Marrow stimulation techniques.

Due to the very low intrinsic activity of human adult cartilage, healing of chondral and osteochondral defects in patients cannot be expected. In treating symptomatic cartilage damage, marrow stimulation methods belong to the most frequently used methods, along with autologous chondrocyte transplantation (ACT) and mosaicplasty. These arthroscopic procedures are generally easy and the marrow stimulation treatment costs relatively little. In recent years, Pridie drilling has been increasingly replaced by the microfracture technique. This modification relies on the same biological principles of promoting resurfacing with the formation of fibro-cartilaginous repair tissue. For the treatment of smaller cartilage defects (<2.5 cm(2)), microfracture still remains the first choice for treatment. The clinical results after microfracture in the knee are age dependent. Younger and active patients (<40 years) with smaller isolated traumatic lesions on the femoral condyles have the best long-term results. The deterioration of the clinical results begins after 18 months and is significantly more pronounced in older patients with defects on the patella-femoral joint and tibia. The inferior quality of the repair tissue, partially incomplete defect filling and new bone formation in the defect area seem to be limitations of these methods. The AMIC (autologous matrix induced chondrogenesis) technique was developed to enable treatment of larger defects by the application of a collagen Type III/I membrane (Geistlich Pharma, Wolhusen, Switzerland), in particular when cell-engaged procedures such as ACT cannot be used for financial reasons or because it is not indicated. AMIC seems to be particularly suitable for treating damaged retropatellar cartilage, which is an advantage because these defects can be hard to treat with standard microfracturing alone. The results of the ongoing studies are awaited to establish whether better results with this technology are achievable in the long term.