[Effect of simulating leg length inequality on spinal and pelvic posture in the elderly]

Objective: To study the effects of simulating leg length inequality on the spine and pelvic posture in standing and walking states and to explore their compensatory laws. Methods: From January to April, a total of 44 healthy volunteers were rasterstereographically examined for spine and pelvis in Institute of Digitized Medicine, Wenzhou Medical University and Department of Orthopaedics, First Affiliated Hospital of Wenzhou Medical University.Volunteers wore uniform shoes, and single 5 mm thick insoles were customized.The simulating leg length inequalities (5-30 mm) were artificially created by increasing insole height.The parameters of 3D body surface parameters and 4D dynamic parameters of the pelvic and spine were measured and statistically analyzed in standing and walking states. Results: In the static standing state, with the increase of the difference of both lower extremities, coronal plane pelvic tilt and sagittal plane pelvic torsion also increased[the maximum value about (10.6±4.3) mm and (3.3±3.5)°], as well as the frontal deviation of the spine [the maximum value about (11.1±17.9) mm]. But the pelvic rotation, vertebral surface rotation angle (rms) and spine sagittal plane deviation were no obvious changes.In the walking state, with the difference between lower extremities increased, the maximum angles of vertebral surface rotation to the left and right and pelvic rotation to the left and right were no obvious changes, but (coronal) spinal maximum offset distance to left and right increased [the maximum value about (9.8±5.1), (10.4±6.9) mm]. Conclusion: The effect of the leg length discrepancy on the pelvic coronal plane and the sagittal plane changes are obvious, but little effect has on the pelvic cross section.The pelvis is compensated by the increase of the inclination of the coronal plane and the sagittal angle at first order.Similarly, the effect on the coronal plane of the spine is more markedly, but the changes of sagittal and cross-section of the spine is less affected, the spine is mainly compensated by the coronal plane bending at second order.