What it is
The acromioclavicular (AC) joint is where the outer end of the collarbone (clavicle) meets the top of the shoulder blade (acromion). Two sets of ligaments hold it together: the AC ligaments around the joint itself, and the stronger coracoclavicular ligaments just below it, which keep the collarbone from riding up.
An AC joint injury, often called a shoulder separation, usually happens from a fall or hit directly onto the point of the shoulder. It is common in football, hockey, rugby, lacrosse, wrestling, cycling and skiing. A separation is different from a shoulder dislocation, where the ball of the shoulder comes out of its socket.
The AC joint can also cause pain without a single injury. Like any joint, it can develop arthritis over time. In people who lift heavy weights, repeated pressing can stress the end of the collarbone and cause distal clavicle osteolysis, sometimes called weightlifter’s shoulder.
Grades of separation
Separations are graded from I to VI (the Rockwood classification) based on which ligaments are injured and how far the collarbone has moved.
- Grade I
A sprain of the AC ligaments. The joint stays in place.
- Grade II
The AC ligaments are torn and the coracoclavicular ligaments are sprained. The collarbone sits slightly higher.
- Grade III
Both sets of ligaments are torn. The end of the collarbone is noticeably raised, creating a visible bump.
- Grade IV
The collarbone is pushed backward, into or through the muscle at the back of the shoulder.
- Grade V
A more severe version of grade III, with a large gap and the overlying muscle attachments stripped away.
- Grade VI
Rare. The collarbone is pushed downward, beneath the front of the shoulder blade, usually after a high-energy injury.
Grades I and II almost always heal without surgery. Grade III is decided case by case. Grades IV to VI usually benefit from surgical repair.
AC arthritis & weightlifter’s shoulder
AC joint arthritis is wear of the cartilage in the joint. It can follow an old separation or develop with age and years of overhead or heavy use.
Distal clavicle osteolysis is a stress reaction at the end of the collarbone, seen most often in people who bench press, do dips or push-ups, or train heavy overhead lifts. The bone becomes irritated and starts to soften.
Both cause an ache right on top of the shoulder that is worse with pressing, reaching across the body or lying on that side.
Symptoms
- Pain on top of the shoulder, right over the end of the collarbone
- A bump at the top of the shoulder after a fall
- Swelling and bruising after an injury
- Pain reaching across your body or overhead
- Pain with bench press, push-ups or dips, or when lying on that side
- Clicking or popping at the top of the shoulder
Diagnosis
Diagnosis starts with a careful history and an examination. The AC joint is usually tender to touch, and bringing the arm across the body often reproduces the pain. X-rays show the position of the collarbone and grade a separation; an X-ray of the other shoulder is sometimes taken for comparison. MRI can show arthritis, bone irritation from osteolysis, or a related injury inside the shoulder. A numbing injection into the AC joint can help confirm that it is the source of pain.
Treatment options
Non-surgical
- A sling for comfort for a short time after an injury, then early, gentle motion
- Ice and anti-inflammatory medication when appropriate
- A guided physical therapy program to restore motion and strengthen the muscles that support the shoulder blade
- For weightlifter’s shoulder, changing how you train: a narrower grip, a shorter range of motion on pressing lifts, and pausing dips and push-ups while the joint calms
- A corticosteroid injection into the AC joint for arthritis or osteolysis
Surgical
- AC joint reconstruction. For high-grade separations (grades IV to VI) and selected grade III injuries, including those that stay painful or weak despite rehabilitation. The collarbone is brought back into position and held with strong sutures or fixation devices, often with a tendon graft to rebuild the torn coracoclavicular ligaments.
- Distal clavicle excision. For AC arthritis or osteolysis that does not improve with non-surgical care. A small amount of bone is removed from the end of the collarbone so the joint surfaces no longer grind, often through small arthroscopic incisions.
- Dr. Komperda will talk through whether surgery makes sense for your grade of injury, your sport or job, and your goals.
Recovery
- Low-grade sprains
Pain usually settles over a few weeks. Motion and strength are rebuilt with therapy, and you can return to sport as comfort and strength allow.
- After distal clavicle excision
A sling is used briefly for comfort and motion begins early. Lifting is reintroduced gradually over the following months.
- After reconstruction: first weeks
The arm is protected in a sling, typically for several weeks, while the repair heals.
- After reconstruction: return to sport
Therapy restores motion, then strength. Return to contact sports and heavy lifting usually takes several months.
Timelines are typical ranges, not guarantees. Recovery depends on the specific injury, the procedure, your health and your rehabilitation, and your plan is individualized.
Questions patients ask
Is a separated shoulder the same as a dislocated shoulder?
No. A separation is an injury to the AC joint at the top of the shoulder, where the collarbone meets the shoulder blade. A dislocation is when the ball of the shoulder comes out of its socket.
Will the bump go away?
In grade III and higher injuries, a bump often remains even after the shoulder feels and works well. A bump on its own is rarely a reason for surgery.
Can I keep lifting with weightlifter’s shoulder?
Often, yes, with changes to your training while the joint calms down. Pain that persists despite those changes may be helped by an injection or a distal clavicle excision.
When is surgery needed?
Most AC joint injuries do not need surgery. It is considered for high-grade separations, and for separations, arthritis or osteolysis that remain painful despite a dedicated course of non-surgical care.
This page is general patient education and is not a substitute for an in-person evaluation.