Lower dislocation rate in total hip arthroplasty for femoral neck fracture after transition from a conventional cup to a dual mobility cup.

Abstract

Dislocation is a major complication of total hip arthroplasty (THA) for femoral neck fractures (FNFs). Dual mobility cups (DMCs) are in clinical practice for patients at risk of dislocation in primary-and revision arthroplasty. This study investigated whether changing routines from conventional THA (cTHA) to DMC for fracture patients at our orthopaedic unit resulted in a reduced dislocation rate. In 2016, a change was implemented in our department's standard procedure for patients undergoing THA for FNFs, replacing the cTHA with DMC as the preferred acetabular component. A search in the medical records retrospectively identified all patients with acute FNFs treated with THA from 2010 through 2021. Age, sex, American Society of Anesthesiologists (ASA) score 3-4 vs. 1-2, surgeon experience (hip specialist vs. orthopaedic surgeon) and cup type cTHA vs. DMC were included in the multivariable Cox regression analysis. After screening and exclusion, 219 patients were included in the analysis: 108 patients treated with cTHA and 111 patients with DMC. The groups did not statistically significantly differ in age, sex and ASA score. There was, furthermore, no statistically significant difference in waiting time to surgery or length of surgery between groups. The follow-up time was longer for cTHA due to a change of routines. Fracture surgery with DMC was predominately performed by a specialized hip surgeon whereas cTHA was predominately performed by a general orthopaedic surgeon. 24 (11 %) patients had at least one dislocation during the study period: 22 in the cTHA group and 2 in the DMC group (p < 0.001). The multivariable Cox regression analysis revealed an independent association between the risk of dislocation and the use of cTHA (compared to DMC) with a hazard ratio (HR) of 14.16 (95 % confidence interval [CI] 2.80-71.75). After implementing a DMC, the occurrence of dislocations in patients with FNFs who underwent THA decreased.