Editing Clavicle (section)

==Structure==
The collarbone is a thin doubly curved [[long bone]] that connects the [[human arm|arm]] to the [[torso|trunk]] of the body.<ref>{{Cite web |title=Why Do We Call It a Collarbone? |url=https://my.clevelandclinic.org/health/articles/16877-clavicle |access-date=2023-09-14 |website=Cleveland Clinic |language=en}}</ref> Located directly above the [[first rib]], it acts as a [[strut]] to keep the scapula in place so that the arm can hang freely. At its rounded medial end (sternal end), it articulates with the [[manubrium]] of the [[sternum]] (breastbone) at the [[sternoclavicular joint]]. At its flattened lateral end (acromial end), it articulates with the [[acromion]], a process of the [[scapula]] (shoulder blade), at the [[acromioclavicular joint]].

{| class="wikitable" align="right" width="250"
| [[File:Clavicula inf.jpg|250px]]<br />[[File:Clavicula sup.jpg|250px]]
|-
| Right clavicle—from below, and from above
|-
| [[File:Gray200.png|250px]]<br />[[File:Gray201.png|250px]]
|-
| Left clavicle—from above, and from below
|}
The rounded medial region (sternal region) of the shaft has a long curve laterally and anteriorly along two-thirds of the entire shaft. The flattened lateral region (acromial region) of the shaft has an even larger posterior curve to articulate with the acromion of the scapula. The medial region is the longest clavicular region as it takes up two-thirds of the entire shaft. The lateral region is both the widest clavicular region and thinnest clavicular region. The lateral end has a rough inferior surface that bears a ridge, the [[trapezoid line]], and a slight rounded projection, the '''conoid tubercle''' (above the [[coracoid process]]). These surface features are attachment sites for muscles and ligaments of the shoulder.

It can be divided into three parts: medial end, lateral end, and shaft.

===Medial end===
The medial end is also known as the sternal end. It is quadrangular and articulates with the clavicular notch of the [[manubrium]] of the [[sternum]] to form the [[sternoclavicular joint]].<ref>{{cite journal |last1=Shane Tubbs |first1=R. |last2=Loukas |first2=Marios |last3=Slappey |first3=John B. |last4=McEvoy |first4=William C. |last5=Linganna |first5=Sanjay |last6=Shoja |first6=Mohammadali M. |last7=Jerry Oakes |first7=W. |title=Surgical and clinical anatomy of the interclavicular ligament |journal=Surgical and Radiologic Anatomy |date=9 July 2007 |volume=29 |issue=5 |pages=357–360 |doi=10.1007/s00276-007-0219-z |pmid=17563831 }}</ref> The articular surface extends to the inferior aspect for articulation with the first [[costal cartilage]].

===Lateral end===
The lateral end is also known as the acromial end. It is flat from above downward. It bears a facet that articulates with the shoulder to form the [[acromioclavicular joint]]. The area surrounding the joint gives an attachment to the joint capsule. The anterior border is concave forward and the posterior border is convex backward.<ref>{{cite book |last1=Wong |first1=Michael |last2=Kiel |first2=John |title=StatPearls |date=2024 |publisher=StatPearls Publishing |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK499858/ |chapter=Anatomy, Shoulder and Upper Limb, Acromioclavicular Joint |pmid=29763033 }}</ref>

===Shaft===
The shaft is divided into two main regions, the medial region, and the lateral region. The medial region is also known as the sternal region, it is the longest clavicular region as it takes up two-thirds of the entire shaft. The lateral region is also known as the acromial region, it is both the widest clavicular region and thinnest clavicular region.
[[File:Clavicle 3d Model.gif|thumb|3D model of the clavicle]]

====Lateral region of the shaft====
The lateral region of the shaft has two borders and two surfaces.
* the anterior border is concave forward and gives origin to the [[deltoid muscle]].
* the posterior border is convex and gives attachment to the [[trapezius muscle]].
* the inferior surface has a ridge called the [[trapezoid line]] and a tubercle; the conoid tubercle for attachment with the trapezoid and the [[conoid ligament]], part of the [[coracoclavicular ligament]] that serves to connect the collarbone with the coracoid process of the scapula.
[[File:Parts Of Clavicle.png|thumb|Parts of clavicle]]

===Development===
The collarbone is the first bone to begin the process of [[ossification]] (laying down of minerals onto a preformed matrix) during [[human embryogenesis|development of the embryo]], during the fifth and sixth weeks of [[Gestational age (obstetrics)|gestation]]. However, it is one of the last bones to finish ossification at about 21–25 years of age. Its lateral end is formed by [[intramembranous ossification]] while medially it is formed by [[endochondral ossification]]. It consists of a mass of [[cancellous bone]] surrounded by a [[compact bone]] shell. The cancellous bone forms via two [[ossification centres]], one medial and one lateral, which fuse later on. The compact forms as the layer of [[fascia]] covering the bone stimulate the ossification of adjacent tissue. The resulting compact bone is known as a periosteal collar.

The collarbone has a [[medullary cavity]] ([[bone marrow|marrow cavity]]) in its medial two-thirds.<ref name="Standring2016">{{cite book |last1=Standring |first1=Susan |title=Gray's anatomy: the anatomical basis of clinical practice .Digital version |date=2016 |publisher=Elsevier |location=Philadelphia, Pa. |isbn=9780702052309 |page=892 |edition=41st}}</ref> It is made up of spongy [[cancellous bone]] with a shell of [[compact bone]].<ref name="Moore-1999" /> It is a [[dermal bone]] derived from elements originally attached to the skull.

===Variation===
The shape of the clavicle varies more than most other long bones. It is occasionally pierced by a branch of the [[supraclavicular nerve]]. In males the clavicle is usually longer and larger than in females. A study measuring 748 males and 252 females saw a difference in collarbone length between age groups 18–20 and 21–25 of about {{convert|6|and|5|mm|in|abbr=on}} for males and females respectively.<ref>{{cite journal |last1=Kaur |first1=H |last2=Harjeet Sahni |first2=D |title=Length and curves of the clavicle in Northwest Indians |journal=Journal of Anatomical Society of India |volume=51 |issue=2 |date=January 2002 |pages=199–209 }}</ref>

The left clavicle is usually longer and weaker than the right clavicle.<ref name="Moore-1999" /><ref>{{cite journal | ref = huysmans
| last1        = A. Bernat, T. Huysmans, F. Van Glabbeek, J. Sijbers, J. Gielen, and A. Van Tongel
| title        = The anatomy of the clavicle: A Three-dimensional Cadaveric Study
| journal    = Clinical Anatomy | year = 2014
| volume = 27
|number =5
|pages = 712–723
| doi          = 10.1002/ca.22288
| pmid        = 24142486
| s2cid = 23982787
}}</ref>

The collarbones are sometimes partly or completely absent in [[cleidocranial dysostosis]].

The [[levator claviculae muscle]], present in 2–3% of people, originates on the transverse processes of the upper cervical vertebrae and is inserted in the lateral half of the clavicle.