Do Stem Design and Surgical Approach Influence Early Aseptic Loosening in Cementless THA?

BACKGROUND: Some studies have revealed an increased risk of early aseptic loosening of cementless stems in THA when inserted through an anterior or anterolateral approach compared with a posterior approach, whereas approach does not appear to be a risk factor in others. Stem design, whether "anatomic" (that is, stems with a curved lateral profile or an obtuse angle at the proximal-lateral portion of the stem) or "shoulder" (that is, straight with a proximal shoulder), may also be associated with a differential risk of aseptic loosening in cementless THA depending on the surgical approach used, but if so, this risk is not well characterized. QUESTIONS/PURPOSES: In this national registry study, we investigated the association between surgical approach and early aseptic loosening of (1) cementless femoral stems with a proximal angular shape (shoulder); and (2) anatomically shaped femoral stems. METHODS: The Dutch Arthroplasty Registry is a nationwide population-based register recording data on primary and revision hip arthroplasty. We selected all primary THAs (n = 63,354) with a cementless femoral stem inserted through an anterior, anterolateral, or posterior approach from 2007 to 2013 with a minimal followup of 2 years. Femoral stems were classified as "anatomic," "shoulder," or "other" (that is, not classifiable as anatomic or shoulder). From the 47,372 THAs with an anatomic or shoulder stem (mean followup, 3.5 years; SD, 1.8 years), 340 (0.7%) underwent revision surgery as a result of aseptic loosening of the femoral stem, 1195 (2.5%) were revised for other reasons, and 1558 patients (3.3%) died. We used Cox proportional hazard models to determine hazard ratios for aseptic loosening of anatomic and shoulder stems for the anterolateral and anterior approaches compared with the posterior approach. RESULTS: After controlling for relevant confounding variables such as sex, American Society of Anesthesiologists score, previous surgery, and coating and material of the femoral stem, we found that there was a stem-approach interaction. Separate analysis showed that shoulder stems had a greater likelihood of early aseptic loosening when the anterolateral approach (hazard ratio [HR], 2.28; 95% confidence interval [CI], 1.43-3.63; p < 0.001) or anterior approach (HR, 10.47; 95% CI, 2.55-43.10; p = 0.001) was used compared with the posterior approach. Separate analysis of the anatomic stems yielded no association with approach (anterolateral: HR, 1.07, 95% CI, 0.70-1.63, p = 0.77; anterior: HR, 1.31, 95% CI, 0.91-1.89, p = 0.15). CONCLUSIONS: In THA, cementless femoral stems with a proximal shoulder are associated with early aseptic loosening when inserted through an anterior or anterolateral approach compared with a posterior approach. An anatomically shaped stem may be preferred with these approaches, although further analysis with larger registry volumes should confirm our results, in particular for shouldered stems when implanted through an anterior approach. LEVEL OF EVIDENCE: Level III, therapeutic study