A piriformis-preserving posterior approach reduces dislocation rate of the hemiarthroplasty in patients with femoral neck fracture

Introduction: The posterior approach (PA) for hemiarthroplasty (HA) in patients with femoral neck fracture (FFN) has a high risk of dislocation; however, by preserving the piriformis muscle, the dislocation rate could be lowered considerably. The aim of this study was to compare the surgical complications of the piriformis-preserving posterior approach (PPPA) and the PA in patients with FNF treated with HA. Methods: On 1 January 2019, the PPPA was introduced at two hospitals as the new treatment standard. The sample size was calculated based on a 5 percentage point dislocation reduction and 25% censoring; a sample of 264 patients per group was determined. An approximately 2-year inclusion period with 1-year follow-up was estimated, including a historical cohort from 2 years before the PPPA introduction. Data were retrieved from health care records and X-ray images from the hospitals’ administrative databases. Relative risk (RR) and 95% confidence intervals were calculated using Cox regression and adjusted for age, sex, comorbidity, smoking, surgeon experience and implant type. Results: There were 527 patients included in the study, of which 72% were women and 43% were above 85 years old. There were no baseline differences between the PPPA and PA groups in sex, age, comorbidity, body mass index, smoking, alcohol, mobility, length of surgery, blood loss or implant positioning, but there were differences in 30-day mortality, surgeon experience and implant type. The dislocation rate reduced from 11.6% in the PA group to 4.7% in the PPPA group (p = 0.004), with an RR of 2.5 (1.2; 5.1). The reoperation rate reduced from 6.8% with the PA to 3.3% with the PPPA (p = 0.022), with an RR of 2.1 (0.9; 5.2), and total surgery-related complications reduced from 14.7% with the PA to 6.9% with the PPPA (p = 0.003), with an RR of 2.4 (1.3; 4.4). Interpretation: Changing from PA to PPPA in patients with FNF treated with HA resulted in a more than 50% reduction in dislocation and reoperation rates. This approach was easily introduced and may enable further lowering of dislocation rates through the sparing of all short external rotators.