METHODS OF RESURFACING OSTEOARTHRITIC KNEE JOINTS
CHONDROPLASTY is the treatment offered for partial thickness damage and involves the removal of any loose pieces and smoothing of the damaged area. This is usually done arthroscopically using hand instruments or the power shaver. Patients are generally allowed to mobilize and weight bear immediately. By performing a chondroplasty some of the roughness and joint irritation caused by frayed and damaged cartilage is reduced. This may not only make walking more comfortable for the patient, but should also reduce some of the overproduction in joint fluid leading to a less swollen knee joint.
2. BONE MARROW STIMULATION TECHNIQUES
A full thickness defect of cartilage presents the surgeon with a challenge, as cartilage left alone has no healing potential on its own. The traditional treatment approach has been based on the observation that under specific circumstances traumatic cartilage defects have filled in with fibro-cartilage (Repair cartilage) providing a blood clot has formed within the defect. Unfortunately this is a rather unpredictable phenomenon. However a substantial increase in success and predictability of cartilage in-growth can be achieved by surgically breaching the subchondral bone layer, henceforth promoting localized bleeding at the injury site (Pridie 'A method of resurfacing osteoarthritic knee joints' J Bone Joint Surg 1959;41-B:618-619). Richard Steadman an orthopaedic surgeon from Vail/Colorado used Pridie's observation and developed what he described as microfracture. (Steadman et al. 'Microfracture' Clin Orthop 2001;391(Suppl):S362-S369). Microfracturing of the subchondral plate encourages the migration of stem cells from the underlying bone marrow into the defect. In this environment such cells have the ability to convert into fibro-cartilage producing cell lines. During the healing process it is important to protect the growing repair cartilage by avoiding full weight bearing for at least 6 to 8 weeks. Unfortunately Fibro-Cartilage has inferior mechanical qualities when compared to hyaline-cartilage. Depending on the size and position of the defect fibro-cartilage might therefore merely delay but not prevent the development of osteoarthritis in the future. Short-term studies have shown favourable rate of survival without increased symptoms.
Mosaicplasty or osteoarticular autograft transplantation (OATS) involves the transfer of osteochondral cylinders/plugs of up to 1cm width and 15mm depth, from non-articulating parts of the knee into the defect (Kish et al. 'Osteochondral mosaicplasty for the treatment of focal chondral and osteochondral lesions of the knee an talus in the athlete' Clin Sports Med 1999;18:45-61). Due to limited surface area available this can only be performed successfully if the damaged area is not larger than 2-3cm2. Concern about increased morbidity of this technique has recently been expressed after reports of anterior knee pain around the harvesting site. Although widely used, no convincing long-term results have yet been published, which would confirm its superiority compared to abrasion arthroplasty.
4. CARTILAGE CELL IMPLANTATION
AUTOLOGOUS CHONDROCYTE IMPLANTATION or ACI is a relatively new technique, which is not widely available (only available in selected institutions in the UK, which are part of a nationwide trial!). It is based on the idea of harvesting patient's own cartilage cells (Chondocytes), grow them in the laboratory and re-implant them into the cartilage defect (Brittberg et al. 'Treatment of deep cartilage defects in the knee with autologous chondrocyte transplantation' N Eng J Med 1994;331:889-895). Early results have been promising and confirmed that it is possible to recreate Hyaline Cartilage.