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Acromioclavicular (AC) Joint Injuries: Anatomy, Rockwood Classification, and Management

Anatomy

The AC joint is a diarthrodial joint between the lateral clavicle and the acromion. Stability is provided by:

  • AC ligaments (superior, inferior, anterior, posterior)—horizontal stability.
  • Coracoclavicular (CC) ligaments: Conoid (medial, vertical) + Trapezoid (lateral, horizontal)—vertical stability.
  • Joint capsule and intra-articular disc (often degenerative by age 40).

Injury Mechanism

Direct force to the adducted shoulder (fall on shoulder, hockey check, football tackle) drives the acromion inferiorly, tearing AC ligaments first, then CC ligaments progressively.

Rockwood Classification

TypeLigament InjuryDisplacementClinical Presentation
IAC sprainNoneTender AC joint, normal X-ray
IIAC torn, CC sprain<25% (clavicle ↑)Prominent clavicle, positive AC compression test
IIIAC + CC torn25–100% (clavicle ↑↑)Obvious step-off; debate: non-op vs. op
IVAC + CC torn + posterior displacementClavicle into trapeziusPain, posterior prominence; surgical
VAC + CC torn + deltotrapezial fascia stripped>100% (clavicle ↑↑↑)Severe tenting; surgical
VIAC + CC torn + clavicle inferior (subcoracoid/subacromial)Rare, high-energySurgical emergency

Diagnosis

  • Clinical: tenderness, step deformity, cross-body adduction pain, piano key sign (clavicle reducible).
  • X-rays: AP, Zanca view (10–15° cephalic tilt), bilateral weighted stress views for Type III decision-making.
  • MRI: if concomitant glenohumeral injury suspected (SLAP tear, rotator cuff).

Management by Type

Type I–II (Non-Operative)

  • Sling 1–2 weeks for comfort.
  • Ice, NSAIDs.
  • Physical therapy: ROM → scapular/rotator cuff strengthening → functional progression.
  • Return: 2–6 weeks (Type I), 6–12 weeks (Type II).
  • Residual prominence common; usually asymptomatic.

Type III (Individualized Decision)

  • Non-operative: Most adults do well; 6–12 week rehab. Persistent pain/dysfunction → late reconstruction.
  • Operative: Overhead athletes, heavy laborers, cosmetic concern, significant displacement. Acute anatomic reconstruction (dog bone, tightrope, suture button) or anatomic coracoclavicular reconstruction (allograft/autograft).

Type IV–VI (Operative)

  • Acute anatomic CC reconstruction + AC repair.
  • Open or arthroscopic-assisted.
  • Post-op: sling 6 weeks, protected ROM, progressive strengthening.

Chronic AC Joint Pain (Post-Traumatic Osteolysis, Arthritis)

  • Distal clavicle excision (Mumford procedure)—open or arthroscopic. 85–90% satisfaction rate.
  • Preserve CC ligaments to maintain stability.

Rehabilitation Principles (All Types)

  • Phase 1: Protect, pain control, pendulums, isometrics.
  • Phase 2: Full passive/active ROM (avoid cross-body adduction 8–12 weeks post-op).
  • Phase 3: Scapular stability, rotator cuff, deltoid, closed kinetic chain.
  • Phase 4: Plyometrics, sport-specific drills, throwing program.

Return-to-Sport Criteria

  • Pain-free full ROM
  • Strength ≥90% contralateral (isokinetic/dynamometry)
  • Functional tests: CKCUEST, seated shot put, Y-balance test
  • Psychological readiness

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