like interface.

Fig 8-5 During fluoroscopy-based pedicle screw placement, the image of a pedicle probe (green) and its predicted direction (red) are displayed as overlays onto two fluoroscopic images. One screw inserted on the contralateral side and a DRB are visible as artifacts in the images.

An alternative representation of tracking data is given in Fig 8-4, which requires the performance of a preoperative planning of the optimal pedicle screw position. This intended implant location is displayed as a red object while the instrument’s current location and orientation are presented by a green line. In order to fulfi ll the plan, the tool has to be aligned with the desired location of the pedicle screw. An additional autopilot of circles helps to further improve proper alignment.

For fluoroscopy-based spinal navigation, the surgeon or radiographer may significantly influence the quality of navigational feedback by the acquisition of suitable images. One or more images are taken intraoperatively and are copied onto the navigation system. The tracked instrument is then simultaneously projected into each of these views creating the impression that several fluoroscopic images have been taken in constant mode at the same time ( Fig 8-5 )

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578

CT-BASED SPINAL NAVIGATION

CT scans still play an important role in the preoperative diagnosis of spinal diseases. Since the image data precisely represent the 3-D topology of the spine and are usually available in a digital format, CT scans were the basis of the fi rst spinal navigation systems to be developed in the mid 1990s [1, 3–7]. Nowadays, CT-based navigation is recommended for more challenging cases involving the placement of screws into the cervical and upper thoracic spine or in previously operated patients with difficult anatomical situations. The application of a CT-based navigation system involves both preoperative and intraoperative steps.

3.1

PREOPERATIVE STEPS

The digital CT data of the patient are loaded into the navigation computer. Manufacturers usually prescribe a special scanning protocol that best suits their systems. Depending on the specific set-up, the data transfer is accomplished through the hospitals’ internal computer network or by means of a data cartridge such as a CD-ROM. Visualization of the image data on the computer monitor allows for a detailed inspection of the case in question. A number of mandatory and optional planning steps are then carried out. For better visualization, a 3-D model of the bony structures can be generated from the scan. This is usually done semi or fully automatically. For the registration of the patient with the CT scan using paired-points matching (see below), anatomical landmarks are marked ( Fig 8-6 ). Their counterparts need to be identified as precisely as possible in situ. Therefore, it is recommended that points which are prominent and easily accessible during surgery are selected. If an intraoperative surface matching is intended, additional data may need to be prepared. Optionally, the position and axis of one or more screws can be defi ned ( Fig 8-7 ). These trajectories serve as the intraoperative goals to be reached during navigation. As a last step, all planning data are stored and transferred onto the intraoperative navigation computer if this is not the machine on which the planning was originally made.

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Fig 8-6 For CT-based navigation, anatomical landmarks are defined preoperatively to enable intraoperative paired-points registration. Here, a location on the right facet joint of L3 is marked with the crosshair.

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Fig 8-7 The optimal trajectory for the placement of a screw into this left L4 pedicle has been marked with a contour of the implant. This information is presented to the surgeon during intraoperative navigation (Fig 8-4) in order to allow precise screw insertion according to the plan.

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3.2

INTRAOPERATIVE STEPS

The application of navigation technology does not usually require any specific patient preparation. However, it must be ensured that there is space in the operating room for the CAS system and that the tracking camera is placed at an optimal distance (1.5–2.5 m) from, and with a free line-of-sight onto, the surgical field ( Fig 8-8 ). During the usual approach to the spine, the surgical staff prepare the system, the navigational tools, and perform the required checks of the hardware and software. As soon as the vertebra to be instrumented is exposed, the DRB is affi xed to the spinous process (see Fig 8-2 ). Special care must be taken to achieve a stable fi xation as this is a prerequisite for accurate navigation. In order to allow for instrument visualization, a registration, also known as “matching”, is carried out. Two complementary techniques are commonly used for this procedure. For a paired-points matching the preoperatively defined landmarks need to be identified on the patient’s anatomy. The navigation system presents all landmarks one after another and prompts the surgeon to mark the corresponding spots with a pointer ( Fig 8-9 ). Depending on the navigation system used, the capture of the associated 3-D data is initiated by means of a foot switch by pivoting the pointer around its tip or by triggering a separate button on the instrument. A total of four to six points are recorded. Due to unavoidable intervertebral motion, the performance of a pervertebral registration acquiring landmarks on one spinal level only is highly recommended. For multilevel instrumentation, it is therefore necessary to move the DRB and redo the registration after the placement of all screws at one level [8].

Fig 8-8 For navigated spinal surgery, the optical camera needs to view the surgical field from a distance of approximately 2 m. In this example, it is placed at the foot-end of the patient. The computer monitor providing navigational feedback to the surgeon is placed on the opposite side of the operating table.

Fig 8-9 Using a pointer, the corresponding locations to the preoperatively defined landmarks (Fig 8-6) are recorded. During this procedure, the pointer and the DRB need to be visible to the tracking camera.

Once all landmarks are acquired, the software calculates the aforementioned transformation matrix and prompts for verification of this result. In tracking mode, the surgeon can

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then use any navigated instrument to touch several locations on the vertebra to be instrumented and verify visually that the associated point in the CT data is displayed with sufficient accuracy (see Fig 8-3 ). In order to improve an insufficiently accurate paired-points matching, a so-called surface matching can be carried out. For this purpose (depending on the navigation system in use), 12 or more additional points arbitrarily distributed on the accessible bony surface are digitized (see Fig 8-3 ). One should note that it is not required to defi ne their counterparts in the CT scan preoperatively. Using this additional data, the software may refine the result of the paired-points matching which usually provides improved accuracy. Subsequently, the screws can be placed under navigational guidance (see Fig 8-4 ). Most navigation systems allow the tracking of all instruments used for screw canal preparation (pedicle awl, pedicle probe, drill bit, drill sleeve) and screw insertion (screwdriver). Usually the instruments need to be calibrated before they can be used, or their proper calibration needs to be verified. Recalibration is required for instruments that come in a nonconstant shape (eg, drill with mounted drill bit or screwdriver with screw attached). For calibration or verification, the instrument is placed into a calibration unit and both objects are presented to the tracking camera. Since the instrument takes a predefined position with respect to the calibration unit during this procedure, the location of its tip and axis can be checked. When the calibrated instruments are then used on the patient, the feedback provided on the navigation screen enables the surgeon to accurately realize the preoperatively planned optimal location, orientation, and insertion depth.

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3.3

OTHER FIELDS OF CT-BASED SPINAL NAVIGATION

In addition to the described open approach to posterior pedicle screw placement at the thoracic, lumbar, and sacral levels, additional fields of application of CT-based spinal CAS have been explored. Although some of these techniques are only applied by a very small number of users, they will be discussed briefly. An alternative technique to posterior instrumentation using transpedicular screws is the implantation of parapedicular screws. Since the exact positioning of this type of screw in the thoracic spine is difficult, the application of a CAS system has been evaluated during an in vitro study [9]. The authors concluded that safe and reliable insertion of parapedicular screws could be achieved. For the cervical spine, pedicle screw placement is less frequent. Nevertheless, navigational techniques can help increase accuracy during this type of operation. They are also useful when inserting C1/2 transarticular screws. The enhanced precision during this procedure was demonstrated during in vitro experiments as well as in a clinical study, where a reduction of the risk of screw misplacement could be demonstrated [10]. Not only does CAS have its field of application in the treatment of degenerative diseases, it can also be applied to cases with cervical fractures. Arand et al used a CT-based system on two patients, but recommended this procedure to experienced surgeons only [11]. Another group presented the case of severe cervical fracture dislocation in which a combined anterior and posterior instrumentation was carried out with the support of a navigation system [12]. Anterior approaches to the spine can also be supported by a CAS system [13]. However, the need to attach a DRB to the operated vertebra makes it necessary to have an additional small skin incision from the posterior to expose the spinous process.

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FLUOROSCOPY-BASED SPINAL NAVIGATION

Surgical navigation based on intraoperatively acquired fluoroscopic images has been introduced as a complementary technique to CT-based navigation in cases where no preoperative CT scan is available, or the additional preoperative and intraoperative efforts cannot be justified [14–16]. Today, fluoroscopy-based spinal navigation is recommended for “standard” cases involving screw placement into the lower thoracic or lumbosacral spine in the presence of normal morphology. Since the images used for navigation feedback are acquired intraoperatively, no preoperative computer-assisted planning is possible.

