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

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... 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.