What Is an Acromioclavicular Joint Injection?

The acromioclavicular (AC) joint is located at the top of the shoulder; it joins the collar bone (clavicle) and the top of the shoulder blade (acromion). The AC joint deteriorates over time as the joint space between the clavicle and acromion decreases with aging. Any injury to the AC joint can result in inflammation and swelling of the joints.

Injection to the AC joint should not be performed in the following conditions:

• Bleeding disorder
• Infection at the site
• Allergic to the contents of the injection
• Joint fracture
• Severe joint damage
• Bedsores
• Less stable joints resulting in falls and injury
• Presence of infection or brittle bones adjacent to the injection site
• Use of blood thinners
• Overlying skin bruise or wound
• Young age
• Unable to remain still for the procedure
• Uncontrolled diabetes mellitus

The patient is either made to stand or sit. The physician identifies the AC joint by examining it. Once the physician identifies the AC joint, a syringe filled with steroid and a local anesthetic is injected into the joint space. The solution should enter the space with minimal resistance. The physician may reposition the needle in case of any resistance. The ultrasonographic technique can enhance the accuracy of the AC joint injection.

The complications of the acromioclavicular joint injection include:

• Infection of the joint (septic arthritis)
• Allergic reactions to the anesthetic agents 
• Infection at the site of injection
• Rupture of blood vessels and nerve
• Increased blood sugar level
• Tendon (tough band of tissue connecting muscle to the bone) rupture
• Reddening of skin
• Light patches on the skin
• Steroid-induced joint inflammation
• Loss of fatty tissue
• Steroid-induced side effects
• Steroid flare-up (pain and inflammation around the site of injection)
• Muscle wasting

Other possible, rare side effects of the AC joint injections are:

• Bruising
• Bleeding
• Pain at the injection site for some days