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Also known as the kneecap.
It is is a thick, circular-triangular bone which articulates with the femur and covers and protects the anterior articular surface of the knee joint.
It is the largest sesamoid bone in the body.
Babies are born with a patella of soft cartilage.
It begins to ossify into bone at about three years of age.
It is a sesamoid bone
The apex, the most inferior part of the patella faces downwards.
The apex is pointed in shape, and gives attachment to the patellar ligament.
The tendon of the quadriceps femoris muscle attaches to the base of the patella as does the vastus intermedius muscle.
The vastus lateralis and vastus medialis are attached to outer lateral and medial borders of patella, respectively.
The upper third of the front of the patella is flattened, and rough, and is attached by the tendon of the quadriceps and often has exostoses.
The middle third of the patella has many vascular canaliculi.
The lower third of the patella culminates in the apex which serves as the origin of the patellar ligament.
The posterior surface is divided into two parts.
The upper three-quarters of the patella articulates with the femur and is subdivided into a medial and a lateral facets.
In the adult the articular surface is about 12 cm2.
The patella articular surface is covered by cartilage.
The articular cartilage of the patella is among the thickest in the human body due to the stress on the patellofemoral joint.
The lower part of the posterior surface of the patella filled by fatty tissue, the infrapatellar fat pad.
A bipartate patella is an anatomical variation in which the patella is split into two parts.
Partite patellas occur almost exclusively in men.
Tripartite and even multipartite patellas may occur.
The upper three-quarters of the patella articulates with the femur.
The upper patella is subdivided into a medial and a lateral facet by a vertical ledge which varies in shape.
Four main types of articular surface can be distinguished:
An ossification center forms at 3-6 years of age
In the patella ossification 2 centers develops at the age of 3–6 years, which ultimately unite.
Its primary function is knee extension, as it increases the leverage that the quadriceps tendon can exert on the femur by increasing the angle at which it acts.
It is attached to the tendon of the quadriceps femoris muscle, which contracts to extend/straighten the knee.
The patella is stabilized by the insertion of the horizontal fibres of vastus medialis into the patella and the prominence of the lateral femoral condyle stabilizes it, discouraging lateral dislocation during flexion.
The retinacular fibers of the patella also stabilize the patella.
It can dislocate, particularly in young female athletes. most often laterally, and may be associated with extremely intense pain and swelling.
Dislocated patella can be relocated into the groove with an extension of the knee.
A patella may be high-riding, unusually small patella, or low-riding patella.
It is prone to injury because of its particularly exposed location.