Common shoulder injury in young athletes | Direct fall onto the point of the shoulder | Graded by the Rockwood classification | Low grades treated nonoperatively, high grades debated
- Mechanism is a direct blow to the point of the shoulder with the arm adducted (a fall in contact sport or off a bike) - the force drives the acromion down and away from the clavicle
- The Rockwood classification (types I to VI) drives treatment: it is based on the direction and amount of clavicle displacement and which ligaments are torn
- Low-grade injuries (types I and II) are treated nonoperatively with a sling and early movement, and long-term outcomes are good despite some later radiographic changes
- High-grade injuries (types IV, V and VI) are generally treated surgically because the clavicle is grossly displaced (buttonholed posteriorly, markedly elevated, or driven downward)
- Type III is the real controversy: meta-analyses show no clear functional advantage for early surgery, so most are given a trial of nonoperative care, with surgery reserved for those who stay symptomatic
- “The acromioclavicular ligaments resist horizontal (anteroposterior) translation; the coracoclavicular ligaments resist vertical (superior) translation - know which fails in which grade
- “Always image and assess BOTH shoulders so you can compare the coracoclavicular distance - the clavicle does not rise, the arm and scapula drop under gravity
- “A type IV injury (clavicle buttonholed posteriorly through trapezius) is best seen on the axillary view - never forget the axillary radiograph
- “Counsel every patient that the cosmetic bump may persist even after good treatment - function, not appearance, is the goal
Clinical Imaging
Recognising and grading the injury on radiographs
The acromioclavicular (AC) ligaments resist horizontal (anteroposterior) translation; the coracoclavicular (CC) ligaments - conoid and trapezoid - resist vertical (superior) translation. Examiners love asking which fails in which grade, so anchor every answer on this.
The Rockwood classification (I to VI) is the framework for management. I and II are nonoperative, IV, V and VI are generally operative, and III is the controversy - learn the dividing lines, not just the list.
A type IV injury has the clavicle buttonholed posteriorly through the trapezius - it can look deceptively mild on the AP film. The axillary view is essential and is what reveals it. Always request it.
Grade by comparing the coracoclavicular distance with the normal side. Remember the clavicle does not truly "rise" - the arm and scapula sag under gravity, so weighted stress views are now largely abandoned.
Memory aids
ACDCRockwood Grades by Ligament Damage
Hook:Climb the ACDC ladder: AC sprain, Complete AC tear, Dislocation of both ligaments, then Catastrophic types IV to VI.
PSIDirections of Displacement (Types IV, V, VI)
Hook:The severe grades go in three directions - PSI: Posterior (IV), Superior (V), Inferior (VI).
BUMPWhat To Check On Examination
Hook:Examine the BUMP - Bump and tenderness, Up-down stability, Movement front-to-back, Provocation and skin.
Overview
The acromioclavicular joint is the small joint where the lateral end of the clavicle meets the acromion of the scapula. It is one of the few bony links between the arm and the axial skeleton, and it is injured surprisingly often - typically in young, active people who fall directly onto the point of the shoulder during contact sport, cycling, or a simple trip.
For the exam, the whole topic hangs on three ideas: the anatomy (two ligament groups controlling two directions of stability), the Rockwood classification (which grades the injury and decides treatment), and the management debate (low grades are easy - nonoperative; high grades are operative; type III is genuinely contested). Get these three threads clear and you can answer almost any question on this joint.
