The quadriceps tendon is the continuation of the quadriceps muscles in the anterior compartment of the thigh where they originate from attachments to the femur (thigh bone) and pelvis. This tendon attaches to the top of the patella (knee cap). The lower end of the patella is attached to the upper end of the tibia (shin bone) by the patellar tendon. This is what is considered to be the extensor mechanism of the leg and is what is responsible for allowing you to straighten your knee.
Traumatic tears of the tendons are associated with a violent contraction of the muscle as the tendon is being lengthened. This can happen when one falls down. People will usually lose the ability to actively straighten their knee. There are 2 distinct disease states that usually affect these tendons. The first is tendinitis, which is an active inflammatory process. This means that your body’s defense systems are responding to an injury that has been sustained to the tendon. This will typically respond favorably to anti-inflammatory type medications and potentially physical therapy.
Tendinosis is a separate process where the tendon undergoes degenerative type changes as a result of repetitive micro-trauma. The blood supply to the affected area of the tendon is disrupted and repair mechanisms for a tendon are impaired which results in a disorganization of the tendon. This lack of structural integrity may increase person’s chances of sustaining traumatic rupture of the tendon. Quadriceps or patellar tendon ruptures generally require surgical repair.
Pain is the most common symptom with tendinitis or tendinosis. This can happen during athletic activities such as running and jumping or with activities of daily living such as walking, stairs or bending. A tendon rupture is usually a very painful injury that is associated with hearing a “pop” in the knee. A person who sustains a rupture of one of these ligaments will not be able to fully straighten their knee.