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Summary
The leg seems to grow a little longer when marks on the medial malleoli at the ankles are compared before and after external rotation of the leg. The leg then shortens after internal rotation. If the leg lengths do not alter the test on that side is said to be abnormal or stuck.
The features of this intriguing test have been known for most of this century but it has not been possible to give a satisfactory clinical explanation for the test.
It has however generally been suggested that the leg acts as a lever on the pelvis which adjusts the sacroiliac joint resulting in the apparent leg length changes and if the test is “stuck” it in turn implies that the sacroiliac joint is itself “stuck”.
This explanation was disproved by performing the test on patients with advanced ankylosing spondylitis in whom the sacroiliac joints had fused and become completely solid. The apparent leg lengths could still be made to change.
This prompted re-examination of sites of pain drawing data from a therapeutic trial and low back pain classification study which hinted at a new explanation. It seems that impairment at a higher level in the low back at the dorso-lumbar junction explains the abnormal “stuck test response”. This was an unexpected finding and probably helps explain the site of mechanism of this and a number of other similar and related tests. Also the side that is “stuck” in the leg test corresponds to the side involved at the dorso-lumbar junction. These findings have been confirmed with subsequent clinical observations.
The stuck response was to indicate that involvement at the dorso-lumbar junction occurs in almost half (46%) of the cases presenting with low back pain. The test also helped explain characteristics of the pattern of rotation strain of the low back.