The influence of prosthetic positioning and proximal femoral morphology on leg length discrepancy and early clinical outcomes of cementless total hip arthroplasty

BACKGROUND: Leg length discrepancy (LLD) is a common complication of total hip arthroplasty (THA). However, the relationship between femoral prosthesis filling, proximal femoral morphology, and acetabular prosthesis positioning with postoperative LLD and clinical outcomes is unclear. The aims of this study were to investigate the influence of canal flare index (CFI), canal fill ratio (CFR), center of rotation (COR), and femoral offset (FO) on (1) postoperative LLD; and (2) clinical outcomes in the two stem designs with different coating distribution. METHODS: The study cohort included 161 patients who underwent primary cementless THA between January 2021 and March 2022 with either proximal coating or full coating stems. Multivariate logistic regression was used to assess the effect of CFI, CFR, COR, and FO on postoperative LLD, and linear regression to assess their effect on clinical outcomes. RESULTS: No statistical difference was found in clinical outcomes or postoperative LLD between the two groups. High CFI (p = 0.014), low ΔVCOR (p = 0.012), and Gender (p = 0.028) were found independent risk factors for LLD one day postoperative. High CFI was also an independent risk factor for postoperative subjectively perceived LLD (p = 0.013). CFR at the level of 2 cm below the LT (p = 0.017) was an independent risk factor for Harris Hip Score. CONCLUSIONS: Proximal femoral morphology and acetabular prosthesis positioning but not femoral prosthesis filling affected the LLD. High CFI was an independent risk factor for postoperative LLD and subjectively perceived LLD, and low ΔVCOR was also an independent risk factor for postoperative LLD. Women were susceptible to postoperative LLD.