Articular cartilage is composed primarily of type II collagen.

Chondrocytes that produce the extracellular matrix are of mesenchymal stem cell origin.

Osteochondral lesions may occur in all three compartments of the knee.

Chondral defects after a patellar dislocation typically are found on the medial patellar facet or lateral trochlea.

Classically, osteochondritis dissecans occurs at the lateral aspect of the medial femoral condyle.

Osteochondral lesions may be traumatic or may have no known history of trauma (osteonecrosis).

Traumatic lesions may be caused by compaction, as with an anterior cruciate ligament tear and lateral-based osteochondral injury, or by a shearing mechanism, as seen with patellar dislocations.

Atraumatic lesions may be found in young persons, as is the case with osteochondritis dissecans, or in elderly persons, as seen with degenerative lesions.

The etiology of osteochondritis dissecans is uncertain. Traumatic, inflammatory, developmental, and ischemic causes have all been proposed but not proven.

Few controlled, prospective outcome studies have been published.

The natural history for juveniles with nondisplaced osteochondritis dissecans is very favorable.

Those diagnosed as adults have a less favorable prognosis. In a study by Linden and Malmo,⁹ 81% of patients had tricompartmental gonarthrosis at an average of 33 years follow-up.

Patients with focal osteochondral lesions typically are active and young, ranging in age from adolescence to middle age.

Often, the history does not include a specific traumatic episode. History and physical findings can be subtle.

Presentation is variable; it may mimic meniscal pathology, with intermittent pain and swelling.

Condylar defects may present with high-impact loading complaints, whereas patellofemoral defects may produce anterior knee pain-type complaints, with stairs and prolonged sitting causing symptoms.

Patients with large cartilage lesions who are candidates for osteochondral allograft transplant surgery may have a history of previous knee surgery and previous attempts at cartilage regeneration by other methods (eg, microfracture, autologous chondrocyte implantation, osteochondral autograft transplant). Many have underlying bony changes or deficient subchondral bone.

Physical findings can be nonspecific and may include joint effusion and painful range of motion.

Tenderness at the defect, on either the condyle, patellar facets, or trochlea, may be elicited.

In the case of patellofemoral defects, patellar mobility and apprehension must be assessed.

Ligament integrity must be determined.

Mechanical alignment must be assessed, and appropriate imaging studies obtained.

Failure to identify and address ligamentous deficiency or mechanical malalignment will lead to compromise of restorative cartilage procedures.

Physical examination of the knee should note the following:

Anteroposterior, lateral, and sunrise views are mandatory to determine overall knee condition, rule out diffuse degenerative arthritis, and assess patellar position within the trochlea.

Large chondral defects may not be visible on plain radiographs or may have a small radiodense bone fragment attached.

“Notch views” may better define more central lesions.

Long-leg mechanical axis views are mandatory in patients with malalignment on physical examination and should be considered in all candidates for osteochondral autograft transfer.

MRI is the best modality to determine the presence, size, and location of cartilage lesions, as well as to determine the integrity of menisci and ligaments. It will also offer information about the supporting bone surrounding the lesion (FIG 1A-C).

Arthroscopy remains the gold standard for evaluation of articular cartilage lesions (FIG 1D).

Meniscal tear

Degenerative arthritis

Patellar instability

Bone contusion

Avascular necrosis

Undiagnosed ligamentous injury

Patients with asymptomatic osteochondral lesions (often found incidentally on standard knee arthroscopy) may be candidates for nonoperative treatment.

Long-term studies may indicate an increased risk for degenerative arthritis with conservative management,⁹ but no randomized controlled studies exist.

Nonoperative treatment should consist of physical therapy to obtain or maintain painless, full range of motion.

Aggravating impact activities should be avoided.

Patients may participate in sports as tolerated.

Unloader braces or shoe wedges may help alleviate mild symptoms.

Osteochondral allograft transplantation often is a two-stage procedure.

The magnitude of the lesion and, occasionally, the diagnosis itself often are not appreciated until first-look arthroscopy (FIG 2).

Size and location of the cartilage lesion is determined.

Lesions 1 cm (>2 cm²) in diameter or larger are considered for allograft transplant. Smaller lesions may be amenable to microfracture or autograft cartilage transplant with single or
multiple plugs. (Lesions with deficient subchondral bone are also considered for allograft transplant.)

The remainder of the knee is inspected to ensure this is not a diffuse cartilage process and to examine the integrity of the cruciate ligaments and menisci.