Accuracy of digital preoperative planning in total hip arthroplasty: Which factors influence the planning precision for cementless short curved stem prostheses via the direct anterior approach?

Purpose In the past few years, using minimally invasive methods, especially the direct anterior approach (DAA), to implant short, curved stems has become more popular. This study aimed to evaluate the concordance between preoperative planning and the implanted short, curved stems and acetabular cups via DAA and examine the role of Gender, Body Mass Index (BMI), Surgeon's experience and Diagnosis on planning precision. Methods A retrospective cohort of patients undergoing primary THA between 2020 and 2024 was reviewed. All procedures utilized the Optimys® short stem and the Anexys® acetabular cup (Mathys AG, Switzerland). Preoperative templating was performed on standardized anteroposterior pelvic radiographs using mediCAD® software (Hectec GmbH, Germany). Stored digital plans were compared with postoperative implant data to determine accuracy for stem size, cup size, and femoral offset. Subgroup analyses assessed the impact of gender, BMI, surgeon experience, and underlying diagnosis on deviations between planned and implanted components. Results Planning accuracy was 82.5% for femoral stems, 85.9% for acetabular cups, and 90.9% for femoral offset. Male gender was significantly associated with moderate cup size deviations (p < .01). Higher BMI showed a borderline association with major cup mismatches, whereas surgeon experience and preoperative diagnosis had no significant effect on planning precision. Conclusion Digital templating for cementless THA with a short-stem prosthesis via DAA provides accuracy comparable to previously published data. Men and severely obese patients are at increased risk for discrepancies in cup sizing. Careful positioning of the calibration marker, particularly in patients with BMI >30, is essential to optimize planning reliability.