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Journal of Manipulative and Physiological Therapeutics Volume 23 * Number 5 • June 2000 0161-4754/2000/$12.00 + 0 76111106867 Š 2000 JMPT
Short-Term Effects of Lumbar Posteroanterior Mobilization in Individuals With Low-Back Pain Michalene Goodsell, GradDipAppSc (ManipPhysio), MAppSc (Physio)," Michael Lee, MBiomedE, t, and Jane Latimer, PhD c
ABSTRACT Objective: To establish the short-term effects of lumbar posteroanterior mobilization in patients with low-back pain, compared with a control intervention. Design: Self-controlled cross-over design. Main Outcome Measures: The force-displacement characteristics of the spine in response tc the application of a posteroanterior force, lumb flexion, and extension range of movement; during flexion, extension, and on worst movement; pain on posteroanterior loading; and overall pain relief. Patients: Twenty-six patients with nonspecific low-back pain who experienced pain on flexion or extension and whose pain settled quickly after provocation, from a physiotherapy clinic and university campus. Methods: Patients received posteroanterior mobilization and a control intervention in an order that was randomly allocated. The magnitude of force in treatment dose was selected by the treat-
INTRODUCTION The term manipulative therapy has been used to describe a range of manual treatments, including oscillatory joint movements (mobilization) and high-velocity thrust procedures (manipulation). 1,2Although some manipulative therapy interventions, manipulation in particular, have been shown to be effective in relieving and hastening recovery from low-back pain, 3.4 there has been little research evaluating other manipulative therapy interventions. Lumbar mobilization has undergone comparatively little investigation. Most studies have used mobilization together with other treatments. For example Farrell and Twomey 5 found that manipulative therapy, ineluding a combination of mobilization and manipulation, produced a more rapid recovery from symptoms than a "control" treatment of microwave diathermy, abdominal exercises, and ergonomic instruction in patients with acute back pain. The
aPrivate practice of physiotherapy, Unandera, Australia. bLecturer, School of Exercise and Sport Science, University of Sydney, Sydney, Australia. CLecturer, School of Physiotherapy, University of Sydney, Sydney, Australia. Submit reprint requests to: Michael Lee, School of Exercise and Sport Science, University of Sydney, PO Box 170, Lidcombe, New South Wales 1825, Australia. E-mall: M.Lee@cchs.usyd.edu.au Paper submitted May 5, 1999, in revision November 8, 1999. doi: 10.1067/mmt.2000.106867
tg physiotherapist. An observer who was blinded to the order of interventions performed all measurements. Outcome measures were recorded before and after each intervention, and change scores were calculated to quantify the effect of the intervention. Results: No significant differences were found between the mobilization and control intervenions in relation to posteroanterior response or age of movement. The score for pain on worst .~ment showed significantly greater improvement tor the mobilization than for the control procedure. Conclusions: Lumbar posteroanterior mobilization was not observed to produce any objectively measurable change in the mechanical behavior of the lumbar spine of patients with lowback pain. Improvement in some pain variables was observed in comparison with a control procedure, but this may be due to a placebo effect. (J Manipulative Physiol Ther 2000;23:332-42) Key Indexing Terms: Lumbar Spine; Low Back Pain; Physical Therapy
manipulative therapy group received a variety of treatments, including passive accessory and passive physiological mobilization, and manipulation as described by Maitland. 6 No indication was given of the frequency of the different treatments or how often manipulation was used, making it difficult to interpret the relative value of lumbar mobilization and manipulation. Koes et al7.8 performed a clinical trial in patients with subacute and chronic back and neck pain, comparing the effect of four interventions: manipulative therapy, consisting of mobilization and manipulation; physiotherapy, consisting of exercise, massage, and electrotherapy modalities; treatment by the patient's medical practitioner, consisting o f prescription of medication and advice; and placebo, consisting of detuned short-wave diathermy and ultrasonography. Greater improvements were observed with both the manipulative therapy and physiotherapy interventions when compared with the medical practitioner treatment. The responses of both manipulative therapy and physiotherapy groups appeared to indicate the presence of a placebo effect. There has been little evaluation of the efficacy of lumbar mobilization alone. A study by Hadler et al 9 directly compared the effect of manipulation and mobilization in patients with acute low-back pain and found a more rapid improvement in both mobility and pain in patients who received manipulation than in a group who received "mobilization without a rotary thrust." However, the mobilization intervention, which consisted of the therapist "firmly flexing the hips
Journal o f Manipulative and Physiological Therapeutics Volume 23 • N u m b e r 5 ° June 2 0 0 0
Effects of PA Mobilization
