Abstract
In the large majority of cases of knee osteoarthritis (OA), total knee replacement (TKA) is the selected treatment, due to its proven durability, satisfactory function and familiarity of surgeons. However in recent years there has been an increase in the numbers of uni-compartmental knees used (UKA), due to more favorable follow-up, improved designs and techniques, quicker and better patient recovery, and less hospitalization costs. Designs have been produced for even lesser invasive components than UKA, including simple spacers, with mixed results. Recently, several studies have been carried out on the wear patterns on the femoral and tibial condyles in OA, showing that the main areas of cartilage loss occur on the distal end of the femur, that area engaged in walking activities, and over a large proportion of the tibial plateau. A study we carried out on the bone pieces resected at TKA surgery showed that no less than 22% of the cases could have been done with a device which resurfaced only the medial side. That figure would have been higher if the patients had been treated earlier, before cartilage wear and deformation had progressed. In a more recent study, we showed the progress of the wear of OA by analyzing MRI scans of 50 patients at various stages of OA. The cartilage wear occurred on areas which were initially the thickest on both the femur and the tibia. This was evidently associated with excessive contact stresses, while the menisci, if they had previously been spreading the load over a large area of the cartilage surfaces, were no longer functional. In this paper it is proposed that the treatment modality of OA could be carried out on a sliding scale, based on MRI analysis together with clinical factors including pain and disability. Early Intervention devices, including UKA, could be used much more frequently if the surgical technique was developed to be reliable, simple and reproducible. Specifically there is space for an Early Intervention device (EI) where only the distal end of the femur and the tibial surface are resurfaced. A design has been produced where a pocket is milled into the distal end of the femur to house a plastic runner, and a thin layer is resected from the proximal tibia for a metal plate with a special keel design. The advantages of such a design are ease of exposure, accurate and simple surgery, minimal tibial resection for long term fixation, reduced wear, and ease of restoration of the original joint line. The wear is assessed using a custom-made wear machine, while fixation is evaluated using FEA. It is proposed that such a device would add a valuable option for the treatment of symptomatic early OA where the functional level of the patient can be maintained, and the progress of OA possibly arrested.
