Patella

Source: Wikipedia, the free encyclopedia.
For other uses, see Patella (disambiguation).
"Kneecap" redirects here. For other uses, see Kneecap (disambiguation).
Patella
Right knee
Details
Pronunciation/pəˈtɛlə/
Originspresent at the joint of femur and tibia fibula
Identifiers
Latinpatella
MeSHD010329
TA98A02.5.05.001
TA21390
FMA24485
Anatomical terms of bone

The patella (pl.: patellae or patellas), also known as the kneecap, is a flat, rounded triangular

mice, cats, birds and dogs, but not in whales, or most reptiles
.

In humans, the patella is the largest

ossify
into bone at about four years of age.

Structure

The patella is a

patellar ligament
.

The front and back surfaces are joined by a thin margin and towards centre by a thicker margin.

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

patellar ligament.[1] The posterior surface is divided into two parts.[1]

  • Human left patella from the front
    Human left patella from the front
  • Human left patella from behind
    Human left patella from behind
  • Flexion and extension of knee
    Flexion and extension of knee

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. Owing 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.

Variation

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.

Development

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]

Function

The primary functional role of the patella is knee extension. The patella increases the leverage that the quadriceps tendon can exert on the femur by increasing the angle at which it acts.

The patella is attached to 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 and by the prominence of the lateral femoral condyle
, which discourages lateral dislocation during flexion. The retinacular fibres of the patella also stabilize it during exercise.

Clinical significance

Dislocation

Main article: Patellar dislocation

Patellar dislocations occur with significant regularity, particularly in young female athletes.[2] It involves the patella sliding out of its position on the knee, most often laterally, and may be associated with extremely intense pain and swelling.[3] The patella can be tracked back into the groove with an extension of the knee, and therefore sometimes returns into the proper position on its own.[3]

Patella baja[4]

Vertical alignment

A patella alta is a high-riding (superiorly aligned) patella. An attenuated patella alta is an unusually small patella that develops out of and above the joint.

A patella baja is a low-riding patella. A long-standing patella baja may result in extensor dysfunction.[5]

Insall-Salvati ratio (A divided by B).[6]

The Insall-Salvati ratio helps to indicate patella baja on lateral

< 0.8 indicates patella baja.[6]

Fracture

Main article: Patella fracture

The kneecap is prone to injury because of its particularly exposed location, and fractures of the patella commonly occur as a consequence of direct trauma onto the knee. These fractures usually cause swelling and pain in the region, bleeding into the joint (hemarthrosis), and an inability to extend the knee. Patella fractures are usually treated with surgery, unless the damage is minimal and the extensor mechanism is intact.[7]

Exostosis

An exostosis is the formation of new bone onto a bone, as a result of excess calcium formation. This can be the cause of chronic pain when formed on the patella.

In animals

The patella is found in

Lepidosaurs), the muscle tendons from the upper leg are attached directly to the tibia, and a patella is not present.[9] In 2017 it was discovered that frogs have kneecaps, contrary to what was thought. This raises the possibility that the kneecap arose 350 million years ago when tetrapods first appeared, but that it disappeared in some animals.[10][11]

Etymology

The word patella originated in the late 17th century from the diminutive form of Latin patina or patena or paten, meaning shallow dish.[12][13]

See also

This article uses anatomical terminology.

References

  1. ^
    ISBN 3-13-533305-1
    .
  2. PMID 18310694
    .
  3. ^
    S2CID 208269986
    .
  4. ISBN 978-953-51-0995-2. (CC-BY-3.0
    )
  5. ^ Yuranga Weerakkody and Frank Gaillard. "Patella baja". Radiopaedia. Retrieved 2018-01-16.
  6. ^ a b Douglas Dennis (2017-02-25). "TKA in Patella Baja (Infera)". Orthobullets. Retrieved 2019-02-08.
  7. ISBN 978-3642347450
    .
  8. ^ Herzmark MH (1938). "The Evolution of the Knee Joint" (PDF). J Bone Joint Surg Am. 20 (1): 77–84. Archived from the original (PDF) on 2008-12-17. Retrieved 2007-11-17.
  9. ISBN 0-03-910284-X
    .
  10. ^ "Frogs have hidden, ancient kneecaps". New Scientist. Jul 15, 2017.
  11. PMID 28667673
    .
  12. ^ New Shorter Oxford
  13. ^ "patella - Origin and meaning of patella by Online Etymology Dictionary". www.etymonline.com.

External links

Look up kneecap in Wiktionary, the free dictionary.
Wikimedia Commons has media related to Patella.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Patella&oldid=1213814983"