twice" while the patient lay on their left and then right side, does not reflect common clinical practice in which several minutes of mobilization would be applied. Nwuga 1° investigated the effect of rotation mobilization on range of movement but not pain in patients with acute back and leg symptoms and evidence of disk protrusion. A greater improvement in total flexion/extension range, lateral flexion and rotation range, and straight leg raise was observed after the rotation mobilization compared with a treatment regimen of short-wave diathermy, flexion exercises, and education. Beattie l) reported a single case study of mobilization treatment of a patient with low-back pain. The patient's range of left lateral bending increased with mobilization on 8 of the 9 occasions of treatment, whereas improvements were not seen when the treatment was withdrawn.ll Two studies 12.13 have demonstrated increases in range of movement immediately after the application of a mobilization intervention applied to symptom-free subjects. Gibson et a112 found that a passive physiological lumbar flexion mobilization applied to subjects with smaller than average range of movement produced a greater increase in flexion range than a control intervention. McCollam and Benson 13 found that a central posteroanterior (PA) mobilization applied to L3, L4, and L5 for 3 minutes at each level produced a greater increase in lumbar extension, but not flexion range, than a control intervention. In contrast, Petty 14 found no change in flexion or extension range of movement after PA mobilization to L3, when treatment was applied to symptom-free subjects for 2 minutes with a mean maximum force of 92.5 N. No studies have investigated the effect of lumbar PA mobilization on patients with low-back pain. The aim of this study was to examine the effects of PA lumbar mobilization on individuals with low-back pain by investigating the short-term effects of mobilization treatment on a range of variables: the mechanical response of the spine to PA mobilization (PA response), pain, and range of movement. Changes in both pain and range of movement are commonly used to evaluate the effect of treatment in clinical practice and research. A more contentious issue is the clinical significance of the mechanical response of the spine to PA mobilization. PA mobilization is frequently used by physiotherapists in the assessment of back pain 6 and involves the therapist applying a PA force over the spinous process of the patient in the prone position. When performing this assessment the therapist seeks to determine the mechanical response of the spine by relating the amount of force applied to the resulting displacement, thus estimating the stiffness of the movement. Information from this test can influence a number of clinical decisions, including which spinal level is treated and the type and dose of treatment applied. Importantly, it has been theorized that hypomobile spinal joints may occur in association with low-back pain, ~s and the stiffness of these joints may be altered by use of manipulative therapy. 2 There is some evidence to support this hypothesis; Latimer et all6 demonstrated that PA stiffness, measured with a mechanical device, is increased in patients with low-back pain compared with when their low-
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• Goodsell et al
Subjects n=26 I GroupA I GroupB n=12 n=14
[
Initial Measurement
Initial Measurement
Second Measurement
Second Measurement
Final Measurement
Final Measurement
I
Fig I. Design of the study. Measurements and interventions for each individual patient were performed on the one day. back pain has been significantly reduced. If such theories are valid, a change in the PA response could occur after mobilization treatment. Investigation of this issue has been hampered by the poor reliability of therapists' assessments of lumbar stiffness. 17,~8To overcome this problem, a number of mechanical devices have been designed to collect force and displacement data during a simulated PA mobilization. ~9,2° A mechanical stiffness device 21 was used in this study to examine the effect of PA mobilization on the PA response.
MATERIALANDMETHODS This study examined the short-term effect of PA spinal mobilization on the PA response, pain, and range of movement by use of a self-controlled experimental design. Mobilization was compared to a control intervention to control for the effects of time, posture, and repeated testing. Patients were randomly allocated by coin toss as they presented for treatment to 1 of 2 groups. Both groups received both interventions, with the groups differing in the order they received them. Group A received mobilization followed by the control intervention, and group B received the control intervention followed by mobilization. The measurements and interventions for each individual patient were performed
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Journal of Manipulative and Physiological Therapeutics Volume 23 • Number 5 • June 2000 Effects of PA Mobilization • Goodsell et al Table I. P a tient characteristics
Patient Group A 1 2 3 4 5 6 7 8 9 10 11 12 Mean SD Range Group B 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Mean SD Range Groups A and B Mean SD Range
Age (yrs)
Height (cm)
Mass (kg)
BMI (kg/m z)
Symptom duration (mos)
McGill pain score
Referred pain?
Spine level
M M M F F F M F M M M M
38 19 56 18 23 69 31 41 24 24 58 47 37.3 17.1 18-69
182.5 171 166 171.5 163 164.5 184 160 183 186.5 190 177 174.9 10.2 160-190
93 66 83 62 56 74 91 61 80 70 98 82 76.3 13.7 56-98
27.9 22.6 30.1 21.1 21.1 27.3 26.9 23.8 23.4 10.2 27.2 26.2 24.8 3.2 20.1-30.1
0.5 2.0 0.5 0.5 1.0 1.5 12 0.5 48 60 60 0.5 15.6 24.8 0.5-60
22 14 13 15 15 20 38 19 4 3 10 17 14.5 9.3 3-38
Y N N N N N N N N N N N
L2 L5 L5 L4 L5 L5 L5 L5 L5 L5 L3 L3
M F F F F M M F F F M F M F
36 45 45 45 47 22 44 60 64 16 23 40 46 44 41.2 13.5 16-64
177 155 181 164 166.5 187 180 156 174.5 160.5 180 163 186 162 170.9 11.1 155-187
85 59 111 64 62 92 75 67 82.5 44 82 48 110 72 75.3 20.2 44-111
27.2 24.6 33.8 23.8 22.4 26.3 23.2 27.5 27.1 17.9 25.3 18.1 31.8 27.4 25.5 4.4 17.9-33.8
0.5 2.0 1.0 1.0 9.0 1.0 1.5 3 1 0.5 1.0 0.5 0.5 0.5 2.2 1.6 0.5-9
10 12 22 16 24 5 27 8 15 8 14 0 9 22 13.7 7.8 0-27
N N N Y N N N N N N N N N N
L3 L3 L5 L5 L5 L5 L5 L3 L5 L5 L3 L5 L5 L3
39.4 15 16-69
172.8 10.7 155-190
75.8 17.2 44-111
25.1 3.9 17.9-33.8
8.1 18.0 0.5-60
14.1 8.4 0-38
Sex
BMI, Body mass index. BMI is calculated as mass + height2. Spine level is the vertebra to which the treatment was applied. See text for method of calculation of the duration of symptoms.
during the one visit. This was done for ethical reasons to minimize delays in treatment. The experimental design is illustrated in Fig 1. The three variables, PA response, pain, and range of movement, were measured initially, after the first intervention, and after the second intervention. The same measurer, who was blinded to the order of intervention, performed all measurements. The measurer had undertaken a training period before data collection to familiarize them with measurement procedures.
