Clavicle anatomy consists of medial end, middle and lateral end. There are many ligaments and muscles connecting to these parts of clavicle.
Clavicle bone is the First bone in the body to ossify (at 5 weeks’ gestation) and last to fuse (medial epiphysis at 25 years of age).
See Also: Clavicle Fractures
Ligamentous Anatomy of the clavicle:
Medial Clavicle articulates with sternal bone forming the sternoclavicular joint
- There is relatively little motion at the sternoclavicular joint.
- Medially the clavicle is secured to the sternum by the sternoclavicular capsule.
- The thickening of the posterior capsule has been determined to be the single most important soft tissue constraint to anterior or posterior translation of the medial clavicle.
- There is also an interclavicular ligament which runs from the medial end of one clavicle, gains purchase from the superior aspect of the sternum at the sternal notch, and attaches to the medial end of the contralateral clavicle.
- Acting as a tension wire at the base of the clavicle, this ligament helps prevent inferior angulation or translation of the clavicle.
- there are extremely stout ligaments that originate on the first rib and insert on the undersurface or the inferior aspect of the clavicle.
Laterally the clavicle articulates with the acromion bone.
- The coracoclavicular ligaments are stout ligaments that arise from the base of the coracoid:
- The trapezoid (more lateral): inserts onto the small osseous ridge of the inferior clavicle.
- Conoid (more medial): inserts onto the clavicular conoid tubercle.
- These ligaments are very strong and provide the primary resistance to superior displacement of the clavicle.
- Their integrity, or lack thereof, plays an important role in the decision making and fixation selection in the treatment of displaced lateral third clavicle fractures.
- clavicle fractures in this location will often have an avulsed inferior fragment to which these ligaments are attached, especially in younger individuals.
- The capsule of the AC joint is thickened superiorly and is primarily responsible for resisting AP displacement of the joint.
- If one is inserting a hook plate for fixation of a very distal fracture, a small defect can be made in the posterolateral aspect of the capsule for insertion of the hook portion into the posterior subacromial space.
Muscular Anatomy of the Clavicle
Medially: the pectoralis major muscle originates from the clavicular shaft anteroinferiorly, and the sternocleidomastoid originates superiorly.
Laterally: the pectoralis origin merges with the origin of the anterior deltoid, while the trapezius insertion blends superiorly with the deltoid origin at the lateral margin.
The medial clavicular fragment is elevated by the unopposed pull of the sternocleidomastoid muscle.
while the distal fragment is held inferiorly by the deltoid and medially by the pectoralis major.
The platysma or “shaving muscle” is variable in terms of thickness and extent, but usually envelopes the anterior and superior aspects of the clavicle and runs in the subcutaneous tissues, extending superiorly to the mandible and the deeper facial muscles.
It is divided during the surgical approach, and is typically included in the closure of the superficial, or skin/subcutaneous layer.
Neurovascular Anatomy of the Clavicle
- The supraclavicular nerves originate from cervical roots C3 and C4 and exit from a common trunk behind the posterior border of the sternocleidomastoid muscle.
- There are typically three major branches (anterior, middle, and posterior) that cross the clavicle superficially from medial to lateral, and are risk during surgical approaches.
- If they are divided, an area of numbness is typically felt inferior to the surgical incision, although this tends to improve with time.
See Also: Brachial Plexus Anatomy
- The subclavian vein runs directly below the subclavius muscle and above the first rib, where it is readily accessible (for central venous access) and vulnerable (to inadvertent injury).
- More posteriorly lie the subclavian artery and the brachial plexus, separated from the vein and clavicle by the additional layer of the scalenus anterior muscle medially.
- subclavian vessels were closest at the medial end, with the vein directly apposed to the posterior cortex of the medial clavicle in some cases.
- In the middle third, the artery and vein were a mean of 17 and 13 mm from the clavicle, respectively, at an approximate angle of 60 degrees to the horizontal (i.e., the vessels were posterior-inferior to the clavicle)
- Laterally, the distances were greater, with the artery and vein a mean of 63 and 76 mm, respectively form the clavicle.
Sternoclavicular joint It forms from clavicle laterally and the sternal bone medially.
It’s a double gliding with an articular disc.
Sternoclavicular joint is the only true joint connecting upper extremity with axial skeleton.
This joint is held by anterior and posterior sternoclavicular ligaments, an interclavicular ligament, and a costoclavicular ligament.
Posterior sternoclavicular ligament is the strongest and primary restraint to anteroposterior instability.
It Rotates 30 degrees with shoulder motion.
Acromioclavicular AC joint
Acromioclavicular AC joint is a Plane/gliding joint with a fibrocartilaginous disc.
Ligaments of Acromioclavicular joint :
- AC ligaments: prevent anteroposterior displacement, they are anterior, posterior, superior and inferior.
- Coracoclavicular ligaments: prevent superior displacement of distal clavicle.
- Trapezoid (anterolateral): it is located approximately 25 mm from AC joint.
- Conoid (posteromedial): it’s stronger than the Trapezoid ligaments, it’s approximately 45 mm from AC joint.
When the arm is maximally elevated, about 5 to 8 degrees of rotation is possible at the AC joint, although the clavicle rotates approximately 40 to 50 degrees.
- Millers Review of Orthopaedics -7th Edition Book.
- Rockwood and Green’s Fractures in Adults 8th Edition book.
- Hyland S, Charlick M, Varacallo M. Anatomy, Shoulder and Upper Limb, Clavicle. [Updated 2021 Jul 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: NBK525990.