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I: sprain; II: AC torn, CC intact; III: AC+CC torn with superior displacement. IV: posterior displacement; V: marked superior displacement; VI: inferior displacement (rare). I–II non-op; III individualized; IV–VI require surgery.
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Acromioclavicular (AC) joint injuries are among the most common shoulder injuries, accounting for approximately 9% of all shoulder girdle injuries and up to 40% of shoulder injuries in contact athletes (rugby, football, American football, ice hockey). They range from simple ligament sprains to complete dislocations with wide displacement of the clavicle relative to the acromion. The Rockwood classification (1984), developed by Charles Rockwood and expanded from the original Tossy (1963) three-type system, divides AC joint injuries into six types based on the degree of clavicular displacement, the direction of that displacement, and the integrity of the various stabilising structures. This classification directly guides management — from conservative for Types I–III to operative for Types IV–VI — and remains the universal standard for AC joint injury description.
| Type | AC Ligaments | CC Ligaments | Deltotrapezial Fascia | Clavicular Displacement | Radiological Findings | Management |
|---|---|---|---|---|---|---|
| Type I — Sprain | SPRAINED (microscopic tears; ligament intact) | INTACT | Intact | None — clavicle in normal anatomical position | Normal X-ray; CC distance normal; AC joint space normal; tenderness on palpation over the AC joint but no radiological abnormality | NON-OPERATIVE — arm sling for comfort; ice; NSAIDs; physiotherapy after pain settles (1–2 weeks); return to sport 1–2 weeks; excellent prognosis |
| Type II — Disruption | RUPTURED (complete tear of AC ligaments) | SPRAINED (intact but partially stretched) | Intact | MINIMAL — the clavicle is slightly elevated (CC ligaments still intact and partially restrain upward displacement); the AC joint space is slightly widened | Slight widening of the AC joint space (<50% elevation of the clavicle relative to the acromion); CC distance slightly increased (<25% increase compared to normal side); the `step` deformity is minimal; stress views (gravity stress — the patient holds a weight in the hand to stress the AC joint) may help differentiate Type II from Type III | NON-OPERATIVE — arm sling for 1–2 weeks; physiotherapy; return to sport 2–4 weeks; same management as Type I but slightly longer recovery; excellent prognosis; no operative intervention required |
| Type III — Complete dislocation | RUPTURED | RUPTURED (complete tear of both trapezoid and conoid) | INTACT but stretched | SUPERIOR displacement of the clavicle (100% displacement — the clavicle is displaced SUPERIORLY by 100% of the clavicular width); the CC interspace is increased by 25–100% compared to the normal side; the acromion descends while the clavicle remains at its height (the `piano key sign` — the distal clavicle can be pressed inferiorly but springs back up when released) | The CC distance is increased (25–100% increase over normal); the AC joint is completely separated; the clavicle appears elevated on the AP shoulder X-ray; gravity stress views confirm the complete CC ligament disruption by showing further widening; compare the CC distance bilaterally | CONTROVERSIAL — the management of Type III AC joint dislocations remains the most debated topic in shoulder surgery; current evidence: most patients achieve satisfactory functional outcomes with non-operative management (3–6 weeks in a sling ± strapping, then physiotherapy); OPERATIVE management (various CC ligament reconstruction techniques or AC joint stabilisation — hook plate, Tight-Rope/ZipTight suture button, CC ligament reconstruction with allograft/autograft) is reserved for: (1) high-demand overhead athletes requiring early return to sport; (2) manual workers; (3) patients with persistent pain and dysfunction at 3 months; (4) type III with significant cosmetic concern; the AAOS and BSSH recommend non-operative as first-line for Type III; operative is NOT routinely indicated |
| Type IV — Posterior clavicle | RUPTURED | RUPTURED | DISRUPTED (clavicle buttonholes through) | POSTERIOR displacement — the distal clavicle is displaced POSTERIORLY through or into the trapezius muscle; the clavicle buttonholes through the trapezius fascia; this is ALWAYS an operative indication because: (1) the trapezius prevents spontaneous reduction; (2) the posteriorly displaced clavicle may compress the brachial plexus or subclavian vessels; (3) closed reduction almost never succeeds due to the trapezius interposition | On AP X-ray, the AC joint appears relatively normal (the posterior displacement is not obvious on AP view); the axillary lateral or `Y` view shows the posterior clavicular displacement; CT is the best investigation to confirm posterior displacement and rule out neurovascular compromise | OPERATIVE — surgical reduction and stabilisation; the clavicle must be extracted from the trapezius; stabilise with CC reconstruction (suture button / hook plate) or AC joint plate; the posterior displacement is the operative indication regardless of the patient`s age or activity level |
| Type V — Gross superior displacement | RUPTURED | RUPTURED | COMPLETELY STRIPPED (the deltoid and trapezius are stripped off the distal clavicle and acromion) | GROSS SUPERIOR displacement — the clavicle is displaced superiorly by >100% of the clavicular diameter (>100% superior displacement compared to the contralateral side); the CC interspace is increased by 100–300% compared to normal; the entire distal clavicle rides above the deltotrapezial fascia | The CC distance is dramatically increased (>100% increase over normal); the clavicle is grossly elevated and the shoulder hangs inferiorly; the `tenting` of the skin by the elevated clavicle may be obvious on inspection; distinguish from Type III by the degree of CC widening (>100% widening = Type V) | OPERATIVE — surgical reconstruction is required for all Type V injuries; the massive soft tissue stripping means that non-operative management produces unacceptable functional results; CC ligament reconstruction (suture button / modified Weaver-Dunn / Clavicular hook plate) + deltotrapezial fascia repair |
| Type VI — Inferior clavicle | RUPTURED | RUPTURED | DISRUPTED | INFERIOR displacement — the distal clavicle is displaced INFERIORLY; it may lodge sub-acromial (behind the acromion and above the coracoid) or sub-coracoid (behind the coracoid process); this is extremely rare and results from very high-energy trauma (direct superior blow on the distal clavicle driving it inferiorly); associated brachial plexus and neurovascular injuries are common | The clavicle appears BELOW the acromion or below the coracoid on AP view (the opposite of all other types where the clavicle is elevated); a truly diagnostic X-ray is the rare abnormality of a clavicle that appears INFERIOR to its normal position; CT confirms the inferior position and associated injuries | OPERATIVE — always operative; the inferior position makes the clavicle irreducible by closed means (it is trapped under the acromion or coracoid); neurovascular assessment and repair if injured; stabilisation after reduction; this is the rarest and most dangerous Rockwood type |
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