AC Joint Sprains (Shoulder Separations)

A "separated shoulder" sounds dramatic, and the name causes real confusion. Patients often hear it and picture the shoulder having come out of its socket — a dislocation. It is a different injury entirely. A shoulder separation is a sprain of the acromioclavicular joint, the small joint at the very top of the shoulder where the collarbone meets the highest point of the shoulder blade. It has nothing to do with the ball-and-socket joint below it. Understanding the distinction, and how these injuries actually behave, takes most of the fear out of a common and generally manageable problem.

AC joint sprain versus dislocation: what's the difference?

The acromioclavicular (AC) joint is where the lateral end of the clavicle articulates with the acromion of the scapula, held together by the AC ligaments and the nearby coracoclavicular ligaments.¹ An AC joint sprain — the "separation" — is an injury to those ligaments. Depending on severity, the joint may be mildly stretched or fully disrupted so the collarbone rides up relative to the shoulder blade.

A glenohumeral dislocation, by contrast, is the ball of the upper arm coming out of the shoulder socket. Same shoulder region, completely different structure and management. When people say "shoulder separation," they mean the AC joint. When they say "dislocated shoulder," they usually mean the glenohumeral joint. Getting this straight matters, because the two are treated nothing alike.

How it happens

The classic mechanism is a direct fall onto the point of the shoulder with the arm tucked at the side — a hockey player driven into the boards, a cyclist over the handlebars, a football or rugby tackle. The force drives the acromion down and away from the clavicle, straining or tearing the ligaments that hold the joint together.² A fall onto an outstretched hand can also transmit force up into the joint. Because of that contact-sport mechanism, AC sprains are among the more common shoulder injuries we see in Winnipeg athletes through hockey and football season.

Grades of AC joint injury

AC injuries are graded by severity, most commonly using the Rockwood classification, which runs from type I through type VI.³ A simplified picture:

• Type I: a mild sprain of the AC ligaments without displacement. Tender, sore, but the joint is stable.
• Type II: the AC ligaments are torn and the coracoclavicular ligaments are sprained; slight displacement, often a small bump.
• Type III: both ligament complexes are disrupted, producing a more obvious step deformity at the top of the shoulder.
• Types IV to VI: higher-energy injuries with significant displacement of the clavicle, which more often prompt surgical consultation.

The visible bump that sometimes remains after a higher-grade injury is a cosmetic change, not necessarily a functional problem — many people recover full, painless function while keeping the bump for good.

How most AC sprains are managed

Here is the reassuring part. The large majority of AC injuries are low grade — types I and II — and these do well with non-surgical, rehab-led care.⁴ Even type III injuries are frequently managed non-operatively, with outcomes broadly comparable to surgery for many patients. Early management focuses on settling pain and protecting the joint briefly; the more important phase is a progressive return to loading.

The rehab arc is straightforward in principle: restore comfortable range of motion, then progressively load the shoulder and the muscles that stabilize the scapula, building toward the demands of the person's sport or work. This is where our guiding principle applies directly — there are no bad exercises, only too much too soon.⁵ The goal is not to protect the shoulder indefinitely but to reintroduce load at a pace the healing joint can handle, so the tissue adapts and the athlete returns to full capacity.

The shoulder also does not work in isolation. How the scapula moves on the ribcage, and how the thoracic spine and even the trunk contribute, all shape how load reaches the AC joint. A rehab plan that only looks at the joint itself misses the surrounding system. That regional, kinetic-chain thinking is the same lens we apply to the overhead athlete, which we cover in detail in our piece on the rotator cuff in the overhead athlete.

When to refer

Most AC sprains do not need surgery, but some situations warrant prompt medical assessment. Higher-grade injuries (types IV to VI) with marked deformity, injuries that fail to progress with appropriate rehab, severe unremitting pain, any suspicion of an associated fracture, or signs of nerve or vascular involvement all justify referral to a physician or orthopaedic surgeon.³ A skin tenting or gross deformity, numbness, or a cold, pale hand are not features to manage conservatively — they need to be seen. For the common low-grade sprain, though, patience and progressive loading do the heavy lifting.

The bottom line

A shoulder separation is a sprain of the AC joint, not a dislocation, and it is usually far less alarming than the name suggests. Most are low grade and recover well with a course of loaded rehabilitation that respects healing timelines and rebuilds capacity across the whole shoulder complex. The bump may or may not stay; function is what matters, and function is what good rehab restores.

References

1. Frank RM, Cotter EJ, Leroux TS, Romeo AA. Acromioclavicular joint injuries: evidence-based treatment. J Am Acad Orthop Surg. 2019;27(17):e775-e788.
2. Mazzocca AD, Arciero RA, Bicos J. Evaluation and treatment of acromioclavicular joint injuries. Am J Sports Med. 2007;35(2):316-329.
3. Rockwood CA. Injuries to the acromioclavicular joint. In: Rockwood CA, Green DP, eds. Fractures in Adults. Lippincott.
4. Beitzel K, Mazzocca AD, Bak K, et al. ISAKOS upper extremity committee consensus statement on the need for diversification of the Rockwood classification for acromioclavicular joint injuries. Arthroscopy. 2014;30(2):271-278.
5. Gabbett TJ. The training-injury prevention paradox: should athletes be training smarter and harder? Br J Sports Med. 2016;50(5):273-280.