Patients Patients were recruited by advertisement at a private physiotherapy practice in the Wollongong area, and at the Faculty of Health Sciences, The University of Sydney, thereby forming a sample of convenience. Patients were included in the study if they complained of a current episode of lowback pain and bad experienced pain in the previous 48 hours; back pain was elicited or increased by active lumbar flexion or extension movements; pain was elicited on appli-
cation of a PA force to the spinous process of 1 or more lumbar vertebrae; it was the clinical impression of the treating physiotherapist that PA mobilization was an appropriate treatment for the patient; and the treating therapist classified the patient's symptoms as nonirritable, z2 that is, symptoms settled quickly after provocation, and also indicated that a grade III or IV mobilization was appropriate in treatment, z2 This criterion was used to help ensure that the patient could safely tolerate the PA force applied in the mechanical measurement of PA stiffness. Patients were excluded from participating when there were known contraindications to manual therapy treatment such as malignancy, inflammatory or infectious disease affecting the spine; positive neurologic signs were found on physical examination; there was a history of lumbar spine surgery; or the patient was pregnant. Twenty-six volunteers (13 men and 13 women) participated in the study. Patient characteristics are described in detail in Table 1. Twenty-six patients were recruited so that the study would have an 80% power to detect a difference in the stiffness coefficient K of 1.2 N/mm. The effect size of 1.2
Journal of Manipulative and Physiological Therapeutics Volume 23 • Number 5 • June 2000
Effects Table
2.
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of PA Mobilization * Goodsell et al
Mean (SD) values of each variable at different stages of the testing procedure Group A
PA Response K (N/mm) D30 (mm) Pain Flexion (mm) Extension (mm) Worst (mm) PA test (mm) Overall (%) Range of movement Finger-to-floor (cm) Flexion (degree) Extension (degree)
Group B
Test 1
Test 2 (after mobilization)
Test 3 (after control)
Test 1
Test 2 (after control)
Test 3 (after mobilization)
15. I 1 (4.77) 5.01 (1.10)
14.82 (4.50) 4.58 (1.15)
14.79 (3.44) 4.70 (1.41)
15.43 (2.86) 4.36 (1.80)
15.69 (3.30) 4.51 (1.54)
15.38 (2.77) 4.61 (1.52)
22 27 40 28
13 (21 ) 22 (20) 24 (21) 27 (25) 35 (38)
11 (20) 18 (19) 20 (22) 31 (30) 29 (47)
30 (23) 32 (25) 39 (21) 27 (29)
28 (24) 30 (26) 36 (23) 36 (29) --4 (26)
25 (20) 20 (17) 25 (16) 26 (25) 15 (33)
15.9 (15.8) 95 (22) 46 (14)
13.4 (15.1) 95 (24) 47 (14)
10.7 (14.1) 97 (21) 47 (14)
(26) (24) (23) (25)
5.7 (6.8) 105 (11) 52 (8)
4.9 (7.6) 106 (13) 52 (11)
3.8 (7.7) 108 (12) 52 (9)
For group A, the mobilization occurred between test 1 and test 2, whereas the control treatment occurred between test 2 and test 3. For group B, the control occurred between test 1 and test 2, and the mobilization occurred between test 2 and test 3.
N/mm was based on the change seen in the study by Latimer et aP 6 wherein patients with low-back pain were measured as their low-back pain resolved. The standard deviation of the population (2.1 N/mm) was derived from several hundred patients tested at the University of Sydney. As can be seen from Table 1, a wide range of ages (range 16 to 69 years, mean 39.4 years, SD 15.0) and duration of symptoms (range 0.5 to 60 months, mean 8.1, standard deviation [SD] 18.0) were represented in the patient sample. The duration of symptoms was defined as the length of time from either the onset of symptoms in individuals with a first episode of low-back pain symptoms, the onset of the recurrence of symptoms in individuals with recurrent low-back pain symptoms, or the current exacerbation of symptoms in individuals ¢vith continuous low-back pain symptoms. The McGill pain score 23,24 was collected to obtain an indication of the range of pain severity in the sample. The scores presented in Table 1 are based on the total pain rating index. The characteristics of the sample in terms of PA response, pain, and range of movement on entry into the study are presented in Table 2. Ethical approval to conduct the study was granted by the University of Sydney Ethics Committee. Before participation all patients signed a consent form and were given a subject information sheet that informed them of the nature and purpose of the study.
Intervention The mobilization intervention consisted of a PA mobilization manually applied to the spinous process of the most symptomatic spinal level for three 1-minute repetitions. The magnitude of the force applied during mobilization was at the discretion of the therapist but was recorded with a custom-made, instrumented treatment couch. The control intervention consisted of each patient lying on the treatment couch in a prone position for 3 minutes. This procedure replicated the main physical characteristics associated with the mobilization intervention, that is, getting into the position of treatment and maintaining the position for the same duration as the treatment. The use of a control intervention
also allowed the effects of time and repeated testing to be taken into account. One therapist, who was an experienced physiotherapist and had a postgraduate qualification in manual therapy, carried out all interventions. This therapist was not the patient's usual treating therapist. A custom-made instrumented treatment couch was used to quantify the vertical component of forces applied to the patient during the mobilization intervention. Previous research has indicated that the vertical component is usually more than 90% of the total sagittal plane mobilizing force. ~ The instrumented couch comprises a steel-framed treatment bed, 4 compression load cells (Precision Transducer Group, LPX50, Precision Transducers, Castle Hill, New South Wales, Australia) interposed between the legs of the treatment couch and the floor, a summing amplifier, and a chart recorder. The instrumented treatment couch was found to have acceptable accuracy in recording known forces applied in a variety of locations on the bed surface. The maximum error in measurement of force was 2.7%, equating to an error of 7 N for loads of 270 N. The maximum vertical component of treatment force applied by the therapist during the mobilization intervention ranged from 60 N to 230 N with a mean of 137 N.
