AC Joint Injuries: Rockwood Classification and Operative Reconstruction for Grade IV-VI

Overview

Acromioclavicular (AC) joint injuries account for approximately 12% of shoulder girdle injuries and are especially prevalent in young, active males involved in contact and collision sports. The spectrum ranges from minor ligamentous sprain to complete dislocation with displacement of the distal clavicle into or through adjacent soft tissues. While low-grade injuries (Rockwood I-II) are universally managed non-operatively and grade III management remains contested, grades IV, V, and VI are generally accepted operative lesions requiring coracoclavicular (CC) ligament reconstruction.

Anatomy and Biomechanics

Static Stabilisers

Normal CC distance is approximately 11-13 mm; a >25% increase versus the contralateral side indicates CC ligament disruption. Complete dislocation can be seen with as little as a 25% increase in CC distance.

Dynamic Stabilisers

The deltoid and trapezius muscle origins from the distal clavicle are disrupted in grade V injuries (and partially in grade IV), contributing to marked superior displacement. The unopposed pull of the sternocleidomastoid muscle on the clavicle further exaggerates the deformity.

Biomechanical Principles of Reconstruction

Anatomic CC ligament reconstruction with a free soft-tissue graft (semitendinosus or anterior tibialis) more closely replicates the tensile stiffness and load-to-failure characteristics of the native conoid and trapezoid ligaments compared to non-anatomic techniques (e.g., classic Weaver-Dunn coracoacromial ligament transfer), which address vertical stability only and have inferior biomechanical properties.

$$\text{CC Distance Ratio} = \frac{\text{Injured CC distance}}{\text{Contralateral CC distance}} \times 100\%$$

• Ratio 25-100% → Grade III
• Ratio >100% → Grade V (combined with complete soft-tissue stripping)
• Posterior displacement without >100% superior displacement → Grade IV

Rockwood Classification

Key Radiographic Principles

• Zanca view (bilateral AC joints on one cassette, 10-15° cephalic tilt, ~50% reduced exposure): gold standard for CC distance measurement and percentage superior displacement; weights are not required for classification
• Axillary lateral view: essential for detecting posterior clavicle displacement in grade IV - diagnosis is routinely missed on AP imaging alone
• Stress views (weighted): rarely required; may help distinguish grade II from III in equivocal cases
• CT: indicated when coracoid process fracture is suspected (base or neck fractures mimic high-grade AC separation with CC ligaments attached to the coracoid fragment); delineates posterior displacement in grade IV; evaluates glenoid fracture extension (surgical threshold ≥5 mm articular displacement)
• CT angiography: indicated when vascular injury is suspected, particularly in grade VI high-energy injuries
• MRI: evaluates CC ligament integrity, deltotrapezial disruption, and concomitant glenohumeral pathology; not routine pre-operatively unless a significant rotator cuff tear is clinically suspected or persistent shoulder dysfunction is disproportionate to the AC injury

Clinical Assessment

History

• Direct blow to the lateral shoulder with the arm adducted (most common mechanism)
• Fall from bicycle, contact sport collision, or occupational injury
• Grade VI: extreme abduction and external rotation with scapular retraction; high-energy polytrauma
• Symptoms: shoulder droop, visible deformity, inability to elevate the arm, localised AC joint pain

Physical Examination

Associated Injuries

• Concomitant glenohumeral pathology in up to 53% of high-grade separations: predominantly articular-sided rotator cuff tears and SLAP lesions; advancing age is the dominant predictor
• High-energy mechanisms (especially grade VI): exclude pneumothorax, rib fractures, brachial plexus neurapraxia, and vascular injury
• Coracoid base/neck fractures, distal clavicle fractures, and (in patients <30 years) medial clavicular physeal injuries may co-exist with high-grade AC separations

Non-operative Management

Immobilisation devices for non-operative treatment include slings, adhesive tape strappings, braces, harnesses, and plaster casts; a simple sling is the most widely applied contemporary method. The principle is to support the weight of the upper extremity to reduce stress on the ligaments. Ice and analgesia during the first week are followed by periscapular strengthening, avoiding heavy lifting and contact sports during the strengthening phase.

For grades I and II, long-term outcomes at 8-10 years demonstrate no significant functional impairment or progressive arthritis compared to the contralateral side.

Grade III management remains controversial. Current evidence does not demonstrate superior functional outcomes for acute surgical treatment versus non-operative management at 12 months; the literature suggests the need for reoperation is higher among patients treated immediately with surgery than among those who undergo primary surgery after failed non-operative treatment. A small subgroup of young, high-level overhead athletes or heavy manual labourers may be offered acute reconstruction given the potential for altered scapular kinematics. The key principle is that patients who fail 3-6 months of supervised non-operative treatment retain excellent results with delayed reconstruction.

