Abstract
BACKGROUND: Hip abductor weakness is common after proximal femoral fracture and may contribute to gait instability. The influence of postoperative hip alignment on early recovery of hip abductor strength during inpatient rehabilitation after surgery remains unclear. OBJECTIVE: To examine longitudinal changes in hip abductor strength and identify factors associated with the operated-to-non-operated hip abductor strength ratio at discharge, focusing on surgical procedure and radiographic alignment. METHODS: This retrospective observational cohort study enrolled 64 patients transferred to a rehabilitation hospital after proximal femoral fracture surgery (34 femoral neck fractures treated with hemiarthroplasty; 30 intertrochanteric fractures treated with cephalomedullary nailing). Hip abductor strength was measured using a handheld dynamometer at rehabilitation admission and discharge and normalized by body weight. Radiographic parameters were measured on supine anteroposterior pelvic radiographs; side-to-side differences (operated minus non-operated) were calculated for the neck-shaft angle, hip center of rotation, femoral offset, and trochanteric height. Multivariable linear regression (ANCOVA-type) was performed with the discharge strength ratio as the dependent variable and the admission strength ratio as an adjustment factor. RESULTS: Hip abductor strength improved on both sides (p < 0.001). The operated side increased from 1.04 ± 0.5 to 1.8 ± 0.7 N/kg and the non-operated side from 1.6 ± 0.6 to 2.3 ± 0.8 N/kg; the operated-to-non-operated ratio improved from 62.7 % to 72.9 %. In the adjusted model (R(2) = 0.325), cephalomedullary nailing (vs hemiarthroplasty) was associated with a higher discharge strength ratio (B = 0.114, p = 0.027). A greater neck-shaft angle difference was also associated with a higher discharge strength ratio (B = 0.0073 per degree, p = 0.011). The admission strength ratio remained a significant predictor (B = 0.245, p = 0.002). CONCLUSIONS: Early recovery of the hip abductor strength ratio after proximal femoral fracture was associated with surgical procedure and postoperative neck-shaft angle asymmetry, independent of baseline strength ratio. Postoperative radiographic alignment may aid in stratifying recovery and tailoring rehabilitation, although causal inference is limited.