The Development of Biodegradable Metallic Screws and Suture Anchors for Soft Tissue Fixation in Orthopaedic Surgery

Surgical treatment for injuries to soft connective tissues are estimated at about 800,000 cases each year in the US. For these surgical procedures, interference screws or suture anchors are needed. Currently, materials used for the devices are non-degradable metals or bioresorbable polymers. However, these materials do lead to complications. Metallic materials suffer from difficulties encountered during revision surgery and interference with magnetic resonance imaging; whereas, polymeric materials lead to device fracture during implantation, inconsistent degradation rates, and poor osteointegration. The overall goal of this dissertation was to explore the use of Mg-based materials as an alternative to the existing materials. Specifically, the studies focused on Mg-based interference screws for ACL reconstruction and suture anchors for rotator cuff repair. First, a Mg-based interference screw was designed and optimized through in-vitro testing and finite element analysis (FEA). At time zero, ACL reconstruction with Mg-based interference screws was found to restore initial joint stability as well as the in-situ load in the ACL close to the levels of the intact. Also, structural properties of the femur-graft-tibia complex (FGTC) with a Mg-based interference screw were comparable as those with a titanium control. In a follow-up study, joint stability and graft function after 12 weeks of healing were found to be comparable to past studies of ACL reconstruction in a goat model using the robotic/UFS testing system. The stiffness and ultimate load of the FGTC at 12 weeks were comparable to those at time zero. These results indicate that Mg-based interference screws allow for proper healing of the graft. Similarly, a Mg-based suture anchor was also designed and developed. Using FEA, the thread depth and pitch of the anchor could be optimized. It was then demonstrated that Mg-based suture anchors could achieve superior fixation over commercially available polymer suture anchors as it could provide a higher stiffness and ultimate load. In summary, the potential of Mg-based alloys for fixation of soft tissues to bone has been clearly demonstrated. We hope that the current findings would help the development of a novel class of biodegradable metallic implants that would ultimately help patients with improved outcomes