Thepatella(pl.:patellaeorpatellas), also known as thekneecap,is a flat, rounded triangularbonewhich articulates with thefemur(thigh bone) and covers and protects the anterior articular surface of thekneejoint. The patella is found in many tetrapods, such asmice,cats,birdsanddogs,but not inwhales,or mostreptiles.
| Patella | |
|---|---|
 Right knee | |
| Details | |
| Pronunciation | /pəˈtɛlə/ |
| Origins | Present at the joint of femur and tibia fibula |
| Identifiers | |
| Latin | patella |
| MeSH | D010329 |
| TA98 | A02.5.05.001 |
| TA2 | 1390 |
| FMA | 24485 |
| Anatomical terms of bone | |
In humans, the patella is the largestsesamoid bone(i.e., embedded within a tendon or a muscle) in the body. Babies are born with a patella of softcartilagewhich begins toossifyinto bone at about four years of age.
Structure
editThe patella is asesamoid boneroughly triangular in shape, with the apex of the patella facing downwards. The apex is the mostinferior(lowest) part of the patella. It is pointed in shape, and gives attachment to thepatellar ligament.
The front and back surfaces are joined by a thin margin and towards centre by a thicker margin.[1]Thetendonof thequadriceps femoris muscleattaches to the base of the patella.,[1]with thevastus intermediusmuscle attaching to the base itself, and thevastus lateralisandvastus medialisare 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 hasexostoses.The middle third has numerousvascularcanaliculi.The lower third culminates in the apex which serves as the origin of thepatellar ligament.[1]The posterior surface is divided into two parts.[1]
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Human left patella from the front -
Human left patella from behind -
Flexion and extension of knee
The upper three-quarters of the patellaarticulateswith 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 bycartilage,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, theinfrapatellar fat pad.
Variation
edit
Emarginations (i.e.patella emarginata,a "missing piece" ) are common laterally on the proximal edge.[1]Bipartite patellasare the result of an ossification of a secondcartilaginouslayer 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:
- Most commonly the medial articular surface is smaller than the lateral.
- Sometimes both articular surfaces are virtually equal in size.
- Occasionally, the medial surface ishypoplasticor
- the central ledge is only indicated.
Development
editIn the patella anossificationcentre 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
editThe primary functional role of the patella is knee extension. The patella increases theleveragethat thequadriceps tendoncan exert on the femur by increasing the angle at which it acts.
The patella is attached to thetendonof thequadriceps femoris muscle,which contracts to extend/straighten theknee.The patella is stabilized by the insertion of the horizontal fibres ofvastus medialisand by the prominence of thelateral femoral condyle,which discourages lateral dislocation during flexion. The retinacular fibres of the patella also stabilize it during exercise.
Clinical significance
editDislocation
editPatellar 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]
Vertical alignment
editApatella altais a high-riding (superiorly aligned) patella. Anattenuated patella altais an unusually small patella that develops out of and above the joint.
Apatella bajais a low-riding patella. A long-standing patella baja may result in extensor dysfunction.[5]
TheInsall-Salvati ratiohelps to indicate patella baja on lateralX-rays,and is calculated as the patellar tendon length divided by the patellar bone length. An Insall-Salvati ratio of<0.8 indicates patella baja.[6]
Fracture
editThe 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
editAnexostosisis the formation of new bone onto a bone, as a result of excesscalciumformation. This can be the cause of chronic pain when formed on the patella.
Other animals
editThe patella is found inplacental mammalsandbirds;mostmarsupialshave only rudimentary, non-ossified patellae although a few species possess a bony patella.[8]A patella is also present in the livingmonotremes,theplatypusand theechidna.In other tetrapods, including livingamphibiansand mostreptiles(except somelepidosaurs), the muscle tendons from the upper leg are attached directly to thetibia,and a patella is not present.[9]In 2017 it was discovered thatfrogshave 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
editThe wordpatellaoriginated in the late 17th century from thediminutiveform ofLatinpatinaorpatenaorpaten,meaning shallow dish.[12][13]
See also
editReferences
edit- ^abcdefPlatzer, Werner (2004).Color Atlas of Human Anatomy, Vol. 1: Locomotor System(5th ed.).Thieme.p. 194.ISBN3-13-533305-1.
- ^Palmu, S.; Kallio, P.E.; Donell, S.T.; Helenius, I.; Nietosvaara, Y. (2008). "Acute patellar dislocation in children and adolescents: A randomized clinical trial".Journal of Bone and Joint Surgery.90(3): 463–470.doi:10.2106/JBJS.G.00072.PMID18310694.
- ^abDath, R.; Chakravarthy, J.; Porter, K.M. (2006). "Patella Dislocations".Trauma.8:5–11.doi:10.1191/1460408606ta353ra.S2CID208269986.
- ^Melloni, Pietro; Veintemillas, Maite; Marin, Anna; Valls, Rafael (2013). "Imaging Patellar Complications After Knee Arthroplasty".Arthroplasty - Update.doi:10.5772/53666.ISBN978-953-51-0995-2.(CC-BY-3.0)
- ^Yuranga Weerakkody and Frank Gaillard."Patella baja".Radiopaedia.Retrieved2018-01-16.
- ^abDouglas Dennis (2017-02-25)."TKA in Patella Baja (Infera)".Orthobullets.Retrieved2019-02-08.
- ^Bentley, G (2014).European Surgical Orthopaedics and Traumatology: The EFORT Textbook.Springer. pp. 2766–2784.ISBN978-3642347450.
- ^Herzmark MH (1938)."The Evolution of the Knee Joint"(PDF).J Bone Joint Surg Am.20(1): 77–84. Archived fromthe original(PDF)on 2008-12-17.Retrieved2007-11-17.
- ^Romer, Alfred Sherwood; Parsons, Thomas S. (1977).The Vertebrate Body.Philadelphia, PA: Holt-Saunders International. p. 205.ISBN0-03-910284-X.
- ^"Frogs have hidden, ancient kneecaps".New Scientist.Jul 15, 2017.
- ^Virginia Abdala; et al. (Jul 2017)."On the presence of the patella in frogs".The Anatomical Record.300(10): 1747–1755.doi:10.1002/ar.23629.hdl:11336/58233.PMID28667673.
- ^New Shorter Oxford
- ^"patella - Origin and meaning of patella by Online Etymology Dictionary".etymonline.
External links
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