Mechanism of injury

• Trauma is the most common mechanism, but the repetitive stress associated with osteochondritis dissecans and chondromalacia patellae are also causes of symptomatic lesions.
• Rotational force in direct trauma is the most common cause of injury to the articular cartilage. In most cases injury is in weight-bearing regions of articular cartilage, and usually in the medial compartment (4 times more common that lateral injuries).^[2]
• Isolated articular cartilage injuries secondary to trauma are rare; more often, articular cartilage injuries are seen with other traumatic injuries to the knee, such as ligamentous or meniscal damage.
• Osteochondral lesions are most common in adolescents.

Articular cartilage has little capacity to repair itself or regenerate. Therefore, cartilage defects repair by forming scar tissue from the subchondral bone. This scar tissue is deficient in type II collagen and has lower load-bearing capacity. This later surface deterioration may progress to give chronic pain and poor function and may, in some cases, lead to early onset osteoarthritis.

Assessment

See separate article Knee Assessment (History and Examination).

• Plain X-rays are of limited value and require skilled interpretation.^[3]
• Magnetic resonance imaging (MRI) - provides accuracy with high levels of reproducibility. Incidental meniscal findings on MRI scan of the knee are common in the general population and increase with increasing age.^[4]
• Delayed, gadolinium-enhanced MRI of cartilage (dGEMRIC) is useful for assessing cartilage health.^[5]
• Examination of the knee under anaesthesia followed by arthroscopy remains the gold standard.

Presentation

• Articular cartilage is avascular and aneural, so pain would not be expected; yet,some patients do present with pain. It may be present at rest and is exacerbated by weight-bearing exercises.
• The knee may give way if a longstanding injury results in substantial muscle wasting or there is associated ligamentous instability.
• Locking is reported if a loose fragment impedes articular movement.
• There may be an effusion.
• Tenderness is found on palpation of the joint line, with pain induced by both passive and active movements.
• Wasting of the quadriceps will be seen later on.
• Crepitus is palpable on passive joint movement in a usually stable knee.

Associated diseases

Knee ligament injuries and fractures may also be present.

Management

Lesions may not be diagnosed or may present late because patients will often give a history of an apparently insignificant trauma. Doctors may fail to understand the importance of an effusion in the knee joint, which always indicates joint disease.

Injuries that are new are given time to settle to see if the chondral lesion will become symptomatic or not. If pain fails to resolve after the initial acute phase, surgical treatment gives better outcomes if done sooner rather than later.

Conservative^[1]

Advise 'RICE': R est (crutches for the initial 24-48 hours); I ce (application of ice on the injured region for 20 minutes of each waking hour during the initial 48 hours after injury); C ompression (with a knee brace or splint, if necessary) and E levation (above the level of the heart).

After pain and inflammation subside, aim to increase strength and pain-free range of motion (ROM). Continuous passive motion enhances the healing potential of articular cartilage:^[5]

• It enables the movement of synovial fluid, allowing better diffusion of nutrients into the damaged cartilage and diffusion out of other materials (such as blood and metabolic waste products).
• It reduces the formation of fibrous scar tissue in the joint; this tends to decrease the range of motion for a joint, which enhances the healing potential of articular cartilage.

Surgical

Treatment of larger and symptomatic lesions is surgical and techniques include arthroscopic debridement, marrow-stimulating techniques, autologous chondrocyte transfers and implantation, and allografts.^[5]

Return to the pre-injury level of sports has been found to be fastest after osteoarticular transplantation (OATS) and slowest after autologous chondrocyte implantation (ACI).^[6]

Complications

• If symptomatic lesions are untreated they may lead to chronic pain and disability and possible early osteoarthritis.
• Significant soft-tissue injuries of the knee and lower leg put the lower leg at risk for compartment syndrome.

Prognosis

Several factors have been associated with improved postoperative recovery:^[6]

• Defect size of less than 2 cm.
• Preoperative duration of symptoms of less than 18 months.
• No previous surgical treatment.
• Younger patient age.
• Higher pre-injury level of sports.

Development of recurrent locking, popping, or effusions after an adequate trial of conservative therapy may suggest the need for surgical intervention.