Acromioclavicular Joint Dislocation

Incidence

• peak in 3rd decade
• Review 520 cases

Type	Number
I	185
II	119
III	204
IV	4
V	7
VI	1

Anatomy

• has fibrocartilage intraarticular disc
• Usually degenerative by 4th decade
• Clavicle may lie superior normally

Stability of ACJ

• Coracoacromial ligs
  • Primary restraint to sup translation
  • Primary suspensory ligament of upper limb
  • Trapezoid Ligament
    • Arises anterolateral on coracoid
    • Inserts trapezoid ridge anterolateral to conoid
    • Almost horizontal in sagittal plane
    • PRIMARY restraint to AXIAL compression
  • Conoid Ligament
    • Arises posteromedial to trapezoid
    • Inverted cone
    • Inserts conoid tubercle
    • Lies vertically
    • PRIMARY restraint to SUPERIOR & ANTERIOR translation
• ACJ Capsule
  • Strongest superiorly
  • As reinforced by acromioclavicular ligament
  • Has incomplete fibrocartilage intra-articular disc arising from it
  • Usually degenerates by 4th decade
• Deltotrapezial Fascia
  • Dynamic stabiliser

Motion at ACJ

• Only small 58 degrees
• 40 degrees at sternocla jt
• Motion is at scapulothoracic rather than ACJ

Classification

Allman grades I to III (1967), Rockwood modified (1989)

Classification of acromioclavicular joint dislocation

Type	Description	Ligament injury
I	ACJ sprain	Incomplete AC ligament injury
II	ACJ disrupted, CCL intact or sprained	Complete AC, incomplete CC
III	Rupture of ACJ and CCL (25 to 100% subluxation)	Complete AC, complete CC
IV	Into trapezius	Complete AC, complete CC
V	High dislocation, more than 1 x clavicle width (100 to 300% subluxation). Disrupted trapezius and deltoid, end of clavicle subcutaneous	Complete AC, complete CC
VI	Subcoracoid dislocation	Complete AC, complete CC

Original publication Allman Fl Jr. Fractures and ligamentous injuries of the clavicle and its articulation. J Bone Joint Surg Am. 1967;49(4):774-84.

Aetiology

• Direct trauma
  • Usually direct fall onto adducted shoulder
    • Clavicle remains in Normal position
    • Arm falls down
    • magnitude of force determines injury severity
• Indirect trauma
  • fall on flexed elbow or outstretched arm

Pathology

• AC ligaments provide horizontal stability, CC ligaments vertical stability
• Trapezoid ligament lies lateral and conoid ligament medial
• Injury progresses from AC ligaments to CC ligaments then deltotrapezial fascia
• Scapula and arm sag inferiorly, giving apparent clavicle elevation
• Type 4 displaces posteriorly through trapezius
• Type 6 subcoracoid displacement is rare

History

• History of Traumatic Event
• Age of patient
  • ? physeal injury
• Previous treatment
  • nonoperative
    • at least 3 months before considering surgery
  • previous surgical procedures
• Symptoms
  • Pain
    • with forward elevation
  • Instability
  • Posterior headache (nuchae)
• Associated injuries
  • distal clavicular fracture
• Functional disabilities

Examination

• Look
• Feel
  • tenderness
• Move
  • ROM
    • inability to lift arm
      • pain with forward elevation and wing out
  • Strength
• Special Tests
  • Stability
    • AP translation
    • Superior – inferior translation
  • Shoulder shrug
    • reduction of the distal clavicle with shoulder shrug differentiates between Type III from type V (distal clavicle buttonhole through deltotrapezial fascia)

Investigations

X-rays

Normal AC Joints

• 51% overriding clavicle
• 2% underiding
• 29% incongruent
• joint width 0.5-7 mm

Technique

• Zanca Views
  • AP shoulder with 10° cephalad tilt
• 1/3 Penetration of shoulder X-ray
• Axillary, outlet and AP views of shoulder in scapular plane
• Cross arm adduction view
  • AP shoulder
  • measure clavicle override
• Stress views occasionally used (10lb weight)

MRI

• labral injury masquerading as ACJ pain

CT Scan

• nondisplaced lateral clavicle or acromion fracture

Differential Diagnosis

• Cervical spine disease: trapezial spasm
• Thoracic outlet syndrome
• Scapular dyskinesis
• Hyperlaxity
• Coracoid fracture

Treatment

Type I

• Nonoperative
  • RICE
  • Broad arm sling
• Avoid heavy stress & contact sport till Free Range of Movement & no pain to palpation

Type II

• Nonoperative
  • RICE
  • Broad Arm Sling 2/52
• Avoid heavy lifting, contact sports 810/52 to allow ligament healing

Type III

• Controversial
  • Only 2 RCT OT vs NonOp
    • Pt outcome 88% satisfaction Op or NonOp
    • Further surgery 59% vs 6%
    • Deformity 3% vs 37%
    • ROM 86% vs 95%
• no indication for Operative reconstruction in literature to date
• Perhaps consider repair in
  • Heavy labourer
  • <25 yr undecided on career

Type IV, V, VI

• Operative
  • Open Reduction and Internal Fixation

Chronic Symptomatic Grade III

• Poor results excision distal clavicle
• Convert long high riding clavicle to short high riding clavicle
• Must reconstruct lig as well

Specific Procedures

• Weaver Dunn Reconstruction

Complications

• Joint stiffness
• Deformity
• CC ligament and soft tissue calcification
• AC OA
• Associated fractures
• Distal clavicle osteolysis

Prognosis

• Weaver Dunn Reconstruction

Complications

• Joint stiffness
• Deformity
• CC ligament and soft tissue calcification
• AC OA
• Associated fractures
• Distal clavicle osteolysis

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.