Clinical Biomechanics 1989; 4: No 4: 249-251
Brief Report
Mechanks of spinal joint manipulation in the thoracic and lumbar spine: a theoretical study of posteroanterior force techniques M Lee
BE BAPPSC
Cumberland College of Health Sciences, Sydney, Australia
Summary Posteroanterior (PA) forces applied to the vertebrae are commonly used for the clinical assessment and treatment of vertebral column disorders. Three strategies for applying PA force in the thoracic and lumbar spine regions were studied. The components of the manipulative force which were directed along, and transverse to, the axis of the vertebra were calculated, and also the sagittal plane moment generaW about the centre of the vertebra was determined. The three different strategies produced quite diierent loads on the vertebrae and all three strategies showed substantial variations across vertebral levels in at least one of the load components.
Relevance The strategy of applying the manipulative force normal to the spinal curve was found to produce the most consistent lodds across vertebral levels. However, practitioners using PA forces should be aware that the sagittal plane moments being produced by the manipulation are likely to be substantial. Therefore the intervertebral joints above and below the point of application of force are not equally affected. Key words: Lumbar spine, thoracic spine, biomachanics, manipulation
Introduction For hundreds of years low back pain has been treated by the application of a force over the spinous processes of a prone patient’. Posteroanterior (PA) force is currently used both in the clinical assessment of spinal movements and for treatment of back disorders2.“. Although the procedures for application of PA force have been described in some detai12, the mechanics of this technique and its variations have not been studied. Grieve’ stated that PA force will produce ‘movement of a dissimilar nature at each region’. White and Panjabi observed that in the thoracic spine there may be rotation combined with translation of the vertebra when the force is directed anteriorly. Two steps are necessary to establish the response of the spine to PA force. Firstly, by considering the Received: 7 March 1989 Accepted: 10 July 1989 Correspondence and reprint requests to: Michael Lee, Department of
geometry of the vertebral column, the components of the applied load must be defined. Secondly, the response of the vertebra to this load must be established by considering the resistance to movement offered by the structures attached to the vertebra. The resistance of these structures has been found experimentally in vitro5’” where the resistance to loads applied to the centre of the vertebral body was calculated. The objective of this investigation was to define the loads induced by the application of PA forces in the thoracic and lumbar regions of the spine. It was aimed to quantify the effective applied load corresponding to three different strategies for the application of PA forces. These three strategies were: (1) an anteriorly directed force; (2) a force applied normally to the spinal curvature; and (3) a force directed towards the centre of the vertebral body.
Biological Sciences, Cumberland
College of Health Sciences. East Street, Lidcombe, Sydney 2141, Australia
Methods
0 1989 Butterworth & Co (Publishers) Ltd 0268-0033/89/040249-03 $03.00
A model of the spine was established using both original and previously published human anthropometric data.
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Figure 1. Variation of transverse (upper three curves) and longitudinal (lower three curves) components of force with vertebral level for the three strategies for application of force. The positive directions for longitudinal force (6,) and transverse force (&) are shown.
The mechanical effect of a 200 N force applied to the spinous process was determined by calculating the force and moment applied to the centre of the vertebral body which would be equivalent to this 200 N force. Forces in the order of 200 N have been measured during spinal physiotherapy treatment’. Equivalent forces and moments at the centre of the vertebra were computed to allow for the subsequent utilization of existing intervertebral joint stiffness data5.h. The present study adopts the data of Nissan and Gilad which represents the most complete available description of normal lumbar vertebral geometry. However, previously published data for the thoracic spine are inadequate. Therefore, the required thoracic vertebral dimensions were obtained by measurement of ten skeletal specimens from which all soft tissue had been removed. Thoracic disc heights were taken from the data of Schultz et al.’ For this investigation, it was assumed that spinal posture in the prone position was the same as that when standing erect. Therefore, the posture data of Stagnara et al.“’ were combined with the vertebral and disc dimensions supplied by Nissan and Gilad’ and Schultz et al.9 and with the thoracic vertebral measurements in order to define the spinal model.
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ferior in its direction. In the lumbar spine this component of the applied force reverses direction again to become 21% of the applied load at L5 level. Directing the applied force towards the centre of the vertebra, (strategy 3) leads to a considerable, superiorlydirected longitudinal component in the thoracic spine. The levels of force are from 24% to 57% of the applied force with the maximum at T7 level. In the lumbar spine, strategy 3 produces longitudinal components which are between 12% and 27% of the applied force. The variation of moments produced by the three approaches is shown in Figure 2. Strategy 3 produces no moment, because the force is directed towards the centre of the vertebra. However, strategies I and 2 result in moments of more than 5 N m at some levels. In the thoracic spine, both generate positive moments which are greatest in the mid-thoracic region (T7-T8). In the lumbar spine, anteriorly directed force produces a large positive moment at L,. The size of the moment decreases at lower levels and becomes negative at L=,. If the force is directed normally to the spinal curve, then the moment is moderately high at L, (3.6 Nm) and decreases to about 40% of this value at Ls.
