Adult Chondral Injury of the Knee

An adult knee chondral injury is a focal or diffuse defect of the hyaline articular cartilage of the femoral condyles, trochlea, patella or tibial plateau.

It follows trauma (twisting, patellar dislocation, ACL rupture), repetitive overload or degenerative wear. It is distinct from osteoarthritis, although a symptomatic focal defect may contribute to early degenerative change.

Cartilage has no blood supply and little capacity to heal, so treatment is matched to the lesion and to the knee around it.

Articular cartilage is hyaline cartilage: mostly water, with a type II collagen network, proteoglycan ground substance and chondrocytes. The subchondral bone plate lies beneath.

It has no blood supply, nerves or lymphatics and is nourished by diffusion from synovial fluid. Adult chondrocytes divide little. A defect that breaches the subchondral plate lets marrow-derived cells in and fills with fibrocartilage (mainly type I collagen), which is mechanically inferior. A defect that does not breach the plate does not heal.

Causes:

• •Acute chondral or osteochondral fracture, including after patellar dislocation (medial patellar facet and lateral femoral condyle)
• •Lesions with ACL or meniscal injury
• •Degenerative chondropathy

Outerbridge grading is arthroscopic and has 4 grades: I softening and swelling; II and III fissuring and fragmentation of increasing extent, not reaching bone; IV full thickness with exposed subchondral bone. The ICRS classification broadly maps onto it.