Alterations of hip Alignment and Mobility Before and After Lumbar Fusion in Patients With Normal hip Joints

Retrospective study.

To clarify the extent to which hip joint mobility increases before and after spinal fusion involving the lumbar spine, and depending on the fused levels.

Postoperative changes in hip alignment and mobility in functional positions in patients without obvious organic hip disease remain unclear, particularly with respect to fused levels.

This retrospective cohort study included patients who underwent lumbar fusion and had functional lateral radiographs obtained preoperatively and 2 years postoperatively in standing, extension and flexed-seated positions. Lumbar mobility (ΔLL), hip mobility (ΔPFA), and hip-lumbar mobility (defined as the sum of lumbar and hip mobility) were calculated as the change from standing or extension to the flexed-seated position. Patients were categorized by the number of fused levels into the S group (1-4 levels) and the L group (≥5 levels). Longitudinal changes were analysed using a mixed-effects model for repeated measures.

The included patients were 100 males and 158 females, with a mean age of 71 years and a mean BMI of 24 kg/m2. In the flexed-seated position, lumbar flexion ability adjusted for pelvic incidence decreased, whereas the pelvic-femoral angle increased after lumbar fusion by a mean of 22° and 8°, respectively, with these changes being more pronounced in the L group. From extension to the flexed-seated position, ΔLL decreased by a mean of 18°, whereas ΔPFA increased compensatorily by a mean of 7° in patients without obvious organic hip disease; however, this increase was insufficient to offset the loss of ΔLL.

Lumbar fusion is associated with a postoperative reduction in hip-lumbar mobility despite compensatory increases in hip motion, particularly in patients undergoing long fusion. These findings highlight the importance of evaluating hip mobility before and after lumbar fusion, given its potential implications for adjacent joint loading.