Does Femoral Morphology Predict the Risk of Periprosthetic Fracture After Cementless Total Hip Arthroplasty?

Periprosthetic femur fracture remains a leading mode of early failure following cementless total hip arthroplasty (THA). The purpose of this study is to determine if a specific femoral morphology is associated with an increased risk of acute, periprosthetic fracture after cementless THA. An institutional arthroplasty registry was used to identify 32 primary, cementless THAs revised for acute, postoperative periprosthetic fracture (“fracture” cohort) within 3 months of the index procedure. Patients were matched 1:2 to 64 THAs without fracture (“control” cohort) for age, body mass index, gender, and stem design. Preoperative radiographic measurements performed on anteroposterior pelvis and femur radiographs included the neck-shaft angle, endosteal width at 4 locations, and external cortical diameter at 2 locations. These measurements were used to calculate the morphological cortical index, canal flare index, canal calcar ratio, and canal bone ratio. Postoperative measurements included canal fill and stem alignment. Statistical analyses included clustered regressions, Fisher’s exact test, and Student’s t-test. The mean endosteal width at 10 cm distal to the lesser trochanter was greater in fracture patients, although not statistically significant (P = .1). However, this resulted in differences in the canal flare index (P = .03), canal calcar ratio (P = .03), and canal bone ratio (P = .03) between the 2 cohorts. These ratios indicate decreased meta-diaphyseal taper in fracture patients. Preoperative femoral neck-shaft angle was more varus in fracture patients (P = .04). Patients sustaining an acute, periprosthetic fracture with cementless femoral fixation after THA had thinner distal cortices and a decreased meta-diaphyseal taper.