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Patellar tendon

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Definition, function and examples of ligaments.

The quadriceps femoris is a four-headed muscle that inserts onto the tibial tuberosity. It extends the knee, and one head (rectus femoris) flexes the hip.

The patella is a sesamoid bone that lies within the quadriceps tendon. The patellar tendon connects the apex of the patella to the tibial tuberosity, and improves the way the quadriceps muscle pulls on the tibia.

In this article we will discuss the gross and functional anatomy of the patellar tendon. We will also explain the clinical relevance of the structure, and provide a summary of key points at the end of the article.

  1. Anatomy
  2. Clinical aspects
  3. Summary
  4. Sources
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Patellar ligament (ventral view)

The patellar tendon runs inferiorly from the patella bone to the tibial tuberosity of the femur. The patella is a large sesamoid (a bone within a tendon) bone with a triangular transverse cross-section that lies within the quadriceps tendon. Another example of a sesamoid bone is the pisiform carpal bone that lies within the tendon of flexor carpi ulnaris.

The patellar tendon originates from the patellar apex and attaches to the tibial tuberosity, which is a bony protrusion on the anterior aspect of the proximal tibia. The patellar tendon could also be referred to by a different name.

A tendon is connective tissue that connects a muscle to a bone. From the perspective of muscle action, the term patellar tendon is correct. Another perspective to consider is that because the patellar ‘tendon’ connects a bone to a bone (patella to tibial tuberosity), it could be referred to as the patellar ligament.  Ligaments are in place to limit movement and the patellar ligament limits flexion of the knee based on its bony attachments. 

The patellar ligament is approximately 5 cm in length. However, its length is not constant and mostly increases from full extension to 30 degrees of knee flexion.

The medial and lateral parts of quadriceps femoris descend on either side of the patella and are inserted onto the upper anterior surface of the tibia. They merge into a continuous capsule, and form the medial and lateral patellar retinacula. The posterior aspect of the patellar ligament is separated from the knee joint by an infrapatellar fat pad and a synovial membrane. An infrapatellar bursa also separates the patellar ligament from the tibia.

Patellar ligament (lateral view)

The function of the patella is to increase the length of the lever arm of the patellar tendon and therefore allow quadriceps femoris to exert a higher moment around the axis of rotation of the knee for a given level of muscle contraction than in the absence of a patella.

Want to test your knowledge of the patella anatomy? Quiz questions are your secret to success.

The patella, whose peak thickness is between 2 and 3 cm, sits against the femur at a location which depends on the degree of knee flexion. This increase in lever arm ensures that knee extension is more efficient, and the action of quadriceps femoris is clearly transmitted through to the tibia.

Knee extension (lateral view)

Test your knowledge on the knee joint with this quiz.

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