HIGHER SEVEN-YEAR FOLLOW-UP SURVIVAL RATE AFTER CT-SCAN 3D-PLANNED UNCEMENTED TOTAL HIP ARTHROPLASTY USING AN ANATOMIC STEM COMPARED WITH A STRAIGHT QUADRANGULAR STEM: A PROSPECTIVE COHORT STUDY OF 873 PATIENTS

Introduction Anatomical femoral stems featuring double sagittal curvature and helitorsion have been shown to restore femoral anteversion more accurately than straight stems. However, comparative data on their medium-term survival remain limited. This study aimed to compare the medium-term failure rates of an anatomic stem with those of a conventional double-tapered straight stem. We hypothesised that improved adaptation to the proximal femur and restoration of femoral anteversion with an anatomic stem would promote more physiological bone remodelling and enhance implant survival. Methods We analyzed prospectively collected data from 756 patients (893 hips; 370 women, 386 men; mean age 62 years, range 16–94) who underwent total hip arthroplasty via a direct anterior approach between 2005 and 2022. The mean follow-up was seven years (SD 3; range 2–19). Three stem designs were used: a short, uncemented anatomic stem (n = 498), a generic double-tapered straight stem (n = 252), and a custom patient-specific anatomic stem (n = 143). All procedures were planned preoperatively using three-dimensional (3D) templating. Custom stems were designed from CT-based reconstructions when accurate 3D anatomical reproduction was not achievable. Kaplan–Meier survival analysis and multivariate Cox regression (adjusted for sex, age, BMI, and ASA grade) were used to estimate implant survival and hazard ratios (HRs) for revision due to mechanical failure. Results At seven years, survival was 95.8% (95% CI 93.0–98.5) for straight stems, 99.0% (95% CI 98.1–99.9) for anatomic stems, and 100% for custom stems. Straight stems showed a higher revision risk than anatomic stems (adjusted HR 4.13; 95% CI 1.78–9.57; p = 0.03), particularly in Dorr A femurs. Conclusion Anatomic stems demonstrated superior medium-term survival compared with straight stems, especially in Dorr A femurs. Custom anatomic stems achieved the best outcomes, even in complex proximal femoral anatomy.