Saturday, September 29, 2018 10:30 am–12:00 pm Applying Deformity Concepts in Your Practice

Abstract

BACKGROUND CONTEXT Recent studies have shown that lumbar fusion procedures are associated with an increased risk of total hip arthroplasty (THA) dislocation. Some authors have speculated that the increased risk of dislocation is caused by mispositioning of the acetabular component due to spinal sagittal imbalance. Unfortunately, the exact relationship between spinal sagittal balance and cup orientation is unknown. Furthermore, hip instability affected by cup orientation changes due to spinal sagittal imbalance remains unclear. PURPOSE To investigate the effect of spinal sagittal alignment on cup anteversion in THA dislocation. STUDY DESIGN/SETTING Retrospective cohort. PATIENT SAMPLE A total of 29 patients that suffered a THA dislocation and had lumbar radiographs prior to their THA. OUTCOME MEASURES Cup anteversion, lumbar lordosis, pelvic incidence, pelvic tilt, and sacral slope before THA. METHODS Patients that suffered a THA dislocation were retrospectively identified. Patients were included if they had lumbar radiographs prior to their THA. Patient characteristics were recorded including history of spinal fusion, surgical approach, primary or revision THA, direction of dislocation, and time from THA to dislocation. Cross-table lateral hip radiographs were used to measure cup anteversion with normal acetabular anteversion defined as 15°±10°. Lateral lumbar spine radiographs were used to measure lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS). Normal sagittal balance was defined as a PI-LL difference of RESULTS Twenty-nine patients had full radiographic imaging. Among these patients, 62.1% dislocated following a primary THA and 37.9% following a revision THA. Abnormal spinal sagittal balance was identified in 20 patients (69.0%). One-fourth (n=8, 27.6%) of patients had undergone spinal fusion prior to THA. Abnormal cup anteversion was demonstrated in 51.7% of all patients (7% with cup anteversion 25°). Presence of a spinal fusion was not associated with cup anteversion, sagittal balance or time to dislocation (p>.05 each). Sagittal balance was not associated with direction of dislocation, time to dislocation, or cup anteversion (p>.05 each). CONCLUSIONS A majority of patients with a THA dislocation demonstrated abnormal sagittal balance. However, sagittal balance was not associated with acetabular cup anteversion. As such, the relationship between spinal deformity and dislocation rates after THA may not be due to inaccurate cup orientation. More work is necessary to further delineate the influence of spinal alignment on THA stability. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.