Accessory bone

{{short description|Additional bone found in some people}} [[File:Fabella with arrow.jpg|thumb|The fabella is present in 10% to 30% of individuals.<ref name="Radiopaedia-fabella">{{cite journal |title=Fabella |journal=Radiopaedia |last1=Luijkx |first1=Tim |last2=Knipe |first2=Henry |date=13 March 2013 |url=http://radiopaedia.org/articles/fabella |access-date=2015-09-18 }}</ref>]] An '''accessory bone''' or '''supernumerary bone''' is a bone that is not normally present in the body, but can be found as a variant in a significant number of people. It poses a risk of being misdiagnosed as bone fractures on radiography.<ref>T.E. Keats, M.W. Anderson, ''Atlas of normal roentgen variants that may simulate disease''. 7th edition, Mosby Inc. 2001, {{ISBN|0323013228}}</ref>

==Wrist and hand==  [[File:Accessory bones of the wrist.jpg|thumb|300px|X-ray of the wrist, with most common accessory bones labeled.<ref>Reference list for image is located at Commons:Template:Accessory bones of the wrist – references.</ref>]] thumb|220px|Prevalence and locations of sesamoid bones of the hand.<ref> - Location and structure: {{cite news|url=http://radsource.us/sesamoid-bones/|title=MRI Web Clinic — June 2014: Sesamoid Bones: Normal and Abnormal|author=Erica Chu, Donald Resnick|work=Radsource: PACS Radiology Systems |date=June 2014 |access-date=2017-11-04}} - Prevalences: {{cite journal |author=Chen W |author2=Cheng J |author3=Sun R |author4=Zhang Z |author5=Zhu Y |author6=Ipaktchi K |display-authors=et al| title=Prevalence and variation of sesamoid bones in the hand: a multi-center radiographic study. | journal=Int J Clin Exp Med | year= 2015 | volume= 8 | issue= 7 | pages= 11721–6 | pmid=26380010 | pmc=4565393}}</ref>

{|class="wikitable" ! Accessory bone !! Prevalence on the right (R) and left (L)<ref>{{cite web|url=http://www.smas.org/bsma/docs/XIV%20BSMA%20Congress/poster%20abstract.pdf|website=Association for Sports Medicine of Serbia (Udruženje za medicinu sporta Srbije)|title=Poster Abstracts|access-date=2017-11-03|year=2006}}, citing: {{cite web|title=A study of the accessory bones of the foot. Incidence in the Greek population-clinical significance|url=http://www.smas.org/bsma/docs/XIV%20BSMA%20Congress/program.pdf |author=Natsis K. |author2=Beletsiotis A. |author3=Terzidis I. |author4=Gigis P.}}</ref> |- | style="color:DarkMagenta;" | Os ulnostyloideum || 1.5% R, 2.4% L |- | style="color:DarkMagenta;" | Os centrale || 1.3% R, 2.1% L |- | style="color:DarkMagenta;" | Os trapezium secundarium || 0.5% R, 2.1% L |- | style="color:DarkMagenta;" | Os styloideum || 1.2% R, 1.2% L |- | style="color:DarkCyan;" | Os radiale externum || 1% R, 0.9% L |- | style="color:DarkCyan;" | Os triangulare || 1% R, 0.9% L |- | style="color:DarkCyan;" | Os paratrapezium || 0.3% R, 0.9% L |- | style="color:DarkCyan;" | Os capitatum secundarium || 0.8% R, 0.3% L |- | style="color:DarkCyan;" | Os hypotriquetrum || 0.5% R |- | style="color:DarkSlateBlue;" | Os hypolunatum || 0.3% L |- | style="color:DarkSlateBlue;" | Os epilunatum || 0.3% R, 0.3% L |- | style="color:DarkSlateBlue;" | Os ulnare externum || 0.3% L |- | style="color:DarkSlateBlue;" | Os pisiforme secundarium || 0.3% R |- | style="color:DarkSlateBlue;" | Os epitrapezium || 0.3% L |- | style="color:DarkSlateBlue;" | Os vesalianum manus || 0.3% L |}

=== Os ulnostyloideum === The ''os ulnostyloideum'' is an ulnar styloid process that is not fused to the rest of the ulna bone.<ref name="O'Rahilly">R. O'Rahilly. ''A survey of carpal and tarsal anomalies.'' J Bone Joint Surg Am. 1953; 35: 626–642</ref> On X-rays, an ''os ulnostyloideum'' is sometimes mistaken for an avulsion fracture of the styloid process. However, the distinction between these is extremely difficult.<ref name="O'Rahilly" /><ref name="Keats">T.E. Keats, M.W. Anderson. ''Atlas of normal roentgen variants that may simulate disease''. 7th edition, Mosby Inc. 2001 {{ISBN|0323013228}}</ref> It is alleged that the os ulnostyloideum has a close relationship with or is synonymous with the os triquetrum secundarium.<ref>A. Köhler. ''Röntgenology. The borderlands of the normal and early pathological in the skiagram. Translated by Arthur Turnbull.'' Ed. 2. Baillière, Tindall & Cox, Londen, 1935</ref>