Anatomy and Biomechanics
The acromioclavicular joint is a plane synovial joint with a small fibrocartilaginous disc that degenerates from early adulthood. Its stability comes from two separate ligament groups, and understanding which controls which direction is the single most useful piece of knowledge in this topic.
| Structure | Where it runs | What it controls | When it fails |
|---|---|---|---|
| Acromioclavicular (AC) ligaments and capsule | Directly across the joint (superior part is the strongest) | Horizontal (anteroposterior) stability - stops the clavicle sliding front-to-back | Torn first - their loss allows the clavicle to translate backward (key in type IV) |
| Coracoclavicular (CC) ligaments - conoid and trapezoid | From the coracoid process up to the undersurface of the clavicle | Vertical (superior) stability - stops the clavicle riding upward | Torn in higher grades - their loss increases the coracoclavicular distance |
| Conoid (the medial CC ligament) | Posteromedial, cone-shaped | Main restraint to superior displacement and a key rotational control | Failure is central to the vertical instability of types III and above |
| Trapezoid (the lateral CC ligament) | Anterolateral, flatter | Resists axial compression and helps horizontal control | Contributes to instability as displacement increases |
| Deltotrapezial fascia | Muscle fascia draping over the joint and clavicle | Adds a final layer of soft-tissue restraint | Stripped only in the worst injuries - its loss permits gross displacement (types IV to VI) |
The practical message is that an injury progresses in a predictable order: first the AC ligaments (horizontal instability), then the CC ligaments (vertical instability and an increased CC distance), and finally the deltotrapezial fascia (gross displacement). This sequence is exactly what the Rockwood classification captures.
Pathophysiology
The injury is a mechanical failure of restraints in sequence, driven by a single force. A direct downward blow to the point of the shoulder (with the arm adducted) drives the acromion and scapula downward and medially while the clavicle, strutted against the sternum, stays put. The result is that the energy is concentrated across the acromioclavicular ligaments and then the coracoclavicular ligaments.
The failure cascade:
- Low energy stretches or partially tears the AC ligaments only - the joint stays reduced (type I) or subluxes a little (type II), and because the CC ligaments hold, the clavicle does not ride up.
- Higher energy completes the AC tear and then ruptures the CC ligaments - the clavicle loses its vertical restraint and the coracoclavicular distance increases (type III).
- The greatest energy also strips the deltotrapezial fascia, removing the last soft-tissue restraint and allowing gross, fixed displacement - posterior (IV), severe superior (V), or inferior (VI).
Because the clavicle is anchored medially at the sternoclavicular joint, the apparent "elevation" of the clavicle is really the arm and scapula dropping under the weight of the limb once the restraints fail - the basis for comparing both shoulders rather than relying on weighted stress views.
The late pathophysiology explains the chronic problems: a torn intra-articular disc and an unstable joint drive post-traumatic osteoarthritis and distal clavicle osteolysis, while a malreduced joint produces scapular dyskinesis and persistent pain even when the acute injury looked modest.
A common exam phrasing: "the clavicle is elevated." Strictly, the clavicle stays put and the weight of the arm pulls the scapula and shoulder downward, so the clavicle only appears to rise. This is why old weighted stress views were unreliable and are no longer routine - and why you always compare both sides on one film.
Classification (Rockwood)
The Rockwood classification divides acromioclavicular injuries into six types based on the direction and degree of displacement and which structures are torn. It expanded the older three-type Tossy system to capture the severe displacement patterns (types IV to VI).
Type I is an AC ligament sprain with no displacement and a normal radiograph - the joint is stable. Type II is a complete AC ligament tear with intact CC ligaments: the joint subluxes and the AC space widens, but the coracoclavicular distance stays near normal because the vertical restraint is preserved. Both are managed nonoperatively.
| Type | What is torn | Displacement | Usual treatment |
|---|---|---|---|
| I | AC ligaments sprained (not torn) | None - joint stable, radiograph normal | Nonoperative: sling, analgesia, early movement |
| II | AC ligaments torn, CC ligaments intact | Joint subluxed, slightly widened; CC distance near normal | Nonoperative: sling and rehabilitation |
| III | Both AC and CC ligaments torn | CC distance increased 25 to 100 percent versus the normal side | Controversial - usually a trial of nonoperative care first |
| IV | AC and CC torn; clavicle buttonholes posteriorly through trapezius | Posterior displacement - seen on the axillary view | Operative - displacement will not reduce itself |
| V | AC and CC torn plus deltotrapezial fascia stripped | Gross superior displacement - CC distance more than 100 percent of normal | Operative |
| VI | AC and CC torn; clavicle driven inferior (subcoracoid) | Very rare; clavicle lies below the coracoid | Operative |
Some surgeons split type III into IIIA (stable, asymptomatic with rehabilitation) and IIIB (symptomatic, dynamically unstable scapula) to help decide who might benefit from surgery - but the headline for the exam is simply that III is the grey zone between clearly nonoperative (I and II) and clearly operative (IV to VI).
