The Unstable Lumbar Segment Definition and Detection

Abstract

It has been proposed that the restraining structures of an individual lumbar segment may become weakened during the early stages of degeneration. The process results in a loss of stiffness in the restraints, compromising their constraining and restoring forces. The effected level would offer less resistance to an applied load and it may displace through excessive range or display abnormal movement patterns. Erratic centrode patterns have been found in cadaveric segments with early disc degeneration. Abnormal ratios between segment translation and rotation have been detected in a group of ten patients with degenerative disc disease. Early attempts to detect abnormal motion radiologically have proved unreliable. Two new techniques are being researched. Some clinicians consider that an unstable lumbar segment can be detected by perceiving abnormal compliance during manual passive accessory tests. These perceptions have been defined biomechanically in terms of an increased neutral zone in the segments. These findings have not yet been validated in cases of proven instability.