Fig 8-10 The image intensifier unit of this fluoroscope is equipped for navigation. Reflective markers (bright spots) allow the tracking camera to assess the fluoroscope’s spatial position during image acquisition and thus enable the navigation system to determine the 3-D location of the recorded image and its associated projection parameters.

4.1

INTRAOPERATIVE STEPS

For the intraoperative usage of fluoroscopy-based navigation, a standard fluoroscope needs to be specially equipped. The device must be integrated into the tracking camera’s coordinate space and equipped with IREDs or marker spheres. They are attached to the image intensifier unit of the C-arm ( Fig 8-10 ) which needs to be visible to the camera system during image acquisition. A complex calibration procedure is carried out during the installation of the device for navigation usage. It involves the attachment of a marker plate to the image intensifier unit. This plate carries a cross or sphere pattern that appears as an overlaid grid in each acquired image and is used to dewarp the images [15]. As an alternative to the precalibration of one marker plate during installation, a double-plate construct consisting of a set of two parallel plates is used by some manufacturers. This approach allows for ad hoc calibration of each acquired image during intraoperative usage of the C-arm [17]. As per CT-based spinal navigation, neither patient positioning nor surgical approach needs to be altered, and a DRB has to be affixed to the spinous process after exposure. Then, one or more single fluoroscopic images of the operated vertebra are taken and copied onto the navigation system through a network connection. For pedicle screw placement, three projections are recommended per screw: • Lateromedial view • Anteroposterior view • So-called “bull’s eye view” This shows the pedicle to be instrumented as a more or less circular projection (see Fig 8-5 ). Depending on the level of the spine to be operated, the “bull’s eye view” is acquired by

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tilting the fluoroscope between 0° and 30° laterally and slightly into a cranial or caudal direction as compared to a strict AP view. During the acquisition of each of the images, the camera system must observe the markers on the fluoroscope and on the DRB. Due to the known calibration parameters of the C-arm, it is then possible to determine the projection model for that particular image acquisition. Mathematically, this information links the coordinate spaces of the DRB and the C-arm image and is equivalent to the result of a manual registration during CT-based navigation. Consequently, fluoroscopic navigation feedback is possible immediately after transferring the images onto the navigation system without any extra registration or verification. Another advantage of fluoroscopy-based navigation is the fact that the projections are copied onto the navigation computer. Not only does this procedure allow removal of the C-arm from the surgical field after image acquisition, but it also permits visualization of the instruments in several projections simultaneously (see Fig 8-5 ).

4.2

generation and transfer to the navigation system. Although the use of this fluoroscope is not limited to the spinal area, several authors have already presented very promising results with it [18].

4.3

OTHER FIELDS OF FLUOROSCOPY-BASED SPINAL NAVIGATION

As per CT-based approaches, fluoroscopy-based systems have been employed by some surgeons for computer-aided support during other types of intervention. Their generally positive experience clearly demonstrates the broad applicability of this technology. Foley described a combined mechanical aiming and navigation system for the percutaneous insertion of pedicle screws and rods. The approach was based on fluoroscopic navigation and even permitted two-level fusion through stab incisions [19]. Fluoroscopy-based navigation can also be supportive in procedures that are conventionally performed in a minimally invasive manner, and an associated application during intradiscal electrothermal therapy was demonstrated [20].

3-D FLUOROSCOPY-BASED NAVIGATION

A new device for intraoperative imaging has been introduced recently. This motorized isocentric fluoroscope performs an automated 190° rotation during which it acquires a series of 100 2-D images. From this data, a 3-D dataset that is similar to a CT scan is reconstructed intraoperatively. Since the dataset is generated with a calibrated and tracked imaging device, there is no need for manual registration either, and navigation within the images is possible immediately after image

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Rose et al demonstrated that this technology can be of advantage during anterior approaches to spinal fractures [21].

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ALTERNATIVE METHODS AND FUTURE TRENDS

Although both techniques described are already well established in many clinics all over the world, there remains room for technical improvements and new fields of application. A number of researchers and manufacturers have presented solutions, or suggested ideas, for addressing some of the existing disadvantages of today’s navigation systems. Two of these aspects are presented here.

5.1

INSTRUMENT TRACKING

Today, surgical instruments are tracked actively or passively during spinal interventions. The active, IRED-based approach allows for smaller instrument design but is only possible with potentially cumbersome cables connecting the instruments with the tracking system. In contrast, passive tracking with reflecting spheres can contribute significantly to the per-case costs, because the spheres should be considered as disposable. Moreover, tracking accuracy can be adversely influenced, eg, by blood splashes on the markers. However, there is one navigation system available that comes with active cableless instruments. These are powered by a battery, thus combining the advantages of passive and active optoelectronic tracking while at the same time overcoming the individual disadvantage of either of the two technologies. A drawback is that comparable solutions will also become available for spine surgery—today’s batteries make the marker probes attached to the instruments considerably heavier than those using conventional tracking technology.

5.2

REGISTRATION ALTERNATIVES

Currently the intraoperative registration of preoperative images is still a crucial step during CAS procedures. On the one hand, the overall accuracy of the navigational feedback largely depends on a precise registration, on the other hand, the trend toward less or even minimally invasive interventions makes the application of “classical” matching strategies as described above more and more difficult, because the direct digitization of bony landmarks requires direct and thus invasive access to the bony surface. A number of alternative methods have been proposed that aim at overcoming this problem. Ultrasound is commonly accepted to be a method for acquiring tissue data noninvasively. A-mode (amplitude mode) ultrasound has been suggested as a “virtual pointer” for the acquisition of single points, which could then serve as input to the established registration algorithms. Although this approach appears to be straightforward in theory, it is lacking practicability. For the ultrasound probe to receive a strong and defi ned echo, it must be oriented vertically to the analyzed surface. For spinal application, only small areas on the transverse process, the articular process, and the spinous process are available for digitization, as a result, positioning and orienting the probe is difficult. B-mode (brightness mode) ultrasound in contrast is easier to handle because it scans a fan-shaped area rather than a single axis. From a technical standpoint, the resulting 2-D images are noisy, and the automated detection of bone contours is a challenging image processing task. Consequently, only experimental results are available for the application of this technique to anatomical areas other than the spine.

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A further alternative to overcome the registration problem is the fusion of preoperative and intraoperative imaging. Not only does the use of fluoroscopic images acquired with a calibrated fluoroscope allow for direct navigation as outlined above, the images can also be analyzed to identify the visualized bony topology and this information can be used for registration with a preoperative CT scan. As for B-mode ultrasound registration, automating the bone contour detection in a reliable way is difficult. Although one manufacturer already offers this feature for spine surgery, the method does not seem to be applicable in every case [22]. More experience is definitely required to better outline the proper field of application for this technique.

DISCUSSION

Computer-assisted, image-based spinal navigation is currently establishing itself in a large number of clinical centers around the world. Some 10 years after its experimental introduction, it could become the gold standard application; especially since its potential to improve the accuracy of pedicle screw placement and reduce the probability of misplacement has been proved in a number of studies [23–25]. Some authors pointed out that in particular the increased visual perception in combination with the tactile feedback provides an ideal situation compared to conventional surgery. However, a number of drawbacks still exist that are related to the usage of a CAS system during spine surgery. For CT-based navigation additional steps are required both preoperatively and intraoperatively, although it has been shown that there is no statistically significant prolongation of the operation time [24]. The most crucial step of spinal navigation using CT remains the need to register the CT scan with the patient. This step is error prone, thus requiring a certain level of experience and discipline, and cannot be done in a less invasive manner. Alternatives that involve intraoperative imaging to make direct digitization obsolete have not reached a sufficient level of perfection yet. As a consequence, minimally invasive computer-assisted spine surgery based on preoperative CT scans will remain a goal for the near future. Fluoroscopy-based navigation techniques do not rely upon the need for intraoperative registration. As some authors have suggested, this makes them a promising candidate for the development of less invasive approaches, although

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navigation is provided within 2-D projective images only, when standard fluoroscopes are used. Especially the missing axial view into the pedicle is a clear disadvantage. The recently introduced 3-D fluoroscope appears to have the potential to revolutionize computer-assisted spine surgery by combining intraoperative registration-free image acquisition with 3-D navigation feedback. In any case, referencing of the operated vertebra using a DRB remains a requirement [8] and no ideas currently evaluated might lead to a minimally or even noninvasive referencing method in the future. Moreover, today’s commonly applied technique of clamping a DRB to the spinous process has its limitations after laminectomies, fractures of the spinous process, or in the presence of poor bone quality. There is no general rule for how to deal with these situations. It is the operating surgeon’s responsibility to decide how to proceed in such a case; it may even become necessary to complete the intervention without navigational support.

