Acromioclavicular Joint Injury and Osteoarthritis

This page covers two different problems. Keep them apart in your head:

The illness script in one line: localised pain right on the AC joint, worst with cross-body reach and overhead — from a fall onto the shoulder in a young athlete, or from nothing in particular in an older adult.

The numbers that matter:

(General population: [1], prospective 4-year case series, n = 158. Athletes: [2], 162 injuries over 17,606 person-years.)

Days lost matters more than grade for a student's conversation: mean 10.4 days for a low-grade injury versus 63.7 days for a high-grade one (Pallis 2012).

⚠️ There is no clinical practice guideline for this pattern — Australian or international. No ACSQHC standard, no RACGP guideline, no AAOS or JOSPT CPG. Anchored to a physiotherapy-authored best-practice review [3] for conservative management of grades I–III, with the ESA–ESSKA Delphi consensus (Rosso et al. 2021) for classification. Both are older or lower-tier than the anchors elsewhere in CliniStudy, and you should say so.

Pattern > Label. The grade sets the conversation. It does not set the decision — §3.

Two pathways, two orders. Traumatic: MAIN PROBLEM → BODY CHART → HISTORY → BEHAVIOUR. Insidious: behaviour before history.

MAIN PROBLEM

Acute: what happened, and can they lift the arm. Insidious: the task — bench press, front rack, sleeping on that side, reaching across the body.

BODY CHART

• Localised, right on the joint. They point with one finger, and that is unusual enough in the shoulder to be informative.
• May refer over the trapezius and into the anterolateral deltoid.
• No referred pain below the elbow — and that is not just a screening question here, it's one of the five variables in the only validated cluster (see below).

HISTORY — the acute pathway

• Fall onto the point of the shoulder, or direct contact. 91% happen in sport; rugby, wrestling and ice hockey have the highest rates (Pallis 2012).
• Could they keep playing? Immediate deformity? Anything visible at the time?
• Age, sex and sport: mean age 39 in the general population, and men are injured roughly 7.6 times as often (Nordin 2020).

BEHAVIOUR

• Aggs: cross-body reach, overhead, bench press and dips, carrying, lying on that side.
• Eases: arm by the side, avoiding horizontal adduction.
• 24-hr: night pain on that side is common and often the presenting complaint.
• Irritability: vigour, severity, time to settle.

The only evidence-based subjective features

Almost everything taught about the ACJ subjective pattern is convention. The exception is a cluster validated against a fluoroscopically guided anaesthetic block in 153 consecutive primary-care shoulder-pain patients [4]. Four of its five variables are history items:

Two numbers worth carrying into §5: the cluster reached AUC 0.791 (95% CI 0.702–0.880), and only 22 of 153 (14%) of that primary-care population turned out to have the ACJ as their pain source at all.

SPECIAL / SCREENING QUESTIONS

General health, fever, recent infection or injection, immunosuppression, malignancy history, weight loss. See §4.

There is no study mapping ACJ pain referral from a controlled injection in healthy volunteers. The ACJ body chart you were taught is convention, not evidence. The cluster above is the part that has been tested.

The grade, and what it actually decides

Rockwood I–VI, from the source that defines all six [5]:

Horizontal stability comes from the AC ligaments; vertical stability from the coracoclavicular ligaments. The Zanca view is the most accurate view for the joint. The axial view is what separates type III from type IV — and an AP will not show you a posteriorly displaced clavicle.

The finding that should change how you use the grade

In 45 acute injuries read by six shoulder surgeons and six residents [6]:

Clinicians agree on what to do more than they agree on what it is. Surgeon experience made no difference. The classification is less reliable than the decision it is supposed to drive — which is a good reason to stop treating the number as the answer.

Where the controversy actually sits: grade III. Everything below II is conservative, everything above V is usually surgical, and III is contested in every source — sub-split by some into IIIA (stable, no overriding clavicle, no scapular dysfunction → non-operative) and IIIB (overriding clavicle plus therapy-resistant scapular dysfunction → consider reconstruction). Recent reviews report a shift toward non-operative management even for type V.

Jones' hypothesis categories that change your plan: precautions (type IV, and the septic joint), sources of symptoms (ACJ vs cuff vs cervical), and patient perspectives and demand — which, per §6, drives the decision more than the grade does.

The grade sets the conversation. Four other things set the decision.