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Patella

Synonym: kneecap
German: Patella

1 Definition

The patella is a flat, disc-shaped bone, triangular from anterior perspective, which is located in front of the knee joint. It is part of its articular surfaces. The patella acts as sesamoid bone in the tendon of the quadriceps femoris muscle. It protects the knee joint and elongates the lever of the quadriceps femoris muscle.

2 Surfaces

2.1 Facies anterior

The front side of the patella is convex and shows small holes where the supplying vessels pass through towards the interior of the bone. It is completely covered by the quadriceps femoris muscle, which caudally continues to transform into the patellar ligament. Further up front, a synovial bursa (prepatellar bursa) provides cushioning and ability to move against the skin.

2.2 Facies posterior

The backside of the patella is covered by articular cartilage in the top two thirds and shows a vertical ridge, which inserts into the intercodylar sulcus between the condyles of the femur. It divides the backside into 2 facets, which again articulate with the condyles of the femur. The lateral facet is significantly broader.

3 Edges

3.1 Margo superior

The superior, strong edge of the patella serves as insertion surface for the quadriceps femoris muscle, to be more exact, for two of its muscle heads: the rectus femoris muscle and the vastus intermedius muscle.

3.2 Margines medialis et lateralis

The medial and lateral edge taper off caudally and serve as insertion area for the vastus lateralis muscle and the vastus medialis muscle.

3.3 Apex patellae

The caudal apex of the patella serves as origin for the patellar ligament, which draws towards the tibia.

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4 Function

The patella enlarges the distance of the force vector of the quadriceps femoris muscle from the rotation center of the knee joint, elongating the lever of the extensor muscle of the thigh. Moreover, it reduces the sliding resistance of the patellar tendon with its cartilage surface. During extension movement, the patella travels a distance of around 8-10 cm over the thigh bone.

5 Variants

6 Clinical presentation

The diseases of the patella comprise amongst others:

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