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Acromioclavicular Joint Injuries

Identifying and Treating 'Separated Shoulder' and Other Conditions

Robert J. Johnson, MD

Practice Essentials Series Editors:
Kim Harmon, MD; Aaron Rubin, MD


In Brief: The acromioclavicular (AC) joint is vulnerable to injury in collision sports and in activities requiring repetitive overhead motions. The spectrum of injury includes sprains and osteoarthritis of the AC joint and osteolysis and fracture of the distal clavicle. With the exception of severe sprains and fractures, most conditions can be managed nonoperatively. The key to successful treatment is prompt and accurate recognition of the severity of AC injuries.

Acromioclavicular (AC) joint injuries are common among athletes involved in collision sports, throwing sports, and overhead activities such as upper-extremity strength training. Though AC injuries are common, the treatments for some of the specific injuries are subject to controversy. From the perspective of the sports medicine physician, the ability to distinguish the AC injuries that can be effectively managed nonoperatively from those best managed by surgical intervention is crucial to optimize the care of the injured athlete.


The AC joint (figure 1) is a diarthrodial joint that sometimes contains a fibrous disk. The inclination of the joint also varies, with a vertical orientation in about 36% of the population and an oblique orientation in 49% (1). The AC joint suspends the arm from the axial skeleton and transmits force from the upper arm to the rest of the skeleton.

[Figure 1]

Stability is maintained through the acromioclavicular ligament that protects against posterior translation and axial distraction of the clavicle and through the coracoclavicular ligaments (the more lateral trapezoid ligament and the more medial conoid ligament) (2). The trapezoid ligament resists axial compression and, secondarily, superior translation. The conoid ligament primarily resists superior and anterior translation. Both the trapezius and deltoid muscles are dynamic stabilizers of the AC joint (3). Motion through the AC joint involves 5° to 8° of rotation (4).

AC Separation

Most AC injuries occur from falling directly on the adducted shoulder. The force of the fall dictates the degree of injury. If the history involves a direct blow to the adducted shoulder, the physical exam is likely to confirm the diagnosis. Radiographs are helpful in clarifying the type of injury. The series should consist of an anteroposterior (AP) view, lateral Y view, and an axillary view to determine AP displacement and associated shoulder injuries. When an AC joint injury is suspected, a 15° cephalad AP view is useful (3). Weighted views are generally of little value and are no longer recommended.

AC dislocations have been divided into six classifications (5) (figure 2). The most commonly used system is the one modified by Rockwood (6). The importance of identifying the injury type cannot be overemphasized because the treatment and prognosis hinge on an accurate diagnosis. Typically, type 1 and 2 injuries are easily managed by the primary care physician. Early recognition of types 4, 5, and 6 is essential because these patients benefit from early surgical consultation and intervention. Management of type 3 injuries remains somewhat controversial.

[Figure 2]

Types 1 and 2. The patient with a type 1 injury will demonstrate local tenderness but no anatomic deformity. All the other types of AC dislocations are characterized by localized tenderness with a deformity or asymmetry to the uninvolved AC joint. Active adduction of the injured shoulder (patient reaches across the chest to grasp the uninjured shoulder) with additional passive adduction by the examiner (crossed-arm adduction test) usually exacerbates the pain.

Type 1 and 2 injuries are treated nonoperatively. An arm sling, ice, and analgesics for comfort are the usual initial treatments. Range-of-motion exercises and strength training to restore normal motion and strength are instituted as the patient's symptoms permit. (See "What to Do About AC Joint Injuries.") Return to sport is allowed when the patient reestablishes nearly normal range of motion and strength, typically within 2 to 3 weeks of injury. When a patient returns to practice and competition in collision sports, protection of the AC joint with special padding is important. A simple "doughnut" cut from foam or felt padding can provide effective protection. Special shoulder injury pads can be placed beneath the regular shoulder pads, or off-the-shelf shoulder orthoses can be used to protect the AC joint after injury.