Clinical Presentation and Examination
The typical patient is a young athlete who fell directly onto the point of the shoulder and now has pain, swelling, and often a visible step or bump at the lateral clavicle.
Direct fall onto the adducted shoulder (rugby, cycling, skiing). Pain localised to the top of the shoulder, worse with overhead and cross-body movements and when carrying a bag on that side.
A step deformity or prominent lateral clavicle (the more severe, the more obvious). Inspect the skin - tenting or threatened skin in a high-grade injury is an urgent surgical sign.
Tenderness directly over the joint. Test vertical stability (press the clavicle down - it springs back, the "piano-key" sign) and horizontal stability (anteroposterior translation), because horizontal instability pushes a borderline type III toward surgery.
Cross-body (cross-arm) adduction reproduces pain by compressing the joint. Scapular dyskinesis (an abnormally moving shoulder blade) suggests a dynamically unstable, symptomatic type III.
Investigations
Diagnosis is clinical and radiographic. The aims of imaging are to confirm the injury, exclude an associated fracture, and grade it accurately, because the grade decides treatment.
| View or test | What it shows | Why it matters |
|---|---|---|
| AP shoulder (both sides on one film) | The joint and the coracoclavicular distance, compared with the normal side | The mainstay - lets you measure the increase in CC distance that defines the grade |
| Zanca view (10 to 15 degrees cephalic tilt, reduced exposure) | A cleaner, less overpenetrated picture of the joint | The dedicated view for the acromioclavicular joint - removes overlap from the scapular spine |
| Axillary view | Anteroposterior position of the clavicle relative to the acromion | The only way to reliably detect the posterior displacement of a type IV |
| Weighted stress views | Displacement with a weight pulling the arm down | Largely abandoned - painful, often unhelpful, and the arm-drop concept makes them unreliable |
| MRI | Ligament detail and associated intra-articular or rotator cuff injury | Not routine; reserved for diagnostic doubt or to plan complex or chronic reconstruction |
If you remember only one investigation point: always look at (or ask for) the axillary view. A type IV injury can look modest on the AP film, and missing the posterior displacement of the clavicle means missing an operative injury. The Zanca view is the dedicated AP view for grading.
Management
Treatment is decided by the Rockwood grade, modified by the patient's symptoms, demands, and dynamic instability.
Low-grade injuries are managed nonoperatively and do very well. The plan is simple:
- Sling for comfort for a short period (days to a couple of weeks)
- Analgesia and ice early
- Early range-of-motion and a graded return to strengthening and sport
- Counsel that a small bump may persist and that late radiographic changes (distal clavicle osteolysis, ossification, mild degeneration) are common but usually do not cause symptoms
A small minority develop persistent pain from post-traumatic acromioclavicular arthritis or distal clavicle osteolysis, which can later be treated with a distal clavicle excision if injection and rehabilitation fail.
In a very high-grade injury (often a type V), the displaced clavicle can tent or threaten the overlying skin. Skin compromise risks an open injury and demands urgent surgical reduction rather than a wait-and-see approach. Always examine the skin over the prominent clavicle.