=== Os centrale === The ''os carpi centrale'' (also briefly ''os centrale'') is, where present, located on the dorsal side of the wrist between the scaphoid, the trapezoid and capitate, radially to the deep fossa of the capitate. The bone is present in almost every human embryo of 17–49 mm length, but then usually fuses with the ulnar side of the scaphoid. Sometimes it fuses with the capitate or the trapezoid. The literature also refers to an ''os centrale'' at the palm of the carpus, but this existence is questioned.<ref name="O'Rahilly"/>

In most primates, including orangutans and gibbons, the os centrale is an independent bone that is attached to the scaphoid by strong ligaments. Conversely, in African apes and humans, the os centrale normally fuses to the scaphoid early in development.<ref>{{Cite journal|last=Schultz|first=Adolph H.|date=1936-12-01|title=Characters Common to Higher Primates and Characters Specific for Man (Continued)|journal=The Quarterly Review of Biology|volume=11|issue=4|pages=425–455|doi=10.1086/394517|issn=0033-5770}}</ref> In chimpanzees, the bone fuses with the scaphoid first after birth, while in gibbons and orangutans this occurs first at older age.<ref>A.H. Schultz. ''Characters common to higher primates and characters specific for man.'' Quart Rev Biol. 1936; 11: 259–283; 425–455</ref> A good number of scholars have construed the scaphoid-centrale fusion as a functional adaptation to knuckle-walking,<ref>{{Cite journal|last1=Richmond|first1=Brian G.|last2=Begun|first2=David R.|last3=Strait|first3=David S.|date=2001|title=Origin of human bipedalism: The knuckle-walking hypothesis revisited|journal=American Journal of Physical Anthropology|language=en|volume=116|issue=S33|pages=70–105|doi=10.1002/ajpa.10019|pmid=11786992|issn=0002-9483|doi-access=free}}</ref> since a fused morphology would better cope with the increased shear stress on this joint during this kind of quadrupedal locomotion. The results from a simulation study have shown that fused scaphoid-centrales show lower stress values as compared to non fused morphologies, thus supporting a biomechanical explanation for the scaphoid-centrale fusion as a functional adaptation for knuckle-walking.<ref>{{Cite journal|last1=Püschel|first1=Thomas A.|last2=Marcé-Nogué|first2=Jordi|last3=Chamberlain|first3=Andrew T.|last4=Yoxall|first4=Alaster|last5=Sellers|first5=William I.|date=2020-02-26|title=The biomechanical importance of the scaphoid-centrale fusion during simulated knuckle-walking and its implications for human locomotor evolution|journal=Scientific Reports|language=en|volume=10|issue=1|pages=3526|doi=10.1038/s41598-020-60590-6 | pmc=7044280|pmid=32103129|issn=2045-2322|doi-access=free|bibcode=2020NatSR..10.3526P }}</ref>

== Ankle == [[File:Accessory bones of the ankle.jpg|thumb|140px|Accessory bones of the ankle.<ref>Reference list for shapes and locations for included bones is located at: Commons:Template:Accessory bones of the ankle – references.</ref>]]

Accessory bones at the ankle mainly include: *''Os subtibiale'', with a prevalence of approximately 1%.<ref name=Gaillard>{{cite web|url=https://radiopaedia.org/articles/os-subtibiale|author=Frank Gaillard |author2=Mohammad Taghi Niknejad |display-authors=et al|title=Os subtibiale|website=Radiopaedia|date=2 March 2013 |access-date=2017-11-05}}</ref> It is a secondary ossification center of the distal tibia that appears during the first year of life, and which in most people fuses with the shaft at approximately 15 years in females and approximately 17 years in males.<ref name=Gaillard /> *''Os subfibulare'', with a prevalence of approximately 0.2%.<ref name="ChampagneCook1999">{{cite journal|last1=Champagne|first1=IM|last2=Cook|first2=DL|last3=Kestner|first3=SC|last4=Pontisso|first4=JA|last5=Siesel|first5=KJ|title=Os subfibulare. Investigation of an accessory bone|journal=Journal of the American Podiatric Medical Association|volume=89|issue=10|year=1999|pages=520–524|issn=8750-7315|doi=10.7547/87507315-89-10-520|pmid=10546424}}</ref>

''Os trigonum'' (further described below) may also be seen on an ankle X-ray.

