Shoulder Injuries: The Acromioclavicular (AC) Joint Skip to main content

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Shoulder Injuries: The Acromioclavicular (AC) Joint

Two surgeons discuss the diagnosis and treatment of acromioclavicular injuries in athletes. El Paso, TX. Chiropractor, Dr. Alexander Jimenez follows the discussion.

Acromioclavicular (AC) joint injuries most often occur in athletic young adults involved in collision sports, throwing sports, along with overhead activities like upper-extremity strength training. They account for 3% of all shoulder injuries and 40% of shoulder sports injuries. Athletes in their second and third decade of life are more often affected(1), and men are injured more commonly than women (5:1 to 10:1)(1,2).

Acromioclavicular dislocation was known as early as 400 BC by Hippocrates(3). He cautioned against mistaking it for glenohumeral (shoulder joint) dislocation and advocated treating with a compressive bandage in an attempt to hold the distal (outer) end of the clavicle in a diminished position. Almost 600 decades later Galen (129 AD) recognized his own acromioclavicular dislocation, which he sustained while wrestling(3). He left the tight bandage holding the clavicle down as it was too uneasy. In today's era this injury is better known, but its treatment remains a source of fantastic controversy.


The acromioclavicular joint combines the collarbone to the shoulder blade and therefore links the arm to the axial skeleton. The articular surfaces are originally hyaline cartilage, which affects to fibrocartilage toward the end of adolescence. The average joint size is 9mm by 19mm(4). The acromioclavicular joint contains an intra-articular, fibrocartilaginous disc which may be complete or partial (meniscoid). This helps absorb forces in compression. There is marked variability in the plane of the joint.


There is little inherent bony stability in the AC joint. Stability is provided by the dynamic stabilizers -- namely, the anterior deltoid muscle arising from the clavicle and the trapezius muscle arising from the acromion.

Additionally, there are ligamentous stabilizers. The AC ligaments are divided into four -- superior, inferior, anterior and posterior. The superior is most powerful and blends with muscles. The acromioclavicular ligaments contribute around two- thirds of the constraining force to superior and posterior displacement; however, with greater displacement the coracoclavicular ligaments contribute the major share of the resistance. The coracoclavicular ligament consists of the conoid and trapezoid. The conoid ligament is fan-shaped and resists forwards motion of the scapula, while the more powerful trapezoid ligament is level and resists backward movement. The coracoclavicular ligament helps bunch scapular and glenohumeral (shoulder joint) motion and the interspace averages 1.3 cm.

Mechanism Of Injury

The athlete who sustains an acromioclavicular injury commonly reports either one of two mechanisms of harm: direct or indirect.

Direct force: This is when the athlete falls onto the point of the shoulder, with the arm usually at the side and adducted. The force drives the acromion downwards and medially. Nielsen(5) found that 70 percent of acromioclavicular joint injuries are caused by an direct injury.

Indirect force: This is when the athlete falls onto an outstretched arm. The pressure is transmitted via the humeral head into the acromion, therefore the acromioclavicular ligament is disrupted and the coracoclavicular ligament is stretched.

On Examination

The athlete presents soon after the severe injury with his arm splinted to his side. The patient may state that the arm feels better using superiorly directed support on the arm. Most motions are limited secondary to pain near the top of the shoulder; the degree varies with the grade of sprain. The hallmark finding is localized swelling and tenderness over the acromioclavicular joint.

In dislocations, the outer part of the collarbone will appear superiorly displaced using a noticeable step deformity (in fact, it is the shoulder which sags beneath the clavicle). Occasionally, the deformity may only be apparent later, if first muscle spasm reduces acromioclavicular separation. Forced cross-body adduction (yanking the affected arm across the opposite shoulder) provokes discomfort. The clavicle can frequently be moved relative to the acromion.

Acromioclavicular Visualisation

The typical joint width measures 1-3mm. It's regarded as abnormal if it is more than 7mm in men, and 6mm in women. Routine anteroposterior views of the shoulder reveal the glenohumeral jointnonetheless, that the acromioclavicular joint is over penetrated and so dark to interpret. Reduced exposure enhances visualization. The individual stands with both arms hanging unsupported, both acromioclavicular joints on one film. Weighted viewpoints (stress X-rays) are obtained with 10-15 lb weights not held but suspended from the individual's wrists. They help differentiate type II-III injuries, but are of little clinical significance and therefore are no longer recommended in our practice.

Classification Of AC Separation

The importance of identifying the injury kind can't be over emphasized because the treatment and prognosis hinge on an accurate diagnosis. The injuries are graded on the basis of that ligaments are injured and how badly they're torn.

