New β Ti alloy mini-prosthesis with low elastic modulus resurfacing articular surface defect in dogs

Objective To assess the effect of a new β Ti alloy mini-prosthesis with low elastic modulus on resurfacing the full-thickness Surface defect of the knee joint in dogs.Methods A full-thickness osteochondral defect of 7 mm in diameter was created at the medial femoral condyle of both hind limbs in 8 healthy adult dogs.The titanium alloy mini-prostheses with high-modulus of elasticity were implanted on the right side(control group)and those with low-modulus of elasticity on the left side(experiment group)to repair the cartilage defects.After 3 months,all the 8 dogs were sacrificed to harvest the specimens.Radiographic,histologic and micro-CT examinations were conducted to observe stability of the mini-prostheses and growth of the bone and cartilage surrounding the implants. Results Radiographic evaluation revealed no indications of device disassembly or subsidence.Bone trabeculae surrounding anchoring screws in the experiment group was visibly more and denser compared with the control group.Micro-CT data revealed that the bone volume fraction,trabecular thickness,trabecular number and tissue mineral density were 0.389%±0.025%,0.049±0.002 μm,8.9±0.4 mm-1 and 652.7 ±12.6 mg/mm3 respectively in the experiment group,compare with 0.253%±0.024%,0.038±0.002 μm,5.9±0.4 mm-1 and 595.2±7.6 mg/mm3 in the control group,with statistically significant differences between the 2 groups(P<0.05).Cartilage around the cap grew well and the surface remained smooth.Periphery of the resurfacing implant was covered by an extension of the superficial cartilage emanating from the defect margins. Conclusions The new β Ti alloy mini-prosthesis with low elastic modulus is favorable toward resurfacing the articular surface defect.The low-modulus of elasticity can improve new bone formation on the implant-bone interface.