RISK OF DISLOCATION BY SURGICAL APPROACH FOLLOWING MODERN PRIMARY TOTAL HIP ARTHROPLASTY

Introduction

There is renewed interest in dislocation after surgical approach with popularization of the direct anterior approach. The purported advantage of both the lateral and direct anterior approaches is decreased risk of dislocation. The purpose of this study was to assess the risk of dislocation by approach following modern primary THA.

Methods

All primary THAs at a single academic institution from 2010 to 2017 were analyzed through our institutional total joint registry. There were 7023 THAs including 3754 posterior, 1732 lateral, and 1537 direct anterior. Risk of dislocation was assessed against the competing risks of revision surgery and death as well as by individual patient and surgical factors including surgical approach. Risk of revision surgery was considered as a secondary outcome. Step-wise selection was utilized to develop multivariable models. Clinical outcomes were documented with the Harris Hip Score (HHS). Mean age was 63 years, 51% were female, and mean body mass index (BMI) was 30 kg/m². Minimum follow-up was 2 years.

Results

The cumulative incidence of dislocation at 1-year and 5-years by approach was as follows: posterior (2.1%; 3.0%), lateral (0.7%; 0.7%), direct anterior (0.4%; 0.4%) (p<0.001) (Figure 1). Compared to the posterior cohort, the adjusted risk of dislocation was decreased for the lateral (hazard ratio [HR]=0.28, p<0.001) and direct anterior cohorts (HR=0.18, p<0.001). The cumulative incidence of revision for instability at 1-year and 5-years by approach was as follows: posterior (0.8%; 1.0%), lateral (0.6%; 0.6%), direct anterior (0%; 0%) (p=0.09). The adjusted risk of all-cause revision surgery was increased among the lateral cohort compared to posterior (HR=1.75, p=0.003) and direct anterior (HR=2.44, p=0.002) and among patients with diagnoses other than osteoarthritis (HR=2.89, p<0.001). Among patients who dislocated, 69 (83%) had anteversion >25° (Figure 2). Mean increase in HHS from preoperative assessment to final follow-up was greatest among direct anterior patients (37 points), followed by posterior patients (33 points), followed by lateral patients (29 points) (p<0.05, all comparisons).

Conclusions

This study documents the risk of dislocation by surgical approach among a large contemporary cohort undergoing primary THA. The risk of dislocation was higher following the posterior approach, whereas all-cause revision surgery was found to be higher following the lateral approach.

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