AC Joint Injections: Understanding Potential Complications and Risks

What are the complications of AC joint injection?

Acromioclavicular (AC) joint injections are generally safe and effective procedures for managing pain and inflammation, but like all medical interventions, they carry potential risks and complications that range from mild and temporary to rare but serious.

Understanding AC Joint Injections

The acromioclavicular (AC) joint is located at the top of the shoulder, where the clavicle (collarbone) meets the acromion (part of the shoulder blade). This joint is susceptible to injury and degenerative changes, leading to pain and dysfunction. AC joint injections, typically involving a corticosteroid and a local anesthetic, are a common therapeutic option aimed at reducing inflammation and providing pain relief. While often beneficial, it's crucial for patients and practitioners alike to be aware of the potential complications.

Common Local Complications

These complications typically occur at or near the injection site and are generally mild and self-limiting.

• Pain and Soreness: It is common to experience increased pain or soreness at the injection site for a few hours to a few days after the procedure. This is often due to the needle passing through tissues or a temporary inflammatory response to the injected solution.
• Bruising and Swelling: Minor bruising and localized swelling are common and usually resolve within a few days. This is due to minor trauma to blood vessels during needle insertion.
• Skin Changes:
  • Skin Depigmentation: In some individuals, particularly those with darker skin tones, a temporary or permanent lightening of the skin (hypopigmentation) can occur at the injection site due to the corticosteroid's effect on melanin production.
  • Fat Atrophy: Less commonly, the fat layer beneath the skin can thin (atrophy), leading to a visible dimple or depression at the injection site. This is usually cosmetic and rarely causes functional issues.

Potential Systemic Complications

While AC joint injections are localized, the corticosteroid can be absorbed into the bloodstream, leading to transient systemic effects.

• Steroid Flare: Also known as post-injection flare, this is a temporary increase in pain and inflammation in the injected joint, typically occurring within 24-48 hours after the injection. It's thought to be a reaction to the corticosteroid crystals and usually resolves on its own within a few days.
• Blood Sugar Fluctuations: Corticosteroids can temporarily elevate blood glucose levels. This is particularly important for individuals with diabetes, who should monitor their blood sugar closely after an injection.
• Facial Flushing: Some individuals may experience a temporary reddening and warming sensation of the face, neck, or chest. This is a benign side effect that resolves spontaneously.
• Adrenal Suppression: With repeated or high-dose corticosteroid injections, there is a theoretical risk of temporary suppression of the body's natural cortisol production by the adrenal glands. This is rare with single, isolated AC joint injections but is a consideration with frequent or multiple joint injections.

Risks of Infection

Infection is a rare but serious complication of any injection. Strict sterile technique is paramount to minimize this risk.

• Superficial Infection: This involves the skin or subcutaneous tissue at the injection site, presenting as redness, warmth, increased pain, or pus.
• Deep Joint Infection (Septic Arthritis): This is a serious complication where bacteria enter the joint space, leading to severe pain, swelling, redness, warmth, fever, and chills. Septic arthritis requires immediate medical attention and aggressive antibiotic treatment, often with surgical drainage, to prevent joint damage and systemic illness.

Neurological and Vascular Considerations

While the AC joint is superficial, there are nerves and blood vessels in the vicinity that could theoretically be affected.

• Nerve Injury: Direct needle trauma to nearby cutaneous nerves (e.g., supraclavicular nerves) can cause temporary or, very rarely, permanent numbness, tingling, or burning sensations in the distribution of the affected nerve.
• Vascular Injury: Accidental puncture of a small blood vessel can lead to localized bleeding or hematoma formation. Significant vascular injury is exceedingly rare given the superficial nature of the AC joint.

Rare but Serious Complications

While extremely uncommon, these complications highlight the importance of proper technique and patient selection.

• Pneumothorax: Although exceedingly rare for AC joint injections due to its superficial nature, if the needle is advanced too deeply or medially, there is a theoretical risk of puncturing the pleura and lung, leading to a collapsed lung (pneumothorax). This risk is significantly mitigated by using ultrasound guidance.
• Tendon/Ligament Weakening or Rupture: While corticosteroids can weaken collagen structures with repeated injections into or directly adjacent to tendons, the AC joint is primarily a synovial joint surrounded by a capsule and ligaments, making this a less common direct complication for the joint itself compared to, for example, a patellar tendon injection. However, careful placement is still important.
• Allergic Reactions: Though uncommon, individuals can have an allergic reaction to the local anesthetic (e.g., lidocaine) or the corticosteroid itself. Reactions can range from mild skin rashes to severe anaphylaxis, requiring immediate medical intervention.

Factors Influencing Risk

Several factors can influence the likelihood of experiencing complications:

• Practitioner Skill and Technique: The experience and precision of the injecting physician are paramount. Use of anatomical landmarks combined with palpation, or preferably, real-time ultrasound guidance, significantly reduces risks.
• Sterility: Adherence to strict aseptic (sterile) technique is critical to prevent infection.
• Patient Health Status: Patients with compromised immune systems, uncontrolled diabetes, or bleeding disorders may be at higher risk for certain complications.
• Frequency of Injections: While not definitively proven for AC joint injections specifically, repeated corticosteroid injections into any joint may theoretically increase the risk of cartilage damage or other long-term effects. Most clinicians recommend limiting injections to 2-3 times per year per joint.

Minimizing Complication Risk

To ensure the safest possible procedure, several best practices are employed:

• Ultrasound Guidance: The use of ultrasound guidance allows the practitioner to visualize the needle in real-time as it enters the AC joint, ensuring accurate placement and avoiding surrounding structures. This is considered the gold standard for AC joint injections.
• Strict Aseptic Technique: Thorough skin preparation with antiseptic solutions and the use of sterile gloves, drapes, and instruments are essential.
• Open Communication: Discussing your medical history, allergies, and any concerns with your healthcare provider before the injection is vital.

When to Seek Medical Attention

While many minor side effects resolve on their own, contact your healthcare provider immediately if you experience any of the following after an AC joint injection:

• Severe or worsening pain that does not subside
• Significant swelling, redness, or warmth around the injection site
• Pus or discharge from the injection site
• Fever or chills
• New or worsening numbness, tingling, or weakness
• Shortness of breath or chest pain
• Signs of an allergic reaction (e.g., rash, hives, difficulty breathing)

Conclusion

AC joint injections are valuable tools in the management of shoulder pain and inflammation. While generally safe, understanding the potential complications, both common and rare, allows for informed decision-making and optimal patient care. By choosing an experienced practitioner, utilizing advanced guidance techniques, and adhering to strict sterile protocols, the risks associated with AC joint injections can be effectively minimized, maximizing the therapeutic benefits for patients.