Impact of proximal femoral shape on leg length discrepancy after total hip arthroplasty

Abstract

To investigate the effect of different proximal femoral shapes on leg length discrepancy(LLD) after total hip arthroplasty(THA). Total 131 patients with osteoarthritis or osteonecrosis received unilateral biological total hip arthroplasty from June 2013 to June 2019. All patients' age, sex, side and pelvis anteroposterior digital radiography were retraspectively analyzed. There were 69 males and 62 females, 57 cases of left hip and 74 cases of right hip. The age ranges from 25 to 89 with an average age of 62 years. There were 48 cases of osteoarthritis and 83 cases of osteonecrosis. In this study, femoral cortical index (FCI) was used as the classification of proximal femoral shape, and bilateral lower limb length differences were measured by preoperative and postoperative pelvis anteroposterior digital radiography. Grouping according to FCI:> 0.6 was Dorr A group, 0.5 to 0.6 was Dorr B group, <0.5 was the Dorr C group, and the relationship between proximal femur morphology and the leg length discrepancy after total hip arthroplasty was determined. The postoperative average FCI was(0.56±0.08) mm and the median LLD was 5.10 mm (IQR -1.00 to 8.80 mm). Three groups were divided according to the level of FCI, and there were no statistically significant differences in gender, age, side, diagnosis and intraoperative fracture rate distribution among three groups. FCI>0.6, the postoperative LLD was 6.30 mm (IQR 1.00 to 10.95 mm). When FCI was 0.5 to 0.6, the postoperative LLD was 5.85 mm(IQR-0.55 to 8.90 mm). FCI<0.5, the postoperative LLD was 1.95 mm(IQR -2.50 to 6.68 mm). LLD comparison of different proximal femoral shape was statistically significant (P<0.05). High FCI increases the risk of lower extremity prolongation after surgery on the affectedside, while low FCI reduces the risk of lower extremity prolongation after surgery on the affected side. The surgeon can assess the shape of the proximal femur of the patient preoperatively and inform the patient in advance of possible changes in leg length of both lower extremities after total hip replacement.