Type 3. The treatment of a type 3 injury is less controversial than in past years. In the 1970s, most orthopedists recommended surgery for type 3 AC sprains (7). By 1991, most type 3 injuries were treated conservatively (8). This change in treatment philosophy was prompted by a series of retrospective studies (9) that showed no outcome differences between operative and nonoperative groups. Furthermore, the patients treated nonoperatively returned to full activity (work or athletics) sooner than the surgically treated groups (10,11). The exceptions to this recommendation include those who perform repetitive, heavy lifting, those who work with their arms above 90°, and thin patients who have prominent lateral ends of the clavicles. These patients may benefit from surgical repair (12).

Nonoperative treatment of a type 3 AC sprain involves the use of a sling for comfort followed by range-of-motion and strengthening exercises when tolerated. The time to return to full activity, typically 6 to 12 weeks, is much longer than for type 1 and 2 injuries. Upon return to practice and play, the AC joint should be protected as suggested for type 1 and 2 injuries. Protection may be used as long as the athlete or athletic trainer feels its use is warranted.

Types 4, 5, and 6. Radiographic findings are the primary method used to diagnose type 4, 5, or 6 fractures. When the injury is diagnosed, an orthopedic surgeon should be consulted for surgical reduction and stabilization. Return to athletic practice and play depends on healing and restoration of near-normal strength and range of motion.

Distal Clavicle Fractures

Fractures of the distal third of the clavicle are much less common than midthird clavicle fractures. Estimates range from 10% to 20% of all clavicle fractures (9). The usual mechanism of injury is a lateral force directed against the point of the shoulder.

When a distal clavicle fracture is suspected, appropriate x-rays include a standard shoulder series (AP view, axillary view, and scapular Y view). Anterior and posterior 45° oblique views and/or a view with 20° to 45° cephalic tilt are recommended to more effectively assess anterior-posterior displacement (9).

Understanding and applying fracture classification is essential for making treatment recommendations and timely, appropriate orthopedic consultations. The classification originally made by Neer was later modified to include four distinct injuries (9).

Type 1 fractures involve the clavicle that is lateral to the coracoclavicular ligaments and thus remain stable and nondisplaced. Treatment involves use of a sling until clinical and radiographic evidence of healing is seen. Rehabilitation is best supervised by a physical therapist or athletic trainer and should include range-of-motion and strengthening exercises that target the rotator cuff and scapular stabilizers. After proper rehabilitation of the shoulder, the athlete can return to play, including collision sports.

Type 2 fractures are more controversial. They have been divided into two subsets, 2a and 2b. Type 2a fractures occur medial to the coracoclavicular ligaments and usually result in fragment displacement. Type 2b fractures occur between the conoid and trapezoid ligaments and also tend to displace, leading to a high incidence of nonunion (22% to 44%) and delayed union (45%) after more than 3 months (9). Since the results of open reduction and internal fixation have generally been favorable, most orthopedic surgeons recommend surgery for type 2 fractures. Since several treatment strategies exist for the management of type 2 clavicle fractures, I encourage discussion of these fractures with an orthopedist.

Type 3 fractures include intra-articular fractures that leave all stabilizing ligaments intact. This fracture can be treated in a manner similar to type 1 fractures. Other fracture types have been described, but their infrequent occurrence does not warrant discussion.


Osteoarthritis of the AC joint may be traumatic or atraumatic, but its true incidence is unknown. Fractures of the distal clavicle and AC dislocations may predispose this joint to osteoarthritis. Repetitive upper-extremity activity can cause mechanical wear of the articular cartilage. Also, age-related deterioration of the articular disk has been associated with osteophyte development at the acromion and bony changes of the distal clavicle (13). Narrowing of the joint space by about 50% appears to be a part of the normal aging process (14).

Radiographic changes have been observed in 10% to 23.4% of the nondominant arms of those who do not use their upper extremities excessively. Changes are noted in almost 62% of the dominant arms of those who participate in occupations and sports that require extensive shoulder use (9). Fortunately, despite the frequency of degenerative changes, few people become symptomatic.

