Background
The acromioclavicular (AC) joint is a diarthrodial joint that joins the distal end of the clavicle with the acromion. It is surrounded by a joint capsule in which lies a meniscal disk. The AC ligaments, comprising the superior, inferior, anterior, and posterior ligaments, help with anteroposterior stability and inhibit superior translation. The coracoclavicular ligaments, comprising the trapezoid and conoid ligaments, insert on the coracoid process and provide superior-inferior stability and inhibit AC joint compression. (See the image below.)
The AC joint usually degenerates over time; however, despite this degeneration, it can remain asymptomatic. With aging, the joint space between the acromion and the clavicle narrows, wearing away the meniscal disk in between the joint. The articular disk begins to break down around the second decade of life. [1] Injection of corticosteroid (combined with an anesthetic) into the AC joint is one method of treatment for AC joint injuries or pathology. Such injuries can occur both in the general population and in those participating in athletics or other physical activities. [2]
Indications
Injections into the AC joint are usually performed for primary osteoarthritis, traumatic osteoarthritis, and distal clavicle osteolysis. [3] Primary osteoarthritis is the leading cause of pain in the AC joint. [4] Traumatic arthritis can occur after injuries such as distal clavicle fractures or AC joint dislocations. Osteolysis is usually seen in weightlifters who have sustained repetitive microtrauma to the shoulder and AC joint. (See Acromioclavicular Injury.)
An analgesic (eg, lidocaine) can be injected into the AC joint to confirm the source of the pain. [4] Injections can be diagnostic, therapeutic, or both. Most clinicians advocate AC joint injections after conservative treatment modalities have been exhausted and pain persists. Conservative treatments include relative rest, activity modification, nonsteroidal anti-inflammatory drugs (NSAIDs), and physical therapy.
Contraindications
Contraindications for AC joint injection include the following [5] :
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Bleeding diathesis
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Infection at the site
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Known hypersensitivity to the contents of the injection
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Skin breakdown at the site
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Fracture of the joint
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Severe joint destruction
Relative contraindications include the following [5] :
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Joint instability
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Infection or severe osteoporosis adjacent to the site
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Anticoagulation therapy
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Overlying skin lesions
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Acromioclavicular joint anatomy.
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Patient (48-year-old woman with preexisting acromioclavicular [AC] joint arthritis), was hit by motor vehicle, which exacerbated her AC joint arthritis. Video courtesy of James R Verheyden, MD.
