The AC joint — acromioclavicular joint — is where the outer end of your collarbone meets the top of your shoulder blade. It's small, sits right under the skin, and takes a beating any time you fall onto the point of your shoulder or take a direct hit to the top of it. Hockey players, cyclists, snowboarders, and anyone who's been in a car accident have often torn the ligaments that hold this joint together.
The grading system
AC sprains are graded I through VI, but the ones you'll actually see clinically are:
- Grade I — mild ligament stretch, pain but no visible deformity
- Grade II — partial ligament tear, slight bump on top of shoulder, moderate pain
- Grade III — complete tear of the AC and coracoclavicular ligaments, obvious step-off deformity (the "piano key" sign)
Grades IV-VI are severe displacements and usually go to surgery.
What to do in the first two weeks
Sling for comfort — usually 1-2 weeks, not longer. Ice regularly. Avoid overhead lifting and cross-body movements. Most importantly, keep the elbow, wrist, and hand moving to prevent stiffness downstream.
The rehab that actually restores function
After the acute phase, we introduce scapular stabilization work (the muscles around your shoulder blade), rotator cuff strengthening, and progressive loading in ranges the joint tolerates. Manual therapy of the thoracic spine and rib cage restores the overhead mechanics that get shut down after any shoulder injury.
The lump usually stays
For grade II and III sprains, the visible bump on top of the shoulder often remains permanently — the ligaments heal in a slightly stretched position. This is cosmetic. Function typically returns fully with proper rehab, and most patients (even grade III) do just as well non-surgically as surgically.
If your shoulder is still weak, painful in overhead motion, or clicking three months after injury, come in for a full assessment. AC joint sprains that don't rehab properly often lead to compensatory rotator cuff and scapular issues down the road.