Complications
| Complication | When it happens | What to do |
|---|---|---|
| Persistent cosmetic bump | After any displaced injury, treated either way | Counsel beforehand - function is the goal, the bump often remains |
| Post-traumatic AC arthritis and distal clavicle osteolysis | Late, after low- and high-grade injuries alike | Injection and rehabilitation first; distal clavicle excision if it fails |
| Loss of reduction / recurrent deformity | After surgery, especially with suture-only constructs | A leading cause of revision - choose a construct matched to the injury |
| Hardware problems | Hook-plate erosion of the acromion; button or suture cut-out | Plan hook-plate removal once healed; counsel about implant-related reoperation |
| Fracture of clavicle or coracoid | Around drill tunnels for CC reconstruction | A recognised technical complication - careful tunnel placement and sizing |
| Infection | After operative treatment | The single commonest surgical complication - meticulous technique and counselling |
The key exam point is that surgery is not risk-free: the complication profile (infection, hardware problems, loss of reduction, and fractures around tunnels) is exactly why the evidence pushes toward nonoperative care for type III injuries that are settling.
Clinical Relevance
Acromioclavicular injuries are bread-and-butter for the shoulder, trauma, and sports clinics and a favourite viva topic because they test clear, structured thinking. In clinic the everyday task is grading the injury correctly and counselling a young athlete on a realistic recovery. In the viva the examiner will push you on the anatomy (which ligament controls which direction), on not missing a type IV (axillary view), and on the type III debate - where a candidate who quotes the evidence and offers a sensible "trial of nonoperative care, surgery for failures" plan stands out. Knowing which grade goes which way, and why, is the core that examiners probe.
Evidence
Operative Versus Nonoperative for Acute High-Grade Dislocations (Systematic Review and Meta-Analysis)
- Meta-analysis of 19 comparative studies, 954 patients with acute high-grade (Rockwood III to V) injuries
- No clinically meaningful difference in functional outcome scores (DASH; Constant difference small and likely not clinically significant)
- Surgery gave better cosmetic appearance and radiographic reduction
- Nonoperative treatment gave faster return to work and far fewer implant complications and infections
Surgical Versus Conservative Treatment of Rockwood Type III (Meta-Analysis)
- Meta-analysis of 10 trials specifically addressing Rockwood type III dislocations
- No significant difference between surgery and conservative care in pain, strength, post-traumatic arthritis, or functional scores (Constant, UCLA, DASH and others)
- Conservative care had less ossification of the coracoclavicular ligament and less distal clavicle osteolysis
- Surgery was better only at maintaining anatomic reduction
Operative Techniques for Acromioclavicular Reconstruction (Systematic Review and Meta-Analysis)
- 58 articles, 1704 patients across many reconstruction techniques (suture-button, TightRope, tendon graft, Weaver-Dunn)
- Overall failure (loss of reduction) rate 20.8 percent and overall complication rate 14.2 percent
- Commonest complications were infection (6.3 percent), coracoid or clavicle fracture (5.7 percent), and hardware or button failure (4.2 percent)
- No difference between open and arthroscopic techniques in loss of reduction, complications, or revision
Long-Term Outcome of Nonoperative Rockwood I and II Injuries (Cohort Study)
- Cohort of 75 patients with Rockwood I and II injuries, median follow-up about 7 years
- Good functional outcome: mean Constant score 88.6 in the injured shoulder versus 93.3 in the uninjured side (small, clinically minor difference)
- Radiographic changes were common - distal clavicle osteolysis in 31 percent and ligament ossification in 29 percent of injured shoulders
- These radiographic changes did not translate into clinically relevant loss of function
Exam Viva Scenarios
Practise clinical reasoning and management decisions out loud
“A 24-year-old rugby player fell onto the point of his shoulder and has a visible bump and tenderness over the lateral clavicle. The examiner shows an AP radiograph with the distal clavicle elevated and asks how you would classify and manage it.”
Framework: I would use the Rockwood classification, which grades these injuries from I to VI based on the direction and degree of displacement and which ligaments are torn. The acromioclavicular ligaments control horizontal stability and the coracoclavicular ligaments control vertical stability.
This film: An elevated distal clavicle with an increased coracoclavicular distance suggests at least a type III - both AC and CC ligaments are torn. I would confirm by comparing the coracoclavicular distance with the normal side on a bilateral film and add a Zanca view, and crucially an axillary view to exclude posterior displacement (type IV).
