Primary total hip arthroplasty after prior osteosynthesis versus osteotomy : distinct risk profiles and the modifying effect of femoral fixation

To compare outcomes after primary total hip arthroplasty (THA) following prior ipsilateral osteosynthesis with prior ipsilateral osteotomy, and to assess whether femoral fixation modifies risk. Using the German Arthroplasty Registry (EPRD; 2012 to 2024), two 1:1 matched analyses were performed: prior osteosynthesis versus no prior surgery (8,643 pairs) and prior osteotomy versus no prior surgery (5,569 pairs), matched on age, sex, BMI category, and Elixhauser score. Kaplan-Meier and Cox regression were used, censoring at death, with adjustment for femoral fixation (cemented, cementless, hybrid, reverse-hybrid). After prior osteosynthesis, hazards were higher for revision (HR 6.93 (95% CI 6.07 to 7.92), periprosthetic femoral fracture (PFF; HR 17.22 (95% CI 12.28 to 24.15)), and infection (HR 3.87 (95% CI 3.05 to 4.91)) compared with controls (all p < 0.001); cemented and hybrid fixation had lower revision and PFF hazards than cementless fixation. After prior osteotomy, revision (HR 2.30 (95% CI 1.89 to 2.80)) and dislocation (HR 9.43 (95% CI 4.55 to 19.56)) hazards were higher; PFF and infection were not significant. Reverse-hybrid fixation was associated with higher revision (HR 2.01 (95% CI 1.27 to 3.19)) and infection (HR 3.71 (95% CI 1.71 to 8.06)) hazards than cementless fixation. Prior osteosynthesis denotes a high-risk, conversion-type THA scenario; cemented-based constructs were associated with lower PPF and revision hazards than cementless fixation. Prior osteotomy confers an intermediate risk profile, mainly driven by revision, dislocation, and loosening. Osteosynthesis and osteotomy histories should not be pooled in preoperative risk assessment before THA.