The effect of simulated knee flexion on sagittal spinal alignment: novel interpretation of spinopelvic alignment.

INTRODUCTION

Many studies regarding spinal sagittal alignment were focused mainly on above-hip structures, not considering the knee joint. Knee-spine syndrome was proposed earlier, but the mechanism of this phenomenon has not been revealed. The aim of the study was to demonstrate how spinopelvic alignment and sagittal balance change in response to simulated knee flexion in normal non-diseased population.

METHODS

Thirty young male were enrolled in the study cohort. Two motion-controlled knee braces were used to simulate knee flexion of 0°, 15°, and 30° settings. Whole spine and lower extremity lateral radiographs were taken at each knee setting of 0°, 15°, and 30° flexion. Spinal and pelvic parameters were measured, including two angular parameters, femoropelvic angle (FPA) and femoral tilt angle (FTA).

RESULTS

The following equation can be made; PT (pelvic tilt) = FPA + FTA. The mean values of FPA and lumbar lordosis decreased significantly at 15° and 30° knee settings compared to the parameters at the 0° knee setting, while the mean values of pelvic tilt and sacral slope rarely changed. Results also showed FTA was not correlated with PT, but strongly correlated with FPA (R = -0.83, p < 0.01).

CONCLUSIONS

The knee flexion resulted in decrease of lumbar lordosis without a significant change of pelvic posture in non-diseased population group.