AC Joint Injuries — Rockwood

Acromioclavicular (AC) joint injuries are common, particularly in young active males involved in contact sports or cycling. They range from minor sprains to complete dislocations with significant displacement. Understanding the anatomy, classification, and evidence-based management is essential for appropriate surgical decision-making.

• AC joint injuries account for approximately 9% of all shoulder girdle injuries; more common in males (5:1 ratio)
• Mechanism: most commonly a direct fall onto the tip of the shoulder with the arm adducted — drives the acromion inferiorly while the clavicle remains supported by the SC joint and surrounding musculature
• AC joint ligaments: superior and inferior AC ligaments — primary restraints to AP translation of the AC joint; relatively weak
• Coracoclavicular (CC) ligaments: conoid (posteromedial, larger) and trapezoid (anterolateral) — primary restraints to vertical displacement; CC ligament disruption = Type III or higher injury
• Normal CC distance: 11–13 mm; increase >50% compared to contralateral side = CC ligament disruption
• Deltotrapezial fascia: fascia investing deltoid and trapezius over the clavicle — disruption leads to dynamic instability; its integrity determines whether Type III injuries behave as stable or unstable
• AC joint horizontal (AP) stability is distinct from vertical stability — some high-grade injuries have significant horizontal instability even after vertical reduction

The Rockwood classification (1998) extends the original Tossy classification from 3 to 6 types and is the universally accepted system.

• Types I and II = conservative; Types IV, V, VI = operative; Type III = controversial
• Type IV: clavicle buttonholed through trapezius — often only identifiable on axillary lateral view; clinically the clavicle appears prominent but does not reduce with arm elevation
• Type VI: rarest; associated with brachial plexus and vascular injuries due to high-energy mechanism

• Clinical exam: AC joint tenderness; step deformity; cross-body adduction pain; O`Brien active compression test positive; horizontal instability assessed with AP stress of clavicle relative to acromion
• Zanca view: 10–15° cephalic tilt AP X-ray of AC joint — reduces overlap of spine of scapula; standard view for AC joint assessment — reduces radiation by 50% compared to standard AP shoulder
• Bilateral stress views: weighted (10 lb) or non-weighted AP views of both AC joints — quantify CC distance increase; >50% increase = Type III; >100% = Type V
• Axillary lateral view: mandatory — identifies posterior displacement (Type IV) which is missed on AP views
• MRI: not routinely required; useful for associated injuries (rotator cuff, labrum), CC ligament integrity, and planning reconstruction
• CT: rarely needed; useful for Type IV with bony injury or complex AC joint pathology

The management of Type III AC joint injuries remains one of the most debated topics in shoulder surgery. Multiple RCTs have failed to demonstrate consistent superiority of surgery over conservative management.

• Conservative management first: sling for 2–3 weeks; physiotherapy targeting periscapular strengthening and rotator cuff rehabilitation; most patients achieve satisfactory function within 3–6 months
• ISAKOS consensus: initial conservative management for Type III; surgery recommended for: manual labourers, overhead athletes, failed conservative treatment at 3 months, and demonstrable horizontal instability
• Approximately 20–30% of Type III injuries treated conservatively develop chronic pain or functional limitation requiring late surgical reconstruction
• Horizontal instability in Type III injuries predicts worse conservative outcomes — assess preoperatively with stress AP radiograph and clinical examination
• Late reconstruction (after 3 months) outcomes are comparable to acute repair in most series — reassure patients that delayed surgery is not inferior

Numerous techniques have been described. Contemporary approaches focus on anatomic CC ligament reconstruction with tendon graft augmented by synthetic devices, rather than the previously used non-anatomic procedures.

• Hook plate: reliable acute fixation; mandatory removal at 3–4 months — subacromial impingement, rotator cuff erosion, and hook fracture if left in situ
• Anatomic CC reconstruction with tendon graft: preferred for delayed reconstruction and revision — recreates conoid and trapezoid ligaments separately in their anatomic positions
• Distal clavicle excision: indicated for AC joint OA or when joint is degenerate — preserves CC ligament complex; do not resect if CC ligaments intact and needed for stability
• Deltotrapezial fascia repair: critical in Type V injuries — must repair at time of reconstruction to restore dynamic stability; failure to repair leads to persistent instability

• Horizontal instability assessment: under-recognised component of AC joint injury; horizontal instability predicts worse conservative outcomes and surgical failure if not addressed; reconstruct both vertical (CC) and horizontal (AC ligament) components in high-grade injuries
• Type IV diagnosis requires axillary lateral view — posterior displacement is not visible on AP; commonly missed clinically; examine for loss of normal posterior clavicular contour and inability to reduce with arm elevation
• Coracoid tunnel fracture: recognised complication of CC reconstruction with synthetic devices (TightRope, Dog-Bone) — particularly with narrow coracoid base; overly medial tunnel placement increases risk; use larger devices and place tunnel in widest part of coracoid base
• Revision AC reconstruction: challenging — assess bone stock at coracoid and clavicle; anatomic tendon graft reconstruction is the preferred revision option; consider coracoclavicular interval bone grafting if significant bone loss at tunnel sites
• Return to contact sport: typically 3–4 months after reconstruction; protecting the reconstruction during the healing phase is critical — no heavy lifting or contact for minimum 12 weeks; graft maturation takes 6–12 months

• Types I and II = conservative; Types IV, V, VI = surgery; Type III = controversial (conservative first)
• CC ligament disruption begins at Type III — CC distance >50% increase vs contralateral
• Conoid ligament = posteromedial, larger; trapezoid = anterolateral — both must be reconstructed in anatomic reconstruction
• Zanca view (10–15° cephalic tilt): best plain X-ray for AC joint; reduces radiation by 50%
• Axillary lateral view: essential — identifies Type IV (posterior displacement) missed on AP
• Hook plate = mandatory removal at 3–4 months; leaving in causes subacromial impingement and rotator cuff erosion
• Weaver-Dunn: non-anatomic; high failure rate for high-grade injuries — anatomic CC reconstruction now preferred
• Type VI: clavicle inferior to coracoid; associated with brachial plexus injury — high energy
• Deltotrapezial fascia repair: critical in Type V — must repair at reconstruction for dynamic stability
• Type III + horizontal instability or manual labour / overhead athlete = relative indication for surgery