Is the position of dual-mobility cup in THA for femoral neck fractures optimal? A retrospective study.

Abstract

Few studies have examined the relationship between the indication of total hip arthroplasty (THA) and the quality of its technical achievement. Implants mispositioning could happen more frequently while THA is performed on acute proximal femur fracture cases. The purpose of this study was to compare the frontal inclination (FTA) of double-mobility cups (DMC) in patients undergoing THA for hip osteoarthritis or fracture. This retrospective study included all patients undergoing THA for hip fracture or hip osteoarthritis. The surgical protocol was identical in all patients and included a systematic DMC implantation. In the postoperative period, the FTA was measured on anteroposterior pelvic radiographs and compared between groups. Malposition was defined for FTA values outside the 35°-55° range. The study included 97 patients: 33 men, mean age: 78.8 years, 45 fractures. The misalignment rate was 55% after THA for fracture versus 33% for hip osteoarthritis (p = 0.02). The mean FTA value was 39° for "fracture" and 43° for "hip osteoarthritis" groups (p = 0.052). The risk for hip dislocation, surgical revision for mechanical or infectious cause was identical in both groups. Misalignment was more frequent when THA was achieved for an acute proximal femur fracture. Several explanations can be proposed: lesser bone quality, incomplete removal of upper acetabular osteophytes which can lead to excessive horizontalization of the cup and surgical procedure performed by younger surgeons in "fracture group". These misalignments don't cause more mechanical complications in the first months after surgery.