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M01.03.030 Acromioclavicular Joint
The acromioclavicular (AC) joint is a plane-type synovial joint located in the shoulder region. It is the articulation between the lateral end of the clavicle and the acromion of the scapula. This article explores its anatomical structure, neurovascular supply, movements, and clinical relevance.
1. Anatomical Structure
1.1 Articulating Surfaces
- Components:
- Lateral end of the clavicle.
- Acromion of the scapula.
- Unique Features:
- Articular surfaces are lined with fibrocartilage instead of hyaline cartilage.
- The joint cavity is partially divided by an articular disc of fibrocartilage.
1.2 Joint Capsule
- Encloses the joint:
- Composed of loose fibrous tissue.
- Internally lined by a synovial membrane.
- Reinforced by fibers from the trapezius muscle posteriorly.
1.3 Ligaments
The AC joint is stabilized by three key ligaments:
| Ligament | Attachment | Function |
|---|---|---|
| Acromioclavicular | Acromion to lateral clavicle | Reinforces the superior aspect of the joint capsule. |
| Conoid (part of CC) | Coracoid process to conoid tubercle of clavicle | Suspends the weight of the upper limb from the clavicle. |
| Trapezoid (part of CC) | Coracoid process to trapezoid line of clavicle | Provides horizontal stability to the joint. |
Note: The conoid and trapezoid ligaments are collectively termed the coracoclavicular (CC) ligament.
2. Movements
- The AC joint permits gliding movements in the:
- Superior/Inferior plane.
- Anteroposterior plane.
- Minimal axial rotation.
- Movements are passive, initiated by actions at other shoulder joints, as no muscles directly act on this joint.
3. Neurovascular Supply
3.1 Blood Supply
| Artery | Source |
|---|---|
| Suprascapular artery | Thyrocervical trunk (subclavian) |
| Thoracoacromial artery | Axillary artery |
- Venous drainage parallels the arterial supply.
3.2 Innervation
- Articular branches of:
- Suprascapular nerve.
- Lateral pectoral nerve.
- Both nerves originate from the brachial plexus.
4. Clinical Relevance
4.1 Acromioclavicular Dislocation
- Cause:
- Direct blow to the shoulder.
- Fall on an outstretched hand.
- Severity:
- Mild: No ligament rupture.
- Severe: Rupture of acromioclavicular or coracoclavicular ligaments.
- Implication: Shoulder drops if the coracoclavicular ligament is torn due to unsupported upper limb weight.
4.2 Management
| Severity | Management |
|---|---|
| Mild | Ice, rest, and physiotherapy. |
| Severe | Ligament reconstruction surgery. |
Note: Do not confuse AC joint dislocation with glenohumeral dislocation, which affects the shoulder’s ball-and-socket joint.
Points to Remember
- The AC joint is a plane synovial joint allowing gliding movements.
- Stabilized by the acromioclavicular and coracoclavicular ligaments.
- Supplied by the suprascapular and thoracoacromial arteries, and innervated by suprascapular and lateral pectoral nerves.
- AC joint dislocations range from minor injuries to severe ligament ruptures requiring surgical intervention.
Figures
- Articulating surfaces of the acromioclavicular joint.
- Major ligaments of the acromioclavicular joint.
- Acromioclavicular joint dislocation.
References
- Gray’s Anatomy
- National Center for Biotechnology Information (NCBI)
- Clinical Orthopedics and Related Research