The knee joint is comprised of four bones. The largest of these is the femur, or thigh bone. Also found in the knee is the tibia, sometimes called the shin bone. Alongside the tibia, on the outside of the leg, is the fibula.
The fourth bone found in the knee is the patella or kneecap. It’s cradled within the patellar tendon, and lies directly in front of the femur. This patella assists in knee extension, increasing leverage by lifting the quadriceps and patellar tendons away from the joint.
The lower end of the femur is rounded into two knob- shaped masses known as condyles. These move against the upper end of the tibia, which is flat. Both the lower end of the femur and upper end of the tibia are covered with articular cartilage, a smooth rubbery material, which allows one surface to glide one upon the other with minimal friction. Sandwiched between the two joints are two distinct masses of fibrocartilaginous material called menisci, which acts as an additional cushion for the joint.
In addition to the meniscus, there is articular cartilage covering the ends of the femur, the top of the tibia, and the back of the patella. Articular cartilage is found throughout the body anywhere two bones meet and glide against each other. The point of meeting and movement for bones is described as the point of articulation, hence the name “articular cartilage.”
As the largest of joints, and the one bearing the heaviest burden, our knees are fortified with an extra layer of cartilage just between the femur and tibia. The menisci protect the articular cartilage by spreading out the forces placed on the joint surfaces during movement. To imagine how valuable this function is, consider that forces on the knee range from about twice our body weight during normal walking, to more than four times our body weight during running activities.
The meniscus also plays a role in shock absorption. Considering the meniscal layer is only about one-fourth of an inch thick, this padding does a remarkable job of softening impact and vibration when our feet hit the ground walking, running, and jumping. Knees with the menisci in top form have a shock absorption capacity that is 20 percent higher than knees in which the menisci have been removed. This underscores the importance of injury prevention when it comes to the knee. Once you damage the shock absorber, you are that much more susceptible to arthritis.
Menisci also aid the knees in maintaining stability. If you placed a ball on a flat surface, you’d have a pretty good idea of what the knee would be like without the meniscus. Except for the ligaments, there would be nothing to keep the femur from rolling right off the tibia. When we are young, menisci are tough but can tear as a result of a sports injury. As we reach our fifth decade of life, menisci can become fragile and often tear with just a slight twist. During arthroscopic surgery of the knee, a knee surgeon will attempt to clean up and remove the torn part of the meniscus, while at the same time trying to preserve as much of it as possible.
Ligaments interconnect the bones of the knee. They are made up of tough collagen fibers, which themselves are relatively inflexible. However, they are arranged with a crimp design that straightens when force is applied and permits the ligaments to endure large internal stresses during normal joint motion. Ligaments are attached to bone in such a manner that there is progressive increase in stiffness as they blend into bone.
The way that ligaments become part of a bone is also important to their function. Ligamentous tissue and bone meet together in a graduation of fibrocartilage and mineralized fibrocartilage, which provides the increasing stiffness as ligament blends into bone.
The four major ligaments of the knee are:
The stability of the knee is largely due to their combined efforts. They are the structures that ultimately hold the tibia and femur together, while permitting motion.
The anterior cruciate ligament (ACL) is deep within the knee. It crisscrosses the posterior cruciate ligament (PCL) and keeps the tibia from sliding too far forward in relation to the femur. The PCL does the opposite. It prevents the tibia from sliding excessively backwards. The PCL is further supported by two minor ligaments: the ligaments of Humphry and Wrisberg.
The ligaments that provide sidewise stability to the knee are the medial collateral ligament (MCL) and lateral collateral ligament (LCL). These ligaments limit side-to-side motion.
Pain is broken down into two categories: acute or chronic. If you fall down and hurt your knee or twist your knee, that is called "acute" knee pain. Chronic pain is something that occurs more gradually over time, often getting worse as weeks and months go by.
Unlike acute pain which can be linked to a specific event or time - like when you fall or twist your knee - chronic pain is more like an ache that is not linked to any event. The knee specialist will ask when and how your pain started to learn more about the potential cause of pain.
