Acromioclavicular Joint Injection

Anatomy and Physiology

The acromioclavicular joint is a planar, diarthroidal synovial joint located at the junction of the acromion process of the scapula and the distal clavicle. This joint plays a pivotal role in shoulder function by stabilizing the scapula superiorly and maintaining joint alignment during arm elevation. The structure of the acromioclavicular joint includes a fibrocartilaginous disc, a joint capsule, and surrounding ligaments (acromioclavicular, coracoclavicular, and coracoacromial), which provide structural integrity to the acromioclavicular joint and facilitate load transmission between the clavicle and scapula.

Capsular ligaments surround the acromioclavicular joint to provide stability superiorly, inferiorly, posteriorly, and anteriorly.[14] The conoid and trapezoid ligaments, which comprise the coracoclavicular ligament, span the distance between the superior surface of the coracoid to the conoid tuberosity and trapezoid ridge of the clavicle. The coracoclavicular ligament prevents vertical displacement of the acromioclavicular joint. The deltoid and trapezius muscles afford dynamic stability to the acromioclavicular joint during clavicular and scapular motion.[15] 

The acromioclavicular joint's small size and superficial location heighten the risk of needle misplacement with landmark-guided techniques. Additionally, the joint's narrow space and intricate ligamentous attachments further complicate accurate needle placement. The proximity of the joint to neurovascular structures, such as the supraclavicular nerve, heightens the risk of nerve irritation or injury during injection.[16] 

Acromioclavicular joint disease commonly arises from degenerative, traumatic, or inflammatory processes. Degenerative changes, particularly osteoarthritis, are prevalent in athletes and laborers who engage in repetitive overhead activities that stress the joint, leading to cartilage erosion, joint space narrowing, and osteophyte formation. Traumatic injuries can sprain or tear the ligaments of the acromioclavicular joint, resulting in instability and promoting arthritic changes over time. Also, rheumatoid arthritis can inflame the synovium, causing joint swelling, pain, and reduced range of motion. A recent systematic review showed that 13% to 95% of adults exhibit radiographic evidence of degenerative arthritis in the acromioclavicular joint.[17]

Indications

Acromioclavicular joint injections function diagnostically, confirming the source of pain and therapeutically providing symptom relief to enhance patient comfort and functional ability.[8] Intraarticular acromioclavicular injections have produced promising short-term outcomes, but studies evaluating mid-term to long-term results of intraarticular acromioclavicular injections are scarce. Results from prior studies have demonstrated positive short-term outcomes for pain relief and shoulder function at a maximum follow-up of 3 weeks.[18] Hossain et al reported significant pain relief for at least 12 months after treatment with a single acromioclavicular injection, while van Riet et al found that only 28% of patients treated with acromioclavicular injection experienced significant benefits in shoulder function and pain relief 1 month after injection.[4][7]

Diagnostic acromioclavicular joint injections can help assess anterior shoulder pain, especially when clinical evaluation and imaging provide inconclusive findings. Symptoms of acromioclavicular joint pathology often include localized tenderness, pain during overhead or cross-body movements, and limited shoulder range of motion. A diagnostic injection with a local anesthetic can help confirm the acromioclavicular joint as the primary pain source, which is particularly useful when considering surgical options.

Therapeutic indications for acromioclavicular joint injections include pain management for conditions like osteoarthritis, inflammatory arthritis, and chronic post-traumatic changes.[8] For patients with osteoarthritis, corticosteroids, hyaluronic acid, and platelet-rich plasma injections can reduce pain and enhance function. They are typically used when conservative treatments like physical therapy, nonsteroidal anti-inflammatory drugs, or lifestyle changes are ineffective. Chronic overuse or traumatic injuries, frequently seen in athletes and laborers, may benefit from corticosteroid injections to control ongoing inflammation and aid in rehabilitation aimed at restoring shoulder mechanics.

Contraindications

Contraindications for acromioclavicular joint injections include fractures or active infections at the injection site, systemic infections, and hypersensitivity or significant allergic reactions to corticosteroids or local anesthetics. Careful consideration is required for patients with coagulopathy or those receiving anticoagulant therapy, as these conditions increase the risk of bleeding. Additionally, individuals with poorly controlled diabetes warrant caution because corticosteroids can significantly elevate blood glucose levels. Repeated injections in close succession should be avoided to reduce the risk of joint degradation and potential long-term complications, such as cartilage damage or chronic instability.

Equipment

Equipment Needed for Acromioclavicular Joint Injections 

The following are used for this procedure:

• Skin antiseptics such as alcohol, betadine, or chlorhexidine
• Sterile gloves, drapes, and 10 cc syringes
• Standard 5/8 or 1.5 inch; 25 or 27 gauge needles
• For ultrasound-guided injections: sterile ultrasound probe covers and ultrasound gel
• For fluoroscopic-guided injections: protective lead aprons and contrast solution

Injectable Options

• Local anesthetics such as lidocaine, ropivacaine, or bupivacaine
• Corticosteroids such as methylprednisolone acetate, triamcinolone acetate, betamethasone acetate, betamethasone phosphate, or dexamethasone phosphate
• Sodium hyaluronate
• Platelet-rich plasma

Adjust the volume and dose according to the patient's body size, comorbidities, and joint size. When combining local anesthetics with corticosteroids or other injectables, ensure compatibility and adhere to recommended dosage limits to avoid overdosage. The AC joint can typically take no more than 2 mL of injectate. 