Apparatus A stiffness measurement device was custom-made to quantify the PA response and is described in detail elsewhere. 21 The device consists of an unpadded couch, a small metal pad (indenter) that applies a PA force to the spine of the patient in the prone position, and a mechanical head that produces movement of the indenter and contains the instrumentation for force and displacement measurement, The device is controlled by a laptop computer that also collects (at 256 Hz) and stores the force and displacement signals produced. The couch consists of a rigid wooden upper surface with detachable aluminium legs for ease of transportation. The mechanical head is attached to a steel bar that is located above the testing bed. To enable easy placement of the patient, the position of the bar can be adjusted, both in its height
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Journal of Manipulative and Physiological Therapeutics Volume 23 • Number 5 • June 2000
Effects of PA Mobilization • Goodsellet al 100 90
................................................................................................... ~ , - ..........
\
80
70 z
60
®
5O
o u_
40 30 20 10
0
2
4
6
Displacement
8
10
12
(ram)
Fig 2. Typical force-displacement curve for PA forces applied to the lumbar region. The gradient of the regression line fitted to the data between 30 and 90 N is the stiffness coefficient (K). The displacement occurring between 0.5 N and 30 N is the variable D30. above the bed and its position along the length of the bed. The mechanical head can be rotated around the bar, allowing the force to be applied at varying angles, either in a caudal or cephalad direction, when testing different lumbar levels. The mechanical head contains a small reversible motor that drives the indenter, an optical encoder that measures the displacement of the indenter, and a linear potentiometer that measures the compression of a spring to determine the force applied to the patient via the indenter. The force and displacement data obtained from PA response testing were analyzed as described by Latimer et al. 21 On each measurement occasion, 5 loading cycles were obtained. However, the force-displacement data for 4 loading cycles only (cycles 2 through 5) were analyzed. Cycle 1 was discarded because of transient behavior on start-up. The remaining 4 cycles were averaged, and a mean force-displacement curve was obtained. The typical force/displacement curve obtained when testing the lumbar spine has 2 main features: a nonlinear region where small forces produce relatively large displacements and a linear region of higher stiffness (Fig 2). Two measures were calculated to quantify these features of the force-displacement curve. As shown in Fig 2, the nonlinear region of the curve was quantified by "D30," the displacement between 0.5 and 30 N (in ram). The linear region of the curve was quantified by "K," the stiffness coefficient (in Newtons per millimeter) obtained by calculating the gradient of a regression line fitted between 30 and 90 N. The correlation between the regression line and the original data was greater than 0.99 in all cases. Therefore the regression line was considered to adequately describe the region of the curve between 30 and 90 N. This method of analysis has been used in a number of
previous studies. 16'21'26
The accuracy of the stiffness measurement device has been evaluated by use of a series of elastic beams. 2~ The results of this testing demonstrated that the stiffness measurement device has an error of less than 3% in measuring stiffness values in the clinical range. The intraclass correlation coefficients (ICC) for test-retest reliability of measurements of PA responses in patients with low-back pain by use of the device were found to be 0.89 for D30 and 0.96 for K. 21 A visual analogue scale (VAS) 27,28 was used to measure the intensity of pain experienced during active lumbar flexion and extension and during PA testing. The VAS consisted of a 10-cm line bounded by word descriptors defining the upper and lower limits of the scale. The descriptors were "Pain as bad as it could possibly be" at the upper end and "No pain" at the lower end. The patient was asked to draw a line across the scale indicating the severity of pain experienced. The distance of the mark from the lower limit was measured with a ruler to the nearest 1 mm. The VAS recordings were used to derive 4 pain measurements: pain on flexion, pain on extension, pain on worst movement, and pain on stiffness testing. The measure of pain on worst movement was obtained by recording the VAS score corresponding to the patient's most painful movement, that is, either flexion or extension. A pair of scaled lines comprising a pain relief scale 29 was used as an overall measure of change in pain. One scaled line, labeled "scale A" was used for cases of relief of pain, whereas "scale B" was used for worsening pain. In both cases one end of the line was marked as "0% No change." For scale A the other end was labelled "100% Complete relief," whereas for scale B the other end was labeled "100% Worse." The patient was asked to identify whether they believed that overall the pain experienced on measurement of flexion, extension, and PA stiffness had been the same, better, or worse than on the previous measurement. If the patient reported they were the same, they were given a score of 0%. If the patient reported the pain was better, they were asked to indicate the amount of improvement by marking scale A, whereas if pain was worse they were asked to mark scale B. The degree of change (ie, the overall change in pain) was measured with a ruler to the nearest 1 mm and then converted to a percentage, with improvement recorded as a positive and deterioration as a negative value. Range of movement in flexion was measured in two ways: a fingertip-to-floor measure and inclinometer readings of lumbar motion. Extension was measured only with the inclinometer. The inclinometer used (Plurimeter-V; Pluri-Gonio Systems, La Conversion, Champs des Pierretes, Switzerland) was an oil-filled pendulum inclinometer. The device was modified slightly by shortening the base because the existing base made it difficult to maintain the device in contact with the spine when the extension was measured in patients with mobile spines. The modified base was 75 mm in length and had 2 cylindrical feet (12 mm diameter, 25 mm long) attached to its lower surface 25 m m apart. The intratherapist reliability of measurements of flexion and extension range made with this device is high (ICC = 0.86 to 0.94). 30 For the
Journal of Manipulative and Physiological Therapeutics Volume 23 • Number 5 • June 2000 Effects of PA Mobilization • Goodsell et al
