Ability of lower teardrop edge to restore anatomical hip center height in total hip arthroplasty

Background The acetabular teardrop is often used to guide acetabular component placement in total hip arthroplasty (THA). Placing the lower acetabular component aspect at the same level as the lower teardrop edge was assumed to restore the hip center of rotation. Here we radiographically analyzed the relationship between cup center and normal contralateral acetabulum center height on unilateral THA using this placement method. Methods A total of 106 unilateral THA cases with normal contralateral acetabula were reviewed and the vertical and horizontal distances in relation to the lower acetabular teardrop edge from both hip joint centers, cup inclination, and anteversion were measured radiographically. The paired t -test was used to compare left and right hip center heights. Scatter plots and Pearson's correlation coefficients were used to evaluate differences in hip center heights, cup anteversion, inclination angles, and medialized cup center distance compared to the contralateral hip joint. Results Cup center height was significantly greater ( P <0.01) than contralateral hip joint center height (93.4% in the 0–5 mm range, 6.6% >5 mm). There was a weak correlation between hip center height difference and inclination ( r =0.376, P <0.01) and between difference and anteversion ( r =0.310, P <0.01) but no correlation between difference and outer cup diameter ( r =0.184, P =0.058) or difference and medialized cup center distance ( r =-0.098, P =0.318). Conclusions Although this method did not exactly replicate anatomic hip center height, the clinical significance of cup center height and anatomic hip center height differences is negligible. This acetabular component placement method has high simplicity, reliability, and stability.