Allman (6) classified acromioclavicular sprains as grades I, II and III, representing respectively, no involvement, partial tearing, and total disruption of the coracoclavicular ligaments. More recently, Rockwood (1) has further classified the more severe injuries as standard III-VI.

The injuries are classified into six categories:

Type I This is the most common injury encountered. Only a mild force is needed to sustain such an injury. The acromioclavicular ligament is sprained with an intact coracoclavicular ligament. The acromioclavicular joint remains stable and symptoms resolve in seven to 10 days. This injury has an excellent prognosis.

Type II The coracoclavicular ligaments are sprained; however, the acromioclavicular ligaments are ruptured. Most players can return to their sport within three weeks. There is anecdotal evidence to suggest that steroid injections into the acromioclavicular joint speed up the resolution of symptoms, but this practice is not universal.

Type III The acromioclavicular joint capsule and coracoclavicular ligaments are completely disrupted. The coracoclavicular interspace is 25-100% greater than the normal shoulder.

Type IV This is a type III injury with avulsion of the coracoclavicular ligament from the clavicle, with the distal clavicle displaced posteriorly into or through the trapezius.

Type V This is type III but with exaggeration of the vertical displacement of the clavicle from the scapula-coracoclavicular interspace 100-300% greater than the normal side, with the clavicle in a subcutaneous position.

Type VI This is a rare injury. This is type III with inferior dislocation of the lateral end of the clavicle below the coracoid


The treatment of acromioclavicular joint injuries varies based on the seriousness or grade of the injury.

Initial treatment: These can be quite painful injuries. Ice packs, anti-inflammatories plus a sling are utilized to immobilize the shoulder and then take the weight of the arm. As pain starts to subside, it is important to start moving the fingers, wrist and elbow to prevent shoulder stiffness. Next, it's important to begin shoulder motion in order to stop shoulder stiffness.

Un-displaced injuries only require rest, ice, and then a slow return to activity over two to six weeks. Major dislocations require surgical stabilization in athletes if their dominant arm is involved, and if they participate in upper-limb sports

Type I & II: Ice pack, anti-inflammatory agents and a sling are used. Early motion based on symptoms is introduced. Pain usually subsides in about 10 days. Range-of-motion exercises and strength training to restore normal motion and strength are instituted as the patient’s symptoms permit. Some symptoms may be relieved by taping (taking stress off acromioclavicular joint). The length of time needed to regain full motion and function depends upon the severity or grade of the injury. The sport and the position played determine when a player can return to a sporting activity. A football player, who does not have to elevate his arm, can return sooner than a tennis or rugby player. When a patient returns to practice and competition in collision sports, protection of the acromioclavicular joint with special padding is important. A simple ‘doughnut’ cut from foam or felt padding can provide effective protection. Special shoulder- injury pads, or off-the-shelf shoulder orthoses, can be used to protect the acromioclavicular joint after injury.

Some Type II injuries may develop late degenerative joint changes and will need a resection of the distal end of the clavicle for pain relief. It is important to note that after a resection of the distal end of the clavicle, particularly in a throwing athlete, there may be formation of heterotopic bone on the under surface of the clavicle which can cause a painful syndrome which presents like shoulder impingement.

Type III: The treatment of type III injury is less controversial than in past years. In the 1970s, most orthopaedic surgeons recommended surgery for type III acromioclavicular sprains(7). By 1991, most type III injuries were treated conservatively(8). This change in treatment philosophy was prompted by a series of retrospective studies(9). These showed no outcome differences between operative and nonoperative groups.

What's more, the patients treated non-operatively returned to full activity (work or athletics) earlier than surgically treated groups(10, 11). The exceptions to this recommendation include people who perform repetitive, heavy lifting, people who operate with their arms above 90 degrees, and thin patients who have prominent lateral ends of the clavicles. These patients may benefit from surgical repair(12).

Any discussion about the management of acute injuries to the AC joint must deal with which of the many methods of surgical therapy described is the best for their situation, but whether surgery should be considered at all. Surgery is generally avoided in athletes participating in contact sports since they will often re-injure the shoulder later on.

Type IV-VI: Account for more than 10-15% of total acromioclavicular dislocations and should be managed surgically. Failure to reduce and fix these will lead to chronic pain and dysfunction.


Surgical repair can be divided into anatomical or non- anatomical, or historically into four types:

● Acromioclavicular repairs (intra-articular repair with wires/pins, percutaneous pins, hook plates).

● Coracoclavicular repairs (Bosworth screws(13), cerclage, Copeland and Kessel repair).

● Distal clavicular excision.

● Dynamic muscle transfers.

● Disadvantages of surgery are that there are risks of infection, a longer time to return to full function and continued pain in some cases.