BIBLIOGRAPHY

Amiot LP, Labelle H, DeGuise JA, et al (1995) Computer-assisted pedicle screw fixation. A feasibility study. Spine; 20(10):1208–1212. 2. Internet: http://www.gehealthcare.com/rad/ savi/nav/instatrak_spine_home.html 3. Nolte LP, Visarius H, Langlotz F, et al (1996) Computer assisted spine surgery—a generalized concept and early clinical experience. J Int Soc Comput Aided Surg; 3:1–6. 4. Foley KT, Smith MM (1996) Image-guided spine surgery. Neurosurg Clin N Am; 7:171–186. 5. Glossop ND, Hu RW, Randle JA (1996) Computer-aided pedicle screw placement using frameless stereotaxis. Spine; 21(17):2026–2034. 6. Kalfas IH, Kormos DW, Murphy MA, et al (1995) Application of frameless stereotaxy to pedicle screw fi xation of the spine. J Neurosurg; 83(4):641–647. 7. Merloz P, Tonetti J, Pittet L, et al (1998) Pedicle screw placement using image guided techniques. Clin Orthop; (354):39–48. 8. Glossop ND, Hu RW (1997) Effects of tracking adjacent vertebral bodies during image guided pedicle screw surgery. Troccaz J, Grimson E, Mösges R (eds), CVRMed-MRCAS’97. Berlin Heidelberg: Springer-Verlag, 531–540. 9. Kothe R, Strauss JM, Deuretzbacher G, et al (2001) Computer navigation of parapedicular screw fi xation in the thoracic spine: a cadaver study. Spine; 26(21):E496–501. 10. Weidner A, Wähler M, Chiu ST, et al (2000) Modifi cation of C1-C2 transarticular screw fi xation by image-guided surgery. Spine; 25(20):2668–2673. 11. Arand M, Hartwig E, Kinzl L, et al (2001) Spinal navigation in cervical fractures—a preliminary clinical study on Judetosteosynthesis of the axis. Comput Aided Surg; 6(3):170–175. 12. Mizuno J, Nakagawa H, Watabe T (2001) Combined anterior and posterior instrumentation in severe fracture-dislocation of the lower cervical spine with help of navigation: a case report. J Clin Neurosci; 8(5):446–450.

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13. Ohmori K, Kawaguchi Y, Kanamori M, et al (2001) Image-guided anterior thoracolumbar corpectomy: a report of three cases. Spine; 26(10):1197–1201. 14. Foley KT, Simon DA, Rampersaud YR (2001) Virtual fl uoroscopy: computer-assisted fl uoroscopic navigation. Spine; 26(4):347–351. 15. Hofstetter R, Slomczykowski M, Bourquin Y, et al (1997) Fluoroscopy based surgical navigation: concept and clinical applications.

Lemke HU, Vannier MW, Inamura K (eds) Computer Assisted Radiology and Surgery. Amsterdam: Elsevier Science, 956–560. 16. Nolte LP, Slomczykowski MA, Berlemann U, et al (2000) A new approach to computeraided spine surgery: fl uoroscopy-based surgical navigation. Eur Spine J; 9(Suppl 1): S78–88. 17. Langlotz F, Nolte LP (2003) CAOS: from theory to the operating room. Techniques in Orthopaedics; 18:140–148. 18. Grützner PA, Wälti H, Vock B, et al (2003) Inherent spinal navigation using fl uoro-CT technology. Langlotz F, Davies BL, Bauer

22. Verheyden AP, Glasmacher S, Hölzl A, et al (2003) First experiences with CT-fl uoromatching navigation of transoral C1 instrumentation in displaced atlas fractures using the ENT headset. Langlotz F, Davies BL,

Bauer A (eds) Computer Assisted Orthopaedic Surgery. Darmstadt: Steinkopff, 386–387. 23. Amiot LP, Lang K, Putzier M, et al (2000) Comparative results between conventional and computer-assisted pedicle screw installation in the thoracic, lumbar, and sacral spine. Spine; 25(5):606–614. 24. Laine T, Lund T, Ylikoski M, et al (2000) Accuracy of pedicle screw insertion with and without computer assistance: a randomised controlled clinical study in 100 consecutive patients. Eur Spine J; 9(3):235–240. 25. Resnick DK (2003) Prospective comparison of virtual fl uoroscopy to fl uoroscopy and plain radiographs for placement of lumbar pedicle screws. J Spinal Disord Tech; 16:254–260.

A (eds) Computer Assisted Orthopaedic Surgery. Darmstadt: Steinkopff, 128–129. 19. Hott JS, Papadopoulos SM, Theodore N, et al (2004) Intraoperative Iso-C C-arm naviagtion in cervical spine surgery: review of the fi rst 52 cases. Spine; 29(24):2856–2860. 20. Ohnsorge JAK, Weisskopf M, Birnbaum K, et al (2003) Is there an indication for a computer-assisted fl uoroscopically navigated needle with the percutaneous therapy of spinal disorders? Langlotz F, Davies BL, Bauer A (eds)

Computer Assisted Orthopaedic Surgery. Darmstadt: Steinkopff, 266–267. 21. Rose S, Maier B, Soylu MS, et al (2003) Computer-assisted, image-guided and minimally-invasive ventral stabilization of thoraco-lumbar spine fractures. Langlotz F,

Davies BL, Bauer A (eds) Computer Assisted Orthopaedic Surgery. Darmstadt: Steinkopff, 308–309.

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John K Webb, Vincent Arlet

5 DEFORMITIES OF THE SPINE 5.1 SCOLIOSIS 5.1.1 IDIOPATHIC SCOLIOSIS

5.1.1.1 EARLY ONSET IDIOPATHIC SCOLIOSIS

GENERAL PRINCIPLES

The majority of surgeons accept that early onset scoliosis occurs before the age of 7. An alternative classification was initially described by James [1] as infantile idiopathic scoliosis (IIS) from birth to 3 years of age, as juvenile idiopathic scoliosis (JIS) from 4 to 9, and from 10 years onward as adult idiopathic scoliosis (AIS).

x-ray, if the RVAD is greater than 20°, then the possibility of progression is 80%; if the measured convex rib-vertebra angle (RVA) is less than 68°, then the risk of progression is 85%. The aim of surgery in this age group is to control the progression of the spinal curvature while at the same time allowing for longitudinal growth of the spine.

This chapter deals with children under the age of 7 (early onset scoliosis). 50–90% of cases of early onset scoliosis resolve and the younger the patient presents, under 1 year, the greater the possibility of resolution. An important factor in the management of early onset scoliosis is predicting the progression of the curve ( Fig 5.1.1.1-1), and once progression is confi rmed on repeated x-rays, treatment should be investigated. The measurement of the rib-vertebra angle difference (RVAD) will indicate the likelihood of progression. On the supine

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RVAD > 20° convex RVA < 68° 80% 85% Fig 5.1.1.1-1 Technique of predicting progression (RVAD) [2, 3].

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Bracing

The classic management of early onset scoliosis is to brace children until the beginning of their adolescent growth phase and then perform a fusion with instrumentation. If the curve presentation is severe, then before the application of a brace, the curve is corrected by the repeated application of a plaster cast, which is applied to the patient under general anesthesia. The anesthetic allows traction to be applied to the spine before the application of the plaster cast and the plaster can then be appropriately molded. Once the curve is corrected to less than 50° it can then be managed by an orthosis. Surgery is generally undertaken when the curve begins to deteriorate, which usually occurs at the beginning of the adolescent growth phase. Surgical indications

Spine surgeons are increasingly offering surgery, with the use of so-called “growing rods”, to children with progressive early onset scoliosis.

