Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

Acromioclavicular (AC) Joint

Definition

The acromioclavicular (AC) joint is the articulation between:

The acromion of the scapula
The distal clavicle

It is a synovial plane joint that permits small gliding movements.

Stability of the AC Joint

AC joint stability is maintained by two major ligament groups:

Acromioclavicular (AC) ligament
Coracoclavicular (CC) ligaments

1. Acromioclavicular (AC) Ligament

Location

Extends between the acromion and clavicle

Function

Provides horizontal stability
Controls anterior–posterior translation of the clavicle

2. Coracoclavicular (CC) Ligaments

Role

Primary stabilizers of the distal clavicle
Prevent superior displacement of the clavicle

Components

Conoid ligament (medial)
Trapezoid ligament (lateral)

Conoid Ligament

Location

Medial component

Insertion

Approximately 4.5 cm from the distal clavicle

Function

Prevents superior displacement of the clavicle

Trapezoid Ligament

Location

Lateral component

Insertion

Approximately 3 cm from the distal clavicle

Function

Resists compression and axial forces

Coracoclavicular (CC) Distance

Definition

Distance between:

Coracoid process
Inferior surface of clavicle

Normal Value

< 12 mm

Clinical Significance

Increased distance suggests AC joint injury

Coracoacromial Ligament

Anatomy

Extends between:
- Coracoid process
- Acromion

Key Point

Does not contribute to AC joint stability

Surgical Importance

Can be used for reconstruction
(e.g., Weaver–Dunn procedure)

Mechanism of Injury

Common Cause

Direct trauma to the shoulder

Typical Scenario

Fall onto the point of the shoulder

Pathophysiology

Downward displacement of the acromion leads to ligament injury

Classification of AC Joint Injuries (Rockwood Classification)

AC joint injuries are classified into six types:

Type I Injury

Pathology

AC ligament sprain
CC ligaments intact

Clinical Features

Pain over AC joint
No displacement

Treatment

Nonoperative

Type II Injury

Pathology

AC ligament rupture
CC ligaments intact

Clinical Features

Partial displacement
Mild increase in CC distance

Treatment

Conservative

Type III Injury

Pathology

AC ligament rupture
CC ligament rupture

Clinical Features

Superior displacement of clavicle (up to 100%)
Increased CC distance
Deformity is reducible

Treatment

Controversial
Usually nonoperative

Surgical Consideration

Athletes
Heavy laborers
Persistent symptoms

Type IV Injury

Pathology

AC and CC ligaments ruptured

Clinical Features

Posterior displacement of clavicle
Clavicle displaced into trapezius muscle

Imaging

Best seen on axillary view X-ray

Treatment

Surgical

Type V Injury

Pathology

Severe ligament disruption

Clinical Features

100% superior displacement
Markedly increased CC distance
Severe deformity (not reducible)

Treatment

Surgical

Type VI Injury

Pathology

Rare injury

Clinical Features

Inferior displacement of clavicle
Clavicle lies below acromion or coracoid
Associated with high-energy trauma

Treatment

Surgical

Pediatric Considerations

Important Concept

In children, apparent AC dislocations are often:

Distal clavicle physeal injuries

Term

Pseudodislocation

Features

CC ligaments remain attached
Periosteal sleeve is intact

Treatment

Usually nonoperative
Excellent remodeling potential

Clinical Examination

Common Findings

Pain over AC joint
Prominent distal clavicle
Shoulder deformity

Reducibility Test

Reducible deformity ? Suggests low-grade injury
Irreducible deformity ? Suggests high-grade injury

Radiographic Evaluation

Standard Views

AP view
Axillary view
Zanca view

Zanca View

Technique

10° cephalic tilt
Reduced X-ray penetration

Advantage

Better visualization of the AC joint

Treatment Principles

Two main approaches:

Nonoperative treatment
Operative treatment

Nonoperative Treatment

Indications

Type I
Type II
Most Type III injuries

Management

Sling (approximately 1 week)
Early range of motion exercises

Possible Outcomes

Residual clavicle prominence
Occasional pain
Mild arthritis

Operative Treatment

Indications

Type IV, V, VI injuries
Selected Type III cases:
- Athletes
- Manual laborers
- Chronic painful instability

Surgical Techniques

1. Coracoclavicular Ligament Reconstruction

Goal

Restore CC stability

Methods

Suture anchors
Button fixation
Sutures around coracoid

2. Hook Plate Fixation

Indication

Acute injuries

Limitations

Subacromial impingement
Hardware-related complications

3. Weaver–Dunn Procedure

Indication

Chronic AC dislocations

Steps

Distal clavicle excision
Transfer of coracoacromial ligament to clavicle

Often augmented with tendon graft

Chronic AC Dislocation (>4 Weeks)

Treatment

Tendon graft reconstruction

Common Grafts

Semitendinosus
Gracilis

Key Exam Points (Quick Revision)

Horizontal Stability

AC ligament

Vertical Stability

Coracoclavicular ligaments

CC Ligament Components

Conoid – medial
Trapezoid – lateral

Normal CC Distance

< 12 mm

Treatment Summary

Conservative

Type I
Type II
Most Type III

Surgical

Type IV
Type V
Type VI

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