What is an osteochondral defect?

What is an Osteochondral Defect?

An osteochondral defect is an injury or abnormality involving both the articular cartilage and the underlying subchondral bone of a joint, representing damage that extends through the cartilage layer into the bone beneath. 1, 2

Anatomic Definition and Pathology

• An osteochondral lesion encompasses damage to both the talar articular cartilage and adjacent bone, distinguishing it from purely chondral (cartilage-only) injuries 2
• The defect involves loss of the normal joint surface architecture, ranging from partial-thickness cartilage damage to complete loss of cartilage with exposed subchondral bone 3
• These lesions differ from acute osteochondral fractures that are immediately detected radiographically following trauma 4

Classification Systems

The severity of osteochondral defects is graded using standardized classification systems 3:

Outerbridge Classification:

• Grade 0: Normal cartilage
• Grade 1: Cartilage softening and swelling
• Grade 2: Fragmentation and fissuring involving area <1.5 cm diameter
• Grade 3: Fragmentation and fissuring involving area >1.5 cm diameter
• Grade 4: Complete loss of cartilage with exposed subchondral bone

Beck Classification provides additional detail for surgical planning, including grades for debonding (loss of fixation to bone with intact cartilage surface) and cleavage patterns 3

Etiology and Pathogenesis

• Osteochondral lesions commonly result from trauma, though they are often unrecognized acutely and lead to chronic defects 1
• Multiple causative factors include trauma, labral tears, femoroacetabular impingement, arthritis, osteonecrosis, and dysplasia 3
• The pathologic process may begin with subchondral bone injury or osteonecrosis, with the overlying cartilage subsequently affected 4
• Biomechanical studies demonstrate these lesions occur in areas of highest joint loading under stress 4

Clinical Significance and Natural History

• When left untreated, osteochondral defects frequently progress to osteoarthritis of the entire joint 1, 5
• The articular cartilage surrounding defects shows catabolic activity with expression of inflammatory markers (IL1β, FGF2), potentially initiating early osteoarthritic disease 5
• In animal models, untreated defects show continuously increasing proteoglycan fragments and collagen levels in synovial fluid, indicating ongoing degenerative joint activity 6
• A critical size defect (defined as 1.4 mm diameter in rat models) will not heal spontaneously and demonstrates rapid subchondral bone plate advancement 5

Common Locations

• In the ankle, osteochondral injuries most commonly involve the talar dome, less commonly the tibial plafond and tarsal navicular bone 3
• In the hip, most chondral injuries are located in the anterior quadrant of the acetabulum (59%) and are frequently associated with labral tears 3
• The knee is the most common site overall for osteochondral lesions, followed by the elbow, with the talus being the third most common site (4% of all cases) 4

Diagnostic Considerations

• Plain radiography may show the abnormality when associated with fracture, osseous cyst, or osteochondral defect, but often fails to show the extent of injury 3
• Radiography is initially negative if injury is limited to articular hyaline cartilage, with studies showing 41% of osteochondral abnormalities of the ankle are missed on plain films 3
• MRI demonstrates high sensitivity (96%) for detecting these lesions and can assess instability, appearing as high signal deep to the lesion on T2-weighted images 3