Biodegradable hybrid screws for ligament-bone interface regeneration

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Anterior Cruciate Ligament injuries are often in the news as they are potentially career ending for footballers and athletes. One of the well-known incidents was seen during 2006 World Cup match between England and Sweden, where Michael Owen ruptured his ACL. This is not just a problem for elite athletes. Approximately 20,000 people in the UK need ACL repair every year and the National Health Service (NHS) performs about 11,000 ACL reconstruction surgeries per year.Reconstructive surgery of the ACL usually involves harvesting replacement ACL graft from the patient's own hamstring tendons. The damaged ACL is removed through arthroscopy (keyhole surgery), then tunnels are drilled in femur (thigh bone) and tibia (shin bone) in the knee joint area. The replacement graft is aligned/positioned through the tunnels, and opposite ends are fixated in the tibial bone tunnel by interference screws. Our clinicians and our medical device partner Xiros have identified an unmet clinical need for new screws and ACL reconstruction devices. Current metallic screws will be eventually rejected by the body as they are bioinert and will undergo fibrous encapsulation, but they can also tear the graft. The aim here is to develop an ideal screw that would be bioactive, to stimulate bonding to bone and regeneration of the connective tissue/ bone interface and biodegradable integrating the graft into the bone. The screw must also be strong, tough and a certain stiffness. Biodegradable polymer/bioactive ceramic composite screws exist, but they often fail and need replacing. This is because the bioactive component is buried in the polymer and the degradation rate of the polymer is uncontrolled and can be catastrophic or cause cysts. Our hybrid screws will overcome those problems, giving strength and a specifically designed biodegradation rate to match the rate of restoration of the bone/connective tissue interface. In some cases, it is not the screw that fails, but the tendon graft, therefore we will also develop a new totally synthetic device that eliminates the need for harvesting from the hamstring and provides more reliable long term performance, while integrating with the host bone.