Knee pain is an extremely common complaint with many different mechanisms of injury. Knee pain can have a gradual onset most often related to overuse or it can be acute in nature with a sudden onset from a single event. Regardless of the cause, a proper diagnosis is vital when determining the best treatment strategy for the injury in question.
The knee cap is one of the most stable joints in the body for a number of reasons. The knee is a hinge joint that is by nature, very stable because of its limited vectors of motion. The knee is made up of four bones, two of which have large adjacent surfaces that are held in close proximity to one another by an extensive ligament and cartilage system. The femur and the tibia, the largest bones that comprise the knee joint, meet to form a hinge joint. The joint is protected in the front by the patella (kneecap) and lastly, the fibula serves as an attachment point for ligament and cartilage structures located on the lateral aspect of the knee. The knee joint is cushioned by articular cartilage that covers the ends of the tibia and femur, as well as the underside of the patella. The lateral meniscus and medial meniscus are pads of cartilage that further cushion the joint, acting as shock absorbers between the tibia and femur. Ligaments help to provide stability for the knee. The medial and lateral collateral ligaments run along the sides of the knee in order to limit excessive sideways shifting of the joint. The cruciate ligaments help to limit forward and backward movement of the tibia and the femur. The anteriror cruciate ligament,or ACL, limits rotation and forward motion of the tibia. The posterior cruciate ligament, or PCL, limits backward motion of the tibia.
The knee joint also serves as a connection point for a number of very large and powerful muscles located on the thigh and the lower leg. These muscle groups are responsible for the majority of the force production needed for walking and running. Examples of these muscles are the quadriceps, hamstrings, and adductor muscles along with the musculature located below the knee.
There are several mechanisms of injury that can lead to knee pain. With gradual onset knee pain, the pain is most often generated by minor yet repetitive trauma to the knee joint resulting from a number of activities or everyday motions. Common overuse injuries sustained by the knee are degeneration to the cartilage (chondromalacia and meniscus degeneration) and bony structures (early/late onset arthritis and stress reaction fractures) as well as muscle overuse syndromes such as muscle strains, tendonitis, and tendonosis. Traumatic injury to the knee also results in several causes of knee pain such as ligament spains, lilgament tears, cartilage tears, fractures, and tendon ruptures.