Cartilage

The knee is one of the most important and most heavily utilized joints in the human body. Although most of us do not realise it, our knees have a lot to endure from our active, modern lifestyle. Sports injuries or other accidents may damage the cartilage of the knee, leading to a cartilage lesion. Cartilage lesions can permanently impair our daily activities, such as climbing stairs, jogging, lifting, squatting and cycling.


Anatomy

The knee joint is made up of three major bones: the thigh-bone (femur), the shin-bone (tibia) and the kneecap (patella). The meniscus on the inside and the outside of the knee acts as a spacer between the upper leg and the shin-bone, equally distributing the pressure on the lower leg. The extremities of the bones that make up the knee joint are covered with a thin layer of cartilage. Cartilage ensures supple knee movements and forms an indispensable part of the knee joint. Joint cartilage is a thin, elastic tissue that protects the bone and makes certain that the joint surfaces can slide easily over each other. A change in the shape, structure or volume of the cartilage may cause any pressure on the knee joint to be painful. There are two types of joint cartilage in the knees: fibrous cartilage (the meniscus) and hyaline cartilage. Fibrous cartilage has tensile strength and can resist pressure. Hyaline cartilage covers the surface along which the joints move. It is white and transparent, like porcelain, and gives a similar resistance to an elastic band when pushed. Although it is scarcely five millimetres thick, it is very sturdy and can resist pressures of up to seven times the body’s own weight. The fibres which make up the cartilage tissue form various layers which each have their own specific function.


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Unfortunately, cartilage will wear — not just over the years, but also as a result of mechanical stress. Additionally, cartilage has a very limited capacity for self-restoration. Moreover, the newly formed tissue will generally consist for a large part of fibrous cartilage of a lesser quality than the original hyaline cartilage. As a result, new cracks and tears will form in the cartilage over time. The reason why cartilage has only a small capacity for self-restoration, and what makes it very unique, is that it does not contain any blood vessels unlike all other tissues in the body. The necessary nutrients are derived exclusively from the liquid in the joint capsule.

Cartilage lesion

Besides chronic stress and wear, cartilage lesions can be caused by:

• fractures involving the knee
• injuries (e.g. sports-related injuries), if the knee is twisted, for example
• the removal of a meniscus, which will increase the pressure on the cartilage
• cruciate ligament injury
• considerable strain on the knee

Any kind of work during which the knees undergo heavy stress may also be detrimental to cartilage.This is especially the case in professions in which people frequently have to walk, lift or squat. Sports injuries also occur more frequently these days. It is particularly sports like running, cycling, skiing and snowboarding which can cause knee injuries. A survey of snow-sport injuries in Scotland1 revealed a rate of 3.7 injuries per 1,000 skier days.

Common complaints

A painful, blocked, locked or swollen knee means a limitation of one’s mobility. Every day activities such as climbing the stairs, getting in and out of bed and tying shoelaces suddenly become troublesome. Knees may be painful, swollen or feel hot to the touch. Sufferers sometimes feel as if their knees are about to give way, or may feel uncertain about their movements.

What causes the pain?

The pain felt by people with a cartilage injury does not come from the cartilage itself, but from the irritated tissue surrounding the cartilage, or from pieces of cartilage that have come loose. If cartilage injuries go untreated, the layer of cartilage will continue to gradually wear away, causing wear of the joint and gradual loss of mobility.