==Foot==  [[File:Accessory and sesamoid bones of the foot - dorsoplantar projection.jpg|thumb|200px|X-ray by dorsoplantar projection, with most common accessory and sesamoid bones of the foot.<ref name=Commons-foot>A reference list for shapes, locations and prevalences for included bones is located at Commons:Template:Accessory and sesamoid bones of the foot – references.</ref>]] 500px|thumb|Lateral projection.<ref name=Commons-foot />

{|class="wikitable" ! Bone !! Prevalence<ref name="NwawkaHayashi2013">{{cite journal|last1=Nwawka|first1=O. Kenechi|last2=Hayashi|first2=Daichi|last3=Diaz|first3=Luis E.|last4=Goud|first4=Ajay R.|last5=Arndt|first5=William F.|last6=Roemer|first6=Frank W.|last7=Malguria|first7=Nagina|last8=Guermazi|first8=Ali|title=Sesamoids and accessory ossicles of the foot: anatomical variability and related pathology|journal=Insights into Imaging|volume=4|issue=5|year=2013|pages=581–593|issn=1869-4101|doi=10.1007/s13244-013-0277-1|pmc=3781258|pmid=24006205}}</ref> |- !colspan=2| Sesamoid bones |- | Sesamoids at the metatarsophalangeal (MTP) joint of the great toe || Always present |- | Sesamoid of the second metatarsal || 0.4% |- | Sesamoid of the third metatarsal || 0.2% |- | Sesamoid of the fourth metatarsal || 0.1% |- | Sesamoids of the fifth metatarsal || 4.3% |- | Sesamoid of the interphalangeal (IP) joint of the great toe || 2–13% |- !colspan=2| Ossicles |- | Os trigonum (not visible in this dorsoplantar projection) || 7–25% |- | Os peroneum || Up to 26% |- | Accessory navicular || 2–21% |- | Os intermetatarseum || 1–13% |- | Os supranaviculare, also called the ''talonavicular bone'' || 1.0–3.5% |- | Os calcaneus secundarium || 0.6–7% |- | Os supratalare || 0.2–2.4% |- | Os vesalianum || 0.1–1% |- | Os talotibiale || 0.5% |}

=== Accessory navicular === thumb|Accessory navicular types, from left to right: Type 1, 2 and 3. {{Main|Accessory navicular bone}} An accessory navicular bone, also called ''os tibiale externum'', occasionally develops in front of the ankle towards the inside of the foot. This bone may be present in approximately 2–21% of the general population and is usually asymptomatic.<ref>{{Cite web | url=http://www.wheelessonline.com/ortho/accessory_navicular |work = Wheeless' Textbook of Orthopaedics|title = Accessory Navicular| date=2 June 2020 }}</ref><ref>{{Cite web | url=http://www.macrorad.com/case-reports/symptomatic-accessory-navicular-bone.html | title=Macrorad Teleradyoloji Olgu Sunumları – SYMPTOMATIC ACCESSORY NAVICULAR BONE}}</ref><ref name="Miller1995">{{cite journal | title=The symptomatic accessory tarsal navicular bone: assessment with MR imaging | vauthors=Miller TT, Staron RB, Feldman F, Parisien M, Glucksman WJ, Gandolfo LH | journal= Radiology | date=June 1995 | volume=195 | issue=3 | pages=849–853 | doi=10.1148/radiology.195.3.7754020 | pmid=7754020}}</ref> When it is symptomatic, surgery may be necessary.

The Geist classification divides the accessory navicular bones into three types.<ref name="Miller1995" />

* Type 1: An os tibiale externum is a 2–3 mm sesamoid bone in the distal posterior tibialis tendon. Usually asymptomatic. * Type 2: Triangular or heart-shaped ossicle measuring up to 12 mm, which represents a secondary ossification center connected to the navicular tuberosity by a 1–2 mm layer of fibrocartilage or hyaline cartilage. Portions of the posterior tibialis tendon sometimes insert onto the accessory ossicle, which can cause dysfunction, and therefore, symptoms. * Type 3: A cornuate navicular bone represents an enlarged navicular tuberosity, which may represent a fused Type 2 accessory bone. Occasionally symptomatic due to bunion formation.

