Knee Tendon Disorders
Normal Anatomy
The bones of the knee are the femur (thigh bone), tibia (shin bone) and patella (kneecap). The femur and tibia meet to form the knee joint which is a hinge with the knee cap(patella) in front of these two bones acting as a mobile shield to protect the joint. The patella slides up and down in a groove in the femur called the femoral groove as the knee is bent and straightened.
Ligaments hold the knee together and give it stability. The medial (inner) collateral ligament (MCL) and outer (lateral) collateral ligament (LCL) limit sideways motion of the knee. The posterior and anterior cruciate ligaments (PCL and ACL) limit forward and backward translational motion of the knee bones, keeping them stable and allowing the knee to function as a unit.
Two structures known as menisci sit between the femur and the tibia and act as cushions or shock absorbers for the knee. Menisci are one of two types of cartilage in the knee. The other type, articular cartilage, is a smooth and very slick material that covers the end of the femur, the femoral groove, the top of the tibia and the underside of the patella. This articular cartilage allows the bones to move smoothly without pain. If this layer wears away, it is called arthritis and then the motion becomes painful.
Tendons connect muscles to the bones of the knee. The quadriceps muscles on the front of the thigh are connected to the top of the patella by the quadriceps tendon, which covers the patella and becomes the patellar tendon. The patellar tendon then attaches to the front of the tibia. The hamstring muscles in the back of the leg attach to the leg bone (tibia) at the back of the knee. The quadriceps muscles straighten the knee and the hamstring muscles bend the knee both of which are required for walking, running or simply standing.
Pathology
The common tendon disorders about the knee include bursitis, tendonitis, quadriceps, and patellar tendon tears. Symptoms associated with tendon disorders about the knee include limited motion due to pain, localized swelling and variable amounts of muscle weakness.
Bursitis is the inflammation of the tendon lining, called the bursa, in the knee which functions as a cellular layer for smooth tendon gliding. These bursa lie above the kneecap (patella) called the pre-patellar bursa, and at the insertion of the hamstring tendons on the upper part of the shin bone (tibia), called the pes anserine bursa. When a bursa is inflamed from a traumatic injury or repetitive activities, localized swelling, pain, and sometimes redness can be present.
When the tendon that connects the thigh bone to the knee cap, quadriceps tendon, or the tendon that attaches the kneecap to the leg bone, patellar tendon, is inflamed it is called quadriceps or patellar tendonitis, respectively. Tendonitis may cause localized pain, swelling, and difficulty performing certain activities or sports.
Quadriceps and patellar tendon tears can occur in patients of any age. These injuries usually occur from a sudden jumping and landing activity or as a result of a fall. These injuries commonly occur while playing sports. X-rays usually show the kneecap either too high or too low based on which tendon has torn. An MRI is sometimes obtained to determine if the tendon is completely torn or partially torn. A physical examination is important to check for injuries to other structures, such as muscles or nerves.
Treatment
Quadriceps and patellar tendon tears can be complete or incomplete. Incomplete tears can often be treated with the use of a brace and physical therapy. Therapists can help with exercises to improve motion and strength around the knee, and to get the patient back to walking normally. Complete tears of the quadriceps or patellar tendon require surgery. Surgery ensures that the tendon is repaired back to the kneecap. After surgery, therapists work with the patient to start bending and straightening the knee, to start strengthening the muscles of the thigh and around the knee, and to put weight on the leg immediately. Once the tendon has healed, most patients are able to return to their usual activities.