• Assessment by a pediatric physician to exclude congenital anomalies of the heart, kidneys, and all other organs. • Assessment of respiratory function. Preoperative planning for a modified Luque trolley instrumentation: • The whole curve must be involved in the instrumentation, typically T4–L3. • An anterior release of the stiff part of the curve is performed to allow increased correction. • An anterior growth arrest is performed on the stiff part of the curve to prevent the crankshaft phenomenon. • The instrumentation should have good anchorage at the end vertebra, either with hooks or preferably with pedicle screws. • The rods should overlap to allow growth. • Sublaminar wires are used to allow segmental correction. • Spinal cord monitoring is essential. • A cell saver is used.

Many surgical techniques, with or without instrumentation, have been described predominantly as causing an arrest in growth—the results were disappointing [4–8]. More recently, more sophisticated instrumentation has been developed which allows for growth of the spine.

Rationale of treatment

Preoperative assessment

The Luque trolley instrumentation allows growth along the rods [10]. The curve must be observed on a regular basis.

The patient is examined to identify any neurological or muscular abnormalities. The following investigations should be undertaken: • MRI under sedation or general anesthetics. • Full-length AP and lateral x-rays. • Bending x-rays.

The purpose of early intervention is to correct the deformity while the curve is still flexible. The greater the initial correction with the instrumentation the better the long-term prognosis [9].

During the adolescent growth spurt approximately 25% of curves deteriorate. It is at this stage that a defi nitive fusion is performed. This approach allows for a favorable cosmetic result at the end of growth.

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Surgical technique

A thoracotomy is performed, the stiff portion of the thoracic curve is released, and a convex epiphysiodesis is carried out using a morselized rib graft ( Fig 5.1.1.1-2 ). A second stage, exposing the spine from a posterior approach, is preferred. The spine is exposed using a standard technique. The soft tissues are dissected from the spinous processes and laminae, taking care not to damage the facet joints. Soft-tissue reflection can be performed using diathermy ( Fig 5.1.1.1-3a ). Sublaminar wires are passed under the lamina ( Fig 5.1.1.1-3b ). Initially Luque rods are bent into a trombone (U) shape with considerable overlap ( Fig 5.1.1.1-4a–b ). The pediatric USS ( Fig 5.1.1.1-4c ) can be used which allows excellent coronal and caudal fi xation.

release

Fig 5.1.1.1-3a–b a The curvature exposed. b Shape of the sublaminar wire.

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Fig 5.1.1.1-2a–b a Area of the softtissue release. b Convex epiphysiodesis.

Fig 5.1.1.1-4a–c a Configuration of U-shaped rods. b Close-up of U-shaped rods. c Instrumentation with the pediatric USS.

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CLINICAL APPLICATIONS

2.1

U-SHAPED GROWING RODS REPLACED BY POSTERIOR SPINAL FUSION (CASE 1)

Case presentation

The child presented at the age of 7 months with a thoracic curve measuring 45° ( Fig 5.1.1.1-5a ). At the age of 1.5 years the curve measured 85° ( Fig 5.1.1.1-5b ). The end vertebrae were T4 and L2. Rationale of treatment

At age 1.5 the curve already measured 85°. One treatment option at this young age is to start a full orthopedic treatment

with serial casting under general anesthesia followed by bracing. Such an orthopedic treatment is long and its predictability is uncertain. A spinal fusion at this young age would require an anterior and posterior fusion and the patient would eventually end up with a very short trunk. Following Winter’s rule of thumb [11] spinal growth can be estimated to be 0.7 mm/segment per year. An early spinal fusion involving 12 segments at this very young age will result in 13.5 cm of lost growth over the next 16 years (12 × 16 × 0.7 mm = 13.5 cm). Therefore, the only other option left open for this patient is a growing system. With such a growing system one can expect to achieve half of the expected growth of the spine.

Fig 5.1.1.1-5a–d a X-ray at 7 months showing a thoracic curve of 45°. b Presentation at 1.5 years of age. Progression of the curve within 11 months. c Insertion of rods at age 1.5 years, no brace was applied. Postoperative result. d Patient aged 12 years and 4 months. Observe the 4 cm lengthening of the spine.

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Surgical treatment

LEARNING POINTS

Instrumentation was inserted between T2 and L3 ( Fig 5.1.1.15c–d ). At the age of 12 years 4 months, when the child was beginning his adolescent growth spurt, the curve started to deteriorate. At this stage a defi nite fusion was performed. The sublaminar wires and U-shaped rods were removed and a posterior spinal fusion was applied ( Fig 5.1.1.1-6a–b ).

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Spinal growth is estimated to be 0.7 mm per segment per year. Modified Luque trolley instrumentation will achieve 50% of the expected growth. Defi nitive fusion must be undertaken if the curve deteriorates in the adolescent growth spurt.

Fig 5.1.1.1-6a–b a AP and lateral postoperative x-rays. b Follow-up at 16 years of age.

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2.2

U-SHAPED GROWING RODS (CASE 2)

Case presentation

LEARNING POINTS

Early diagnosis is essential.

This young boy presented at the age of 1.5 with a 63° curve ( Fig 5.1.1.1-7a–c ). The end vertebrae were T4 and L1. U-shaped rods were inserted as described earlier in this chapter (see 1 General principles) ( Fig 5.1.1.1-7d–e ). The curve did not deteriorate and the rods have not been removed. At the age of 17, the young man had an excellent cosmetic result ( Fig 5.1.1.1-8 ).

If the curve is progressive, then operate early. Regular follow-up is essential. Convert to defi nitive fusion if curve progresses beyond 45°.

63°

Fig 5.1.1.1-7a–e a–c X-ray at presentation, age 1.5 years. d–e Postoperative x-rays, AP and lateral views.

e Fig 5.1.1.1-8 Excellent cosmetic result at age 17.

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2.3

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SUBFASCIAL GROWING RODS (CASE 3)

Case presentation

A 5.5-year-old boy presented with right thoracic scoliosis, which was progressive despite bracing. His past medical history was significant for congenital cardiopathy, which had been operated on, and mild mental retardation. The Cobb angle measured 75° ( Fig 5.1.1.1-9 ). It was decided to use a modified growing instrumentation and subsequently, a four-rodpediatric instrumentation was inserted between T2 and L3. Rationale of treatment

This patient is only 5 years old and already has a significant deformity. Because of his young age, the preservation of some spinal growth is essential. Placement of the hooks and screws

Fig 5.1.1.1-9a–c Prepoperative x-rays and clinical picture.

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is planned on the standing preoperative x-rays ( Fig 5.1.1.1-9a ). The top claw is inserted at the upper thoracic level due to the thoracic kyphosis and the bottom claw is inserted between L2 and L3. Additionally, in this case sublaminar wires are to be inserted at the apex of the curve to control the apex. Once the patient is anesthetized, K-wires are inserted ( Fig 5.1.1.1-10 ) before the spine is exposed to mark the emplacement where the implants will be inserted. No exposure of the spine is done at this stage to prevent spontaneous fusion of the exposed spine. The spine is then exposed only at those levels that necessitate implants. The vertebrae at the top and bottom claws are fused. Sublaminar wires are passed at the apex of the curve. The growing rods are then inserted and passed underneath the

c Fig 5.1.1.1-10 K-wires serve as radiographic markers to limit the surgical exposure of the spine

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fascia, then under the sublaminar wires and connected together with dominoes ( Fig 5.1.1.1-11). Gentle distraction between each pair of rods is then carried out.

LEARNING POINTS

4 years later, after five subsequent lengthening procedures, the patient’s spine has remained straight and the deformity stable( Fig 5.1.1.1-12 ). One can observe a 4 cm lengthening of the spinal segment. However, careful attention to the x-rays shows that one of the bottom hooks has pulled out.

Fig 5.1.1.1-11a–d a–b Postoperatively the deformity was corrected to 40°. The authors deliberately inserted four rods instead of the two classically used rods on the concave side and the patient was not immobilized with any kind of brace after the surgery. c–d After 1-year follow-up and two lengthening procedures.

Subcutaneous rods can allow the spine to grow if sequentially lengthened every 9–12 months. This technique exposes the rod to breakage or mechanical complication. The use of four sliding rods may obviate the need of a brace and decrease the incidence of mechanical complications compared to the classic two sliding rods system that requires a brace.

