Lumbar segmental instability: a criterion-related validity study of manual therapy assessment
BACKGROUND
Musculoskeletal physiotherapists routinely assess lumbar segmental motion during the clinical examination of a patient with low back pain. The validity of manual assessment of segmental motion has not, however, been adequately investigated.


METHODS
In this prospective, multi-centre, pragmatic, diagnostic validity study, 138 consecutive patients with recurrent or chronic low back pain (R/CLBP) were recruited. Physiotherapists with post-graduate training in manual therapy performed passive accessory intervertebral motion tests (PAIVMs) and passive physiological intervertebral motion tests (PPIVMs). Consenting patients were referred for flexion-extension radiographs. Sagittal angular rotation and sagittal translation of each lumbar spinal motion segment was measured from these radiographs, and compared to a reference range derived from a study of 30 asymptomatic volunteers. Motion beyond two standard deviations from the reference mean was considered diagnostic of rotational lumbar segmental instability (LSI) and translational LSI. Accuracy and validity of the clinical assessments were expressed using sensitivity, specificity, and likelihood ratio statistics with 95% confidence intervals (CI).


RESULTS
Only translation LSI was found to be significantly associated with R/CLBP (p < 0.05). PAIVMs were specific for the diagnosis of translation LSI (specificity 89%, CI 83-93%), but showed poor sensitivity (29%, CI 14-50%). A positive test results in a likelihood ratio (LR+) of 2.52 (95% CI 1.15-5.53). Flexion PPIVMs were highly specific for the diagnosis of translation LSI (specificity 99.5%; CI 97-100%), but showed very poor sensitivity (5%; CI 1-22%). Likelihood ratio statistics for flexion PPIVMs were not statistically significant. Extension PPIVMs performed better than flexion PPIVMs, with slightly higher sensitivity (16%; CI 6-38%) resulting in a likelihood ratio for a positive test of 7.1 (95% CI 1.7 to 29.2) for translation LSI.


CONCLUSION
This study provides the first evidence reporting the concurrent validity of manual tests for the detection of abnormal sagittal planar motion. PAIVMs and PPIVMs are highly specific, but not sensitive, for the detection of translation LSI. Likelihood ratios resulting from positive test results were only moderate. This research indicates that manual clinical examination procedures have moderate validity for detecting segmental motion abnormality.