Numerical and Experimental Investigation of a New Load-sharing Implant for Early-onset Knee Osteoarthritis
Knee osteoarthritis (OA) is one of the major causes of musculoskeletal impairment in adults. This disease is mainly characterised by progressive degeneration of the articular cartilage and, to date, there is no known cure for it. Initiation and progression of the OA pathology is associated with knee loading conditions. For younger, active patients with knee OA, common treatments include non-invasive options in order to manage symptoms before considering, as a last resort, the surgical options, in particular the gold standard treatment: knee replacement. Recently developed load-sharing implants could be considered as suitable options lying between the symptom management and invasive treatments. One such implant is comprised of femoral and tibial components, and removes excessive load through the knee joint by attachment to the medial side. This patient-specific implant would be suitable for early-onset knee osteoarthritis and can be used for younger active patients, as no major modification in the knee joint is required. This research aimed to study the influence of the implant on tibiofemoral joint contact mechanics and bone remodelling using numerical and experimental methods. To do so, Finite Element (FE) knee models and cadaver knee specimens were used. Initially, a FE model was used for conducting stress analysis in the cartilage, then to implement an adaptive bone remodelling method. Periprosthetic Bone Mineral Density (BMD) changes induced by this new implant were investigated in the femur and tibia for the first time. The surgical procedure as well as the effects of the implant on the joint space and contact pressure were also studied using cadaver specimens and accurate real-time pressure measurement sensors. A prototype of the implant was made based on a 3D model of the specimen reconstructed using MR images. Through numerical and experimental investigations, it was deduced that this new implant can increase the joint space and effectively reduce the load going through the medial compartment, without affecting greatly the periprosthetic bone density. Specifically, after attachment of the implant, the maximum von Mises stress and contact pressure experienced by the femoral cartilage were reduced by 40% and 35%, respectively. Also, in the medial compartments of the femur and tibia, bone mineral density increased by approximately 3.4% and 4.1%, respectively, and the density for the fixation holes of both bones increased by around 2.2%. Moreover, according to the experimental contact pressure measurements, the implant reduced the load on the medial side by approximately 18% under all loading conditions. The implant was attached to the bone with a smaller incision than that used for total knee replacement, and without any bone resection or damage to soft tissue. During flexion and extension of the knee specimen, the implant did not cause any hindrance. According to the above points, this implant can be considered to be a minimally invasive treatment, which might slow down progression of knee OA without any significant adverse events and/or any detrimental influence on future surgical procedures.