Fig 5.1.1.1-12a–b Follow-up after 4 years. 4 cm lengthening of the spine is visible. Also note the pullout of one of the bottom hooks.

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CONCLUSION

Progressive early onset scoliosis can create severe spinal deformities and can lead to severe respiratory failure in later life. It is very important to recognize these curves at an early stage. A full workup is essential to ensure there is no underlying cause of the deformity. Correction should be obtained with growing rods. Careful follow-up and conversion to a defi nite fusion, if necessary, will give a good cosmetic result in most cases. Growing rods should not be used in most cases beyond the age of 8, because the benefit of further growth is probably not justified.

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BIBLIOGRAPHY

James JI, Lloyd-Roberts GC, Pilcher MF (1959) Infantile structural scoliosis. J Bone Joint Surg Br ; 41-B:719–735. 2. Mehta MH (1972) The rib-vertebra angle in the early diagnosis between resolving and progressive infantile scoliosis. Bone Joint Surg Br ; 54(2):230–243. 3. Kristmundsdottir F, Burwell RG, James JI (1985) The rib-vertebra angles on the convexity and concavity of the spinal curve in infantile idiopathic scoliosis. Clin Orthop Relat Res ; (201):205–209. 4. Smith AD, Von Lackum WH, Wylie R (1954) An operation for stapling vertebral bodies in congenital scoliosis. J Bone Joint Surg Am ; 36(A2):342–348. 5. Morgan TH, Scott JC (1956) Treatment of infantile idiopathic scoliosis. J Bone Joint Surg Br ; 38-B(2):450–457. 6. Roaf R (1963) The treatment of progressive scoliosis by unilateral growth arrest. J Bone Joint Surg Br ; 45:637–651. 7. Piggott H (1971) Posterior rib resection in scoliosis. A preliminary report. J Bone Joint Surg Br ; 53(4):663–671. 8. Luque ER (1982) Paralytic scoliosis in growing children. Clin Orthop Relat Res ; (163):202–209. 9. McMaster MJ, Macnicol MF (1979) The management of progressive infantile idiopathic scoliosis. J Bone Joint Surgery Br ; 61(1):36–42. 10. Pratt RK, Webb JK, Burwell RG, et al (1999) Luque trolley and convex epiphysiodesis in the management of infantile and juvenile idiopathic scoliosis. Spine ; 24(15):1538–1547. 11. Winter RB (1977) Scoliosis and spinal growth. Orthop Rev ; 6(1):7–25.

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DEFORMITIES OF THE SPINE SCOLIOSIS IDIOPATHIC SCOLIOSIS LATE ONSET IDIOPATHIC SCOLIOSIS

Introduction ………………………………………………………………………………………………… 345

2 2.1 2.2

General treatment principles …………………………………………………………………………… 348 Nonoperative treatment ………………………………………………………………………………… 348 Surgical treatment ………………………………………………………………………………………… 348

3 3.1 3.2 3.3 3.4 3.5 3.6 3.7

Clinical applications ……………………………………………………………………………………… Thoracolumbar curve—anterior surgery (CASE 1) …………………………………………………… Rigid right thoracic curve—anterior release, posterior surgery (CASE 2) ……………………… Double thoracic curve—posterior fusion (CASE 3) ………………………………………………… Right thoracic curve—minimally invasive anterior surgery (CASE 4) …………………………… Right thoracic curve—instrumentation with pedicle screws (CASE 5) ………………………… Rigid right thoracic curve—instrumentation with pedicle screws (CASE 6) …………………… Long right thoracic curve—posterior surgery (CASE 7) ……………………………………………

Conclusion ………………………………………………………………………………………………… 364

Bibliography ………………………………………………………………………………………………… 365

350 350 351 354 356 358 360 362

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5 DEFORMITIES OF THE SPINE 5.1 SCOLIOSIS 5.1.1 IDIOPATHIC SCOLIOSIS

5.1.1.2 LATE ONSET IDIOPATHIC SCOLIOSIS

INTRODUCTION

Definition

Classification

Late onset or adolescent idiopathic scoliosis is a 3-D structural deformity of the spine occurring during adolescence. Lateral _ 10° according to Cobb on standing x-ray), vertebral curvature (> rotation, and changes of the sagittal profi le are present.

Traditionally, the deformity is classified according to the localization of the apex of the primary scoliotic curve (cervical, thoracic, thoracolumbar, lumbar, and double major curves). The King-Moe classification [2] takes into consideration curve flexibility and distinguishes between different curve patterns (types I to V, Table 5.1.1.2-1). However, the classification was developed originally for Harrington instrumentation. The King-Moe classification does not include the assessment of the sagittal profi le, the rotational aspects of the secondary curve(s), nor the patient’s age (remaining growth). It is not suitable for dealing with implant patterns with complex third-generation instrumentation systems. Therefore, further steps have been added to overcome the drawbacks mentioned above and make the classification feasible for preoperative planning.

Etiology

The exact etiology is unknown. There is general agreement on a multifactor genesis with a hereditary background. Prevalence

Prevalence is 1–4%. Active treatment is needed in 2–3 patients out of 1,000 and surgery is indicated for about 1 in 10,000 patients. The gender ratio girls/boys is 5.4/1 for curves greater than 21° [1].

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Newer, more sophisticated classifications have been proposed ( Table 5.1.1.2-2 ) [3]. So far, however, their superiority with respect to patient outcome has not been demonstrated in prospective studies.

E E

CSL

E E

CSL

S E S

CSL E

Type I

CSL E

E S S

•

S-shaped curve in which both thoracic curve and lumbar curve cross midline

•

Lumbar curve larger than thoracic curve on standing x-ray

E = end vertebra S = stable vertebra CSL = centre sacral line

Flexibility index a negative value (thoracic curve _> lumbar curve on standing x-ray, but more flexible on side-bending) Type II

Type III

•

S-shaped curve in which thoracic curve and lumbar curve cross midline

•

Thoracic curve _> lumbar curve

•

Flexibility index _> 0

•

Thoracic curve in which lumbar curve does not cross midline (so-called overhang)

Type IV

•

Long thoracic curve in which L5 is centered over sacrum, but L4 tilts into long thoracic curve

Type V

•

Double thoracic curve with T1 tilted into convexity of upper curve

•

Upper curve structural on side-bending

Table 5.1.1.2-1 King-Moe classification types I–V: criteria for curve patterns.

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Lumbar spine modifier

Curve type (1–6) Type 1 main thoracic

Type 2 double thoracic

Type 3 double major

Type 4 triple major

Type 5 TL/L

Type 6 TL/L-MT L = lumbar MT = main thoracic PT = proximal thoracic TL = thoracolumbar

* T5–12 sagittal alignment modifier: –, N, or + < 10° – (hypo) N (normal) 10–40° + (hyper) > 40°

1A*

2A*

3A*

4A*

1B*

2B*

3B*

4B*

1C*

2C*

3C*

4C*

5C*

normal

PT kyphosis

TL kyphosis

PT & TL kyphosis

normal

6C*

Possible sagittal structural criteria (to determine specific curve type)

Table 5.1.1.2-2 Various curve types in the Lenke classification system of adolescent idiopathic scoliosis.

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TL kyphosis

Redrawn from www.spinal-deformity-surgeon.com/classification.html

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GENERAL TREATMENT PRINCIPLES

2.1

NONOPERATIVE TREATMENT

Brace treatment in the management of adolescent scoliosis remains controversial—many surgeons still prescribe braces as recommended in the literature. Brace treatment may alter the natural history of the disease in mild cases [4]. Ideally, if bracing is to be prescribed, it is indicated during the growth period (Risser 1 and 2) in curves of 25–30° with documented progression.

2.2

Rationale of treatment

• The goal of the operation is a solid fusion with optimal curve correction to achieve an acceptable cosmetic result, ie, a balanced spine in the coronal and sagittal plane and level shoulders. • Maximum curve correction is not always necessary. • Decision-making process concerning correction technique, operative approach, length of instrumentation/ fusion, and amount of correction should be based on a thorough review of clinical and radiographic data.

