GROWING YOUR OWN CARTILAGE

BY OLIVER S SCHINDLER, MD MFSEM(UK) ÖFD(ORTH) FRCS(ORTH)

HISTORICAL DEVELOPMENTS Opposing joint surfaces are covered with hyaline cartilage, the lining responsible for smooth and frictionless movement. The word “cartilage” originates from the Greek hyalo, meaning “glass”, and the Latin cartilage, meaning “gristle”. When we talk about cartilage we often refer erroneously to the soft cartilage or meniscus, a crescent-shaped structure that is located between the femur (thigh bone) and tibia (shin bone). Through being triangular in cross-section, the meniscus functions as a knee-joint stabiliser and stress dissipater. Even as far back as the eighteenth

century, surgeons were aware that surface cartilage, once damaged, had little ability to heal. William Hunter, a British surgeon, was quoted as saying “From Hippocrates to the present age it is universally allowed that ulcerated cartilage is a troublesome thing and that once destroyed it is not repaired” (1). Since the days of Hunter, it has become apparent that joint surface damage, if left untreated, invariably deteriorates and eventually spreads to surrounding areas. The end result of such a process is often the development of debilitating osteoarthritis (2). Many clinicians have engaged in a desperate attempt to find ways to facilitate durable cartilage repair (3,4). Treatment of articular cartilage

defects in the knee has been at the centre of attention over the past few years, as the number of young adults with joint injuries continues to grow. It has been estimated that in the UK 10,000 patients each year suffer cartilage damage, most often caused through sporting activities, which warrant repair (5). In a high proportion of these patients, the treatment opportunity is lost either through delay in diagnosis or through failure to recognise the condition altogether (5). Damage to articular cartilage may

DAMAGE REPRESENTS A MAJOR CHALLENGE

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IDENTIFICATION OF SURFACE CARTILAGE

Due to a lack of blood supply, articular cartilage, the lining of the joints, has a limited capacity for natural healing. Once damaged through injury or repetitive strain, cartilage becomes degenerate, eventually leading to osteoarthritis. Early treatment is therefore essential, particularly in young and active individuals. The ability to regenerate surface cartilage is one of the major advances in orthopaedic surgery for decades. Gene technology has allowed the growth of harvested cartilage cells outside the human body. Once re-implanted, autologous chondrocytes have the potential to improve the repair of cartilage defects. The most advanced of these techniques is matrix-guided autologous chondrocyte implantation (MACI), which has been shown to provide histologically and functionally normal articular cartilage.

be related to acute trauma, overuse, ligament instability, leg mal-alignment (bowed or knocked knees), menisectomy (removal of shock absorber cartilage) or osteochondritis dissecans (6). Acute cartilage defects may arise from a fall or a direct blow, but more often they occur as a result of twisting forces while the knee is exposed to full load-bearing. In such an environment, shear forces combined with joint compression forces create a build-up in tension between the surface cartilage and the underlying bone. As a result, the surface cartilage may delaminate from its under-surface, creating a “full-thickness” cartilage defect (see Fig. 1). Symptoms may be apparent immediately but often do not occur for many months or even years after the primary insult. If the damage to the articular surface remains untreated, it will lead to fibrillation and fragmentation of the damaged area, which in turn will affect the opposing surface. Over time, cartilage degeneration and osteoarthritis will develop.

STRUCTURE OF SURFACE OR HYALINE CARTILAGE Surface or hyaline cartilage is a material that consists of a mixture of substances. Apart from water, which represents almost 75%, the principle components are collagen fibrils and the gel-like hydrated glycoproteins creating the cartilage matrix. Encased within this matrix are relatively few highly specialised cartilage cells, known as chondrocytes (7). Chondrocytes have the ability to renew matrix elements

throughout life and hence play a vital role in maintaining joint homeostasis (8). Mechanically, cartilage represents a fluid-filled permeable porous structure, providing slipperiness, resilience, durability and strength (9). It also acts as a shock absorber, cushioning the bone from forces greater than five times body weight. Under normal circumstances, and in the absence of joint trauma or deformity, surface/hyaline cartilage allows for frictionless and painless movement throughout life.

DOES CARTILAGE NOT HEAL?

Spontaneous healing of all musculoskeletal tissues begins with an inflammatory response, which is dependent on the tissue’s blood supply. Blood carries the vital ingredients to facilitate tissue repair. Surface cartilage, however, lacks both a blood supply and lymphatic drainage, making it ill-equipped to instigate a satisfactory repair process by producing new cartilage. If blood vessels were present in cartilage, it would significantly weaken the matrix and subsequently impair its mechanical properties (7).

SYMPTOMS

The identification of surface cartilage damage represents a major challenge as there are no specific signs or symptoms that the injured person may present with. It is of paramount importance that the clinician, general practitioner (GP) or physiotherapist expresses a high degree of suspicion if the patient fails

sportEX medicine 2009;40(Apr):6-9