fingertip-to-floor measure the patient stood on a box 20 cm high and bent forward, reaching the fingertips toward the floor. A plastic tape measure was used to measure the distance of the fingertips to the floor to the nearest 5 mm. With the patient standing on a box, it was possible to obtain measurements for individuals who were able to reach beyond the normal level of the floor. The intratherapist reliability of this procedure is high (ICC = 0.98). 31 Procedure
A brief history of the patient's back pain was obtained, including details of the location and duration of symptoms, previous episodes of pain, factors precipitating the onset of pain, and daily activities that exacerbated pain. The patient then completed the McGill pain questionnaire, 23 which provided a multidimensional rating of pain severity over the 24 hours before testing. The patient's height and mass were also recorded. A passive manual examination of the lumbar spine 2z was performed to determine which spinal level would be treated with the mobilization intervention. Both the treating therapist and a measurer applied a rhythmic PA force to each lumbar spinous process of the patient in the prone position and noted the most symptomatic level. Where the measurer and therapist both selected the same spinal level, the spinous process and adjacent intervertebral spaces were marked. Where different levels were initially selected (in 4 cases), the patient was reexamined, and the findings were compared until a level could be agreed on. The measurer then performed the initial measurements of range of movement, pain, and PA stiffness. The starting position of the fingertip-to-floor measurement was standardized by having the patient stand with their toes at the edge of the platform, heels together and knees straight. The patient was instructed to place their right hand over their left so that the tips of the middle fingers were aligned and then reach down with their fingertips as far as possible toward their toes without bending their knees. At the end of the movement, the measurer marked the level of the right middle finger and measured the distance to the floor to the nearest 0.5 cm. The measurement was recorded and the mark removed before a second measurement was obtained repeating the same procedure. The final measurement was calculated by averaging the two scores and subtracting the height of the box, that is, 20 cm. The inclinometer measurements of flexion and extension range were then obtained, and the severity of pain experienced with these movements were recorded. Inclinometer measurements were performed in a similar manner to that described by Waddell et al. 3° Inclinometer readings were made at the level of the T12-L1 interspinal space and marked with the patient in the standing position. The feet of the inclinometer were placed on either side and at equal distances from the T12-L1 marker. The feet of the device were placed firmly over the skin in an attempt to maintain even pressure through both feet. Inclinometer measurements of flexion were first performed. The inclination at the T12-L1 marker was measured with the patient in a relaxed standing posture,
then the inclinometer was held at T12-L1 while the patient reached forward with the hands as far as possible toward the toes while keeping the knees straight. With the patient fully flexed, another reading was made at TI2-L1. The amount of flexion was calculated by subtracting the standing T12-LI value from the flexion T12-L 1 value. Immediately after measurement of flexion range, the patient was asked to record on a VAS the intensity of pain experienced when flexing. To obtain inclinometer measurements of extension range, readings were made in a similar manner to the flexion readings. For the extension position the patient crossed their arms across their chest and arched backward as far as possible without bending their knees. Immediately after measurement of extension range, the patient was asked to record on a VAS the intensity of pain experienced when extending. The PA response at the most symptomatic lumbar level was then measured. The position adopted by the patient for each PA test was standardized. The patient lay prone on the testing bed with their knees over a pillow and their arms in the position most comfortable for them, either by their side or above their head. This arm position was noted and kept consistent for each test. The mechanical head was angled in either a cephalad or caudal direction, depending on the level being tested. The directions used were cephalad 5.5 degrees for L2 and L3, caudal 4.5 degrees for L4, and caudal 16 degrees for L5. These directions have been used in previous research 2~.26 and are within the range used by experienced physiotherapists.~ Before PA stiffness testing, at least 2 preliminary cycles were applied to precondition the viscoelastic tissues before testing. The patient was questioned regarding the level of discomfort and any concerns regarding the testing. Testing then commenced, with data being collected for 5 cycles at a frequency of 0.5 Hz, applying forces up to approximately 100 N. During testing, the patient was asked to hold their breath at functional residual capacity to standardize the lung volume at which testing was performed, because it has been demonstrated that breathing may confound stiffness measurements. 32 Immediately after the stiffness test, the patient was asked to record on a VAS the intensity of pain experienced during the test. The patient then received the mobilization or control interventions depending on their allocated group. Group A received the mobilization intervention, whereas group B received the control intervention. The measurer left the room while the therapist applied the appropriate intervention. On completion of the intervention, the measurer was recalled, and the measurement procedures described above were repeated exactly. At the end of the second series of measurements, the patient was asked to use the pain relief scale to describe the overall change in pain. The patient compared the overall intensity of pain during the second series of measurements with the overall pain experienced during the initial series of measurements. The measurer again left the room and the second intervention was then applied; the control procedure for group A, mobilization for group B. When the measurer returned, the measurements
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Journalof Manipulativeand PhysiologicalTherapeutics Volume23 • Number5 • June2000 Effects of PA Mobilization
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Goodsell et at
Table 3. Mean difference scores calculated corresponding to changes associated with either mobilization or control treatment
Change with mobilization Variable PA response K (N/mm) D30 (mm) Pain Flexion (mm) Extension(mm) Worst (mm) PA test (mm) Overall (%) Range of movement Finger-to-floor(em) Flexion(degree) Extension (degree)
