Overview

An acromioclavicular (AC) joint injury, often called a separated shoulder, happens when the small joint on top of your shoulder — where your collarbone meets your shoulder blade — is sprained or torn. It's different from a shoulder dislocation, even though people sometimes use the terms interchangeably. AC joint injuries are common in contact sports and falls, and most heal well without surgery (OrthoInfo).

What Is It?

The acromioclavicular (AC) joint is where the outer end of your collarbone (clavicle) meets a bony process on your shoulder blade called the acromion. This joint is held together by several ligaments, and an injury here — often from a direct fall onto the shoulder — can stretch or completely tear these ligaments.

Injuries are graded from Type I (mild sprain, ligaments stretched but intact) to Type VI (severe, ligaments completely torn with significant displacement), with Types I-III being the most common (StatPearls).

Anatomy Involved

The AC joint is stabilized by the AC ligaments directly around the joint, plus the coracoclavicular ligaments a short distance away, which anchor the collarbone to another part of the shoulder blade. More severe injuries typically involve both sets of ligaments.

What This Structure Normally Does

The AC joint allows your shoulder blade to rotate and adjust as you move your arm, helping coordinate movement between your collarbone and the rest of your shoulder complex. It's a small joint, but it plays an important role in smooth, full-range arm motion, especially overhead.

Common Causes

A direct fall onto the top or side of the shoulder
A direct blow to the shoulder, common in contact sports (football, hockey, rugby)
Falling onto an outstretched hand, which can transmit force up into the AC joint
Cycling accidents, a frequent cause given the fall pattern involved

AC joint injuries account for a substantial share of shoulder injuries overall, and the most common mechanism is a direct fall or blow to the top of the shoulder, which forces the shoulder blade downward relative to the collarbone, straining or tearing the stabilizing ligaments (StatPearls).

Risk Factors

Participation in contact or collision sports
Cycling, skiing, or other fall-prone activities
Previous AC joint injury
Activities involving falls onto the shoulder or outstretched arm

Common Symptoms

Pain and tenderness right on top of the shoulder
Visible bump or step deformity at the outer end of the collarbone (more noticeable in higher-grade injuries)
Swelling over the joint
Pain with reaching across the body
Weakness with overhead or reaching movements
A feeling of grinding or clicking within the joint

Seek immediate medical care if: there's a significant visible deformity or "step" at the top of the shoulder, severe swelling, numbness or tingling in the arm, or inability to move the shoulder after a fall or collision — these need prompt evaluation to rule out fracture or more severe ligament injury.

Pain Location

Pain is typically well-localized to the top of the shoulder, directly over the small bony bump where the collarbone meets the shoulder blade. It's usually easy to pinpoint with a finger, unlike deeper joint pain.

Pain Pattern

Pain is often sharp immediately after the injury and can remain quite tender to direct touch for days to a couple of weeks. It typically worsens with specific movements — especially reaching across the body — and improves with rest and support.

Movements That Commonly Hurt

Reaching across the body (like buckling a seatbelt on the opposite side)
Lifting the arm overhead
Lying on the affected shoulder
Carrying a bag over that shoulder
Any direct pressure or bump to the top of the shoulder

Activities That Become Difficult

Contact sports or activities with fall risk
Overhead lifting
Carrying a backpack or shoulder bag
Push-up or bench press style exercises
Sleeping on the affected side

Common Misconceptions

"AC joint injury and shoulder dislocation are the same thing." They're different — a dislocation involves the main ball-and-socket joint, while an AC injury affects the small joint on top of the shoulder where the collarbone meets the shoulder blade.
"A visible bump means I need surgery." Even with a visible bump from ligament injury, many Type I–III injuries are managed successfully without surgery.
"It's fully healed once the pain goes away." Ligament healing and full strength can take longer than pain resolution alone suggests, especially for higher-grade injuries.

