The Effectiveness of Cerclage Wiring on Stabilizing Intra-Operative Femoral Fractures During Cementless Total Hip Arthroplasty in Canines.

Abstract

Force is required to prepare the bone and achieve the initial press fit for an uncemented hip implant during Total Hip Arthroplasty (THA) surgery. In some situations, this force may cause of an intra-operative femoral fracture resulting in an unstable implant, subsidence, and pain for the patient. Many of the less extensive fractures can be repaired with cerclage wire or cables. This study aimed to evaluate the ability of double loop cerclage wire(s) to restore the stability of the implant-bone interface after a simulated intra-operative fracture. Nine femora from euthanized canine were harvested for in vitro testing. The femora were prepared for implantation of an uncemented femoral stem (BFX™ series, BioMedtrix, Boonton, NJ). They were then potted and mounted in a materials testing machine (MTS 858 Mini Bionix II, Eden Prairie, MN). The implant was driven to a clinically appropriate height, struck with 3 impacts (simulating seating hammer blows), and then the stem loaded to failure. Once a fracture occurred, the implant was extracted, the femur was repaired with appropriate cerclage, re-broached, and re-implanted. The repaired specimen was then tested in the same fashion as the intact bone. During loading, the displacement of the implant relative to the bone was measured using a linearly variable differential transformer LVDT. The force to initiate subsidence, the peak force at failure, and the peak subsidence distance were compared between intact (pre-fracture) and repaired (post-fracture) specimens using ANOVA with blocking by specimen. The wired specimens demonstrated a higher force to initiate subsidence than the intact specimens (2378.8N ± 656.9N c.f. 1705.1N ± 584.5N; p= 0.0019). The wired specimens also sustained a higher peak force at failure than the intact specimens (3309.0N ± 609.14N c.f. 2276.3N ± 855.6N; p=0.0022). Furthermore, the wired specimens did not subside a significantly greater amount than the intact specimens (Intact: 3.90mm, SD=2.09mm; Wired: 6.71mm, SD=3.66mm; p-value = 0.0600). Cerclage wiring of intra-operative femoral fractures was able to restore the integrity of the femur and enable a stable implant-bone interface to be achieved.