SURGICAL TREATMENT

There are no strict evidence-based rules concerning the indication for surgery in adolescent idiopathic scoliosis (AIS). The decision is based on Cobb angle measurements, as well as the assessment of vertebral rotation, spinal balance, sagittal profi le, cosmetic appearance, and the stage of skeletal maturity. Surgery is usually indicated in patients presenting curves with a Cobb angle greater than 45°. Curves with a Cobb angle less than 40° rarely need an operation. Curves of 35–40° in an premenarche immature child, Risser 0, will inevitably deteriorate, and early surgery is recommended in such cases, when progression is fi rst identified. The operation consists of instrumentation, correction, and fusion with bone graft. In severe cases release with or without traction may be necessary. Anterior, posterior, and combined techniques are used.

The long-term patient outcome after fusion for AIS is satisfactory in the majority of cases [5–7]. However, no correlation could be established between clinical outcome and the amount of curve correction [7, 8]. Complications of operative treatment are [9]: • • • • • • •

Spinal imbalance Wound infection Nonunion Spinal cord injury Pain at bone graft sites Scapulothoracic pain Loss of lumbar lordosis

Removal of instrumentation should be avoided and should not be undertaken before 2 years. If removed early, it may lead to a loss of correction even if the posterior fusion has healed [7]. The benign natural history of AIS should be kept in mind. Overtreatment should be avoided.

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Preoperative investigations

Radiographic assessment

• History – Age of onset – Onset of menarche – Pain – Birth and developmental history • Physical examination, including subtle neurological assessment

• Posteroanterior standing x-ray of the whole spine – Cobb measurement of primary and secondary curve(s) – Assessment of apical rotation in each curve – Frontal balance • Bending x-rays (AP and lateral) of primary and secondary curve(s) – Cobb measurement (flexibility) – Change (decrease) of apical rotation • Lateral standing x-ray of the whole spine – Measurement of thoracic kyphosis and lumbar lordosis – Junctional kyphosis, if present – Sagittal balance – Other pathology (eg, spondylolysis)

Physical examination

• • • • • • • • • • •

General condition Spinal balance (frontal and sagittal) Shoulder balance Leg length equality Scoliotic curve(s) Rib hump(s) Sagittal profi le Spine mobility Lower extremity neurology Hamstring tightness Abdominal skin reflexes (an asymmetry may be indicative of a syringomyelia)

Further special attention should be paid to skin changes like dimples, scars, hair patches, and pigmentation (café au lait spots).

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Preoperative planning

The decision concerning the operative approach is based on clinical features and the radiographic analysis of the curve pattern. It has to be decided: • Which curve(s) will be fused. • How many vertebrae will be included. • Which correction principle (translation, rod rotation, cantilever) will be used. • How much curve correction (maximum or submaximum) should be achieved.

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CLINICAL APPLICATIONS

3.1

THORACOLUMBAR CURVE—ANTERIOR SURGERY (CASE 1)

Surgical treatment

Case presentation

A 16.5-year-old female presented with a significant thoracolumbar curve ( Fig 5.1.1.2-1a ). Her menarche began 4 years previously. The standing x-rays showed a 48° thoracolumbar curve with a normal sagittal plane and a correction to 18° on bending ( Fig 5.1.1.2-1b ). The apex of the curve was at the thoracolumbar junction. There was no mid-thoracic curve. Therefore, it was classified as a Lenke 5AN. The King-Moe classification was made for thoracic curves and does therefore not apply to this case.

An anterior thoracolumbar approach is performed. The diaphragm is partially exposed, and the discs between T8 and T12 are completely excised. Appropriate instrumentation is inserted ( Fig 5.1.1.2-2a ). At the 4-year follow-up a good cosmetic result has been achieved ( Fig 5.1.1.2-2b ). Rational of treatment

Choosing an anterior approach allows a shorter fusion— in this case the procedure saves two levels. It is generally acknowledged that such an approach saves levels and probably achieves a better correction. The current trend for insertion of screws in each segment posteriorly may suggest that anterior surgery is no longer justifiable although there are no long-term results to substantiate this claim.

T6 18° T5 12 48° L1

a Fig 5.1.1.2-1a–b a Preoperative clinical photographs showing the deformity.

b b Appropriate preoperative standing and bending x-rays show a curve of 48° which corrects to 18°.

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3.2

RIGID RIGHT THORACIC CURVE—ANTERIOR RELEASE, POSTERIOR SURGERY (CASE 2)

Case presentation

A 15-year-old female presented with thoracic and lumbar curves; her neurology was normal. She had a right thoracic rib hump which measured 5 cm and a lumbar hump which measured 2 cm ( Fig 5.1.1.2-3a–b ). The thoracic curve was 85° bending to 65°, and the lumbar curve was 52° bending to 25° ( Fig 5.1.1.2-3c ). The scoliosis was classified as a King-Moe type II and Lenke 3C+. Surgical treatment

An anterior release is performed on the thoracic curve through a standard thoracotomy. Posterior instrumentation is performed from T4 (upper end of curve) to L1 ( Fig 5.1.1.2-4 ).

b Fig 5.1.1.2-2a–b a Postoperative x-rays. b Clinical photographs 4 years following surgical treatment.

LEARNING POINTS

Anterior excision of disc and anterior instrumentation save spinal levels and allow more derotation.

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a Fig 5.1.1.2-3a–c a Preoperative clinical photographs showing the King-Moe type II, Lenke 3C+ adolescent idiopathic scoliosis.

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85°

30°

36°

23°

14°

48°

65°

26°

52°

25°

c Fig 5.1.1.2-3a–c b Preoperative AP x-ray shows a thoracic curve of 85° and a lumbar curve of 65°. The sagittal profile shows the thoracic curve T5–12 to be 46° and the lumbar curve to be 26°. c Bending x-rays reveal the thoracic curve correcting from 85° to 52°, and the lumbar curve from 65° to 25°. Note that the lumbar curve derotates to the left on bending.

b Fig 5.1.1.2-4a–b a After correction a very satisfying sagittal and coronal balance has been achieved. Correction of T5–12 from 85° to 30° and of T12–L4 from 65° to 23°. b A good cosmetic result has been achieved.

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Rationale of treatment

An anterior release is performed because the bending x-ray of the thoracic curve does not correct to less than 45° (52°). The anterior release does allow increased correction of the thoracic curve. This is the classic and accepted approach at the present time. However, the anterior approach is becoming more and more debatable, because the use of multiple posterior pedicle screws that are inserted into the thoracic spine are more effective than the classic hybrid system in correcting the spine [10, 11]. It is important to save the lumbar curve from fusion, if possible. Curves that correct to less than 25° and derotate at the apex to more than 50% on the bending x-rays can be left unfused. There is still a risk of 10–15% of the spine being unbalanced, and if that occurs, an extension of the fusion will be necessary. If the lumbar curve does not fully correct, then the magnitude of the curve on the bending x-ray should be taken into consideration when correcting the thoracic curve. It is advisable not to correct more than the maximum correction of the lumbar curve on bending. If the thoracic curve is corrected to more than the end point of the lumbar bending x-ray, the patient may be decompensated to the left in the coronal plane.

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LEARNING POINTS

An anterior release is recommended, if the bending x-rays do not correct to less than 45°. This classic teaching is being challenged by the use of multiple posterior pedicle screws. Try to avoid fusing the lumbar curve in King-Moe type II curves (Lenke 1C, 3C). Curves that bend to less than 25° do not necessarily need to be fused. Check the derotation of the apex vertebra of the lumbar side on side-bending x-rays. If the derotation corrects to less than 50% of the bending x-ray and if the curve bends to less than 25–30°, then fusion of the lumbar spine is not necessary. Warn the patient’s parents that there is always a possibility of decompensation and that an extension of the fusion may be necessary.

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3.3

DOUBLE THORACIC CURVE—POSTERIOR FUSION (CASE 3)

Case presentation

A 13-year-old girl presented with an upper thoracic curve of 30°, a main thoracic curve of 68°, and a lumbar curve of 46° ( Fig 5.1.1.2-5 ). Clinically, the shoulders were balanced ( Fig 5.1.1.2-5a ). She was 1 year postmenarche. Abdominal reflexes were absent; therefore, an MRI was requested and the result was normal. Bending x-rays showed a correction of the upper thoracic curve to 25°, the main curve to 28°, and the lumbar curve to 4°—the latter showing derotation of the apical lumbar vertebra ( Fig 5.1.1.2-5b ). Because she had level shoulders and the upper thoracic curve did not correct to less than 25°, this was considered as a double thoracic curve or King-Moe type V or Lenke 2BN.

