Simulation and experimental investigation of bone “through-growth” on stability of interpositional orthopedic implant
Knee osteoarthritis (OA) is one of the most common joint diseases in the world, affecting a staggering 86.7 million people worldwide in the year 2020. Osteoarthritis is characterized by the breakdown of cartilage in the joints, leading to pain, stiffness, and limited mobility in patients. Knee malalignment is an important predictor of knee OA. High tibial osteotomies (HTO) are an effective treatment for knee osteoarthritis particularly for patients with varus knee malalignment. The purpose of an HTO is to correct the load-bearing axis of the knee joint, redistributing the overload from the damaged medial compartment to the lateral compartment. While obesity is a common comorbidity to OA, it can be a contraindication for HTO’s due to the increased load on the HTO plate. A newly patented HTO device has been developed to address this issue for obese patients. This device includes an implant that occupies the osteotomy space and provides additional mechanical strength. There are 5 openings or “windows” that go through this implant, to provide an opportunity for bone through-growth. This is a pilot study that focuses on how to optimize the windows’ design to create better initial and long-term stability. Simulation and experimental testing procedures were developed. The radius of curvature on the edge of the windows and the amount of bone through-growth in the windows were varied. The maximum load for extraction was recorded and observations were made on the failure mechanisms of the implant-bone assembly. The results indicate that a sharper radius on the windows’ edge increased the overall implant stability. It also found that greater through-growth depth resulted in superior stability within the assembly. The results provide a framework for future interpositional implant design and bone through-growth studies.