Change with control
Group A
Group B
GroupsA and B
GroupA
Group B
Groups A and B
-0.31 -0.43
-0.32 +0.10
--0.31 -0.14
-0.03 +0.12
+0.32 +0.14
+0.16 +0.13
-9.2 -.4.9 -15.9 -0.7 -35.4
-3.4 - 10.0 -11.3 -9.9 -15.4
-6.1 -7.4 -13.4 -5.7 -24.7
-I .9 -3.5 -3.5 +4. I -28.9
-2.1 -2.0 -3.4 +9.2 +4.1
-2.0 -3.0 -3.5 +6.9 -11.1
+0.9 +0.2 +0.8
+2.7 + 1.6 -0.5
+ 1.9 +0.9 +0.9
+ 1.I +2.7 + 1.5
+2.4
+ 1.8
+0.3 -0.2
+ 1.4 +1.4
Pain scores are recorded in millimeterschange in locationof pain score on VAS, except for the overall pain reliefscale, which is measuredas a percentage. The positivesignsrepresentan increasein a variablein associationwith that intervention.The signsof fingertips-to-floormeasureshave been adjusted so a positivesign represents an increase in rangeof movement,correspondingto a lower positionof the fingertips. Table 4. Values of F from results of analysis of variance to test for differences between treatments (mobilization versus control), between groups (group A versus group B) and interactions between these 2 effects (interaction)
Variable PA Response K (N/mm) D30 (mm) Pain Flexion(mm) Extension(mm) Worst (mm) PA test (mm) Overall (%) Range of movement Finger-to-floor(cm) Flexion(degree) Extension(degree)
Group A vs group B
Mobilization vs control
Interaction
0.64 3.05
0.16 0.97
0.09 0.84
1.25 0.29 0.61 0.85 5.29*
1.64 1.42 6.37* 3.29 2.63
0.89 0.62 0.34 1.08 0.61
3.42 0.15 2.90
0.004 0.04 0.15
0.01 0.67 0.001
*Significant,P < .05, F~t = 4.26. were repeated. After this final series of measurements, the patient was again asked to use the pain relief scale to compare the intensity of pain experienced in the final series of m e a s u r e m e n t s with that experienced during the second series of measurements. Data analysis
A total of 10 dependent variables were used for statistical analysis: K, D30, pain on flexion, pain on extension, pain on worst movement, pain on stiffness testing, overall change in pain, fingertip-to-floor distance, flexion range, and extension range. Difference scores were computed representing the change in each variable (postintervention value minus preintervention value) associated with the mobilization and control interventions. The statistical analysis method was 2 x 2 factorial analysis of variance with repeated measures on one factor. One factor w a s group (ie, mobilization-first or control-first) and the other was intervention (ie, mobilization or control). The significance level was set at et = .05. Correlations were also per-
formed to evaluate whether a relationship existed between change in K and the age of the patient, the chronicity of the injury, their initial stiffness, whether the patient's pain responded to PA mobilization, whether their extension range increased with mobilization, and the force applied by the therapist in the treatment.
RESULTS The means and standard deviations of each variable on each of the three measurement occasions are given in Table 2. The mean values of the difference scores of each variable, representing the change associated with the mobilization or control treatment are given in Table 3. The results of the statistical analyses are given in Table 4. As can be seen in Table 2, there were small changes only in the mean value of the mechanical variables describing the PA response and the measures of range of movement. The two variables describing the PA response, K and D30, showed mean changes between tests of less than 2% and less than 6%, respectively. This change in "K" is likely to be within the range of random variation. The range of movement values for flexion and extension changed by up to 3% and 2%, respectively. The fingertip-to-floor distance showed a greater percentage change because the values were all nearer to zero, but the magnitudes of the changes were also small. A number of the pain scores demonstrated proportionately larger changes in the mean values between tests, but they also showed much greater variability across the group, as evidenced by the large standard deviations. In group A pain on flexion decreased by an average of 41% between test 1 and test 2, that is after mobilization, and decreased by 15% between test 2 and test 3, after the control procedure. In group B pain on flexion decreased by an average 7% after the control procedure (between test I and test 2) and decreased by 11% after the mobilization, between test 2 and test 3. In group A pain on extension decreased a similar amount in association with each of the procedures (19% and 18%), but group B showed a much larger decrease in average pain level after mobilization (33%) compared with the
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earlier control intervention (6%). When the pain scores were expressed as the pain on the worst movement, both groups showed a larger change during the mobilization procedure (group A 40%, group B 31%) than the control procedure (group A 17%, group B 8%). For both groups pain on PA testing showed a mean decrease associated with the mobilization (smaller for group A), but an increase associated with the control procedure. The patients' overall assessment of the change in pain produced by each intervention (overall change in pain) showed that, on average, the pain improved for both groups after mobilization; in group A (35%) more than in group B (15%). However, the response after the control intervention differed between the 2 groups, with group A showing an improvement in overall pain (29%) after the control intervention but group B showing a slight worsening (4%) of pain. The main questions addressed in this study were whether PA mobilization of the lumbar spine would cause a greater change in PA response, pain, and range of movement than a control intervention, in a population of patients with lowback pain. There was no significant difference between the effect of the two interventions with respect to the two PA response variables, the stiffness coefficient K and displacement D30. Analysis of the pain variables indicated that the pain on the worst movement decreased significantly (P < .05) with mobilization when compared with control, although there was no difference between the effect of the 2 interventions in terms of overall change in pain, or any of the other pain variables. In addition, no significant difference was found between the effect of mobilization and control on any of the three range of movement measures. Comparison between group A (mobilization first) and group B (control first) showed that there was a significant order effect in relation to only 1 variable, the overall change in pain (P < .05). Group A showed a greater improvement in overall pain (averaged across both mobilization and control interventions) than group B.
