Shoulder

AC Joint Injury / Separation

Name: AC Joint Injury / Separation
Creator: Dr. Kwang Lee

견봉쇄골 관절 손상

Traumatic disruption of AC joint ligaments causing superior clavicle displacement

Written and edited by Dr. Kwang Lee, D.C., L.Ac. · Updated 2026-10-04

How common: Common Sports Injury (10% of shoulder injuries)
Typical age: Ages 20–40

What is it?

Direct blow to shoulder tears AC then CC ligaments in sequence. Rockwood classification I–VI grades severity based on ligament damage and clavicle displacement.

Commonly affected: AC and CC ligaments (degree varies by Rockwood grade I–VI)

How it develops

Direct Shoulder ImpactFall onto shoulder: acromion is driven inferiorly while clavicle maintains position
AC Ligament TearGrade I–II: AC ligament sprained or torn; CC ligaments intact
CC Ligament DisruptionGrade III+: CC ligaments torn; distal clavicle displaces superiorly
Step-Off DeformityVisible and palpable prominence of distal clavicle above acromion

Symptoms

AC Joint Point TendernessExquisite tenderness directly over the AC joint (distal clavicle/acromion)
Step-Off Deformity (Grade III+)Visible superior displacement of distal clavicle — tenting of skin
Restricted Shoulder MovementPain with shoulder elevation and cross-body adduction
Piano Key Sign (Grade III+)Depressed distal clavicle springs back up — positive piano key sign

How it is examined

Cross-Body Adduction TestPassively adduct arm across chest — reproduces AC joint pain
Piano Key TestDepress distal clavicle — bounces back up = positive (Grade III+)
Rockwood GradingGrades I–VI based on CC distance widening and clavicle displacement on stress X-rays

Imaging

Bilateral stress X-rays (Zanca view) measure CC distance increase. Grade III: 25–100% increase; Grade IV–VI: complete displacement.

Superior clavicle displacement
Increased CC distance (vs. normal <13mm)
Determine Rockwood grade

MRI evaluates AC and CC ligament integrity, concurrent soft tissue injuries, and labral pathology.

AC/CC ligament signal abnormality
Joint effusion
Concurrent RC or labral pathology

Non-surgical care

Grade I–II: Sling + Ice + NSAIDsGrade I–II: arm sling 2–4 weeks, ice, NSAIDs — almost all resolve without surgery
Grade III: Conservative vs. Surgery (Controversial)Grade III: most treated conservatively with rehab; surgery for overhead athletes/manual workers

Conservative options are generally tried first. Medications listed here can have side effects — discuss them with your prescriber.

When surgery is considered

Grade IV–VI (complete displacement); Grade III in high-demand overhead athletes

Procedures that may be discussed

CC ligament reconstruction (TightRope/DogBone fixation)
Hook plate fixation (remove at 3 months)
Weaver-Dunn procedure

Outlook

Grade I–II: full recovery 6–8 weeks. Grade III conservative: 90% functional recovery. Grade IV–VI: require surgery.