How Is Lumbar Fusion Associated With Compensatory Hip Motion After THA?
Hiroyuki Tokuyasu1,2, Eiki Tsushima2, Mitsuru Takemoto3
1Department of Rehabilitation, Kyoto City Hospital, Kyoto, Japan.
Clinical Orthopaedics and Related Research
|March 6, 2026
Summary
Lumbar fusion after total hip arthroplasty (THA) increases compensatory hip flexion, with more fused levels leading to greater hip motion. Preoperative imaging can help predict this increased risk of dislocation.
Area of Science:
- Orthopedic Surgery
- Spine Surgery
- Hip Arthroplasty
Background:
- Patients with total hip arthroplasty (THA) may compensate for reduced spinal motion after lumbar fusion by increasing hip flexion.
- The relationship between the number of fused spinal levels and compensatory hip motion post-lumbar fusion is not well understood.
- Predicting postoperative compensatory hip motion changes before lumbar fusion is challenging.
Purpose of the Study:
- To determine if lumbar fusion after THA is associated with resting spinopelvic alignment or compensatory hip changes.
- To assess if the number of fused spinal segments correlates with increased compensatory hip motion.
- To evaluate if this increase in hip compensatory motion can be predicted preoperatively.
Main Methods:
- Retrospective analysis of 109 patients with lumbar fusion after THA.
- Functional lateral radiographs in standing, relaxed-seated, and flexed-seated postures before and after surgery.
- Measurement of spinopelvic alignment parameters (e.g., pelvic incidence, lumbar lordosis, pelvic tilt) and hip angle (pelvic-femoral angle).
- Multivariable regression analysis to associate fused levels with changes in pelvic-femoral angle (PFA) in the flexed-seated position.
Main Results:
- Lumbar fusion led to improved Oswestry Disability Index scores and reduced back pain.
- Post-lumbar fusion, increased lumbar lordosis and pelvic-femoral angle (PFA) were observed in the flexed-seated position, indicating greater compensatory hip flexion.
- The number of fused spinal levels significantly correlated with the increase in PFA in the flexed-seated position (standardized β = 0.39, p = 0.002).
- A regression model predicted the increase in PFA based on the number of fused levels and preoperative hip angle (R² = 0.43, p < 0.001).
Conclusions:
- Preoperative flexed-seated radiographs in THA patients undergoing lumbar fusion are valuable.
- This data aids spine surgeons in discussing dislocation risks with patients and hip surgeons, supporting shared decision-making.
- Future research using 3D imaging is needed to explore multiplanar hip motion and dislocation risk during functional activities.