Common clinical complaints of those who have AC arthritis are diffuse, lateral shoulder pain and/or local AC-joint pain. Nocturnal exacerbation is common. Upper-extremity activity and activities of daily living involving the shoulder aggravate the symptoms (9). The physical exam commonly reveals local tenderness to palpation of the involved joint. Active and passive range of motion of the shoulder may intensify symptoms. Crossed-arm adduction of the involved shoulder with additional passive adduction by the examiner also aggravates pain. X-rays of the painful shoulder demonstrate typical degenerative changes of bony sclerosis, subchondral cysts, osteophytes, and joint-space narrowing (15).

Treatment of osteoarthritis of the AC joint parallels that for other degenerative joints. Common recommendations include activity modification, physical therapy, nonsteroidal anti-inflammatory drugs (NSAIDs) or other analgesics, and corticosteroid injections. Although not widely investigated, corticosteroid injections of the AC joint provide symptom relief for 20 days to 3 months (16). Injection of the AC joint is performed from a superior approach using a 23- or 25-gauge needle (figure 3: not shown) with 1 mL of local anesthetic mixed with 1 mL of an intermediate- or long-acting corticosteroid. Most experts recommend limiting injections to the AC joint to three over 3 to 6 months.

When conservative therapy fails, options include arthroscopic or open excision of the distal clavicle.

Osteolysis of the Distal Clavicle

Atraumatic osteolysis of the distal clavicle occurs in various disease states such as rheumatoid arthritis, hyperparathyroidism, infection, multiple myeloma, and scleroderma (9), and in patients who do extensive upper-extremity weight training (see "Osteolysis of the Distal Clavicle: Readily Detected and Treated Shoulder Pain," December 2021). The pathophysiology of osteolysis is unclear. One hypothesis involves a stress fracture-like phenomenon in which repetitive stress leads to bony resorption (17).

Clinically, the symptoms reported by athletes who have osteolysis mimic those reported by patients who have osteoarthritis. Pain over the AC joint or pain in the deltoid region is common. Push-ups, dips, and bench presses often aggravate symptoms. Throwing also triggers pain. On physical exam, pain with crossed-arm adduction and palpable tenderness at the AC joint are consistent with osteolysis. When present, loss of the subarticular cortex and demineralization at the clavicle tip appear before obvious characteristic erosion of the distal clavicle. Erosion of the clavicle tip results in the loss of 0.5 to 3 cm of bone (9). Clavicle erosion may be accompanied by erosion of the acromion.

X-ray changes may take weeks to months to occur. A bone scan performed to confirm the diagnosis demonstrates increased uptake over the distal clavicle and, occasionally, increased uptake in the acromion (18). Magnetic resonance imaging exhibits altered signal intensity in the distal clavicle but is not necessary to make a definitive diagnosis.

Treatment options are virtually identical to those recommended for osteoarthritis—modification of activities, NSAIDs or other analgesics, and rest. Reparative processes may occur over 4 to 6 months. Joint widening may persist. Over time, the distal clavicle remineralizes but takes on a tapered appearance compared with the normal architecture (9). When symptoms develop, the athlete should be instructed to discontinue the pain-provoking exercises. Weight lifters should avoid locking the elbows during the bench press, use a narrower grip on the bar, and avoid bending the elbows below horizontal. For patients whose pain is not responding to exercise modifications and conservative treatment, distal clavicle resection may be a necessary next step.

Ready to Respond

Both traumatic and atraumatic AC joint injuries are commonly seen by physicians on the sideline, in the training room, and in the clinic. Understanding the spectrum of injury in the context of acute trauma or repetitive activity enables the clinician to correctly diagnose, treat, and, if indicated, refer for orthopedic consultation. This strategy ensures optimal care for active patients.


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Dr Johnson is the director of primary care sports medicine in the department of family practice at Hennepin County Medical Center in Minneapolis. He is an editorial board member of The Physician and Sportsmedicine. Address correspondence to Robert J. Johnson, MD, HCMC Primary Care Sports Medicine, 5 West Lake St, Minneapolis, MN 55408; address e-mail to [email protected].