The knee is a hinge joint formed by the femur and tibia, designed mainly to provide flexion (bending) and extension (straightening) and to support the body above it during weight-bearing. The patellofemoral joint is the joint formed by the articulation of the patella (knee cap) on the front surface of the femur, and is a separate joint to the knee joint itself.
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Being a weight-bearing joint, the knee is subject to repetitive stresses during walking and running, twisting and jumping and as such, prone to injury during load-bearing sports and activities. Common sports injuries affecting the knee include ligament sprains, where a ligament is stretched quickly beyond its elastic limit resulting in a tear, or in more severe cases a rupture. Such examples would be a rupture of the anterior cruciate ligament (ACL) or a sprain of the medial collateral ligament (MCL). These are frequently seen in football, tennis and skiing where rapid changes of direction on a fixed foot occur regularly. Weight-bearing and impact sports can often lead to repetitive stresses through the meniscal structures (cartilage) of the knee, causing tears and sometimes requiring surgery by way of an arthroscopy.
Wearing of the knee joint itself can occur over time, causing arthritic changes to occur, though these can range from minor degenerative changes to severe osteoarthritis within the knee. Individuals with mild wear and tear in their knee may have no pain at all, therefore signs of degeneration or mild osteoarthritis found on X-ray do not always indicate a symptomatic knee. Knee joints with severe osteoarthritis may have difficulty bending or straightening fully, and may begin to collapse down on the side that is wearing the most. Severely arthritic knees may need surgical intervention by way of a unicompartmental knee replacement or total knee replacement, depending upon the age of the individual and the extent and location of the degeneration within the knee.
Knee problems can present themselves in many forms and pain may be experienced at the front, either side, or at the back of the knee. Issues can arise from the ligaments of the knee, the patellofemoral joint (knee cap joint) and the muscle / tendon structures around the knee, and of course from the knee joint itself, including its cartilage and bony surfaces. Where an individual feels their knee pain, is not always in the same location as the structures at fault, as pain can also be referred to the knee from other associated areas of the body.
The patellofemoral joint (knee cap joint) at the front of the knee is a frequent source of pain and associated symptoms. Though it is a relatively small joint, it is subject to large forces and stresses generated through the joint during activities such as climbing stairs, squatting down and landing from jumping. It's position and motion at the front of the knee within the 'trochlear notch' of the femur varies hugely between individuals, and it's orientation during movement relies heavily upon the action of the quadriceps muscles, the stability of the patellofemoral ligaments and the other connective tissues supporting this joint. 'Maltracking' of the patella occurs when these soft tissue structures do not provide an optimal balance amongst one another, causing an uneven pull of the patella without opposite constraint. Individuals with a maltracking patella may report clicking or the feeling of locking of the patella when the knee extends from a flexed position, and this may or not be accompanied by pain.
Symptoms experienced around the knee do not necessarily mean that there is a structural defect at the knee itself. Knee pain can arise as a result of 'biomechanical' issues from incorrect alignment of the lower limb in some way. For example, if the position of the ankle is abnormal when the foot is on the floor in weight-bearing, the rest of the body will have to adapt to this position in order for a person to remain forward facing - the result of this is that each joint above the ankle will have to adjust its position slightly to accommodate the abnormality at the bottom of the chain. Biomechanical problems in the lower limb can lead to muscle imbalances developing over time, which then become habit and difficult for an individual to correct. The knee joint and the patellofemoral joint are often the areas that compensate for this positional fault the most, causing a less than ideal joint position, altered stresses and consequently irritation and pain.
Knee problems are diverse and the underlying causes can vary hugely between individuals. As such, the management of these problems depends upon the nature of the problem, a person's associated medical conditions, their age, their lifestyle and their goals. Most knee presentations can be managed successfully by way of physiotherapy intervention, and may require the involvement of a podiatrist in order for the fault to be holistically and optimally treated.