Unicompartmental knee replacement: some unanswered questions.

Within the past 5 years, there has been a resurgence of interest in doing unicompartmental knee replacement, which was encouraged by reports of easier recuperation, decreased hospital stays, and good functional results. Before doing a unicompartmental replacement, the surgeon should answer four important questions: Is the disease truly unicompartmental? Can this be determined on a clinical examination and standard radiographs, or are more sophisticated studies such as a bone scan or an arthroscopy required? Second, if the patient does have unicompartmental disease are there any specific contraindications to the surgery? The absence of an intact anterior cruciate ligament, and presence of an inflammatory arthroplasty have been said to be contraindications. Is crystalline arthropathy a contraindication? What are the limits of fixed deformity in varus or flexion that can be corrected by a unicompartmental replacement? Overcorrection of angular deformities has in the past led to increased wear of the opposite compartment. Therefore, how much should the knee be corrected? What surgical technique should the surgeon consider? Should the tibial components be inset into the bone or onset. Although it has been alleged that instrumentation is not necessary, obtaining proper alignment often cannot be obtained without the use of instruments. Finally, should the implants be inserted with or without acrylic cement, and what is the minimal polyethylene thickness that is permissible?