Management: Types I and II are nonoperative. For a type III I would start nonoperatively - sling, analgesia, and early structured rehabilitation - and reassess at a few weeks. Surgery is reserved for those who stay symptomatic, especially heavy manual workers or overhead athletes with horizontal instability or scapular dyskinesis. Types IV to VI are generally operative.
Counselling: I would warn him the cosmetic bump may persist whatever we do, and that the evidence shows no clear functional advantage to early surgery for a type III.
“A 38-year-old manual labourer has a grossly prominent clavicle after a motorbike crash, with the skin tented over it. The coracoclavicular distance is more than double the normal side. How do you proceed and what are the surgical options and risks?”
Recognition: Gross superior displacement with a coracoclavicular distance more than 100 percent of the normal side is a type V injury. The tented skin is a red flag - it threatens an open injury and pushes toward urgent surgical reduction rather than a trial of nonoperative care.
Assessment: Full trauma assessment first, then focused examination of the skin and neurovascular status, AP, Zanca and axillary radiographs, and consideration of CT or MRI if the picture is complex or chronic.
Surgical options: The aim is to reduce the joint and restore the coracoclavicular relationship. Options include coracoclavicular fixation or reconstruction (suture-button devices, suture loops, or tendon graft for anatomic reconstruction), a hook plate (effective but usually removed later because it can erode the acromion), and the modified Weaver-Dunn coracoacromial ligament transfer for chronic cases. Open and arthroscopic approaches give similar results.
Risks: I would counsel him that failure rates (loss of reduction) and complications are substantial - around a fifth lose reduction, and infection, fracture of the clavicle or coracoid around tunnels, and hardware problems all occur. There is no single best technique.
Anatomy
- AC ligaments resist horizontal (anteroposterior) displacement
- CC ligaments (conoid and trapezoid) resist vertical (superior) displacement
- Conoid is the main superior restraint; trapezoid resists axial compression
- Deltotrapezial fascia stripped only in the worst injuries (types IV to VI)
Rockwood Classification
- I - AC sprain, normal radiograph; II - AC torn, CC intact, subluxed
- III - both AC and CC torn, CC distance up 25 to 100 percent (controversial)
- IV - posterior (buttonholed through trapezius); V - superior over 100 percent
- VI - inferior (subcoracoid), very rare
Investigations
- AP both shoulders to compare coracoclavicular distance
- Zanca view - dedicated AP view of the joint
- Axillary view - essential to detect a type IV
- Weighted stress views largely abandoned; MRI only for doubt or planning
Management and Red Flags
- Types I to II nonoperative; types IV to VI operative; type III trial of nonoperative first
- No clear functional benefit from early surgery for type III (meta-analyses)
- Tented or threatened skin (often type V) means urgent surgery
- Surgery carries real risk - loss of reduction about 20 percent, infection commonest
Guidelines, Registries and Global Practice
- Consensus across regions is strongest at the extremes: types I and II are managed nonoperatively, and types IV, V and VI are managed operatively. This is reflected in major trauma and sports-medicine teaching worldwide (AAOS-aligned US practice, BOA/UK practice, and AO Foundation principles for the surgical constructs).
- Type III is where guidance differs, but the difference is one of threshold rather than principle. The pooled evidence (multiple meta-analyses) shows no clear functional advantage for early surgery, so most guidance now favours an initial trial of nonoperative care with surgery reserved for persistent symptoms - a position increasingly shared across the FRCS, FRACS, and ABOS curricula.
- The "type IIIA versus IIIB" refinement (stable and asymptomatic versus dynamically unstable and symptomatic) is used in many centres to select the minority of type III patients for surgery, particularly overhead athletes and heavy manual workers.
- Global practice variation in the surgical technique (hook plate versus suture-button versus tendon-graft reconstruction, open versus arthroscopic) largely reflects local expertise, implant availability, and cost rather than clear evidence that one is superior - the systematic-review data show comparable outcomes between open and arthroscopic methods.