Operative Management

Indications

Polytrauma patients with AC joint injuries have demonstrably worse shoulder functional outcomes, supporting a lower threshold for operative management in this group.

Surgical Goals

1. Anatomic reduction of the AC joint
2. Restoration of CC ligament function (vertical and horizontal stability)
3. Repair of the deltotrapezial fascia (mandatory in grades IV-VI)
4. Distal clavicle resection in chronic cases (typically >6 weeks) to address AC arthrosis

Evolution of Surgical Techniques

Anatomic Coracoclavicular Ligament Reconstruction

This is the contemporary standard. Key examination points:

Graft options:

Critical technical principles (high-yield viva points):

• Tunnels are placed through the coracoid base and the distal clavicle at positions corresponding to the footprints of the native conoid (posteromedial) and trapezoid (anterolateral) ligaments
• Excessive medialisation of clavicular tunnels is associated with a significantly higher failure rate - this is the single most important technical error to avoid
• The coracoid tunnel carries a risk of coracoid fracture; minimising tunnel number and diameter reduces this risk
• Backup CC stabilisation (suture tape, TightRope-type device, or supplemental fixation) is usually required for a successful outcome and protects the graft during biological incorporation
• The deltotrapezial fascia must be repaired to restore dynamic stability
• In chronic cases, the distal clavicle is often resected and the coracoacromial ligament may be transferred to the distal clavicle (modified Weaver-Dunn); backup CC stabilisation remains necessary
• Distal clavicle resection alone in a dislocated AC joint worsens instability; CC stabilisation is mandatory

Hook Plate

• Provides rigid fixation acutely for grades IV-V
• The hook sits in the subacromial space posterior to the AC joint
• Mandates a planned second operation for plate removal (typically 3-6 months) to prevent subacromial impingement and acromion erosion
• Supported by retrospective studies, a biomechanical study, and operative results of an RCT
• May be combined with anatomic ligament reconstruction

Arthroscopic-Assisted Reconstruction

• Allows simultaneous treatment of concomitant glenohumeral pathology (SLAP tears, rotator cuff lesions)
• Benefits: preservation of deltotrapezial fascia, less soft-tissue disruption, faster recovery, less pain
• Technique: subcoracoid visualisation, ACL-guide-assisted tunnel drilling through coracoid and clavicle, CC fixation with suture tape or graft loops
• Associated glenohumeral injuries found in up to 53% of high-grade separations; however, current evidence does not support routine pre-operative MRI arthrogram or mandatory intervention for concomitant pathology unless a significant rotator cuff tear is clinically suspected
• Significant learning curve; complication profile not inferior to open techniques

Complications

Outcomes

• Acute non-operative management of grade III demonstrates equivalent or superior early functional scores versus acute surgery, with no functional difference at 12 months
• Need for reoperation is higher after immediate acute surgery than after initial non-operative treatment followed by delayed reconstruction
• A small but persistent proportion (~10-20%) of non-operatively managed grade III-V injuries are symptomatic and require delayed reconstruction; this group retains excellent outcomes with delayed surgery
• Anatomic reconstruction with semitendinosus autograft demonstrates superior clinical and radiological outcomes compared to modified Weaver-Dunn in prospective comparative studies
• Polytrauma patients with high-grade AC injuries have worse outcomes by both disease-specific and general health measures, supporting lower operative thresholds
• Overall failure (~21.8%) and complication (~14.2%) rates remain relatively high across all techniques; no single technique has demonstrated clear superiority in high-quality prospective trials

Paediatric Considerations

• True AC ligamentous dislocation is uncommon in skeletally immature patients; equivalent force more commonly produces a physeal injury (Salter-Harris I or II) through the distal clavicular physis, as the physis is weaker than the ligament complex
• The AC and CC ligaments may remain intact with the clavicle displacing through the periosteal sleeve - the radiographic appearance may simulate a high-grade AC dislocation ("pseudodislocation")
• Most pseudodislocations remodel with non-operative management; the intact periosteal sleeve facilitates bone regeneration
• In adolescents approaching skeletal maturity, true ligamentous disruption can occur; management mirrors adult principles
• Concomitant medial clavicular physeal injury has been reported in patients <30 years with posterior AC dislocation and may require open reduction of the epiphyseal fracture to facilitate AC joint reduction

Management Summary