Abstract and Introduction
Cartilage injuries in the knee are common and can occur in isolation or in combination with limb malalignment, meniscus, ligament, and bone deficiencies. Each of these problems must be addressed to achieve a successful outcome for any cartilage restoration procedure. If nonsurgical management fails, surgical treatment is largely based on the size and location of the cartilage defect. Preservation of the patient's native cartilage is preferred if an osteochondral fragment can be salvaged. Chondroplasty and osteochondral autograft transfer are typically used to treat small (<2 cm2) cartilage defects. Microfracture has not been shown to be superior to chondroplasty alone and has potential adverse effects, including cyst and intralesional osteophyte formation. Osteochondral allograft transfer and matrix-induced autologous chondrocyte implantation are often used for larger cartilage defects. Particulated juvenile allograft cartilage is another treatment option for cartilage lesions that has good to excellent short-term results but long-term outcomes are lacking.
Focal cartilage defects result in disability that may be similar to osteoarthritis. Symptoms include pain, swelling, stiffness, and locking or catching, all of which can limit patient activities. These lesions are often traumatic, as in the case of a patellar dislocation or concomitant anterior cruciate ligament (ACL) injury, but can also be caused by chronic repetitive overload. They may also be found incidentally on MRI or at the time of knee arthroscopy, which is an important distinction from a symptomatic defect. Cartilage lesions are problematic because hyaline articular cartilage has limited ability to regenerate in response to damage. Fibrocartilage filling may occur but many will progress with eventual development of arthritis.
Radiographs are often unrevealing in a patient with acute knee pain after a cartilage injury. However, an effusion may be noted or a loose body may be present in the case of an osteochondral fracture. MRI is the preferred imaging modality to evaluate the depth, size, and location of a cartilage lesion and the subchondral bone.
There are several cartilage lesion categorization systems. The Outerbridge Classification described in 1961 is based on open or arthroscopic inspection of the cartilage surface. Outerbridge grade 0 describes normal cartilage, grade 1 represents cartilage softening to dynamic probing, grade 2 are partial thickness lesions less than 1.5 cm in diameter, grade 3 lesions are greater than 1.5 cm in diameter or have a full thickness fissure, and grade 4 lesions involve complete cartilage loss with exposed subchondral bone. The International Cartilage Repair Society Classification is also based on visual inspection of the cartilage and can guide management. Grade 0 describes normal intact cartilage. Grade 1 involves superficial cartilage lesions with softening, blistering, or fissures. Grade 2 cartilage lesions include fraying and fissures that are <50% of the cartilage depth. Grade 3 lesions describe cartilage loss that is >50% of the cartilage depth down to the calcified cartilage layer. Finally, grade 4 lesions are full-thickness cartilage lesions with exposure and involvement of the subchondral bone.
Small cartilage lesions, typically defined as less than 2 cm2, are treated with a variety of options to include débridement, microfracture, fixation of unstable lesions, osteochondral autograft, or occasionally osteochondral allograft (OCA). Larger lesions are more typically managed with OCA or a cell-based option, such as matrix-induced autologous chondrocyte implantation (ACI). A patient with multiple large diffuse lesions throughout the knee should be carefully evaluated because this likely represents an osteoarthritis process. Some young, motivated patients can achieve good results, but older individuals may not be cartilage restoration candidates and may require arthroplasty.
J Am Acad Orthop Surg. 2020;28(22):914-922. © 2020 American Academy of Orthopaedic Surgeons