Knee diagram.svg
Right knee
Originspresent at the joint of femur and tibia fibula
Anatomical terms of bone

The patella, also known as the kneecap, is a thick, circular-triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as mice, cats and birds, but not in whales, or most reptiles.

In humans, the patella is the largest sesamoid bone in the body. Babies are born with a patella of soft cartilage which begins to ossify into bone at about three years of age.


The patella is a sesamoid bone roughly triangular in shape, with the apex of the patella facing downwards. The apex is the most inferior (lowest) part of the patella. It is pointed in shape, and gives attachment to the patellar ligament.

The front and back surfaces are joined by a thin margin and towards centre by a thicker margin.[1] The tendon of the quadriceps femoris muscle attaches to the base of the patella.,[1] with the vastus intermedius muscle attaching to the base itself, and 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 coarse, flattened, and rough, and serves for the attachment of the tendon of the quadriceps and often has exostoses. The middle third has numerous vascular canaliculi. The lower third culminates in the apex which serves as the origin of the patellar ligament.[1] The posterior surface is divided into two parts.[1]

The upper three-quarters of the patella articulates with the femur and is subdivided into a medial and a lateral facet by a vertical ledge which varies in shape.

In the adult the articular surface is about 12 cm2 (1.9 sq in) and covered by cartilage, which can reach a maximal thickness of 6 mm (0.24 in) in the centre at about 30 years of age. Due to the great stress on the patellofemoral joint during resisted knee flexion, the articular cartilage of the patella is among the thickest in the human body.

The lower part of the posterior surface has vascular canaliculi filled and is filled by fatty tissue, the infrapatellar fat pad.


In this X-ray, an anatomical variation of the patella can be seen – the bipartate patella, in which the patella is split into two parts.

Emarginations (i.e. patella emarginata, a "missing piece") are common laterally on the proximal edge.[1] Bipartite patellas are the result of an ossification of a second cartilaginous layer at the location of an emargination. Previously, bipartite patellas were explained as the failure of several ossification centres to fuse, but this idea has been rejected.[citation needed] Partite patellas occur almost exclusively in men. Tripartite and even multipartite patellas occur.

The upper three-quarters of the patella articulates with the femur and 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:

  1. Most commonly the medial articular surface is smaller than the lateral.
  2. Sometimes both articular surfaces are virtually equal in size.
  3. Occasionally, the medial surface is hypoplastic or
  4. the central ledge is only indicated.


In the patella an ossification centre develops at the age of 3–6 years.[1] The patella originates from two centres of ossification which unite when fully formed.[citation needed]

Other Languages
العربية: رضفة
Avañe'ẽ: Penarã
বাংলা: চক্রিকা
башҡортса: Тубыҡ ҡапҡасы
български: Коленно капаче
bosanski: Čašica
català: Ròtula (os)
čeština: Čéška
Deutsch: Kniescheibe
ދިވެހިބަސް: ފިޔަން ކަށިގަނޑު
Ελληνικά: Επιγονατίδα
español: Rótula
Esperanto: Patelo
euskara: Errotula
فارسی: کشکک
français: Patella (os)
galego: Rótula
한국어: 무릎뼈
Ido: Patelo
Bahasa Indonesia: Tulang lutut
עברית: עצם הפיקה
Latina: Patella
latviešu: Ceļa kauls
lietuvių: Girnelė
Nederlands: Knieschijf
नेपाल भाषा: पुलिक्वँय्
日本語: 膝蓋骨
norsk: Kneskjell
polski: Rzepka
português: Patela
română: Patelă
русский: Надколенник
Scots: Patella
slovenčina: Jabĺčko
slovenščina: Pogačica
کوردی: کەشکەژنۆ
srpskohrvatski / српскохрватски: Iver (anatomija)
svenska: Patella
Tagalog: Suklob-tuhod
తెలుగు: జానుఫలకము
Türkçe: Diz kapağı
українська: Наколінок
Winaray: Nuwaytuway
粵語: 欂櫨蓋
中文: 髌骨