DISCUSSION Although mobilization is frequently used in the management of low-back pain, there has been relatively little investigation of its effect on low-back pain symptoms or the mechanism whereby it achieves these effects. It is frequently proposed that manipulative therapy interventions, such as mobilization, alter symptoms via an effect on the mechanical properties of the spine, 33-35 and therefore a change in the mechanical response of the spine might be expected to occur after treatment. However, our study did not demonstrate a change in the mechanical response of the spine as measured by the PA response variables, the stiffness coefficient K or the displacement D30, or the measures of range of movement. The finding that PA stiffness did not change after mobilization is in agreement with the only previous study evaluating the effect of a manipulative therapy intervention on PA stiffness, in which a PA thrust manipulation was found to have no effect on PA stiffness in the thoracic spine of symp-
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tom-free patients. 36 Although a different response might have been expected in patients with low-back pain, this was not found in the group studied. A number of factors need to be considered in interpreting the absence of a change in PA response. One factor may be that the treatment did not produce a sufficient change in pain for a change in stiffness to be detected. A previous investigation that examined the PA response in patients with back pain when they had comparatively high levels of pain and on follow-up when pain was significantly reduced found that PA stiffness did decrease as pain levels decreased. '6 In the study by Latimer et al, t6 patients with low-back pain demonstrated a significant (8%) change in K in association with a 90% improvement in the VAS score for pain during PA testing. In contrast, the group A and group B patients in our study showed 4% and 28% improvements, respectively, in the VAS for pain during PA testing. The patients in the study by Latimer et a l l 6 w e r e also observed over a longer time frame (that is, the mean time between tests was 21.16 days, S D = 9.91). A limitation of our study was that the treatment was applied on only a single occasion. Future studies addressing the effect of particular treatments on mechanical variables such as the PA response may need to evaluate changes over a number of treatment occasions. Other aspects of treatment dose, such as the force used in treatment and the number of cycles of loading, may also account for the failure to demonstrate a change in the mechanical variables. In this study the treatment grade and force were selected by the therapist who applied the treatment on the basis of her assessment of the patient, as is the case in clinical practice. This decision was made because of a lack of data that would have enabled the selection of an appropriate standardized treatment force. Interestingly, although all treatments were applied by the same therapist who had considerable manual therapy experience, a large range of maximum treatment forces was used, from 60 to 230 N. This variation tends to justify the original decision not to standardize the treatment force because the use of a single standardized force would have been contrary to the clinical situation. Post hoc analysis found no correlation between treatment force and changes in K, suggesting that level of force was not a significant factor influencing whether the mechanical response changed. Other aspects of treatment dose that may have contributed to the ability of the intervention to affect the mechanical responses are the duration and number of repetitions of the mobilization and the number of treatment sessions. In this study the duration of mobilization was standardized to three 1-minute repetitions, a duration of treatment commonly used in clinical practice. It is possible that a greater number of treatment sessions may have produced a change in stiffness, because studies that have demonstrated an increase in range associated with mobilization have usually applied treatment over a period of weeks. 5,J° A study that reported an improvement in range associated with only one treatment session of mobilization used a similar "grade" of mobilization but for a greater duration than in this study. 13 Further research is required to
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investigate the possible effects of these aspects of treatment dose. A second explanation for the absence of a change in PA response is that changes did occur but only in a subgroup of the measured group. The difficulties in diagnosing and therefore classifying low-back pain are well recognized, making it difficult to obtain a homogeneous group of patients with back pain. In view of the introductory nature of the stiffness findings, this being the only study that has examined the effect of an intervention on PA response in patients with pain, and the trend for the stiffness variable K to change in the direction expected, the data were examined further to determine whether a subset of the group was more likely to demonstrate a change in K. A number of factors could arguably influence the likelihood of stiffness changing with mobilization. These include the age of the patient, the chronicity of the injury, their initial stiffness, whether the patient's pain responded to PA mobilization, whether their extension range increased with mobilization, and the force applied by the therapist in treatment. To determine the relation of these factors to the changes in K observed, a post hoc correlation analysis was performed. A low but statistically significant correlation of 0.4 was found between the patients' ages and their change in K, indicating that younger patients were more likely to demonstrate a decrease in stiffness with mobilization. Agerelated changes in the biochemical and structural characteristics of spinal tissues, in particular to the intervertebral disk, are well documented. 37-39 In addition, pathologic changes such as disk degeneration, which are not necessarily a consequence of aging but are more observed in old age, might affect the spines of older patients. 3s Therefore structural differences between the spines of young and old patients might account for the tendency for stiffness changes to occur only in younger patients. The finding that some of the variability in stiffness change was related to age may have implication for future research investigating the effect of interventions on PA stiffness, suggesting that populations should be grouped on the basis of age. Although a low correlation was observed between change in K and age, the other variables analyzed failed to correlate with a change in K. The correlations found between change in K and these variables were as follow: duration of symptoms (r = - . 19, P = .36), initial value of K (r = -.26, P = .20), change in pain on worst movement (r =-.34, P ---.09), change in pain on stiffness testing (r = -.09, P = .65), change in extension range (r = -.29, P = .16), and treatment force (r = -.08, P = .71). These findings do not allow the identification of any subgroup other than the younger group that may be more likely to demonstrate a change in PA stiffness. It is possible that the failure to demonstrate a significant change in range of movement or the PA response may be due to the sensitivity of the devices used to measure these parameters. The stiffness measurement device has been shown to be sensitive to change, with the device recording a change in the PA response when a force was applied toL3 in patients admitted with low-back pain and when their lowback pain had resolved. ~6 It may be the case in this study,
