Shoulder Subacromial Injections 

Impingement syndrome and rotator cuff disorders (see the images below) are common causes of shoulder pain.^[1] These conditions are difficult to differentiate clinically. Both are chronic, painful conditions that result from inflammation, damage, or both to the structures that lie within the subacromial space. These structures include the subacromial bursa and the rotator cuff tendons.

Both conditions are treated the same initially. Nonoperative treatment should begin with measures to reduce pain and inflammation, including activity modification, modalities, and nonsteroidal anti-inflammatory drugs (NSAIDs).^[2] If this is not effective, some patients may benefit from a subacromial corticosteroid injection.

Corticosteroid injections can decrease inflammation and improve function,^[3] thus permitting improved range of motion and facilitating rehabilitative and strengthening exercises.^[4]

One study tested botulinum toxin type B for subacromial injections and concluded that botulinum toxin type B may be an alternative to steroid injections.^[5]

As with most joint and soft tissue injections with corticosteroids or anesthetics, subacromial injections can be used either diagnostically or therapeutically.^[2]

• A diagnostic joint injection with or without a corticosteroid can help differentiate if shoulder pain is result of the structures that lie within the subacromial space (ie, subacromial bursa or rotator cuff). This can help differentiate impingement syndrome from other shoulder disorders such as osteoarthritis of the glenohumeral or acromioclavicular joints and labral tears. If pain resolves or decreases following injection, then the pain is likely attributable to inflammation of either the subacromial bursa or the rotator cuff. Furthermore, this injection is particularly helpful in differentiating between shoulder weakness caused by impingement, in which shoulder strength improves after injection, and a true rotator cuff tear, where no change in strength is noted following injection.^[4]
• Therapeutic joint injection provides pain relief and functional improvement in symptomatic subacromial impingement syndrome, rotator cuff disorders, and adhesive capsulitis.^[6] This is completed through delivering the corticosteroid to either the subacromial bursa or the rotator cuff.

• Bacteremia, cellulitis of overlying skin, and adjacent osteomyelitis are often considered absolute contraindications because of the potential risk of seeding the joint with bacteria. In these situations, the procedure should only be performed when septic arthritis is strongly suspected as the cause of overlying inflammatory changes, and only after consultation with an orthopedist.
• Relative contraindications include chronic infection distant to injection site, allergy to injectate, diabetes mellitus, or uncontrolled coagulopathy.

• Cooling spray or local anesthetic may be used.
• If a local anesthetic is used, use a separate 25-gauge needle to raise a wheal at the site of the injection by inserting the needle about 1 cm below the skin surface. For more information, see Local Anesthetic Agents, Infiltrative Administration.

• Sterile gloves
• Bactericidal skin preparation solution
• Needle, 1.5 inch, 22-25 gauge
• Syringe, 10 mL
• Lidocaine 1% without epinephrine (or similar local anesthetic), 5 mL
• Corticosteroid, 1-2 mL (For more information, see Corticosteroid Injections of Joints and Soft Tissues.)
• Sterile gauze
• Sterile adhesive bandage

• The patient should be seated upright in a comfortable position with the arm hanging unsupported by the patient's side.

Note: Opinions differ regarding single- versus two-needle injection technique. The single-needle technique is less painful. The two-needle technique prevents the possibility of flocculation of steroid crystals in the local anesthetic after mixing. Proponents of the two-needle technique also suggest that injection of the local anesthetic first numbs the area, making the subsequent injection more tolerable. The single-needle technique is described below.

• Discuss the risks, benefits, and alternatives with the patient. Obtain informed consent.
• The patient should be seated upright in a comfortable position with the arm hanging unsupported by the patient’s side.
• Palpate and mark the distal posterolateral edge of the acromion.
• Wear sterile gloves during the procedure.
• Prepare and drape the site in a sterile manner with povidone-iodine (Betadine), chlorhexidine gluconate (Hibiclens), or isopropyl alcohol.
• Insert the needle inferior to the posterolateral edge of the acromion. The needle is directed medially and slightly anteriorly. This places the needle tip beneath the acromion.
• Always aspirate before injecting to ensure the needle tip is not placed intravascularly.
• Inject the 6-7 mL corticosteroid/local anesthetic preparation. The injectate should flow freely without any significant resistance.
• Dress the site with a sterile adhesive bandage.
• Encourage the patient to ice the area immediately following the injection and to avoid strenuous activity with the involved shoulder for remainder of the day.

  A 77-year-old woman with a long history of chronic right shoulder impingement. A posterior approach for subacromial injection is performed. Video courtesy of James R Verheyden, MD.

• In general, subacromial injection with corticosteroids should not be performed more than 4 times per year.
• If the patient has a contraindication to the use of corticosteroid, then a diagnostic block may be performed using only local anesthetic. After the injection, patients with impingement syndrome experience temporary relief of symptoms and increased range of motion and strength.
• In the setting of a rotator cuff tear, corticosteroid injections should be used judiciously. The injection may decrease inflammation and provide short-term pain relief, but steroid injections also weaken the involved tendon.^[3]
• Never inject if significant resistance is encountered. Reposition the needle and reattempt until minimal resistance is encountered.
• Treatment of impingement or rotator cuff syndrome should involve physical therapy.^[4]
• If no improvement is observed following injection, further imaging is indicated.

Complications are uncommon and often insignificant but include the following:

• Iatrogenic infection: The risk of inducing joint infection is low when sterile technique is used.
• Injection of corticosteroids directly into a tendon or tendon insertion can sometimes result in tendon rupture.
• Corticosteroids may cause a transient rise in blood glucose levels in patients with diabetes mellitus.
• Subcutaneous corticosteroid injection may also cause skin hypopigmentation and fat atrophy.