Results The sign conventions and calculated forces and moments are shown in Figures 1 and 2. Figure 1 shows that for all three strategies there is relatively little variation in the component of force transverse to the axis of the vertebra. Longitudinal force varies substantially throughout the thoracic and lumbar vertebral column, with the exception of strategy 2, where the force remains constant at zero. When the force is directed anteriorly (strategy I ) the upper thoracic spine (T1-T7) experiences a superiorly directed component of force up to 29% of the applied force. In the lower thoracic spine, this component becomes in-
Discussion and conclusions The geometric model of the spine used here will not be valid for all patients. Insufficient data are available to predict the variations of vertebral geometry that are likely in a large population. In the present model, different methods of measurement were used to locate the thoracic and lumbar spinous processes. Therefore, comparisons between data on the thoracic and on the lumbar spine should be made with caution. Withinregion comparisons are more valid. The longitudinal component of an anteriorly directed force can be relatively large. It reaches about 30% of
Lee: Spinal joint manipulation 251
the applied load in the thoracic spine and about 15% of the applied load in the lumbar spine. To avoid generating longitudinal forces the practitioner can apply the force normal to the spinal curve. By doing this the variation of moments reduces slightly. If strategy 3 is adopted, which produces no moment about the centre of the vertebra, then large longitudinal components of force will occur in the thoracic spine (Figure 1). Large moments affecting the superior and inferior intervertebral joints can be generated by strategies 1 and 2. The maximum calculated moments can produce intervertebral shear forces of a magnitude similar to those produced by the transverse force. The size of the sagittal moment is clinically significant because it leads to an uneven distribution of load on adjacent intervertebral joints. The large positive moments found in strategies 1 and 2 will tend to increase the shear reaction force at the joint below and to decrease it at the joint above. Of the three strategies considered, the application of force normally to the spinal curve would appear to be the most useful. Using this approach, the force has no longitudinal component and the moment, although always of significant magnitude, is not as variable as when the force is applied anteriorly. The effects of the PA force will depend on both the load (defined by the size of the moment and by the two components of force) and the movement which occurs in response to that load. The movement will vary at different vertebral levels, even if the same load components are applied, because of variations in the stiffness of the intervertebral joints. Further research is needed to establish the movements which would occur in response to the loads which have been computed in the present investigation. When assessing the symptom behaviour of the patient, or the movement of the spine on application of PA
forces at each vertebral level, perceived variations in patient response may be due to changes in the manner in which the vertebrae experience the applied load. Changes in the longitudinal component of the force or in the moment may alter the proportion of resistance offered by the discs, zygapophyseal joints or other structures. Hence, the symptoms arising from these structures may be altered. Therefore, if the likely effects of this manipulative procedure are to be appraised fully, the magnitude of the longitudinal force component and the sagittal plane moment must be taken into account. References
Schiotz EH, Cyriax J. Manipulation Past and Present. London: William Heinemann Medical Books Ltd, 1975 Maitland GD. Vertebral Manipulation, 5th edn. London: Butterworths, 1986 Grieve GP. Mobilisation of the Spine, 4th edn. Edinburgh: Churchill Livingstone, 1984 White AA, Panjabi MM. Clinical Biomechanics of the Spine, 1st edn. Philadelphia: J.B. Lippincott Co., 1978 Panjabi MM, Brand RA, White AA. Three-dimensional flexibility and stiffness properties of the human thoracic spine. J Biomech 1976; 9: 185-92 6 Edwards WT. Hayes WC, Posner I, White AA. Mann
RW. Variation of lumbar spine stiffness with load. J Biomech Eng 1987; 109: 35-42 7 Matyas TA, Bach TM. The reliability of selected techniques in clinical arthrometrics. Aust J Physiother 1985: 31: 175-99 8 Nissan M, Gilad I. Dimensions of human lumbar vertebrae in the sagittal plane. J Biomech 1986; 19: 753-8 9 Schultz AB, BelytschkoTB, Andriacchi TP. Galante JO. Analog studies of forces in the human spine: mechanical properties and motion segment behaviour. J Biomech 1973; 6: 373-83 10 Stagnara P, de Mauroy JC, Dran G. Gonon GP. Costanzo G. Dimnet J. Pasquet A. Reciprocal angulation of vertebral bodies in a sagittal plane: approach to references for the evaluation of kyphosis and Iordosis. Spine 1982; 7: 335-42