knee

knee The knees and kneeling have many cultural and social associations. The joints themselves reveal mechanical and physiological features superbly appropriate to their crucial role in the standing or moving body — but susceptible eventually to wear and tear.

The knee joint is functionally a hinge joint, which principally allows movements of the lower leg forwards (extension) and backwards (flexion), although a limited degree of rotation is also possible towards the end of extension. Extension is achieved by a group of four large muscles at the front of the thigh (quadriceps), whilst muscles at the back of the thigh (hamstrings) produce flexion. The lower end of the femur articulates, through two condyles, with the top of the tibia, which is shaped rather like a plateau. In addition to the cartilage covering the surfaces of these bone-ends, there is another piece of cartilage (meniscus) separating them on each side. These can be torn by rotational injuries, particularly in football and rugby players, a condition commonly referred to as torn cartilage.

This hinge joint is a less stable arrangement than a ‘ball and socket’ joint like the hip, and the stability of the knee is achieved by a combination of tough ligaments, the extensor and flexor muscles spanning the joint, and the fibrous capsule of the joint. The cruciate ligaments (so called because they cross over within the joint) are of particular importance as they prevent fore and aft instability. These ligaments are a common site of damage — again, in contact sports such as football and rugby — and damage can sometimes end a lucrative career despite reconstructive surgery. Lateral stability is achieved by the ligaments on each side of the knee. When it is injured or inflamed, excess fluid can collect in the joint (effusion) making it swell and stiffen. As the knee is relatively accessible, this fluid can be removed (aspirated) and drugs (often steroids) injected directly.

The stresses on the knee, as a large weight-bearing joint, make it a major site for development of osteoarthritis in later life. This can be treated by complete joint replacement (total knee arthroplasty).

Because it is the largest joint in the human body, which sustains some of the greatest stresses and which is seriously injured with relative ease, the knee is traditionally and symbolically a site of vulnerability. ‘Kneecapping’, for instance, is a practice associated with terrorists and organized crime groups; it involves destroying the kneecaps, either by shooting someone in the knees or by shattering them, typically with a baseball bat. The result is not life-threatening, but extremely painful and permanently disabling. To be ‘brought to one's knees’ is to be in a position of submission and desperation; to be ‘cut off at the knees’ is to be humiliated and disabled.

To kneel voluntarily is to submit symbolically to a higher authority. Kneeling during prayer, bowing to social superiors, and getting on one's knee to propose marriage or to be knighted, are all expressions of reverence or humility. In Japanese tea ceremonies, guests greet one another with a kneeling bow. Before it became an expression of humility, however, kneeling in prayer was a way of indicating one's proximity to the underworld. Today, Christians kneel when receiving a blessing or the Eucharist, and Muslims kneel in prayer facing Mecca; Jews did not reject kneeling in worship until after Christians adopted it as part of their practice.

As a symbol of vulnerability, the knee has also been a point of erotic encounter, especially as the place where the first touch between two people occurs. Playing ‘kneesies’, for instance, meant rubbing or touching knees in a flirtatious and surreptitious manner, especially while seated where such activity would be concealed, as under a dining table. Eric Rohmer's film Claire's Knee tells the story of an older man infatuated by a younger woman; her knee is the first focus of his desire when he encounters her on a ladder in an orchard. Fashions which exposed women's knees were considered daring and risqué in the 1920s — a sign of new freedoms; however, by the 1940s short pants were acceptable for both men and women.

In ancient Greece, for something to be ‘on the knees of the gods (theón en gounasi)’, meant that it was totally beyond human control or knowledge.

William R. Ferrell, and Kristen L. Zacharias

See musculo-skeletal system.See also cartilage; joints; skeleton; religion and the body.