Mid-Term Results After 517 Primary Total Hip Arthroplasties With a Shortened and Shoulderless Double-Taper Press-Fit Stem: High Rates of Aseptic Loosening.

Abstract Background Shorter double-taper stems with reduced lateral shoulders facilitate implantation via the muscle-sparing direct anterior approach and are becoming increasingly popular. We observed an unusually high number of cases of aseptic loosening with the use of a modified stem. Therefore, the aim of this prospective single-centre study was to assess safety and efficacy of this cementless stem. Methods A total of 486 consecutive patients receiving 517 primary THAs using the MonoconMIS stem were prospectively followed up for a mean period of 5.29 years (SD, 1.47). Surgical and clinical data, complications, and revision surgeries were analyzed. WOMAC score was recorded before surgery and at one year and five years after surgery. Results Overall 5-year implant survival rate was 95.2%. Individual component survival rates were 96.1% for stem, 99.4% for acetabular cup, and 99.0% for isolated mobile component exchange. The most common reasons for revision were periprosthetic fracture (1.5%), aseptic stem loosening (1.4%), and infection (1.0%). WOMAC score improved significantly from 49.57 (SD, 21.42) at baseline to 13.33 (SD, 16.47) at one year and 9.84 (SD, 14.45) at five years after surgery. Aseptic stem loosening occurred only in patients with Dorr type A proximal femur morphology. Conclusion The evaluated femoral stem is associated with revision rates higher than what has been reported for other implants. The WOMAC scores suggest adequate efficacy. Our data do not support the use of the MonoconMIS for primary THA in patients with Dorr type A proximal femur morphology.