Agreement Between Proximal Femoral Geometry and Component Design in Total Hip Arthroplasty: Implications for Implant Choice.

BACKGROUND: The present study aimed to analyze the agreement between proximal femoral geometry of adult hips and femoral component design in total hip arthroplasty.

METHODS: Anatomical femoral offset (FOAnat) and the anatomical neck-shaft angle (NSAAnat) of 800 adult hips were measured by computed tomography scans, and anatomical femoral neck height (FHAnat) was calculated. Corresponding best-fit implants of the most common hip system (standard, high offset and varus variant) were identified for each hip. Finally, the precision of the best possible anatomic reconstruction was assessed.

RESULTS: The mean FOAnat was 38.0 mm (range: 19.8-57.9 mm, standard deviation [SD]: 6.4 mm), the mean NSAAnat was 130.8° (range: 107.1°-151.9°; SD: 6.5°), and the mean FHAnat was 32.6 mm (range: 14.4-52.0 mm; SD: 5.5 mm). In 450 (56.3%) hips, the standard variant was identified to be the best-fit implant, followed by the varus (n = 282, 35.3%) and the high offset (n = 68, 8.5%) variants. The mean minimal distance from the best-fit implant was 4.5 mm (range: 0.1-20.2 mm, SD: 3.4 mm). Excellent agreement (distance: <2 mm) between hip anatomy and best-fit implant was found in 203 (25.4%) hips, combined excellent and acceptable agreement (distance: <6 mm) in 569 (71.1%) hips, whereas 213 (28.9%) hips were graded as poor (distance: ≥6 mm).

CONCLUSION: The present study revealed a mismatch between proximal femoral anatomy of a relevant proportion of adult hips and implant geometry of the most common femoral component in total hip arthroplasty.