30° 30° 68°

46°

25° 28°

4°

R4 a

Fig 5.1.1.2-5a–b a Preoperative clinical photographs. b Preoperative x-rays show an upper thoracic curve of 30°, a thoracic curve of 68°, and a lumbar curve of 46°. The sagittal curve measures 30°. Note the level shoulders.

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Surgical treatment

LEARNING POINTS

Posterior spinal fusion and instrumentation is performed between the upper end vertebra T2 and the stable vertebra L1 ( Fig 5.1.1.2-6a ). The postoperative photographs show a wellbalanced spine ( Fig 5.1.1.2-6b ).

Look for an upper thoracic curve especially if the shoulders are level or the wrong shoulder is elevated. Upper thoracic curves which do not correct to less than 25° need to be fused.

Rationale of treatment

The upper curve only corrects to 25° and is classed as a structural curve. It is therefore included in the fusion. It is also important to be aware of the level shoulders in the preoperative clinical and radiological pictures. If this would have been only a major thoracic curve, then the left shoulder would be low.

24°

Fig 5.1.1.2-6a–b a Postoperative x-rays show a good correction to 24°. The instrumentation is from T2 to L1. b Postoperative clinical photographs.

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3.4

RIGHT THORACIC CURVE—MINIMALLY INVASIVE ANTERIOR SURGERY (CASE 4)

approach, except the screws are placed with the use of an image intensifier. The levels chosen are T5–10 ( Fig 5.1.1.2-8a ).

Case presentation

Rationale of treatment

A 14.5-year-old girl, Risser 3, presented with a scoliosis and the x-rays revealed a curve of 48° ( Fig 5.1.1.2-7 ). Her menarche began 1.5 years before presentation at the clinic. On side-bending, the curve corrected to 25° as measured on the x-rays. The girl had a normal thoracic kyphosis. This curve was classified as a King-Moe type III or Lenke 1AN.

It is important to appreciate that the classic standard approach for treatment in this case would be posterior instrumentation from T4 to L1. The surgery for late onset adolescent scoliosis is essentially performed for cosmetic reasons.

Surgical treatment

Anterior minithoracotomy is performed. The transverse incision is 4–5 cm long on the apex of the curve in the midaxillary line. The apex of the curve needs to be identified with an image intensifier. Beneath the skin, two thoracotomies are performed; each incision allows access to the appropriate levels. The anterior procedure is the same as a normal anterior

The minimally invasive anterior approach gives an excellent corrective result and allows good vertebral derotation, and with rib head resection excellent rib hump correction can be obtained ( Fig 5.1.1.2-8a ). The scar is in the mid-axial area and is well concealed ( Fig 5.1.1.2-8b ). At least three vertebral segments are saved by using this technique and the extensive anterior release, which must include the removal of the rib heads at T9 and above, results in increased

48° 25° 0°

a Fig 5.1.1.2-7a–b a Preoperative clinical pictures.

b b Preoperative x-rays with a curve of 48° correcting to 25° when bending. A sagittal angle of 35° is visible. The lumbar curve corrects to 0°.

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correction of the rib deformity. The removal of the rib heads probably has the same effect as a costoplasty. The use of an anterior approach is probably only justified in routine cases if significant growth remains in the vertebral column. Severe stiff curves, of more than 70° on bending x-rays, are technically difficult to instrument through an anterior approach. The majority of surgeons use minimally invasive surgery rather than thoracoscopic techniques. The results of using multiple pedicle screws, especially in the more mature child (Risser 3 and 4), gives the same results as anterior surgery [10].

LEARNING POINTS

Remember that the classic approach for the treatment of a King-Moe III, Lenke 1AN scoliosis would be a posterior instrumentation. In experienced hands anterior surgery is an option. Minimally invasive anterior surgery allows a more acceptable cosmetic result. Anterior surgery allows increased derotation of the spine. Anterior surgery improves the rib hump in comparison to a posterior approach.

Fig 5.1.1.2-8a–b a After correction a very satisfying sagittal and coronal balance has been achieved. b A good cosmetic result has been achieved.

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3.5

RIGHT THORACIC CURVE—INSTRUMENTATION WITH PEDICLE SCREWS (CASE 5)

Case presentation

A 14-year-old girl, 2 years postmenarche, was seen for a recently discovered spinal deformity. On examination the shoulders were level, she had an asymmetrical waist, but her coronal balance was satisfactory ( Fig 5.1.1.2-9a ). The x-rays showed a right thoracic curve (overhang type) with an apex at the level of T9/10. The Cobb angle was measured at 58°, and the stable vertebra was L3 ( Fig 5.1.1.2-9b ). As the lumbar spine did not cross the midline, this curve was classified as a King-Moe type III and as a Lenke 1AN. Side-bending x-rays showed the curve to be relatively flexible (22°).

a Fig 5.1.1.2-9a–b a Preoperative clinical photographs show the adolescent idiopathic scoliosis King-Moe type III, Lenke 1AN.

Surgical treatment

The patient undergoes posterior spinal fusion from T5 to L2 with pedicle screws ( Fig 5.1.1.2-10 ). Postoperatively, she shows an excellent Cobb angle correction and is perfectly balanced in the sagittal and coronal plane. Rationale of treatment

According to the King-Moe rule and Harrington instrumentation, the fusion must extend down to the stable vertebra. Following these rules, fusion should have been made to L3, which was bisected by the mid-sacral line. The increased correction offered by a pedicle screw fusion allows the distal screw to fi nish one level before the stable vertebra with a satisfactory result. In this case, pedicle screw fi xation is chosen not only to increase the correction of the Cobb angle, but to translate the apical vertebra and improve the apical rotation as well, so the rib prominence would smoothen out.

b b Preoperative AP and lateral x-rays including side-bending views.

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LEARNING POINTS

The use of multiple pedicle screws is technically difficult and costly. In King-Moe type III or Lenke 1A curves it is possible to stop the fusion posteriorly one level short of the stable vertebra. Pedicle screw fi xation for this type of curve provides optimal correction of the clinical deformity.

a Fig 5.1.1.2-10a–c a Postoperative x-rays.

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b b Postoperative clinical photographs.

c c 2-year follow-up x-rays.

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3.6

RIGID RIGHT THORACIC CURVE—INSTRUMENTATION WITH PEDICLE SCREWS (CASE 6)

Case presentation

A 12.5-year-old girl, Risser 1, onset of menarche 6 months earlier, presented with a severe thoracic and lumbar deformity. On examination she had level shoulders and significant loss of coronal balance—a large thoracic rib deformity was seen ( Fig 5.1.1.2-11a ). The x-rays showed an upper thoracic curve of 25° (bending to 18°), a lower thoracic curve of 92° (bending to 60°), and a lumbar curve of 76° (bending to 36°) ( Fig 5.1.1.2-11b ). The curve was classified as a King Moe II and Lenke 3 because the upper thoracic curve corrected to 18°. Because of the severity of this curve, ie, over 70°, traction x-rays were performed at the time of surgery when the patient was anesthetized. These showed the thoracic curve correcting to 54° and with added lateral pressure to 52°. The lumbar curve corrected to 30° ( Fig 5.1.1.2-11c ).

Surgical treatment

In view of these fi ndings, a pedicle screw instrumentation is undertaken between levels T2 and L2 ( Fig 5.1.1.2-12a ). Postoperatively, the thoracic curve corrects to 28° and the lumbar curve passively corrects to 35°. Cosmetic appearance shows good correction of the deformity with level shoulders, but she still has a mild lumbar curve ( Fig 5.1.1.2-12b ). Coronal balance corrected over the next 6 months.

b Preoperative standing and bending x-rays: forced bending corrects the upper thoracic curve from 25° to 18°, the lower thoracic curve from 92° to 60°, and the lumbar curve from 76° to 36°.

25° 92°

76°

18° 86°

36° 60°

Fig 5.1.1.2-11a–c a Preoperative clinical photographs.

