2 The condition, current treatments and procedure
2.1 Chondral damage (that is, localised damage to the articular cartilage) in the knee can be caused by injury or arthritis, or it can occur spontaneously (a condition called osteochondritis dissecans). It can also occur because of knee instability, muscle weakness or abnormal unbalanced pressures, for example, after an injury to a ligament or meniscal cartilage. In young people, the most common cause of cartilage damage is sporting injuries. Symptoms associated with cartilage loss include pain, swelling, instability, and joint catching and locking, and may lead to degenerative changes in the joint (osteoarthritis).
2.2 There is no uniform approach to managing cartilage defects in the knee. Treatment options depend on the size of the defect and its location. There are 2 main categories of procedure: those intended primarily for symptom relief and those that also try to re-establish the articular surface. Interventions that aim to re-establish the articular surface include marrow stimulation techniques (such as abrasion arthroplasty, Pridie drilling and microfracture), mosaicplasty (also known as osteochondral transplantation) and autologous chondrocyte implantation (in which chondrocytes harvested from the knee are cultured and implanted into the damaged cartilage). Interventions that aim to relieve symptoms include knee washout (lavage) with or without debridement, osteotomy and knee replacement.
2.3 Mosaicplasty (also called osteochondral autologous transfer mosaicplasty) is a technique for creating an osteochondral autograft. Small cylindrical osteochondral plugs are harvested from the periphery of the patellofemoral area (because it bears less weight) and inserted into drilled tunnels in the affected weight-bearing part of the knee joint. The procedure is done in a single sitting, commonly by open surgery but sometimes arthroscopically when perpendicular access to the harvesting and implantation sites is feasible. The harvesting and implantation process is repeated until about 70% of the defective area is filled, with minimal spacing between plugs. The number and size of plugs used may vary depending on lesion size and mosaicplasty technique. A drain may be needed postoperatively, and the patient is advised not to weight bear for 4 to 8 weeks depending on the size and location of the treated defect. Passive mobilisation after surgery is done for 2 to 4 weeks, progressing to active mobilisation and physiotherapy that is continued for several months.