Joints - Acromioclavicular joint (ACJ) Flashcards
What type of joint is an ACJ?
Plane type synovial joint
What are the articulating surfaces of the ACJ?
Lateral end of clavicle and acromion of scapula. It has two atypical features:
1) Articular surfaces of the joint are lined with fibrocartilage (as opposed to hyaline cartilage).
2) The joint cavity is partially divided by an articular disc - a wedge of fibrocartilage from the upper part of the capsule.
What the features of the joint capsule?
Consists of a loose fibrous layer which encloses the two articular surfaces. It also gives rise to the articular disc. The posterior aspect of the joint capsule is reinforced by fibres from the trapezius muscle.
As would be expected of a synovial joint, joint capsule is lined internally by a synovial membrane. This secretes fluid into the cavity of the joint.
What are the of the ACJ?
Intrinsic:
1) ACJ ligament - runs horizontally from the acromion to the lateral clavicle. It covers the joint capsule, reinforcing its superior aspect.
Extrinsic:
2) Conoid ligament - runs vertically from the coracoid process of the scapula to the conoid tubercle of the clavicle.
3) Trapezoid ligament - runs from the coracoid process of the scapula to the trapezoid line of the clavicle.
Collectively, the conoid ligament and the trapezoid ligament are known as the coracoclavicular ligament. This suspends the weight of the upper limb from the clavicle.
What is the neurovascular supply of the ACJ?
There are two vessels involved:
1) Suprascapular artery - arises from the subclavian at the thyrocervical trunk.
2) Thoraco-acromial aratery - arises from the axillary artery.
The veins of the joint follow the major arteries.
The ACJ is innervated by articular branches the suprascapular and lateral pectoral nerves. They both arise directly from the brachial plexus.
What is the movements of the ACJ?
Axial rotatation
Anteroposterior movement
All movement is passive and initiate by movements at other joints.
Clinical relevance: ACJ dislocation
Occurs when articulating surfaces of the joint are separated. It is associated with joint soft tissue damage.
It commonly occurs from a direct blow to the joint, or a FOOH.
The injury is more serious is ligament rupture occurs (at the acromioclavicular or coracoclavicular).
If the coracoclavicular ligament is torn, weight of the upper limb is not supported and the shoulder moves inferiorly. This increases the prominence o the clavicle.
Management of the AC joint dislocation is dependent on injury severity and impact on quality of life. The treatment options range from ice and rest, to ligament reconstruction surgery.
Note: this injury is not to be confused with a shoulder dislocation - an injury affecting the glenohumeral joint.