Local Anesthetic Dosing Suggestions for Acromioclavicular Joint Injections

• Lidocaine

  • Concentration: 1% or 2%
  • Dose: 1 to 2 mL (maximum single dose: 300 mg for 1%; 600 mg for 2%, depending on patient size and comorbidities)
  • Duration of action: 1 to 2 hours

• Bupivacaine

  • Concentration: 0.25% or 0.5%
  • Dose: 1 to 2 mL (maximum single dose: 175 mg for bupivacaine only; 225 mg if mixed with epinephrine)
  • Duration of action: 4 to 6 hours for 0.25%; up to 8 hours for 0.5%

Corticosteroids Dosing Suggestions for Acromioclavicular Joint Injections 

• Methylprednisolone acetate (depo-medrol)

  • Dose: 20 to 40 mg
  • Volume: typically mixed with 0.5 to 1 mL of local anesthetic
  • Onset/duration: 24 to 48 hours for onset; lasts weeks to months

• Triamcinolone acetonide (Kenalog)

  • Dose: 10 to 40 mg
  • Volume: usually combined with 0.5 to 1 mL of local anesthetic
  • Onset/duration: 24 to 48 hours for onset; lasts weeks to months

• Betamethasone acetate/betamethasone sodium phosphate (celestone soluspan)

  • Dose: 6 to 12 mg (total for combination preparation)
  • Volume: mixed with 0.5 to 1 mL of local anesthetic
  • Onset/duration: rapid onset (hours); lasts weeks to months

• Dexamethasone sodium phosphate

  • Dose: 4 to 8 mg
  • Volume: usually mixed with 0.5 to 1 mL of local anesthetic
  • Onset/duration: onset within hours; lasts 1 to 2 weeks (shortest duration of corticosteroids)

Personnel

The procedural team typically includes a clinician experienced in acromioclavicular joint injections, a nurse or medical assistant, and an operator skilled in using a fluoroscopic C-arm or ultrasound. For platelet-rich plasma (PRP) therapy cases, personnel trained in PRP processing systems may also be required to prepare the sample before injection. All team members should be proficient in managing potential complications associated with the procedure to ensure patient safety and optimal outcomes.

Preparation

The risks and benefits of the procedure should be thoroughly discussed with the patient. Informed consent must be obtained per institutional policies. Before the injection, a time-out should be performed to verify the patient’s identity and the correct injection site. The patient should be seated or semi-reclined on the examination table. After identifying the injection site, it should be marked, cleansed with a skin antiseptic solution, and covered with sterile drapes.

PRP injections start by drawing 15 to 60 mL of the patient’s blood, depending on the required volume and concentration of PRP. The blood is placed in a centrifuge, which separates platelets and plasma from other components, creating a concentrated platelet-rich plasma layer. The PRP layer is carefully extracted following centrifugation to preserve platelet integrity and minimize dilution with other blood elements. The prepared PRP is subsequently drawn into a syringe, making it ready for injection.

Technique or Treatment

Landmark-Guided Injection

• Site preparation

  • Identify the acromioclavicular joint by palpating the clavicle distally until its endpoint. Palpate the small depression just lateral to the termination of the clavicle, which is the joint space.
  • Clean the injection site thoroughly with an antiseptic solution.
  • Optional: Use a skin marker to mark the injection site directly over the acromioclavicular joint line for accurate needle placement.

• Injection preparation

  • Prepare the syringe with the injectable chosen for the procedure (analgesic, corticosteroid, sodium hyaluronate, or PRP). 
  • Attach a 25- or 27-gauge needle to the syringe.

• Injection technique

  • Insert the needle perpendicular to the skin and directly into the acromioclavicular joint space. Angling the needle slightly toward the distal clavicle can be helpful.
  • Advance slowly, feeling for a reduction in resistance as the needle enters the joint space.
  • Aspirate to confirm that there is no blood return before injection.
  • Inject the medication slowly into the joint.

• Post-injection care

  • Remove the needle, apply gentle pressure to the site to prevent bleeding, and cover with a sterile bandage.

Ultrasound-Guided Injection

• Injection site and ultrasound preparation

  • Set up the ultrasound machine and select a high-frequency linear transducer (10 to 15 MHz) to visualize the superficial acromioclavicular joint.
  • Identify the acromioclavicular joint on ultrasound by locating the bony landmarks of the distal clavicle and acromion and confirming the joint space.
  • Clean the skin with an antiseptic solution and apply sterile ultrasound gel to the injection site. Place the probe in a sterile cover to maintain a sterile field.

