Copyright 2009
Author John Udall MD
Definition
The patellar tendon is a large structure which connects the inferior pole of the patella to the proximal tibia. It is responsible for transferring enormous loads generated by the quadriceps to extend the knee during normal ambulation as well as more explosive activities like running and jumping.
Its unique structural features include its length which is about equal to the length of the patella. If the ratio of the patellar tendon to patella is larger then 1.2, this condition is termed patella alta and indicates either an elongated tendon or a ruptured tendon. If the ratio is less then 0.8, this is termed patella baja, and this indicates a scarred down tendon. Either of these conditions can alter the ability of the tendon to effectively keep the patella from tracking appropriately, and can therefor lead to pain or increased wear of the patella.
Its origin is on the inferior pole of the patella and it inserts onto the tibial tubercle, a large bony prominence on the proximal tibia.
Common diseases include patellar tendonitis and patellar rupture. Patella baja and patella alta are also indications of inappropriate tendon length which can occur in total knee procedures, high tibial osteotomies, or rupture. Patellar tendonitis is also known as jumper’s knee, and can affect active, young patients. It will cause pain with any activity that requires leg extension, particularly explosive activities such as running and jumping. Rupture of the tendon rarely happens in the young athlete, and is more common in patients greater then 40 years of age.
Commonly used diagnostic procedures include physical exam, plain x-rays, and MRI. Physical exam will show lack of ability to extend the knee if the tendon is ruptured, and tenderness to palpation and resisted extension in those with patellar tendonitis. MRI can show inflammation about the tendon, and can better define full or partial tears. Although the tendon can’t be directly visualized with plain x-rays, the length of the tendon can be measured and compared to the length of the patella (see above).
Patellar tendonitis is treated with physical therapy, NSAIDs, and somteimes a Chopat strap to take pressure off the tendon. Ruptures require surgicall repair of the tendon.
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