Patellar Tendinitis

Patellar tendinitis is an overuse injury involving the tendon between the patella and the tibia (the patellar tendon). The patellar tendon is the attachment of the quadriceps muscle to the tibia. The role of the quadriceps, and therefore the role of the tendon, is to extend the knee. Aggravation of the patellar tendon is a common source of pain. This is caused by repetitive trauma to the tendon, frequently associated with jumping, kicking, or running. The process of injury is usually a repetitive microtrauma with acceleration and deceleration (as occurs with jumping and landing) and extrinsic loading of the tendon. The individual forces cause only slight injury, but there are not adequate periods of rest for the tendon to heal. The process of repeated microtrauma leading to the development of tendinitis is similar to the process leading to stress fractures. Because it occurs frequently under the repetitive loading of jumping, patellar tendinitis is frequently referred to as jumper's knee.

The name tendinitis suggests that it is the result of an inflammatory process; however, pathologically there is usually little or no evidence of acute inflammation. Pathologic evaluation reveals a mucoid substance separating the collagen bundles. There may also be evidence of microscopic or partial tearing of the tendon. These findings are consistent with degenerative change. Regenerative changes may also be seen, including increased cellularity and neovascularization—the growth of small blood vessels throughout the tendon. Because of this, other terms commonly used for this condition are patellar tendinosis and tendinopathy, which suggest a degenerative change or any abnormality of the tendon instead of only inflammation (Figure 1).

Clinically affected individuals complain of pain over the tendon. This usually is noticed as a progression of symptoms over days or weeks. Occasionally, there may be a more rapid onset of pain with one step or jump. The most common location of pain is the proximal portion of the tendon just beneath the patella.

In the early stages, the pain is present only after a hard activity or workout. It may be noticed at the beginning of the activity and may diminish after a warm-up. The pain will then progress to last longer. It will last through the entire workout and then occur during other periods of activity throughout the day. Again, activities that load the tendon will tend to be the most painful. This includes going up or down the stairs, squatting, kneeling, and lifting or carrying weight. If left untreated, the condition will progress to a painful state even at rest. The following table classifies patellar tendinopathy according to four grades:

There are multiple intrinsic and extrinsic factors that may predispose one to patellar tendinosis. Intrinsic factors include knee alignment, hamstring, and quadriceps tightness, core hip and girdle strength, and motion of the ankle and knee. Any restriction of complete ankle or knee motion may increase the force across the patellar tendon at impact. Excessive pronation or excessive fast pronation (with a neutral foot) will create excessive force on the patellar tendon. Finally, a rigid cavus foot may also predispose to patellar tendinosis. Extrinsic factors include the magnitude of the force, the duration of the force, and the angle of the knee when maximal stress is applied. Harder playing surfaces, such as concrete, transmit a greater force than softer surfaces, such as [Page 1036]grass. A longer workout will increase the total duration of the impact. Impact with the knee in a flexed position, as occurs when running uphill or lunging, creates greater stress along the patellar tendon.

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