The acromioclavicular (AC) joint is a common pain generator in patients presenting with shoulder pain. The incidence of AC joint pain is reported to be roughly 0.5 per 1000/year in primary care. Pain in the AC joint can be traumatic or non-traumatic. Traumatic AC joint pain is typically the result of a direct blow to the superior or lateral aspect of the shoulder. The impact results in a partial or complete tear of the ligamentous structures within the joint, more commonly known as a separated shoulder, and frequently occurs in contact sports such as football and hockey. Patients with separated shoulder often present with a notable deformity over their superior shoulder and pain directly over the AC joint. Traumatic AC joint pain is treated either conservatively with a sling and relative rest or with surgery if the injury is high-grade or severe.
Patients with non-traumatic AC joint pain are usually older than 40 years of age and will typically present with focal shoulder pain located over the superior aspect of the shoulder. The pain is usually insidious and made worse with cross-body adduction of the shoulder. Patients may also describe a grinding sensation in their shoulder. On physical exam, patients will typically have tenderness directly over the AC joint. Bringing the patient’s affected arm into adduction by having them reach across their body often reproduces the pain.
The most common non-traumatic causes of pain in the AC joint are overuse, degenerative changes, and distal clavicle osteolysis. Conservative management, including physical therapy, activity modification, and NSAIDs, are the first line of treatment.
In patients with chronic AC joint pain refractory to initial management, AC joint injections can be both diagnostic and therapeutic, resulting in significant relief. Providers must remain up to date on the indications, possible complications, and most effective methods of performing this procedure to benefit patients suffering from this condition maximally. This article reviews acromioclavicular (AC) joint injections and highlights the role of the healthcare team in performing this procedure.
The acromioclavicular (AC) joint is part of the shoulder girdle and connects the distal clavicle to the acromion of the scapula. A fibrocartilaginous disk and synovial membrane are within the joint. The acromioclavicular (AC) ligament provides horizontal stability to the joint, whereas the coracoclavicular (CC) ligament, consisting of the trapezoid and coronoid ligaments, provides vertical stability. The coracoacromial ligament, as well as the attachments of the deltoid and trapezius muscles, provide additional stabilization.
Like most joint injections, AC joint injections can be performed after or concomitantly with other conservative measures, including physical therapy, NSAIDs, and activity modifications. For patients with suspected AC joint osteoarthritis, an AC joint injection is possible for diagnostic purposes. Other indications include known AC joint osteoarthritis and distal clavicle osteolysis refractory to initial treatment modalities. Distal clavicle osteolysis usually results from prior trauma to the shoulder or from repetitive heavy lifting. A separated shoulder is not a standard indication for injection, although post-traumatic degenerative conditions are a relative indication in specific clinical settings.
Contraindications to AC joint injections include infection in or around the joint (septic arthritis), hypersensitivity or known allergy to the injected solution, skin breakdown at the injection site and a fracture at the proposed injection site. Caution is advisable in patients on anticoagulation or with known bleeding disorders.
Equipment needed for this procedure includes:
Medical providers to include physicians, nurse practitioners, or physician assistants can perform AC joint injections. It is helpful to have a nurse present to assist with preparing the patient.
The clinician should discuss the risks/benefits of the procedure with the patient and the patient, provider, and witness should sign a consent form. A time-out should be performed before starting the procedure.
The patient should be in a seated position with his/her arm hanging to the side. To identify the AC joint, palpate the clavicle distally until its endpoint. Palpate the small depression just lateral to termination of the clavicle; this is the joint space. After identifying the AC joint, prepare the site with a cleaning solution such as chlorhexidine, and following preparation, insert the needle from the superior anterior approach and aim the needle inferiorly. If meeting resistance, redirect the needle slightly until it enters the joint space. Once in the joint, inject the solution slowly. Ultrasound, if available, can significantly improve the accuracy of AC joint injections. The patient should remain seated for a few minutes following the injection in case they have a vasovagal response.
Upon completion of the injection, reevaluate patient and have them passively range the shoulder to determine whether there is clinical improvement. Inform the patient that pain can get worse over the next 48 hours if a steroid flare occurs. If the pain does worsen, instruct the patient to treat with ice and NSAIDs.
Complications of this procedure are not common but include infection, lack of improvement in pain or worsening of pain, hypopigmentation of the overlying skin, and fat atrophy.
If performed correctly, AC joint injections can be both diagnostic and therapeutic, resulting in significant pain relief for affected patients. The duration of relief varies from patient to patient and can last weeks to months. Steroid injections can be repeated, but clinicians should be pursued with caution as multiple injections can result in degradation of joint cartilage over time.
An AC joint injection is a minor procedure that can provide patients significant pain relief. As is the case with all procedures, it is not without risk. The importance of communication and coordination of care amongst the provider, nurse, and patient cannot be understated. Pharmacists may be involved in the preparation of the anesthetic and need to have clear communication with the rest of the team, although, in the outpatient setting, nurses will more likely perform this task. Providers should clearly communicate expectations and precautions to the healthcare team and the patient to drive excellent outcomes. Nurses should also be aware of these return precautions as they are often the first ones on the healthcare team to communicate with the patient and family. They should work with the surgeon to keep the family informed and contact the team if unexpected complications arise. Interprofessional teamwork is crucial to obtaining the best outcomes in AC joint injection therapy. [Level V]
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