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Plane synovial joint between the acromial end of clavicle and the medial margin of acromion process of scapula.
Clavicular facet: Small, oval, and convex.
Acromial facet: Small and concave.
Both are covered by fibrocartilage.
Usually incomplete, wedge-shaped fibrocartilage dividing the joint cavity partially.
Improves congruence and absorbs shock.
| Ligament | Attachment | Function |
|---|---|---|
| Capsular ligament | Surrounds joint, thin above, thick below | Allows limited gliding |
| Superior & Inferior acromioclavicular ligaments | Between acromion and clavicle margins | Strengthen capsule |
| Coracoclavicular ligament (chief stabilizer) | From coracoid process to clavicle | Suspends scapula from clavicle |
Divided into two parts:
Conoid ligament – cone-shaped; from base of coracoid to conoid tubercle of clavicle.
Trapezoid ligament – broad; from upper surface of coracoid to trapezoid line of clavicle.
➡ Function: Prevents separation of clavicle from scapula during shoulder depression or heavy weight carrying.
Superiorly: Trapezius muscle.
Inferiorly: Supraspinatus and subacromial bursa.
Anteriorly: Deltoid.
Lateral supraclavicular nerve and nerve to subclavius (C5, C6).
From suprascapular and thoracoacromial arteries.
Small gliding and rotatory movements between acromion and clavicle.
Occur during:
Elevation & depression of scapula.
Protraction & retraction of shoulder.
Movement limited by coracoclavicular ligament; main movement transmitted to SC joint.
Strength of coracoclavicular ligament.
Partial articular disc acting as buffer.
Deltoid and trapezius forming a muscular roof.
Shoulder separation (AC dislocation):
Results from fall on shoulder.
Partial tear: AC ligaments only.
Complete tear: Both AC and coracoclavicular ligaments → prominent “step deformity” with clavicle displaced upward.
Degenerative arthritis:
Common in athletes and manual laborers due to repetitive load.
Clavicle (at SC and AC joints).
Scapula (gliding over thoracic wall — scapulothoracic movement).
| Movement | Plane / Axis | Muscles Involved |
|---|---|---|
| Elevation | Vertical (coronal) | Trapezius (upper fibers), Levator scapulae, Rhomboids |
| Depression | Vertical (coronal) | Pectoralis minor, Subclavius, Lower trapezius |
| Protraction (abduction of scapula) | Around vertical axis | Serratus anterior, Pectoralis minor |
| Retraction (adduction of scapula) | Around vertical axis | Middle trapezius, Rhomboids, Latissimus dorsi |
| Upward rotation of scapula | Around sagittal axis | Upper & lower trapezius, Serratus anterior |
| Downward rotation of scapula | Around sagittal axis | Levator scapulae, Rhomboids, Pectoralis minor |
Full abduction of upper limb (180°) requires combined movement at:
Glenohumeral joint (~120°)
Scapulothoracic movement (~60°)
→ Known as the scapulohumeral rhythm.
During elevation of limb, clavicle:
Elevates, rotates backward, and retracts slightly at SC joint.
These coordinated motions give shoulder its wide range of movement and stability.
Winged scapula: Paralysis of serratus anterior (long thoracic nerve lesion) → scapula projects posteriorly when pushing against wall.
Dropped shoulder: Injury to spinal accessory nerve → trapezius paralysis.
Painful arc syndrome: Limited elevation due to supraspinatus tendon impingement under acromion.
Place the cadaver prone; expose the posterior shoulder region.
Identify acromion process and lateral end of clavicle.
Reflect overlying trapezius and deltoid to expose the joint capsule.
Clean the superior and inferior acromioclavicular ligaments.
Identify and trace the coracoclavicular ligament:
Medial conoid part to conoid tubercle.
Lateral trapezoid part to trapezoid line.
Open the joint capsule; observe the fibrocartilaginous articular disc.
Move scapula to demonstrate gliding and rotation of acromion on clavicle.
Note relationship of supraspinatus tendon and subacromial bursa beneath the joint.
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