Acromioclavicular Joint
Type
Plane type of synovial joint.
Located approximately 2.5 cm medial to the point of the shoulder.
Articular Surfaces
- Small facet on the lateral end of the clavicle
- Small facet on the medial margin of the acromion process of the scapula
Both surfaces covered with fibrocartilage.
The joint cavity is partially subdivided by an incomplete (often perforated) wedge-shaped articular disc.
Ligaments
Acromioclavicular Ligament
- Fibrous band extending from acromion to clavicle
- Strengthens the joint superiorly
Coracoclavicular Ligament
The main bond of union between the scapula and clavicle; lies away from the joint itself.
Consists of two parts:
| Part | Attachment (below) | Attachment (above) |
|---|---|---|
| Conoid (inverted cone) | Root of coracoid process, just lateral to scapular notch | Conoid tubercle on inferior surface of clavicle |
| Trapezoid (horizontal band) | Upper surface of coracoid process | Trapezoid line on inferior surface of lateral clavicle |
The two parts are united posteriorly and often separated by a bursa.
Function: Largely responsible for suspending the weight of the scapula and upper limb from the clavicle. Strongest ligament of the upper limb.
Blood Supply
- Suprascapular artery
- Thoracoacromial artery
Nerve Supply
- Lateral supraclavicular nerve
Movements
Permits rotation of the acromion (and scapula) relative to the lateral end of the clavicle — associated with movements of the scapula during overhead activities.
During terminal elevation: acromioclavicular joint moves maximally (as the clavicle can no longer rotate further at the sternoclavicular joint).
Clinical Notes
- Dislocation (shoulder separation): May follow a severe blow on the superolateral shoulder. The clavicle overrides the acromion (upward displacement of lateral clavicle)
- In severe dislocation: both acromioclavicular and coracoclavicular ligaments are torn → shoulder separates from clavicle and falls under the weight of the limb
- A portion of the epiphyseal line of the proximal humerus is intracapsular (for glenohumeral joint) — septic arthritis may follow metaphyseal osteomyelitis