Relationships Between Femoral Offset Change and Clinical Score Following Bipolar Hip Arthroplasty in Femoral Neck Fractures

Background This study aimed to investigate the relationship between femoral offset(FO) and clinical outcomes of patients with femoral neck fracture following bipolar hip arthroplasty(BHA). Methods A hospital registry-based retrospective study, involving 520 patients who underwent BHA for femoral neck fracture and with a minimum follow-up of one year, Dong-A university hospital, from December 1, 2003, to September 31, 2018, was carried out. Excluding those with unclear medical records, a previous surgical history on the affected or contralateral hip, a congenital deformity and preoperative trauma history of the hip, high-energy multiple trauma, a history of neurodegenerative disease or cerebrovascular disease, a total of 77 patients were included in the analysis. The subjects were 54 females and 23 males. The mean age of patients was 74.6(65–95) years old and the mean follow-up period was 30.5 (12–136) months. For clinical assessment, postoperative pain visual analogue scale(VAS) and Harris hip score (HHS) were analyzed at each follow-up period. For radiological assessment, the difference in leg length discrepancy (LLD) and FO was measured. FO nearest to the real value was calculated using the values corrected for magnification and rotation errors on the anteroposterior view of plain radiographs taken at the first year of follow-up. In statistical analyses, the statistical significance between FO and clinical outcomes was analyzed using the Pearson correlation tests with SPSS v. 25.0. A value of p < 0.05 was considered statistically significant. Results The difference in mean FO postoperatively was 6.7(± 4.8) mm, and the difference in mean postoperative LLD was 4.9 (± 3.4). The mean HHS was 77.1(± 7.7), 82.3(± 8.6), 83.4(± 7.7), and 86.4(± 6.7) at 1st, 3rd, 6th and 12th postoperative months, respectively. In the analysis using the Pearson correlation coefficient, the correlation coefficient between FO and HHS in 1-year follow-up was − 0.38, and a significant outcome was found (p = 0.001). Of HHS domain, the correlation coefficient for function in 1-year follow-up was − 0.42, revealing a significant outcome (p = 0.0001). Conclusions There was a stastically significant correlation between clinical oucomes and FO difference at 1 year after BHA in patients with femoral neck fractures older than 65 years.