Patellar Tendinitis is an extremely common malady that can plague almost anyone, from athletes to laborers. It originally took on the nickname of "Jumper's Knee" because it frequently appeared in athletes who performed a lot of jumping and landing activity. Such exertions subject the knee to high shock-impact forces, which are one of the apparent causes of patellar tendinitis. The patellar tendon is a broad, thick, ligament-like structure that connects the lower portion of the patella (kneecap) to the prominent bump on the front of the upper tibia ("shin-bone") known as the tibial tubercle (see FIGURE 1). The patellar tendon is what doctors tap with a rubber hammer when they test your knee reflexes.

FIGURE 1 - Basic knee anatomy, showing the patella (kneecap) in the front of the joint. The patella is connected to the quadriceps (frontal thigh) muscle above it by way of the quadriceps tendon. It is connected to the tibia below by the patellar tendon. The latter tendon is much more commonly afflicted with tendinitis than the former.

For unknown reasons, the insertion (attachment) of the middle fibers of the patellar tendon to the lower border of the patella is particularly vulnerable to mechanical irritation, inflammation and ultimately tendon fiber degeneration and breakdown (see FIGURE 2). The patellar attachment sites of the medial (inner side) tendon fibers and lateral (outer side) tendon fibers are much less commonly affected than that of the middle fibers. Under the microscope, the disease process associated with jumper's knee is characterized by cellular inflammation and degenerative breakdown of tendon fibers directly where the tendon attaches to the patella, and in more advanced cases, within the upper third of the tendon itself.

FIGURE 2 - Schematic anatomy diagram demonstrating the most common site of the inflammation and microscopic tissue breakdown that characterizes patellar tendinitis.

Patellar tendinitis can be thought of as the "tennis elbow of the knee". While surgery is only infrequently required for effective treatment, jumper's knee can be quite annoying and difficult to cure at times. It can appear in a variety of circumstances, many of which do not involve running or jumping at all! One common cause of patellar tendinitis is a direct contusion or impact blow, such as may occur when you fall down onto the frontal aspect of your knee, or if you strike the front of your knee on an unseen object while walking. Another common cause is altered gait and thigh muscle mechanics, as may occur during limping or partial weight-bearing while using crutches following knee injury or surgery. In my experience I have learned that over-use, abnormal use or occasionally even under-use of the knee can lead to this common knee condition!