however, that if the changes observed after mobilization were extremely small, they were not detected by the stiffness measurement device. This may also hold true for the tools used to measure range of movement. For example, the fingertip-to-floor distance could have been measured to the nearest 0.1 cm instead of 0.5 cm. Although the sensitivity of the equipment may be a potential limitation of the study, it should be remembered that if the changes experienced after mobilization are so small then they will also be clinically undetectable. Manipulative therapy treatments are primarily used to relieve patients' symptoms, and therefore relief of pain is a primary indicator of the effect of treatment. The results of this study indicate that PA mobilization of the lumbar spine produced a greater decrease in the intensity of pain experienced on active movement than a control intervention. Although there have been studies evaluating the effect of several mobilization procedures on range of movement, ~0-t3 no studies have examined the effect of an individual lumbar mobilization on low-back pain. Three measures of pain intensity on active movement were obtained in this study: pain on flexion, pain on extension, and pain on worst movement, either flexion or extension. With mobilization there was a 35% improvement in the mean pain on worst movement (13.4 _ 13.3 mm on 10 cm VAS) compared with an 11% improvement with control intervention (3.5 - 11.6 mm). Although a significant change in pain on worst movement was observed, no significant difference was found between mobilization and control for the two other measures of pain on active movement. This finding might be explained by patients experiencing pain on only flexion or extension, with little or no pain on the other direction of movement. Thus the measures of pain on flexion and pain on extension would have a more limited ability to demonstrate a change in symptoms. The pain on worst movement measure, by use of the more painful direction of movement, would be better able to demonstrate a change in symptoms when only one direction of movement was painful and would therefore be a more sensitive indicator of change. The patients' overall perception of the benefit of treatment, as measured by the parameter overall change in pain, demonstrated a different pattern of change across the two groups, indicating that this measure was influenced by the order in which patients received the mobilization and control interventions. When mobilization was received first, the patient reported a beneficial effect, and this effect carried over to the period of the control intervention. Thus group A (mobilization first) reported a similar improvement associated with both mobilization and control intervention. In contrast, when the control intervention was received first, the patient reported a worsening of symptoms with control intervention, and this worsening appears to have influenced the perception of benefit with mobilization such that for group B, the improvement in pain associated with mobilization was less than the improvement associated with either mobilization or control intervention in group A. The
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observed order effect may be explained by either the physical or psychological effects of the control intervention being different depending on when it was received. The control intervention controlled for the effect of extraneous physical factors associated with mobilization, that is, the effect of active movement and PA stiffness measurements, as well as the effect of the patient getting on and off the treatment couch, and maintaining the treatment position. These physical factors may have affected the patient's symptoms such that, when mobilization was received first, the improvement produced by mobilization created a situation where the physical factors associated with control produced a further improvement in symptoms. However, when control intervention was received first, without the beneficial effect of mobilization, these same test procedures exacerbated symptoms. The order that the interventions were received may also have produced psychological effects that influenced the patient's perception of changes in symptoms. The control intervention did not control for the psychological effects of treatment because patients were aware whether they were receiving the "beneficial" mobilization intervention or the "inactive" control intervention. Therefore the fact that the active treatment was withheld, if only for a short period, in the control-first group, may have produced a negative perception of the effect of intervention. If the order effect on the overall change in pain was solely caused by psychological factors, then all the pain variables might be expected to demonstrate the same trend, that is, a worsening of symptoms after the control intervention in group B patients. However, examination of the findings for the other subjective pain variables indicates that this was not the case. Rather, the pain on the active movement measures (pain on flexion, pain on extension, and pain on worst movement) improved with control intervention in both groups, with only pain on stiffness testing demonstrating an increase with control intervention. Therefore both physical and physiological factors may have contributed to the order effect. Future studies could allow a washout period, that is, a greater time to elapse between the two interventions to determine whether the order effect on the overall change in pain would persist. However, the lack of information regarding the time course of treatment effects would make it difficult to determine what the optimum washout period should be. One limitation of this study is the absence of an adequate placebo intervention that controls for changes in pain. This study included a control intervention that controlled for the extraneous physical factors associated with mobilization, with the aim of accounting for factors other than mobilization that may have been responsible for any changes in PA stiffness observed. However, the control intervention did not control for psychological effects associated with treatment that might produce a relief of pain. Consequently, the improvement in pain observed might be interpreted as being due to psychological factors, particularly in the absence of a change in the other physical parameters of PA stiffness and lumbar range of movement. The difficulty in providing an adequate
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alternative intervention that controls for the placebo effect is an ongoing problem in manipulative therapy research.
CONCLUSION The findings of this study indicate that PA mobilization can reduce the intensity of pain experienced when a patient moves their spine actively. This finding suggests that PA mobilization may be a useful intervention to relieve pain in some patients with back pain. At present, the mechanism of effect of manipulative therapy procedures such as PA mobilization is not clear, although the theory that manipulative therapy changes the mechanical properties of the spine is widely held. Our study found that pain improved with mobilization whereas PA response and range of movement measures did not, thus opening this theory to question. In our study no link between a change in pain and changes in the mechanical response of the spine could be established. Therefore our findings suggest that the change in pain may have been produced by other mechanisms, such as psychological mechanisms. A low correlation was observed between changes in the stiffness variable K associated with mobilization and the patient's age, with younger patients more likely to demonstrate a decrease in stiffness associated with mobilization. This finding may be useful for further studies investigating the effect of interventions on PA stiffness, suggesting that future investigation restricting the patient's age might be more likely to demonstrate a change in stiffness.
ACKNOWLEDGMENT We thank Dr Louise Ada for her helpful comments during the manuscript preparation and Sue Barker for her valuable assistance in the testing of the patients.
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