The effect of a plaster cast on lumbosacral joint motion. An in vivo assessment with precision motion analysis system.

STUDY DESIGN: This study was conducted to assess the effect of a plaster cast on the mobility of the lumbosacral joint in 10 patients with chronic low back pain. During static and dynamic exercises, movements between the proximal vertebra (L4 or L5) and the sacrum were registered in 10 patients without a support and after the application of a plaster cast, and with and without unilateral hip immobilization, respectively.

OBJECTIVES: To investigate whether plaster casts actually immobilize the lumbosacral joint.

SUMMARY OF BACKGROUND DATA: The presumed stabilizing effect of a lumbar orthosis on the lumbosacral joint has been the subject of many studies in the past years, and contradictory reports have been published.

METHODS: The measurements were performed by means of Precision Motion Analysis System, an optoelectronic three-dimensional motion analysis system using infrared light. The patients were asked to perform maximal spinal flexion to extension, maximal pelvic tilt (static test conditions), and to walk within the measurement volume (dynamic test condition). This procedure was repeated with the patients wearing a plaster cast with and without unilateral hip fixation. Mobility was expressed in translations and rotations around three axes. For statistical analysis, repeated measurements two-way analysis of variance was used.

RESULTS: Considerable rotations were found only in the sagittal plane. Both plaster casts appeared to decrease mobility during the static test conditions. During the dynamic test condition, however, no significant decrease of mobility of the lumbosacral joint by either of the casts could be observed. In both cast conditions, considerably more sagittal rotation was found during walking than with the other two exercises.

CONCLUSION: In the sagittal plane, a plaster cast with or without unilateral hip immobilization can decrease motion during spinal flexion-extension. This stabilizing effect on the lumbosacral joint could not be observed during walking.