Acute Sports Injuries - HYALINE CARTILAGE

This post follows on from acute sports injuries in bones. Hyaline (or articular) cartilage lines the articular surface of bone regions forming synovial joints. It provides a smooth, lubricated surface allowing for low-friction gliding and possesses viscoelastic properties which facilitate the absorption and distribution of loads to the underlying subchondral bone. This means hyaline cartilage is principally exposed to compressive loads. Acute joint subluxation or dislocation, as well as acute ligament sprain or rupture can lead to locally high compressive forces and the superimposition of shearing forces due to excessive joint translation. This can lead to an acute chondral (cartilage) or osteochondral (cartilage + underlying bone) injury.

Articular cartilage is radiolucent and so most chondral injuries aren't visible on conventional radiology, meaning they are often underdiagnosed. However, with the development of magnetic resonance imaging and direct visualisation via arthroscopy, it's become clear that chondral injuries are far more common than previously realised. Clinicians need to maintain a high index of suspicion for chondral involvement if an apparently 'simple joint sprain' remains swollen and painful for longer than expected, despite the presence of normal X-rays. Common sites for chondral and osteochondral injuries are the femoral condyles, superior articular surface of the talus, the capitellum of the humerus and patella.

Chondral injuries are a concern due to poor healing ability and their contribution to the development of premature osteoarthritis. Articular cartilage has limited regenerative and repair capacity due to its avascular nature. Classification systems have been developed to quantify the severity of chondral damage and guide prognosis. Scales generally extend from 0 (normal) to 4 (exposed bone for chondral injuries, fragment displacement for osteochondral lesions), with higher scores indicating greater damage and a worse prognosis.

Chondral and osteochondral injuries in young active people represent a therapeutic challenge. The hope is to permit a return to participation whilst minimising cartilage degeneration and the need for early arthroplasty (joint replacement). Treatment options for chondral injuries range from palliative techniques (e.g. chondroplasty to smooth loose edges of damaged cartilage and arthroscopic washout to remove debris) to techniques aimed at stimulating cartilage repair or restoration. Reparative techniques include abrasion arthroplasty, drilling and microfracture (bone marrow stimulation) whereas restorative techniques include autologus osteochondral mosaicplasty, osteochondral allograft transplantation, and chondrocyte and mesenchymal stem-cell based therapies. This involves cells being implanted into the cartilage lesion and covered with a periosteal or collagen membrane cover.

Treatment choice depends on the size of chondral/osteochondral lesion, with great debate continuing as to the most effective approach. Return to sport depends on a range of factors, including athlete age, duration of symptoms, level of play, repair tissue morphology, lesion size, type and location, and the number of surgeries and concomitant procedures.

Quite a wordy read but so interesting! Stay tuned to learn about acute injuries to the fibrocartilage...

REFERENCES

Brukner, P., 2012. Brukner & Khan's clinical sports medicine. North Ryde: McGraw-Hill.