Acromioclavicular Joint Injection

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.)

Acromioclavicular joint anatomy.

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]

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 for AC joint injection include the following[5] :

• Bleeding diathesis
• Infection at the site
• Known hypersensitivity to the contents of the injection
• Skin breakdown at the site
• Fracture of the joint
• Severe joint destruction

Relative contraindications include the following[5] :

• Joint instability
• Infection or severe osteoporosis adjacent to the site
• Anticoagulation therapy
• Overlying skin lesions

Informed consent must be obtained from the patient prior to the acromioclavicular (AC) joint injection.

Patients should be made aware of the rare, but possible, side effects of AC joint injections, including the following:

• Allergic reaction
• Pain at the injection site or transient increase in pain at the injection site in the days following injection
• Infection
• Bleeding
• Bruising

Patients receiving a steroid injection should be made aware of the possible transient increase in blood sugar levels, as well as the risk of avascular necrosis (AVN), steroid arthropathy, and systemic effects (eg, hot flashes, mood changes, insomnia, psychosis, and adrenal supression).[6] Although these adverse reactions are rare, it is essential that they be disclosed to the patient.

AC joint injection is performed with the following equipment:

• Needle, 25 gauge, 1-1.5 in. (~2.5-3.8 cm)
• Syringe, 3-5 mL
• Povidone-iodine swabs or solution
• Gauze pads, 4 × 4 in. (~10 × 10 cm)

No consensus exists on the type or amount of steroids to be used for an AC joint injection. Typically, 0.25-0.5 mL of one of the following steroids is injected[7] :

• Betamethasone sodium phosphate
• Betamethasone acetate
• Methylprednisolone, 40 mg/mL

Anesthesia

Typical anesthetics used include 0.5-1 mL of 1-2% lidocaine or 0.25-0.5% bupivacaine. A 2007 survey of western US physicians by Skedros et al found broad variations in the amount of anesthetic injected for painful shoulder conditions, with surgeons using larger volumes.[8]

Positioning

The patient can sit or stand, with the affected arm in a neutral position at the side.

To locate the acromioclavicular (AC) joint line, palpate the acromion from the lateral edge medially until it meets the clavicle. Alternatively, follow the clavicle laterally until it meets the acromion. At the lateral edge of the clavicle, a bony rim lies 2 cm medial from the joint line. At the articulation of the acromion and the clavicle, a slight depression is usually evident; this depression indicates the joint line.[9]

After the medial edge of the acromion and the distal edge of the clavicle are palpated and the AC joint has been accurately identified, attach a 25-gauge needle to a 3-mL syringe that contains the solution of local anesthetic and steroid.

Inject into the joint space using a superior and anterior approach. The injectate should enter the space smoothly and with minimal resistance. If resistance is encountered, reposition the needle. To further open the joint space, the patient’s arm can be pulled into full lateral rotation. (See the video below.)

There is evidence to suggest that ultrasonographic (US) guidance may enhance the accuracy of AC joint injection.[10, 11, 12, 13, 14] In a study performed by Park et al, patients with symptomatic AC joint osteoarthritis who received US-guided intrarticular steroid injection (IAS) had better functional status and pain control at 6-month follow-up than patients who received palpation-guided IAS.[12]

Complications of AC joint injection include the following:

• Anaphylactic reaction to the anesthetic agents used
• Introduction of a pathogen into the joint space with development of  septic arthritis
• Damage to nerve and blood vessels

Rare but possible complications include the following:

• Systemic effects of the steroid
• Elevated blood sugar levels (in patients with diabetes)
• Tendon rupture
• Hypopigmentation of the skin
• Facial flushing
• Steroid arthropathy
• Fat atrophy
• Muscle wasting
• Steroid flare reaction