Etiology — what causes it

AC joint injury typically follows a direct fall onto the shoulder (acromion impact) or onto an outstretched arm. Degenerative AC arthritis is common with age and repetitive overhead loading.

Epidemiology — who gets it

AC sprain is common in contact sports (rugby, hockey, football) and cycling. AC osteoarthritis affects most adults over 50 to some degree on imaging.

Clinical signs

Point tenderness over the AC joint, positive cross-body adduction test, painful reach behind the back, positive O'Brien test (active compression — useful for both AC and labral pathology). Visible step deformity in higher-grade sprains.

Symptoms

Localized pain on top of the shoulder, worse with overhead and across-body reaching, lying on the affected side, and resisted compression of the joint. Higher-grade sprains may have visible deformity.

Best evidence for chiropractic treatment

Rockwood grading guides management. Grade I–II — conservative care with sling for comfort, then progressive scapular and shoulder loading. Grade III is increasingly managed conservatively with good outcomes (Korsten et al., BMJ). Grade IV–VI typically warrant surgical consultation. For osteoarthritis, load management, scapular control, and progressive loading are first-line; injection is a useful adjunct in selected refractory cases.

Subtypes

  • Rockwood I. Sprain without ligament rupture. Conservative care, return to play in 1–3 weeks.
  • Rockwood II. AC ligament rupture, CC intact. Conservative care typically, return in 4–6 weeks.
  • Rockwood III. AC and CC ligament rupture. Increasingly managed conservatively with good outcomes.
  • Rockwood IV–VI. Severe displacement. Surgical consultation typical.
  • AC osteoarthritis. Degenerative; conservative care is first-line, injection in selected refractory cases.

When to seek emergency care

Some symptoms need urgent medical attention — not a chiropractic visit. Call 911 or go to the nearest emergency department for: progressive limb weakness, loss of bowel or bladder control, saddle anesthesia (numbness in the groin/inner thighs), severe unrelenting pain unrelieved by position, signs of fracture after significant trauma, chest pain, stroke-like symptoms (face drooping, arm weakness, speech changes), or any rapidly worsening or unusual symptom.

Bottom line

Most AC joint problems respond to conservative care. Grade III is no longer automatic surgery — outcomes are often comparable with active rehab.