Factors associated with mechanical complications following primary total hip arthroplasty through a modified direct anterior approach using custom stems.

Purpose: To determine the rate and risk factors of mechanical complications (MCs) within two years following total hip arthroplasty (THA) through direct anterior approach (DAA) using custom stems, and to compare findings to other surgical approaches in the literature.

Methods: The study included a consecutive series of 479 patients (529 hips) that had undergone primary THA through the DAA using uncemented custom stems between 02/2014 and 04/2017. There were 301 men and 228 women, with a mean age of 55.9 ± 11.6, and a mean body mass index (BMI) of 25.8 ± 4.3 kg/m². All patients were contacted by phone at a minimum follow-up of two years, and those who reported complications were prescribed radiographic imaging and asked to attend clinical assessment. MCs were defined as periprosthetic fracture, aseptic loosening, dislocations, prosthesis failure, prosthesis malposition, or subsidence.

Results: At two years follow-up, the rate of MCs was 3.2% (17 hips).The MCs comprised four femoral fractures, three aseptic stem loosening, three cup malpositions, three subsidences, two acetabular fractures, one stem malposition, and one dislocation. Ten hips (1.9%) required revision due to MCs. Compared to patients with no MCs, patients with MCs had significantly greater native femoral anteversion (16.7 ± 7.5º vs. 21.1 ± 9.7º, p = 0.042), more Charnley class C (13% vs. 41%, p = 0.008), fewer diameter 36 mm heads (45% vs. 18%, p = 0.044), and performed less intense physical activity (49% vs. 12%, p = 0.006) and sports (66% vs. 35%, p = 0.048). Multivariable analyses suggested that MCs were associated with greater native femoral anteversion (Odds Ratio [OR] = 1.08, p = 0.020) and Charnley class C (OR = 3.47,p = 0.027), but were inversely associated with intense physical activity (OR = 0.19, p = 0.047).

Conclusion: The rate of MCs within 2 years following THA through DAA using custom stems was 3.2% and the rate of revision due to MCs was 1.9%, which is within the range reported in the literature on other surgical approaches for THA. Furthermore, the presence of MCs was associated with greater native femoral anteversion and Charnley class C, but was inversely associated with intense physical activity.