Biomechanical evaluation of the primary stability of three different types of femoral stem fixations for canine total hip replacement

Abstract Background: Total hip arthroplasty is the main salvage procedure performed for hip osteoarthritis in dogs. Two main types of femoral stems are available: cemented stems, which offer excellent primary stability but are subject to aseptic loosening in the long term, and cementless stems, which have good long-term outcomes but lack primary stability. The adjunction of a neutral rod through the neck of the cementless stem to the lateral cortex of the femur could offer better primary stability before osteointegration. The aim of this study was to compare the primary stability of three different femoral stems, cemented (cFS), press-fit cementless (pfFS), and rod-press-fit cementless stems (r-pfFS), by measuring their transverse displacement on cyclic assays and resistance to subsidence with unidirectional load compression parallel to the longitudinal axis of the femur.Results: The force-displacement and stress-strain curves were assessed. The work necessary for subsidence, strain to failure, and mean strain of the cyclic assays were calculated. No significant differences were observed in transverse displacement (p=0.263) or mean strain (p=0.244) during the cyclic tests or in work necessary for subsidence (p=0.079) or strain to failure (p=0.075). The cFS and r-pfFS were significantly more resistant to subsidence than was the pfFS (p<0,05). No significant differences were observed between the cFS and r-pfFS groups (p=0.48).Conclusions: Cementless femoral stems with transfixing rods offer significantly higher stability to compressive load parallel to the longitudinal axis of the femur than do standard cementless stems and a level of stability comparable to that of cemented stems. r-pfFSs may be valuable in limiting the subsidence and micro-motion of press-fit femoral stems and thus improving the state of osteointegration of the prosthesis during the short-term postoperative period.