Does Femoral Component Loosening Predispose to Femoral Fracture?: An In Vitro Comparison of Cemented Hips

Abstract

The incidence of femur fracture around total hip arthroplasties continues to increase at substantial cost to society. These fractures are frequently associated with a loose femoral component. Consequently, we sought to test whether femoral component loosening predisposes to periprosthetic femoral fracture. Because many periprosthetic femoral fractures are spiral in nature, we evaluated the torsional characteristics of the implanted femur in which the only design variable was instability of the femoral component. We used synthetic (polyurethane) (n = 15) and paired cadaveric femora (n = 10) with specimens divided into two groups: well-fixed and loose cemented stems. Each specimen was tested mechanically in internal rotation until failure. For the synthetic specimens, torque to failure was reduced by 38%, whereas stiffness was decreased 54% for the loose group compared with the well-fixed group. For the cadaveric specimens, torque to failure was reduced by 58%, whereas stiffness decreased 70% for the loose group compared with the wellfixed group. Fracture patterns were similar between synthetic and cadaveric femora with a proximal spiral pattern in loose specimens and more distal fracture patterns with well-fixed stems. Based on our data, patients with loosened femoral components are at risk for fracture at a substantially lower torque than those with well-fixed components.

Late peri-prosthetic femoral fracture as a major mode of failure in uncemented primary hip replacement

“…Furthermore, aseptic loosening has been shown to be an important risk factor for this fracture after cemented THR. 2,22,41,[44][45][46] Although two hips showed significant osteopenia of the proximal femur at the time of fracture, in our study using uncemented stems we did not find pre-fracture evidence of loosening of the femoral component at the last follow-up examinations. At the last clinical and radiological evaluation before peri-prosthetic femoral fracture, all the stems were considered to be well fixed.…”

Periprosthetic Femur Fractures

“…[18][19][20][21]25 Risk factors for periprosthetic femoral shaft fractures about hip arthroplasty femoral stems are related to the age of the patient, gender, index diagnosis, presence or absence of osteolysis, presence or absence of aseptic loosening, primary or revision status, the specific type of implant used, and whether cemented or noncemented technique was used. 24,[26][27][28][29][30][31][32][33][34][35][36][37][38][39] Identifying risk factors can both improve patient counseling and potentially improve efforts at fracture prevention.…”

Periprosthetic Fractures: Epidemiology and Future Projections

“…This has been borne out in biomechanical studies in synthetic and cadaveric femora. 18 Early detection of osteolysis and loosening of femoral components, by routine clinical and radiographic follow-up, may limit the incidence of periprosthetic fracture. 16 In one study, the authors found that 70% of the stems were considered to be loose at the time the patient sustained the fracture.…”