OBJECTIVE: To determine the extent of sagittal plane rotation of the pelvis during lumbar spine posteroanterior loading.

DESIGN: Quantitative study.

SETTING: Biomechanics Laboratory, Faculty of Health Sciences, University of Sydney.

PARTICIPANTS: Ten male and female subjects with no recent history of significant low back pain.

INTERVENTION: A mechanical device was used to apply forces to the L3 spinous process. Data were collected during slow cyclical loading.

MAIN OUTCOME MEASURE: The stiffness of the posteroanterior movement at the point of loading was measured, together with the sagittal plane rotation of the pelvis and the resistance to rotation provided by the bed on which the subject lay.

RESULTS: Mean pelvic rotation was 2.1 degrees per 100 N applied force (SD 1.01 degrees/100 N). Mean posteroanterior stiffness was 13.4 N/mm (SD 3.13 N/mm) and resistance to pelvic rotation was 2.71 Nm/degree of pelvic rotation (SD 0.84 Nm/degree).

CONCLUSION: During posteroanterior force application there is pelvic rotation of a magnitude that may be sufficient to have clinical significance. Abnormalities found during lumbar posteroanterior force application may originate in tissues caudad to the lumbar spine itself.

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