=== Os trigonum === The ''os trigonum'' or ''accessory talus'' represents a failure of fusion of the lateral tubercle of the posterior process of the talus bone. Is estimated to be present in 7–25% of adults.<ref name="NwawkaHayashi2013" /> It can be mistaken for an avulsion fracture of lateral tubercle of talus (Shepherd fracture) or a fracture of the Stieda process. In most cases, Os Trigonum will go unnoticed, but with some ankle injuries it can get trapped between the heel and ankle bones which irritates the surrounding structures, leading to Os Trigonum Syndrome.<ref>{{Cite web | url=https://www.foot-pain-explored.com/os-trigonum.html | title=Os Trigonum Syndrome: Causes, Symptoms & Treatment|work = Foot Pain Explored|first = Chloe|last = Wilson|date = 3 November 2021}}</ref>

<gallery> File:Os trigonum - Os talonaviculare.jpg File:Os trigonum 1.jpg File:Os trigonum2.jpg File:Os trigonum 3.jpg </gallery>

=== Less common accessory bones === thumb|600px|left|Image also including the locations of rare accessory bones of the foot: 1=Os cuneometatarsale I plantare, 2=os uncinatum, 3=os sesamoideum tibialis posterior, 4=os sesamoideum peroneum, 5=os cuboideum secundarium, 6=os trochleare calcanei, 7=os in sinus tarsi, 8=os sustentaculum tali, 9=os talocalcaneale posterius, 10=os aponeurosis plantaris, 11=os subcalcaneum, 12=os sesamoideum tibialis anterior, 13=os cuneometatarsale I tibiale, 14=os intermetatarsale I, 15=os cuneometatarsale II dorsale, 16=os paracuneiforme, 17=os cuneonaviculare, 18=os intercuneiforme, 19=os intermetatarsale IV, 20=/os talonaviculare, 21=os vesalianum pedis, 22=os tibiale externum, 23=os talotibiale dorsale, 24=os supratalare, 25=os calcaneus secundarius, 26=os subtibiale, 27=os subfibulare, 28=os retinaculi, 29=os calcaneus accessorius, 30=os trigonum, 31=os supracalcaneum, 32=os tendinis calcanei {{clear}}

== Other locations == [[File:Verkalkungen im Ligamentum nuchae - Roe seitlich.jpg|thumb|150px|Bone tissue in the nuchal ligament.]] ===Neck=== *Nodules in the posterior margin of the nuchal ligament form bone tissue in approximately 11% of males and 3–5% in females after the third decade of life, and may then be regarded to be sesamoid bones.<ref name="pmid14047360">{{cite journal| author=SCAPINELLI R| title=Sesamoid Bones in the Ligamentum Nuchae of Man | journal=J Anat | year= 1963 | volume= 97 | issue=Pt 3 | pages= 417–22 | pmid=14047360 | pmc=1244202 }}</ref>

===Shoulder=== thumb|130px|Os acromiale. *An os acromiale forms when any of its four ossification centers fail to fuse. These four ossification centers are called (from tip to base) pre-acromion, meso-acromion, meta-acromion, and basi-acromion. In most cases, the first three fuse at 15–18 years, whereas the base part fuses to the scapular spine at 12 years. Such failure to fuse occurs in between 1% and 15% of cases.<ref>{{Cite journal | last1 = Warner | first1 = Jon J.P. | last2 = Beim | first2 = Gloria M. | last3 = Higgins | first3 = Laurence | journal = The Journal of Bone and Joint Surgery | date = September 1998 | volume = 80 | issue = 9 | pages = 1320–6 | title = The Treatment of Symptomatic Os Acromiale | doi = 10.2106/00004623-199809000-00011 | pmid = 9759817 }}</ref><ref name="Sammarco">{{cite journal| last=Sammarco| first=VJ| date=March 2000| title=Os acromiale: frequency, anatomy, and clinical implications| journal=J Bone Joint Surg Am| volume=82| issue=3| pages=394–400| pmid=10724231| doi=10.2106/00004623-200003000-00010}}</ref> It rarely causes pain.

===Vertebral column=== *An ''Oppenheimer ossicle'' is found in approximately 4% (range 1–7%) of individuals.<ref name=Radiopaedia-Oppenheimer>{{cite web|url=https://radiopaedia.org/articles/oppenheimer-ossicle-1|title=Oppenheimer ossicle|author=Dr Henry Knipe |display-authors=et al|website=Radiopaedia|date=6 November 2013 |access-date=2017-11-05}}</ref> It is associated with the facet joints of lumbar spines. It usually occurs as a single, unilateral ossicle at the inferior articular processes, but can also occur at the superior articular processes.<ref name=Radiopaedia-Oppenheimer />

===Knee=== *The fabella is present in 10% to 30% of individuals.<ref name="Radiopaedia-fabella" />

== See also == * Accessory muscle

== References == {{reflist}}

Category:Accessory bone Category:Bones