Risk factors for revision surgery due to dislocation within 1 year after 111,711 primary total hip arthroplasties from 2005 to 2019: a study from the Norwegian Arthroplasty Register

BACKGROUND AND PURPOSE: Dislocation of a hip prosthesis is the 3rd most frequent cause (after loosening and infection) for hip revision in Norway. Recently there has been a shift in surgical practice including preferred head size, surgical approach, articulation, and fixation. We explored factors associated with the risk of revision due to dislocation within 1 year and analyzed the impact of changes in surgical practice. PATIENTS AND METHODS: 111,711 cases of primary total hip arthroplasty (THA) from the Norwegian Arthroplasty Register were included (2005–2019) after primary THA with either 28 mm, 32 mm, or 36 mm femoral heads, or dual-mobility articulations. A flexible parametric survival model was used to calculate hazard ratios for risk factors. Kaplan–Meier survival rates were calculated. RESULTS: There was an increased risk of revision due to dislocation with 28 mm femoral heads (HR 2.6, 95% CI 2.0–3.3) compared with 32 mm heads. Furthermore, there was a reduced risk of cemented fixation (HR 0.6, CI 0.5–0.8) and reverse hybrid (HR 0.6, CI 0.5–0.8) compared with uncemented. Also, both anterolateral (HR 0.5, CI 0.4–0.7) and lateral (HR 0.6, CI 0.5–0.7) approaches were associated with a reduced risk compared with the posterior approach. The time-period 2010–2014 had the lowest risk of revision due to dislocation. The trend during the study period was towards using larger head sizes, a posterior approach, and uncemented fixation for primary THA. INTERPRETATION: Patients with 28 mm head size, a posterior approach, or uncemented fixation had an increased risk of revision due to dislocation within 1 year after primary THA. The shift from lateral to posterior approach and more uncemented fixation was a plausible explanation for the increased risk of revision due to dislocation observed in the most recent time-period. The increased risk of revision due to dislocation was not fully compensated for by increasing femoral head size from 28 to 32 mm.