Subacromial Space Injection
Pain Reliever, Diagnostic Tool
William O. Roberts, MD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 27 - NO. 4 - APRIL 1999
Some of the most common presentations in a primary care office relate to shoulder pain; disorders of the rotator cuff and potential look-alikes such as referred neck pain or acromioclavicular (AC) joint arthritis are chief among the causes. The differential diagnosis can be difficult, particularly among older patients. And, of course, patients want relief of pain. Subacromial space injection using anesthetic with or without corticosteroid can assist in both phases of management.
Diagnostic and Therapeutic Uses
Subacromial space injection is used for several reasons. The first is for determining whether shoulder pain is due to rotator cuff inflammation (tendinitis) or rotator cuff disruption (tear). Subacromial injection of anesthetic takes just minutes and can eliminate the need for costly magnetic resonance imaging (MRI). Pain can inhibit muscle contraction, mimicking weakness secondary to a tear. An injection of the subacromial space relieves the pain. If strength returns after injection, the cause of the pain is more likely to be inflammation than disruption, and the next step is treatment with aggressive physical therapy. If strength does not return, the cause may be a tear. At this point, the patient may require surgical evaluation, including an MRI.
A second common reason for the procedure is to distinguish AC joint pain from subacromial pain. This involves a two-step sequence of injection of the AC joint with 1.0 to 1.5 mL of anesthetic, followed by injection of the subacromial space (see figure 1 and text, below), if necessary. The solution for injection of the AC joint can include all short-acting anesthetic, equal parts short- and long-acting anesthetic, or 5 to 10 mg steroid with anesthetic solution to equal 1.5 mL.
Subacromial space injection can also be used for injection of corticosteroid to reduce inflammation and to achieve long-term pain relief for tendinitis and bursitis. This method for "curing" tendinitis has not been documented in clinical studies, but it has resulted in short- and long-term pain relief. Although the use of corticosteroid is not required for diagnostic injections, many physicians include it in the solution with the hope of longer relief of pain.
Anticipate syncope. The most "patient friendly" position for this procedure is a posterior approach inferior to the acromion process while the patient is seated. However, vasovagal reactions can occur, and a history of syncope with procedures may be a reason to avoid this posterior sitting approach. Alternatively, the procedure can be done with the patient in the lateral decubitus position, affected shoulder up.
Locate the site. When using the posterior sitting approach, locate the injection site by palpating the corner of the acromion process and making a fingernail cross or pen-point dimple about 1 cm inferior to the medial corner of the process. An injection mark is helpful in patients who have a thick fat layer but may not be necessary in thin patients whose anatomy is well defined. After marking the injection site, cleanse the skin with an antiseptic solution.
Prepare the solution. An adult subacromial space will comfortably tolerate 10 mL of injected solution, and injection of this volume will result in uniform distribution of the medication throughout the area. An effective mixture includes 1 mL of triamcinolone hexacetonide (20 mg/mL) with 5 mL of 1% lidocaine and 4 mL of 0.5% bupivacaine hydrochloride for a total of 10 mL of solution. For an injection without corticosteroid, use an equal mix of fast- and long-acting local anesthetics.
Needle and needle angle. After drawing up the medications with an 18- to 22-gauge needle, change to a 25-gauge needle that is 1.25 to 1.5 in. long for insertion. No local anesthetic is needed with the smaller gauge needle.
The patient should sit on an exam table so that he or she may be easily laid down should syncope occur. Grasp the shoulder with the thumb on the posterior border of the acromion and the index finger on the coracoid process as shown in figure 1. The entry point is located just lateral to the thumb and just below the medial corner of the acromion process. The joint is entered with the needle aimed upward about 15° toward the coracoid process (figure 1). This angle is important because a needle angled medial to the coracoid process in the horizontal plane will enter the glenoid space.
Insertion. Insert the needle parallel to the undersurface of the acromion and feel for the resistance changes as it passes through the different tissue layers. A "pop" can usually be felt as the needle passes into the subacromial space.
Entry into the subacromial space is generally simple. However, if the acromion or head of the humerus is encountered during the joint entry, back the needle off and advance slowly with the redirected needle. An unexpected increase in needle resistance may indicate entry into ligament or the supraspinatus tendon.
Injection and withdrawal. The needle should be inserted to nearly its full length. Before injecting into the space, aspirate to ensure there is no return of blood. The smaller 25-gauge needle will have a greater resistance to injection than a larger-gauge needle, and it takes practice to get the feel of normal injection flow. If there is unexpected flow resistance to the injection, withdraw the needle slightly to see if the flow resistance decreases.
There is usually minimal or no bleeding following withdrawal of the needle. If there is no bleeding, cover the site with bacitracin ointment and an adhesive strip. If bleeding occurs, apply sustained pressure until the bleeding stops, apply bacitracin, and then cover the entry wound with an oversized gauze pad and compression tape.
Despite correct technique, complications can occur, including allergic and toxic reactions to the medications. Be prepared for the unexpected, and have the necessary equipment available to handle an emergent reaction to the medication.
Coding this procedure can be confusing but is important for appropriate reimbursement. If the injection is part of a diagnostic work-up or a treatment procedure associated with an evaluation or reevaluation of the shoulder, the appropriate coding should include either (1) an evaluation code (99213 or 99214) with a 25- modifier or (2) a consult code (99241, 99242, 99243, 99244, or 99245), together with a procedure code for shoulder injection (20610).
Dr Roberts is a family physician at MinnHealth SportsCare in White Bear Lake, Minnesota, and medical director of the Twin Cities Marathon. He is a fellow of the American College of Sports Medicine, a charter member of the American Medical Society for Sports Medicine, and an editorial board member of The Physician and Sportsmedicine.