AC Joint Separation
What Is an AC Joint Separation?
The acromioclavicular (AC) joint is the small joint at the top of the shoulder where the collarbone meets the shoulder blade. It’s held in place by a group of ligaments that can be stretched or torn when the shoulder absorbs a direct impact. Despite the name “separation,” this injury doesn’t involve the ball-and-socket joint itself — it’s specifically an injury to this smaller joint and its supporting ligaments at the top of the shoulder.
What Causes an AC Joint Separation?
- A direct fall onto the top or point of the shoulder, with the arm tucked at the side — the classic mechanism, common in cycling, skiing, and contact sports
- A fall onto an outstretched arm, transmitting force upward into the AC joint
- Direct contact or collision during sports
What Are the Symptoms of an AC Joint Separation?
- Pain localized to the top of the shoulder, directly over the joint
- Swelling and tenderness at the top of the shoulder
- In more significant injuries, a visible bump or step-off deformity, where the end of the collarbone appears to sit higher than the shoulder blade
- Pain with reaching across the body or lifting the arm overhead
- Discomfort when sleeping on the affected side
How Are AC Joint Separations Graded?
AC joint injuries are graded from I to VI based on how much the ligaments are damaged and how far the collarbone shifts out of its normal position:
- Grade I–II — mild to moderate sprain of the ligaments, without significant shifting of the bone
- Grade III — complete tearing of the main supporting ligaments, with noticeable but moderate displacement
- Grade IV–VI — more severe displacement, sometimes with the collarbone shifting behind or below its normal position
This grading system helps guide whether nonsurgical care or surgery is the more appropriate path.
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Treatment Options for an AC Joint Separation
Nonsurgical treatment is generally recommended for Grade I, II, and most Grade III injuries:
- A sling for comfort during the initial painful period
- Ice and anti-inflammatory medication
- Physical therapy to restore motion and strengthen the surrounding shoulder muscles
- Most patients regain excellent function, even though a cosmetic bump at the top of the shoulder may remain permanently
Surgery is more often considered for higher-grade injuries (Grade IV–VI), for Grade III injuries in patients with high physical demands who don’t respond well to nonsurgical care, or for chronic, painful separations that failed initial conservative treatment. Surgical treatment, called AC joint reconstruction, restores the ligaments that support the joint. Learn more on our AC Joint Reconstruction page.
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Dr. Palsis specializes in the treatment of knee, shoulder, and sports injuries.