• Injection preparation

  • Prepare a syringe with the injectable chosen for the procedure (analgesic, corticosteroid, sodium hyaluronate, PRP). 
  • Attach a 25- or 27-gauge needle.

• Injection technique

  • Using the ultrasound probe, locate the acromioclavicular joint in a transverse or longitudinal view, confirming the joint space and needle pathway.
  • Insert the needle using an in-plane or out-of-plane technique, advancing slowly toward the acromioclavicular joint space under ultrasound guidance.
  • Observe the needle's position in real time, ensuring entry into the joint capsule.
  • Once the needle is within the joint, aspirate to confirm no blood return, then inject the medication slowly, visualizing the solution and filling the joint space on an ultrasound.

• Post-injection care

  • Remove the needle, apply gentle pressure to the site to prevent bleeding, and cover with a sterile bandage.

Fluoroscopic-Guided Injection

• Site preparation

  • Palpate the acromioclavicular joint by identifying the bony landmarks of the distal clavicle and acromion.
  • Clean the injection site with an antiseptic solution such as chlorhexidine or iodine, and mark the injection entry point over the acromioclavicular joint line.
  • Prepare the fluoroscopic unit, positioning it to achieve an optimal anterior-posterior view of the acromioclavicular joint.

• Injection preparation

  • Prepare the syringe with the injectable chosen for the procedure (analgesic, corticosteroid, sodium hyaluronate, or PRP). 
  • Attach a 25- or 27-gauge needle to the syringe.

• Injection technique

  • Position the needle perpendicular to the skin, aligned with the fluoroscopic anterior-posterior view of the acromioclavicular joint.
  • Insert the needle toward the joint space, adjusting the fluoroscope to maintain optimal visualization of the needle’s path.
  • Once the needle is near the joint, inject a small amount of contrast dye under fluoroscopy to confirm accurate placement within the joint space.
  • After confirming proper placement, inject the prepared medication into the joint.

• Post-injection care

  • Withdraw the needle, apply pressure to prevent bleeding, and place a sterile bandage over the site.

Complications

Although rare, possible complications of acromioclavicular joint injections include:

• Infection
• Bleeding or hematoma formation
• Allergic reaction
• Post injection pain
• Joint degradation
• Tendon or ligament damage
• Neurovascular injury

Complications associated with corticosteroid injections include:

• Skin and soft tissue atrophy
• Hypopigmentation
• Tendon weakening or rupture
• Joint cartilage damage
• Elevated blood glucose levels (especially in patients with diabetes)
• Systemic effects such as facial flushing, mood changes, insomnia, and increased blood pressure

Complications associated with hyaluronic acid injections include:

• Joint effusion
• Skin reactions
• Stiffness or decreased range of motion
• Synovitis
• Systemic reactions such as headaches or nausea
• Infection or foreign body reaction

Complications associated with PRP injections include:

• Calcification within the injected tissue
• Joint effusion

Clinical Significance

Acromioclavicular joint injections provide diagnostic and therapeutic benefits in managing acromioclavicular joint pathology. These injections are commonly utilized to confirm the diagnosis of acromioclavicular joint disorders and to alleviate symptoms associated with inflammation or degenerative changes in the joint.

Diagnostic Benefit of Acromioclavicular Joint Injections

The primary diagnostic purpose of acromioclavicular joint injections is to determine whether the acromioclavicular joint is the source of shoulder pain. This is achieved by injecting a local anesthetic, with or without a corticosteroid, into the joint. Significant pain relief following the injection confirms the joint's involvement, helping differentiate it from other potential causes of shoulder pain, such as rotator cuff pathology.

Therapeutic Benefit of Acromioclavicular Joint Injections

Acromioclavicular joint injections are also used therapeutically to reduce inflammation and provide symptomatic relief for conditions such as osteoarthritis, traumatic injuries, or inflammatory conditions of the joint. The corticosteroid component of the injection can reduce inflammation and pain, thereby improving function and quality of life. In some instances, repeated injections may be required to sustain symptom relief. These injections are typically part of a comprehensive management plan that may also include physical therapy or, in more severe instances—surgical intervention.

Enhancing Healthcare Team Outcomes

The interprofessional team ensures patient safety and optimizes outcomes during acromioclavicular joint injections. Advanced clinicians take the lead in diagnosing acromioclavicular joint pathology, selecting suitable candidates for injection, and performing the procedure, often with imaging guidance for precision. Nurses support by ensuring patient comfort, preparing the injection site with sterile techniques to prevent infection, and educating patients on post-procedure care and monitoring for adverse effects.

Pharmacists review medications for potential contraindications, such as anticoagulants or allergies, and guide appropriate corticosteroid dosing to minimize systemic risks. Physical therapists contribute by designing rehabilitation programs to reduce pain, enhance shoulder range of motion, and restore functional strength, fostering long-term shoulder health. This collaborative approach, paired with comprehensive patient education and close monitoring, maximizes the therapeutic benefits of acromioclavicular joint injections while minimizing risks and complications.