Abstract
Low back pain is a very common complaint in medicolegal cases. However, and contrary to many other conditions, there are no objective medical exams that are able to help establish impairment rating.
Testing the function of the trunk may, however, help back pain assessment. Many different principles of trunk function testing have been described.
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Range of motion (ROM)
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Isometric strength measures
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Isokinetic strength testing
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Isoinertial strength and velocity measures
Of all these techniques, isoinertial testing provides the closest simulation of natural movement and therefore seems the most appropriate for clinical trunk testing and assessment of spinal function.
Functional assessment may enable a good estimation of remaining functional status and therefore permits a reasonable measure of the functional loss compared with age and sex matched databases. Nevertheless, for this measure to be reliable and valid one must be sure that the subject exerted a maximal performance: a maximal voluntary effort. Only then can the measured function be used to assess handicap.
Different techniques have been elaborated to recognize maximal effort. The most accepted appears to be reliability (or reproducibility) of performance which postulates that impaired subjects will generate lower but reproducible performance. It has been well-validated in different areas of strength testing: hand grip, elbow flexors, knee extensors, shoulder press and posturography. In trunk testing, it has been established for isokinetic and isoinertial measures. A possible reliable submaximal performance has been shown to be possible in some specific conditions which are not usually found in low back pain sufferers. Furthermore, the measure of the coefficient of variance (CV), sometimes proposed, is not a reliable way to assess reproducibility of performance.
The meaning of submaximal performance must be carefully understood, it may be the result of many factors like misunderstanding of instructions, fear of reinjury, anxiety, psychological distress and in some cases symptom amplification or malingering. The latter hypothesis can only rarely be determined with a reasonable degree of certainty.
Instrumented function assessment can help to determine the degree of impairment in case of maximal effort. That is it’s major interest and use. A submaximal effort will not help to determine impairment but does not necessarily indicate a conscious attempt at symptom magnification or malingering, and requires further investigation. It cannot by itself inform the sincerity of the complainant. Functional assessment can be used to find a fair compensation in case of maximal effort. It cannot be used to chase so called “malingerers” if this effort is not realised. There is no such thing as a lie-detector of back function.
The abstracts were prepared by Dr P Dolan. Correspondence should be addressed to him at the British Orthopaedic Association, Royal College of Surgeons, 35-43 Lincoln’s Inn Fields, London WC2A 3PN.
