Dislocation rate and its risk factors in total hip arthroplasty with concurrent extensive spinal corrective fusion with pelvic fixation for adult spinal deformity.

BACKGROUND: Though there are several reports on the high dislocation rates following total hip arthroplasty (THA) before or after spinal surgery, the literature specific to extensive spinal corrective fusion with pelvic fixation for adult spinal deformity is limited. This study determined the rate and risk of hip dislocation after THA and extensive spinal corrective fusion. METHODS: We retrospectively analyzed the data of 23 adults (27 hips) who underwent both extensive spinal corrective fusion with pelvic fixation and THA between 2010 and 2018. Surgery-related characteristics were investigated from medical records, while standing anteroposterior pelvic radiographs and lateral spinal radiographs were used to measure spinal alignment parameters and THA acetabular orientation. Patients were grouped based on the occurrence of dislocation, and the rate and risk of dislocation were compared. RESULTS: The rate of THA dislocations was extremely high-22% (6 of 27 hips) of patients. All dislocations occurred posteriorly in patients with prior THAs that were performed using the posterior approach. The pelvic tilt was significantly greater in patients with THA dislocations (p = 0.02) than in those without. Cup radiographic anteversion in the supine (p = 0.02) and standing (p = 0.05) positions was significantly smaller in patients with dislocations than in those without. CONCLUSION: Total hip arthroplasty concurrent with extensive spinal corrective fusion with pelvic fixation for adult spinal deformity has an extremely high rate of posterior hip dislocation. The posterior surgical approach and prior THA were high risk factors for dislocation. Hip and spine surgeons need focused pre-surgical planning to account for this risk.