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Rationale of treatment

screws/hooks). Today, surgeons must decide if the use of multiple level pedicle screws is justifiable when compared to an anterior release and posterior hybrid system. The insertion of pedicle screws at each level is the most demanding of techniques with a probable increase in neurological complications.

The surgery for late onset adolescent idiopathic scoliosis is essentially performed for cosmetic reasons. The technique of using multiple pedicle screws is chosen in CASE 5 and in CASE 6. In CASE 2, an anterior release is described because the thoracic bending x-rays do not show a correction to less than 45°. This has already been described as the classic approach for stiff curves.

In this case, it is to be expected that with pedicle screws both the thoracic and the lumbar curves would correct to 25–30°. As it is, the lumbar curve corrects down to 30°, which is why it does not need to be instrumented. The lumbar curve follows the thoracic curve. It is better to have a 30° mobile lumbar curve than a fusion down to L4 or L5. The upper thoracic curve is fused, although it is defi ned by the Lenke classification system as nonstructural (corrects to less than 25° on side-bending). The shoulders are level. One would normally

The anterior release is debatable because the use of pedicle screws at each level in the thoracic spine has been shown to be effective in correcting the spine. Recent publications [10– 13] report that increased correction can be obtained by this technique and that it is superior to an anterior release and a posterior instrumentation using a hybrid construct (pedicle

30°

54°

52°

c Fig 5.1.1.2-11a–c c Traction x-rays done while the patient is anesthetized with lateral pressure over the apex.

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Fig 5.1.1.2-12a–b a Postoperative AP and lateral x-rays with the curves corrected to 28° and 35° respectively after instrumentation from T2 to L1. b Postoperative clinical photographs.

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expect the left shoulder to be low with a major thoracic curve. In this case the shoulders are level and therefore correction of the major thoracic curve alone may lead to tilted shoulders. Therefore, it is better to fuse the upper thoracic spine to ensure level shoulders.

LEARNING POINTS

Standard flexible thoracic curves can be corrected with posterior hybrid systems (pedicle screws and hooks). If the curve does not correct to 70° measured on bending x-rays, a traction x-ray with the patient anesthetized may give added information that will change the preoperative plan of instrumentation.

3.7

LONG RIGHT THORACIC CURVE—POSTERIOR SURGERY (CASE 7)

Case presentation

A 14-year-old girl presented with an impressive spinal deformity with coronal imbalance at 1 year postmenarche. She had a marked imbalance, waist-line asymmetry, and significant rib prominence ( Fig 5.1.1.2-13a ). The standing x-rays showed the curve with an apex at T10 and end vertebrae at T7 and L2; the Cobb angle measured 55° ( Fig 5.1.1.2-13b ). This curve was classified as a King-Moe type IV because the L4 vertebral body was tilting into the curve. According to the Lenke classification, the closest pattern this curve resembles is type 5C. As the sagittal profi le was satisfactory, the sagittal modifier would have been N (= normal).

Stiff curves which do not bend down to less than 45° can be corrected with an anterior release and a posterior hybrid system. Stiff curves that correct to less than 70° can alternatively be corrected by using pedicle screws in multiple levels, providing that the spine surgeon is experienced with the technique of pedicle screw insertion in the thoracic spine. If significant growth is left, then anterior instrumentation can be combined with a growth arrest procedure. Alternatively, multiple posterior pedicle screws will probably prevent the so-called “crankshaft phenomena”. Anterior instrumentation is technically difficult, if the bending x-ray does not correct to less than 60°.

a Fig 5.1.1.2-13a–b a Preoperative clinical photographs.

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Rationale of treatment

Classically, according to King-Moe type IV, these curves need to be fused to the stable vertebra, which in this case is L4. However, if one looks carefully at the side-bending x-rays, the lumbar spine is partially flexible and nonstructured. The distal fusion can fi nish at the vertebra where the lower end plate of a vertebra becomes horizontal on the concave bending x-ray. One could theoretically stop where the end plates become horizontal (on bending x-rays), in this case at L3. A posterior spinal fusion is performed between T6 and L3 ( Fig 5.1.1.2-14 ). LEARNING POINTS

King-Moe type IV, Lenke 5C are long thoracic/lumbar curves with a low thoracic apex. The use of pedicle screws allows fusion to L3 rather than to the L4 vertebra. a

Fig 5.1.1.2-14a–c a Postoperative clinical photographs. b Postoperative x-rays. c The clinical photographs at 2-year follow-up show the curve to be nicely corrected.

Fig 5.1.1.2-13a–b b Preoperative x-rays including bending views.

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Deformities of the spine Scoliosis

CONCLUSION

Planning and decision making in the treatment of adolescent idiopathic scoliosis is a stepwise process including the patient’s history, physical examination, and thorough radiographic analysis of the deformity. King-Moe and/or Lenke classifications are used to understand the basic curve pattern. Additional steps (assessment of sagittal profi le, rotational stiffness, and skeletal maturity) are considered in order to decide on the instrumentation pattern and correction principle. The goal of surgery is a balanced spine and level shoulders. This is achieved by optimal curve correction, which is not necessarily maximum correction. Straighter is not always better. The operative procedure has to be performed with great care. Severe complications may occur. The benign natural history of late onset idiopathic scoliosis should be kept in mind. One should carefully weigh the risks against the benefits.

AOSPINE MANUAL—CLINICAL APPLICATIONS

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Idiopathic scoliosis Late onset idiopathic scoliosis

BIBLIOGRAPHY

1. Rogala EJ, Drummond DS, Gurr J (1978) Scoliosis: Incidence and natural history. A prospective epidemiological study. J Bone Joint Surg Am ; 60(2):173–176. 2. King HA, Moe JH, Bradford DS, et al (1983) The selection of fusion levels in thoracic idiopathic scoliosis. J Bone Joint Surg Am ; 65(9):1302–1313. 3. Lenke LG, Betz RR, Harms J, et al (2001) Adolescent idiopathic scoliosis. A new classifi cation to determine extent of spinal arthrodesis. J Bone Joint Surg Am ; 83(8):1169–1181. 4. Nachemson AL, Peterson LE (1995) Effectiveness of treatment with a brace in girls who have adolescent idiopathic scoliosis: A prospective, controlled study based on the data from the Brace Study of the Scoliosis Research Society. J Bone Joint Surg Am ; 77(6):815–822. 5. Danielsson AJ, Wiklund I, Pehrsson K, et al (2001) Health-related quality of life in patients with adolescent idiopathic scoliosis: a matched follow-up at least 20 years after treatment with brace or surgery. Eur Spine J ; 10(4):278–288. 6. Dickson JH, Erwin WD, Rossi D (1990) Harrington instrumentation and arthrodesis for idiopathic scoliosis. A twenty-one-year followup. J Bone Joint Surg Am ; 72(5):678–683. 7. Helenius I, Remes V, Yrjonen T, et al (2002) Comparison of long-term functional and radiologic outcomes after Harrington instrumentation and spondylodesis in adolescent idiopathic scoliosis. A review of 78 patients. Spine ; 27(2):176–180. 8. D’Andrea LP, Betz RR, Lenke LG, et al (2000) Do radiographic parameters correlate with clinical outcomes in adolescent idiopathic scoliosis? Spine ; 25(14):1795–1802. 9. Bridwell K (1994) Adolescent idiopathic scoliosis. Surgical Treatment.

10. Luhmann SJ, Lenke LG, Kim YJ, et al (2005) Thoracic adolescent idiopathic scoliosis curves between 70 degrees and 100 degrees: is anterior release necessary? Spine ; 30(18):2061–2067. 11. Arlet V, Jiang L, Ouellet J (2004) Is there a need for anterior release for 70–90 degrees masculine thoracic curves in adolescent scoliosis? Eur Spine J ; 13(8):740–745. 12. Suk SI, Lee SM, Chung ER, et al (2005) Selective thoracic fusion with segmental pedicle screw fi xation in the treatment of thoracic idiopathic scoliosis: more than 5-year follow-up. Spine ; 30(14):1602–1609. 13. Kim YI, Lenke LG, Kim J, et al (2006) Comparative analysis of pedicle screw versus hybrid instrumentation in posterior spinal fusion of adolescent idiopathic scoliosis. Spine ; 31(3):291–298.

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