What is an AC joint injury?
The acromioclavicular (AC) joint is the small joint at the top of the shoulder where the end of the collarbone (clavicle) meets the shoulder blade. Strong ligaments hold the two bones together.
An AC injury — often called a “shoulder separation” — happens when these ligaments are sprained or torn, usually by a fall directly onto the point of the shoulder. Injuries are graded from a mild sprain to a complete separation with an obvious step at the top of the shoulder.
Signs and symptoms
- checkPain at the top of the shoulder right over the joint.
- checkA visible bump or step in more significant separations.
- checkPain reaching across the body or lifting overhead.
- checkTenderness directly over the end of the collarbone.
Causes & risk factors
- A fall directly onto the point of the shoulder.
- Cycling and contact-sport collisions.
- A direct blow to the top of the shoulder.
- Reaching across the body under load, irritating an existing joint.
How it is diagnosed
The diagnosis is usually clear from the history and the appearance and tenderness of the joint. X-rays confirm the grade of separation and the position of the collarbone — sometimes taken while holding a weight to reveal the full extent.
Treatment options
Most AC injuries — even those with a visible bump — recover well without surgery.
Sling & rehabilitation
Lower-grade injuries settle with a short period in a sling, pain relief, and a graded return to movement and strength.
Reconstruction
High-grade separations, or persistent pain and weakness, may be treated by reconstructing the torn ligaments.
Many people are left with a small, painless step at the top of the shoulder after a separation. This is usually cosmetic — function and strength typically return regardless.
Recovery & outlook
Lower-grade injuries usually settle over a few weeks, with a return to sport once strength and comfortable overhead movement return. Surgical cases follow a protected, staged programme over a few months. The outlook is good, with most people regaining a strong, functional shoulder.