Review Question - QID 219909

Patients who undergo total hip arthroplasty with prior spinal fusion the lumbosacral junction are at increased risk of dislocation.

The spino-pelvic relationship plays a critical role in primary total hip arthroplasty (THA), influencing hip biomechanics, implant positioning, and postoperative outcomes. The spine and pelvis move in coordination, affecting pelvic tilt and acetabular orientation across different postures, such as standing and sitting. In cases where patients have reduced spino-pelvic motion due to a stiff spine (where the pelvis fails to tilt posteriorly while sitting), the femoral neck may impinge on the anterior acetabular rim, which can force the head toward a posterior dislocation. To mitigate this risk in patients with spinal stiffness, surgeons may choose to position the acetabular cup with increased anteversion or use a dual mobility implant. Both approaches aim to reduce the risk of dislocation in this high-risk group.

Salib et al. reviewed their series of 84 patients who underwent lumbar fusion prior to THA. Patients were stratified into three groups depending on the length of lumbar fusion and whether or not the sacrum was involved. The authors report a higher risk of dislocation in patients whose spinal construct involved sacral fusion. Furthermore, they found increased anterior pelvic tilt in the sacral fusion cohort compared to one-level and multi-level fusion groups. The authors recommend higher stability implants in this high-risk cohort to reduce the risk of dislocation.

Buckland et al. performed a Medicare database review of patients who underwent primary THA and lumbar spinal fusion. Patients who had undergone both lumbar fusion and THA were then divided into two groups: 1 to 2 levels, and 3 to 7 levels of fusion. The authors found that patients with a previous history of lumbar spinal fusion have a significantly higher rate of dislocation and patients with 3 to 7 levels of fusion had a higher rate of dislocation than patients with 1 to 2 levels of fusion.

Figure A demonstrates a long posterior spinal fusion that includes the lumbosacral junction. Figure B shows a short segment construct of L4-L5 with an ALIF cage.

Incorrect Answers
Answers 2-5: While these prior treatments may contribute to the rigidity of the spine, lumbosacral fixation/fusion, which limits dynamic pelvic movement, is most likely to contribute to future instability.