These two terms are sometimes used together. However, technically they differ. A strain occurs when a muscle is overworked or overstretched. Sprain relates to ligaments, or tendons. For instance a strain can occur at the start up of a new exercise regime. If the body is not properly stretched, than sudden impact can tear muscles, ligaments, tendons, and soft tissues. As our body becomes accustomed to an exercise, say running, it compensates forpotential injuries by strengthening muscles and ligaments. If we start a running program after living a relatively sedentary lifestyle, our body has not had a chance to compensate yet, and we are more prone to a strain.
If you are about to start up an exercise program remember to STRETCH before embarking upon the new activity. That is crucial. Also try to ease into the program allowing your body to strengthen before pushing it to the limit.
Sprains relate to an over-stretched or torn ligament. Usually, the sprain is tender or swelling occurs and it can look black and blue like a bruise. This is a little more serious because this indicates a torn ligament. Tears are more severe than strains or sprains. When muscles, ligaments, or tendons are torn they are actually disrupted. The torn ends grossly disrupt the continuity of their structure.
The location of the injury should clarify any confusion over whether it is a sprain or strain. Strains occur in the muscles of the neck, back, thighs and calves. Sprains are found around joints—knees, ankles, or wrists.
An increase in interest in sports seems to have been the catalyst for more and more ligament problems every year. In fact, there are more than 50,000 hospital admissions for ligament repair. Interestingly, women are 8 times more likely to have an ACL tear than men. Some experts theorize it may relate to high heals or anatomy. The ACL (anterior cruciate ligament) and the MCL tend to be particularly susceptible to injury during sports. The cause is generally turning quickly and twisting the knee, slowing down when running, and landing from a jump. High risk sports include soccer, skiing, basketball, and tennis.
Meniscal tears stem from sports-related injuries or even from seemingly innocuous activities such as squatting. Athletes who play football, basketball, and tennis as well as adults over the age of 40 are especially prone to meniscus tears. The type of movement that most often causes meniscal injury is one in which the foot is firmly planted on the ground while the knee is twisted. Shoes with cleats often contribute to this type of injury by anchoring the lower leg into the ground and preventing it from moving with the knee.
A bone can break for a number of reasons. A traumatic injury such as a car accident can cause a bone to break. Other causes for bones breaking can be "stress" fractures where a bone is used repetitively and because of compression, it breaks.
Sometimes, especially while doing something physically strenuous, we can throw a joint out of alignment with the bone. Although nothing breaks, the alignment is off. This is called dislocation.
Chondromalacia indicates a degenerative condition that results from chronic wear on the kneecap. Over time this cartilage may fray and soften. It is a degenerative condition, which occurs as the result of chronic wear of the kneecap against the femur. The articular cartilage gradually softens and then frays. In other circumstances, it can stem from one particular, traumatic incident. Symptoms for this condition could be pain at the front of the knee, especially when walking up and downhill, stiffness after prolonged sitting, and a grinding or clicking sensation as the knee is flexed and extended. This condition is more common in middle age. It happens mostly to women and can stem as early as in the teenage years.
This is a degenerative joint disease stemming from wear and tear on the knee usually affecting those in middle age and older. Osteoarthritis causes the cartilage to erode away. Symptoms include pain, stiffness, and swelling that at first happens once in a while but can progress to chronic pain.
Unlike osteoarthrits, this type of arthritis does not erode the cartilage slowly, rather it inflames the joint (usually many joints at one time) until the joints are ruined. Rheumatoid arthritis is most common in middle aged women, but can affect people of all ages.
Inflammation of the joints can occur when a small granual of sodium urate (related to gout) or calcium phosphorate (related to chondrocalsinosis) gets lodged in the joint. The effect is similar to getting a piece of sand trapped in your eye. It irritates the surrounding inflammation. Middle-aged men are most prone to this sort of arthritis.
Between the tendon and the skin are small sacs called bursae which allow the skin to smoothly and painlessly slide over bones. When the bursae become inflamed, any knee movement can cause pain. In the knees, one function of the bursae is to allow the knee cap to move around freely without pain. Repetitive kneeling and/or direct impact on the knee can cause the bursae to swell and cause pain. Those in professions where the knees are often bent such as masonry, house cleaning, carpet layers, and electricians are more likely to experience post-patellar bursitis. At other times, the condition can occur when the sacs become infected. Usually for this ailment surgery is not necessary (although may be called upon in extreme cases) and treatment includes avoiding bending of the knees and relieving pressure to the knee cap.