Articular cartilage covers the articulating portions of the knee, including the distal femur, proximal tibia, and patella. Articular cartilage is composed of hyaline cartilage, which is the smoothest form of cartilage, allowing for low-friction joint motion. This layer of cartilage has no direct blood supply and is susceptible to injury with little regenerative potential. More advanced cartilage lesions can lead to degenerative joint disease or arthritis.

The medial and lateral menisci are composed of fibrocartilage, and play an important role in the articulation between the femur and tibia. The menisci contribute significantly to the knee’s natural function and motion. They fill the void between the joint and the surrounding synovium and capsule, which prevent the synovium and capsule from being drawn into the joint during motion. Additionally, the menisci increase the weight-bearing surface of the knee, thus distributing the load and decreasing the contact pressure between the femur and tibia. They also play a role in joint stability, as they are cup-shaped structures, which increases the joint’s congruence with the femur, contributing to the stability of the knee. Last, they are believed to be responsible for joint fluid movement and lubrication. The menisci have a variable blood supply. The blood vessels enter from the periphery, thus the peripheral portion of the meniscus has the most pronounced blood supply, while the inner portion has the least blood supply and is essentially avascular. Zones of vascular supply have been described that help guide treatment in the setting of meniscus tears (Figure 46.1). The most peripheral zone is the red-red zone, which is approximately the peripheral 25% of the meniscus, where the blood supply is the best. The red-white zone is at the junction of the vascular peripheral meniscus and the inner avascular portion of the meniscus. The white-white zone is the avascular peripheral meniscus. Injuries in the red-red zone are most likely to heal, as that is where the blood supply is best. Injuries in the red-white zone have the potential to heal, while injuries in the white-white zone are unlikely to heal.

Both the articular cartilage and menisci are susceptible to injury and degeneration. This can be thought of as a spectrum of disease. Younger patients typically sustain a trauma to the knee, which results in an articular cartilage injury or meniscus tear, and are often seen in the setting of a concomitant ligament injury. Older patients, who may have thinner, weaker, and less pliable cartilage and menisci, may sustain an injury with relatively little trauma.

Lesions or damage to the articular cartilage surface leave rough areas on the joint surfaces, potentially leading to pain, swelling, and mechanical symptoms, such as locking or catching of the knee joint. In some cases, articular cartilage can be completely dislodged and float around the joint, which is called a loose body. These may also lead to mechanical symptoms, particularly locking or catching of the joint. The treatment of a cartilage lesion depends on the patient’s symptoms, age, location, and size of the defect. This chapter focuses primarily on chondroplasty, which is performed primarily in the setting of another procedure, such as partial meniscectomy, loose body removal, or ligament reconstruction. It is uncommon to perform chondroplasty alone. In younger patients with cartilage injuries, advanced cartilage reconstructive or regenerative procedures, such as autologous chondrocyte implantation, may be preferred. In older patients, with degenerative articular cartilage thinning or a full-thickness lesion, chondroplasty alone does not generally provide durable pain relief and improved function. Therefore, joint replacement may be considered for these patients.

Similarly, meniscus tears can be degenerative or acute/traumatic. The symptoms are similar to those of articular cartilage injury, including pain, swelling, locking, and catching. Displaced meniscus tears should be suspected in the setting of knee locking. The patient’s age and activity level, as well as location of the meniscus tear, go into the medical decision on what may be the best treatment option for the patient. Typically, knee arthroscopy and partial meniscectomy are indicated in the settings of persistent pain that has failed conservative treatments, meniscus tears in the avascular zone (white-white)
zone, and for displaced meniscus tears causing mechanical symptoms. Chondroplasty is often performed during the same surgery to smooth any rough or displaced articular cartilage lesions.