For the individual with a chronic AC joint dislocation or subluxation that remains painful after three to six months of closed treatment and rehabilitation, surgery is indicated to improve functioning and comfort.

For sequelae of untreated type IV-VI, or painful type II and III injuries, the Weaver Dunn technique is advocated. This entails removing the lateral 2cm of the clavicle and reattaching the acromial end of the coracoacromial ligament to the cut end of the clavicle, thus reducing the clavicle to a more anatomical position.

Postoperatively, the arm is supported in a sling for up to six weeks. Following the first two weeks, the patient is permitted to use the arm for daily activities at waist level. After six weeks, the sling or orthosis is discontinued, overhead actions are allowed, formal passive stretching is instituted, and light stretching using elastic straps is initiated. Stretching and strengthening are begun slowly and gradually. The athlete shouldn't return to their sport without restriction until full strength and range of motion has been recovered. This usually occurs four to six months following operation.


AC joint injuries are an important source of pain at the shoulder area and have to be assessed carefully. The management of these injuries is nonoperative in the majority of cases. Type I and II injuries are treated symptomatically. The present trend in uncomplicated type III injuries are a non operative strategy. In the event the athlete develops following problems, a delayed reconstruction might be undertaken. In athletes involved in heavy lifting or prolonged overhead activities, surgery may be considered acutely. Type IV-VI injuries are generally treated operatively.

No matter what kind of treatment is chosen, the ultimate purpose is to restore painless function to the wounded AC joint so as to reunite the athlete safely and as quickly as possible back to their sport. It is possible in the vast majority of acromioclavicular joint injuries.


Reza Jenabzadeh and Fares Haddad

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2. Dias JJ, Greg PJ. Acromioclavicular Joint Injuries in Sport: Recommendations for Treatment. Sports Medicine 1991; 11: 125-32.
3. Adams FL. The Genuine Works of Hippocrates (Vols 1,2). New York, William Wood 1886.
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5. Nielsen WB. Injury to the Acromioclavicular Joint. J Bone Joint Surg 1963; 45B:434-9.
6. Allman FL Jr. Fractures and Ligamentous Injuries of the Clavicle and its Articulation. J Bone Joint Surg Am 1967;
49:774- 784.
7. Powers JA, Bach PJ: Acromioclavicular Separations: Closed or Open Treatment? Clin Orthop 1974; 104 (Oct): 213-223
8. Cox JS: Current Methods of Treatment of Acromioclavicular Joint Dislocations. Orthopaedics 1992; 15(9): 1041-1044
9. Clarke HD, Mc Cann PD: Acromioclavicular Joint Injuries. Orthop Clin North Am 2000; 31(2): 177-187
10. Press J, Zuckerman JD, Gallagher M, et al: Treatment of Grade III Acromioclavicular Separations: Operative versus
Nonoperative Management. Bull Hosp Jt Dis 1997;56(2):77-83
11. Galpin RD, Hawkins RJ, Grainger RW: A Comparative Analysis of Operative versus Nonoperative Treatment of Grade III Acromioclavicular Separations. Clin Orthop 1985; 193 (Mar): 150-155
12. Larsen E, Bjerg-Nielsen A, Christensen P: Conservative or Surgical Treatment of AC Dislocation: A Prospective, Controlled, Randomized Study. J Bone Joint Surg Am 1986;68(4):552-555
13. Bosworth BM. Complete Acromioclavicular Dislocation. N Engl. J. Med. 241: 221-225,1949.

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The information herein is not intended to replace a one-on-one relationship with a qualified health care professional, licensed physician, and is not medical advice. We encourage you to make your own health care decisions based on your research and partnership with a qualified health care professional. Our information scope is limited to chiropractic, musculoskeletal, physical medicines, wellness, sensitive health issues, functional medicine articles, topics, and discussions. We provide and present clinical collaboration with specialists from a wide array of disciplines. Each specialist is governed by their professional scope of practice and their jurisdiction of licensure. We use functional health & wellness protocols to treat and support care for the injuries or disorders of the musculoskeletal system. Our videos, posts, topics, subjects, and insights cover clinical matters, issues, and topics that relate to and support, directly or indirectly, our clinical scope of practice.* Our office has made a reasonable attempt to provide supportive citations and has identified the relevant research study or studies supporting our posts. We provide copies of supporting research studies available to regulatory boards and the public upon request. We understand that we cover matters that require an additional explanation of how it may assist in a particular care plan or treatment protocol; therefore, to further discuss the subject matter above, please feel free to contact us. Dr. Alex Jimenez DC, MSACP, CCST, IFMCP*, CIFM*, ATN* email: phone: 915-850-0900 Licensed in: Texas & New Mexico*