Upper Limb

1. THE ACROMIOCLAVICULAR JOINT
Dr M Idris Siddiqui

3. THE ACROMIOCLAVICULAR JOINT
• The acromioclavicular joint is
a plane type synovial joint.
• Atypical synovial joint because bony surfaces are
covered by fibrocartilage not hyaline cartilage
• It is located where the lateral end of
the clavicle articulates with the acromion of
the scapula.
• The joint can be palpated during a shoulder
examination; 2-3cm medially from the tip of the
shoulder (formed by the end of the acromion).
RJL

4. Articulating surfaces of the AC joint
• The acromioclavicular joint consists of an
articulation between the lateral end of the clavicle
and the acromion of the scapula.
• It has two atypical features:
– The articular surfaces of the joint are lined
with fibrocartilage (as opposed to hyaline cartilage).
– The joint cavity is partially divided by an articular disc –
a wedge of fibrocartilage suspended from the upper part
of the capsule.

5. Joint Capsule
• 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.
• Joint capsule is lined internally by a synovial
membrane.
– The upper part of the capsule is thickened to form
acromioclavicular lifament.

6. Ligaments
1.Acromioclavicular:
– runs horizontally from the
acromion to the lateral clavicle.
It covers the joint capsule,
reinforcing its superior aspect.
2.Coracoclavicular ligament:

7. Coracoclavicular ligament:
• Conoid part :
• Cone-shaped fibrous band,runs vertically .
• The apex is attached to the root of the coracoid process just
lateral to the scapular notch and base is attached to the conoid
tubercle on the inferior surface of the clavicle.
• Trapezoid part:
• A horizontal fibrous band that extends from upper
surface of the coracoid process to the trapezoid
ridge on the inferior surface of lateral end of the
calvicle.
• It is a very strong structure, effectively suspending the weight
of the upper limb from the clavicle.

11. Important Relations
• Anteriorly:
–The deltoid muscle
•Posteriorly:
–The trapezius muscle
• Superiorly:
–The skin

12. Neurovascular Supply
• Vessels
– The arterial supply to the joint is via two vessels:
• Suprascapular artery – arises from the subclavian artery at the
thyrocervical trunk.
• Thoraco-acromial artery – arises from the axillary artery.
– The veins of the joint follow the major arteries.
• Nerves
• Articular branches of the suprascapular and lateral
pectoral nerves (C5,6)from the brachial plexus.
• Consistent with the Hilton law (joints are supplied by articular
branches of the nerves supplying the muscles that act on the
joint).

13. Movements
• The acromioclavicular joint allows a
degree of :
– Axial rotation and anteroposterior movement.
• As no muscles act directly on the joint, all
movement is passive, and is initiated by
movement at other joints (such as the
scapulothoracic joint).

14. Clinical Relevance
Acromioclavicular Dislocation
• Acromioclavicular joint dislocation (also known as a
separated shoulder) occurs when the two
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
fall on an outstretched hand.
• The injury is more serious if ligamental rupture
occurs (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 of the clavicle.