Dr. James A. Nicholas, who as team physician for the New York Jets performed four operations on Namath's knees, says flatly, "The knee is the most poorly constructed joint in the body, given the torques and loads it takes in sports. And not just in football. Everything from plain running and jumping to bike riding, almost everything people do for recreation, is tough on the knee."
At its most fundamental, the knee acts as a hinge between the femur (thigh bone) and the tibia (leg bone). It is so flexible that when you sit, the two bones separate so that they are barely touching. But when you stand, the bones lock firmly together, forming a strong, unified structure. The end of the thigh bone resembles a rounded knob, the end of the tibia is relatively flat. Yet these two fit together perfectly, working against each other without friction, smooth as ball bearings rolling in a cup of oil.
Along with acting as a hinge, the knee glides, slides, twists, rocks and rolls. These movements occur over five different planes and points of contact between bones while the knee is supporting the bulk of the body through a variety of velocities, torques and pressures. The knee's delicate apparatus is expected to function flawlessly through all manner of self-inflicted trauma—jumpers' jolts and linebackers' impacts, joggers' heels thud-thud-thudding against pavements and backpackers' feet jarring down hillsides, explosive sprints and sharp veers, wrenching zig-outs and screeching halts, cleats caught in plastic grass, spikes snagged on second base, skates twisted in rutted ice.
It is a lot to ask of a joint that was designed two and a half million years ago.
Briefly, the anatomy of the joint that gives the leg both explosive power and tree-trunk strength is this: the thigh bone is connected to the leg bone by a series of ligaments. They form the basic structural support to the joint through their tension and stability. There are four major ligaments. The medial collateral ligament running up the inside of the leg and the lateral collateral running up the outside keep the joint stable from side to side. In the joint, between the bones, are the anterior and posterior cruciate ligaments, which cross. They prevent the two bones from slipping backward or forward out of the joint. No matter how powerful the muscles around the knee, without strong resilient ligaments the joint would be useless. A sound working ligament is a wonder to behold. Gray's Anatomy describes it as being "pliant and flexible, so as to allow perfect freedom of movement, but strong, tough, and inextensible, so as not to yield readily under the most severely applied force...."
The kneecap or patella rides in a groove in the lower end of the thigh bone. It lies in a large tendon connecting the quadriceps muscle on the front of the thigh to the leg bone. Behind the patella, filling the spaces within the joint, is a material known as synovial tissue. It is a delicate membrane of connective tissue that secretes a thick, viscid substance—"glairy, similar to the white of an egg," says Gray's. This synovial fluid lubricates the structures of the joint. Secreted excessively when the joint is hurt or irritated, the fluid used to be called "water on the knee."
Then there is the famed and troublesome knee cartilage known as interarticular fibrocartilage. Such cartilage is found in only a few joints of the body, and Gray's speaks of it as rather heroic stuff. "These cartilages are found in those joints which are most exposed to violent concussion and subject to frequent movement. Their uses are to obliterate the intervals between opposed surfaces in their various motions; to increase the depths of the articular surfaces and give ease to the gliding movements; to moderate the effects of great pressure and deaden the intensity of the shocks to which the parts may be subjected." (Two other joints with similar cartilage are the wrist and the jaw.)
There is also cartilage behind the patella and a lining of cartilage on the top of the tibia, where it comes into contact with the femur. This works basically as a shock absorber, a super-slippery cushion that affords a satiny surface for the thigh bone to ride on with a minimum of friction. It is this cartilage that is most frequently torn, cut, pinched or loosened in knee injuries. The sections of it are called menisci because they resemble a lens or meniscus. The medial meniscus is on the inside of the tibia and the lateral meniscus is on the outside. They are half-moon shaped, and anatomists refer to them as the semi-lunar cartilage.
There is a thick and powerful structure of muscles and tendons in the thigh and leg that works to flex, drive and support the knee. Three major muscle groups are involved: the gastrocnemius (calf), the quadriceps femoris (front of thigh) and the hamstrings (back of thigh). The conditioning of muscles is essential for a sound athletic knee, but muscle injuries are rarely as crippling as those that involve the intricacies of the joint itself.
The number of possible combinations of knee injuries and resulting forms of instability is staggering. Dr. Kerlan says exasperatedly, "People ask me, 'What really is wrong with Bobby Orr's knee?' I tell them I've never seen it, that there could be any one of 11 things wrong." Dr. Nicholas says, "I can tell you off the top of my head 30 different things that could cause pain in the knee—and I wouldn't even mention the most common, which is wear and tear on the tendons of the patella."