Modular and Non-modular Conical Tapered Stems in Total Hip Arthroplasty for Crowe III and IV Hip Dysplasia

Conical stems are effective in total hip arthroplasty for high-degree dysplasia, but no comparative studies about modular and non-modular versions are available. By comparing 3 conical stems in 3-dimensional (3D) computed tomography (CT)-based simulations in Crowe III and IV dysplasia, the study sought to assess the rate of implants allowing correct biomechanical reconstruction and the correlations between the 3 stem reconstructions and native hip morphology.

Using a 3D CT-based simulation, 3 different conical stems (single-taper, modular neck, and proximal junction modularity) were implanted in the same high-degree dysplastic hips. Proximal biomechanical restorations (femoral fitting, combined anteversion, offset reconstruction, leg lengthening, and tilt) were compared, and correlations with native anatomy were assessed. After a power analysis, 61 hips in 55 patients were included, with a mean age at CT of 56.26 ± 10.71 years: 41 hips (67.21%) were classified as Crowe III and 20 (32.79%) as Crowe IV.

The rate of global acceptability (matching all 6 reconstructive parameters) was similar between the 3 stems: W, 52.5%; A, 47.5%; and M, 55.7% (p = 0.66). No single stem demonstrated superior performance in any reconstructive parameter (p > 0.05). No specific native anatomical features favored one stem design over another; the primary predictors for each femoral reconstruction were native center of rotation height and cup medialization. Native femoral anteversion had no impact on the reconstruction.

Similar proximal biomechanical reconstructions were provided by modular and non-modular stems: modular stems should be used with caution even in high-grade dysplastic hips, but may be useful in high offset anatomies.