Large Femoral Heads and Select Dual-Mobility Bearings Are Associated with Reduced Instability in Contemporary Posterior Approach Total Hip Arthroplasty.

BACKGROUND: Postoperative dislocation is considered the main drawback of posterior approach total hip arthroplasty (THA). Thinner highly cross-linked polyethylene and dual-mobility bearings allow maximizing femoral head diameter per a given cup size. This study evaluated dislocation rates as large femoral head bearings were introduced into a practice over an 11-year period. METHODS: A total of 1,511 consecutive primary THAs were retrospectively reviewed. Demographics, implant sizes, femoral head-acetabular cup ratio, and dislocation status were collected from the electronic medical record. Data were evaluated using time series analysis techniques as larger femoral heads, thinner polyethylene liners, and dual-mobility bearings were introduced. The cohort was 57% women with mean age and body mass index of 62 years (range, 13 to 93) and 31 kg/m2 (range, 13 to 54). RESULTS: The overall dislocation rate was 0.98%. Use of femoral head sizes ≥40-millimeters increased from 4% from the years 2010 to 2016 to 51% in the years 2017 to 2021, correlating with a 50% reduction in dislocation rate from 1.4 to 0.7% (p=0.279). Also, no dislocations occurred in patients who had dual mobility bearings or ≥40-millimeter femoral heads (p=0.007). Twelve of 14 dislocations occurred in cases with head-cup ratio <0.7 (p=0.013). Thirteen of 14 dislocations were in women (p=0.005). CONCLUSION: Maximizing the femoral head diameter per given cup size correlated with a decrease in dislocation rate in modern posterior approach THA. Furthermore, these results suggest that dual-mobility articulations should be reserved for high-risk patients or patients in whom a 40-millimeter femoral head is not possible.