Articular cartilage

Structure and function of articular cartilage

Covers bony surface in joints, allows low-friction joint movement, absorbs biomechanical forces, stabilizes joint. Resist tension and compression.

Most common forces and mechanisms of articular injury

Unexpected or sudden movements, increased cartilage loading, repetitive impact loading

Grade 0

Normal healthy

Grade 1

softening, inflammation/swelling

Grade 2

partial thickness loss with fissure at surface

Grade 3

High thickness loss with fissure too subchondral surface

Grade 4

Full thickness loss with exposed subchondral bone

Pathophysiology of articular cartilage

lacks blood vessels and lymphatic vessels (can’t heal on its own). Bone may provide some blood to area.

Signs/symptoms of injury

Pain, swelling, catching/locking, popping, stiffness, reduced ROM, instability.

Repair process of ECM damage without visible disruption

Response: new matrix synthesis. outcome: chondrocytes restore matrix if-collagen fibrillary network remains intact, viable chondrocytes are in the area, continue loading does not cause ECM degradation faster than chondrocytes repair ECM

Repair process of chondral fracture

response: chondrocytes proliferate and synthesize ECM. outcomes: response not robust enough for cells to fill ECM defect, response stops but defect remains, may worsen with continue loading.

Repair process of Osteochondral fracture

response: hemorrage, fibrin clot formation, migration of MSCs, synthesis of type I and type II collagen and proteoglycans in defect. Outcomes: chondral defect is partially filled w/ “hayline-like” fibrocartilage, bone can remodel, inferior tissue will degrade over time due to loading.

Debridement

smooth edges to decrease symptoms and catching

Microfracture

debridement down to subchondral bone. makes hole in bone to cause bleeding Imigration of MCSs to go through osteochondral fracture process.

mosaicplasty

plugs healthy bone and cartilage into injury, inserts them into defect

autologous chondrocyte implantation

assists bone to build new cartilage. Takes out chondrocytes from injury site and proliferates them in a lab and injects them back into the injury site. Allows body to have a robust response and builds new cartilage.