What Usually Makes It Worse

Returning to contact sports or heavy lifting before adequate healing
Repeated direct pressure on the joint (e.g., carrying a heavy bag on that shoulder)
Skipping a period of protective support in more significant injuries
Reaching across the body repeatedly during the acute phase

What Usually Makes It Better

A short period of rest and support, often with a sling for higher-grade injuries
Ice to manage pain and swelling in the initial days
Gradual, guided return to movement and strengthening
Avoiding direct pressure on the joint while it heals

Self-Care Options

Rest and temporary sling support if recommended
Ice for 15–20 minutes several times a day in the first few days
Over-the-counter pain medication if appropriate for you
Avoiding direct pressure (like backpack straps) on the injured area
Gentle range-of-motion work once acute pain settles, to avoid stiffness

Conservative Treatment

Sling immobilization for a short period, typically 1–2 weeks for milder injuries
Physiotherapy to restore motion and rebuild shoulder strength
Gradual return to activity based on healing progress and injury grade
Manual therapy alongside a progressive exercise program

Type I and II AC joint injuries, and many Type III injuries, are generally managed successfully with conservative treatment, without needing surgery (OrthoInfo).

Medical Treatment Options

X-ray imaging to confirm the grade of injury and rule out fracture
Sling or brace support during initial healing
Corticosteroid injection for persistent pain in select cases
Surgical reconstruction of the ligaments for higher-grade injuries (Type IV-VI) or persistent symptomatic instability after conservative treatment

Recovery Timeline

Lower-grade AC joint sprains (Type I-II) often improve substantially within 2–6 weeks. Higher-grade injuries (Type III and above) can take 6–12 weeks with conservative care, or longer with surgical reconstruction. For a detailed breakdown, see the AC joint injury recovery timeline.

Returning to Work

Desk-based work often resumes within a few days to a week. Manual labor or contact-sport-related occupations may need 2–6 weeks or more, depending on injury grade and job demands.

Returning to Sport

Return to sport is typically graded based on injury severity — lower-grade injuries may allow return within 2–4 weeks once pain and strength allow, while higher-grade injuries or those requiring surgery often need 3–4 months before returning to contact sport, guided by strength testing and clearance from a healthcare provider.

Possible Complications

Persistent bump or visible deformity at the joint, even after healing (more common with higher-grade injuries)
Chronic AC joint pain or arthritis developing over time
Ongoing instability with higher-grade untreated injuries
Reduced overhead strength if not appropriately rehabbed

Prevention

Using proper technique and protective equipment in contact sports, along with maintaining good shoulder strength, can help reduce risk of AC joint injury. See General Shoulder Health and Posture for related guidance.

Frequently Asked Questions

Is a separated shoulder the same as a dislocated shoulder? No. A separated shoulder refers to injury of the small AC joint on top of the shoulder, while a dislocated shoulder involves the main ball-and-socket joint. They have different mechanisms and treatment approaches.

Will the bump on my shoulder go away? For milder injuries, swelling-related bumps often reduce over time. With higher-grade ligament injuries, a permanent small bump from the shifted collarbone position is common, even after full functional recovery.

Do I need surgery for an AC joint injury? Most lower-grade injuries (Type I-III) don't require surgery. Surgery is more often considered for higher-grade injuries or when symptoms persist despite conservative treatment.

How long should I wear a sling? This depends on injury grade, but a common initial period for milder injuries is around 1–2 weeks, transitioning to gradual movement as comfort allows.

Can I still work out with an AC joint injury? Lower-body and non-aggravating exercises can often continue. Upper body and overhead exercises are typically modified until pain and strength improve.

Will my shoulder be as strong as before? Most people regain excellent functional strength, especially with lower-grade injuries and a consistent rehab program.

Clavicle Fracture — a different injury from a similar fall mechanism, sometimes confused with a severe AC joint separation
Shoulder Dislocation — a different joint but sometimes confused with AC joint injury due to similar fall mechanisms
Shoulder Impingement Syndrome — can develop secondary to altered shoulder mechanics after AC joint injury
Shoulder Osteoarthritis — can develop in the AC joint years after an untreated or severe injury

References

StatPearls (NCBI Bookshelf). "Anatomy, Shoulder and Upper Limb, Acromioclavicular Joint." https://www.ncbi.nlm.nih.gov/books/NBK534803/
OrthoInfo (AAOS). "Acromioclavicular (AC) Joint Injuries (Separated Shoulder)." https://www.orthoinfo.org/en/diseases--conditions/acromioclavicular-ac-joint-injuries-separated-shoulder/

This information is for education only and is not a medical diagnosis. InjuryAtlas does not replace an assessment by a qualified health professional. If you have severe pain, visible deformity, numbness, loss of function, or symptoms that are getting worse, seek medical care promptly.

Acromioclavicular (AC) Joint Injury