Original Research

Comparison of Anterior and Posterior Cortico­steroid Injections for Pain Relief and Functional Improvement in Shoulder Impingement Syndrome

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Subacromial impingement syndrome (SIS) is the most common cause of shoulder pain. Treatment options for SIS include conservative modalities such as use of nonsteroidal anti-inflammatory drugs, physical therapy, and subacromial corticosteroid injections (CSIs). Although studies have found improvement in pain, function, and range of motion after CSI, the effect of injection route (anterior or posterior) on shoulder pain in patients with SIS has not been investigated.

In the study reported here, patients were randomly assigned to 2 treatment groups: anterior CSI and posterior CSI. Pain was assessed with a visual analog scale (VAS) and function with the Single Assessment Numeric Evaluation (SANE). Patients were evaluated before injection (baseline) and 1, 3, and 6 months after injection.

Of the 55 patients enrolled, 25 received anterior CSI and 30 received posterior CSI. The 2 groups showed no significant difference in VAS pain at baseline or 1, 3, or 6 months after injection. SANE scores were statistically different at 3 months. Each group had significantly less pain and better function 1, 3, and 6 months after injection than at baseline. Age, sex, and body mass index did not significantly affect the efficacy of anterior or posterior CSIs.

In patients with SIS, subacromial CSI reduces pain and improves function for up to 6 months. These effects are no different for anterior and posterior injection routes. As a result, clinicians should rely on their clinical acumen when selecting injection routes, as anterior and posterior are both beneficial.


 

References

Take-Home Points

  • When conservative treatments for SIS do not resolve symptoms, inflammation and pain can be reduced with use of subacromial CSI.

  • Both anterior CSI and posterior CSI significantly improved pain and function for up to 6 months

  • CSI combined with structured PT produced significant improvement in pain and function in patients with SIS, regardless of injection route used.

  • Clinical response to CSI may not depend on injection accuracy.

  • Clinicians should rely on their clinical acumen when selecting injection routes, as anterior and posterior are both beneficial.

Shoulder pain, a common clinical problem, occurs in 7% to 34% of the general population and in 21% of people older than 70 years. 1Subacromial impingement refers to shoulder pain resulting from mechanical impingement of the rotator cuff underneath the coracoacromial arch between the acromion and the humeral head. 2,3 Subacromial impingement syndrome (SIS) is the most common cause of shoulder pain, resulting in significant functional deficits and disability. 3

Treatment options for SIS include conservative modalities such as use of nonsteroidal anti-inflammatory drugs, physical therapy (PT), and subacromial corticosteroid injections (CSIs). Studies have found short- and long-term improvement in pain, function, and range of motion after CSI. 4-8 Subacromial CSI can be administered through an anterior or a posterior route. 4,9 There have been several studies of the accuracy of anterior and posterior CSIs,10-12 with 2 studies finding similar accuracy for these routes. 10,11 However, there may be a sex difference: In women, a posterior route may be less accurate than an anterior or a lateral route. 12

Although the accuracy of anterior and posterior routes has been studied, their effect on clinical outcomes has not. We conducted a study to understand the effects of anterior and posterior CSIs on SIS. As one of the accuracy studies suggested anterior CSI is more accurate—the anterior route was theorized to provide easier access to the subacromial space 12—we hypothesized patients treated with anterior CSI would have superior clinical outcomes 6 months after injection. 12,13

Materials and Methods

Study Participants and Randomization

After this study received Institutional Review Board approval, patients with shoulder pain of more than 3 months’ duration and consistent with SIS were screened for inclusion. Eligible patients had pain in the anterior biceps and over the top of the shoulder with overhead activities as well as one or more clinical findings on physical examination: Hawkins-Kennedy sign, Neer sign, painful arc, and infraspinatus pain (pain with external rotation).

Patients were excluded if their history included prior subacromial CSI, adhesive capsulitis (inability to passively abduct shoulder to 90 ° with scapular stabilization), calcific tendonitis, radiographic evidence of os acromiale, cervical radiculopathy, Spurling sign, neck pain, radiating arm pain or numbness, sensory deficits, or neck and upper extremity motor dysfunction. Also excluded were patients with full-thickness rotator cuff tear, weakness on arm elevation, positive "drop arm sign," or high-riding humerus on standing shoulder radiograph. Patients who had work-related injuries or who were involved in worker compensation were excluded as well.

Enrolled patients were randomly assigned (with use of a computer-based random number generator) to receive either anterior CSI or posterior CSI.

Injection Procedures

All patients were administered 5 mL of lidocaine 1% (without epinephrine) and 2 mL (80 mg) of triamcinolone by 2 board-certified orthopedic surgeons using a 22-gauge 1 ½-inch needle. For patients who received their subacromial CSI by the anterior route, the arm was held in 0° of abduction and 20° of external rotation. The needle was inserted medial to the humeral head, lateral to the coracoid process, beginning 1 cm inferior to the clavicle with the needle directed posteriorly and laterally toward the acromion. 10 For patients who received their CSI by the posterior route, the arm was held in 0° of abduction, the posterolateral corner of the acromion was identified by palpation, and the needle was inserted 1 cm inferior and medial to this point with the needle directed anteriorly and laterally toward the acromion. 10,12 In both groups, the subacromial space was identified when a drop in pressure was felt during needle insertion. Accuracy was assessed post hoc by asking patients to grade their response to the injection on a visual analog scale (VAS); VAS score was used as a surrogate for improvement. All patients had a positive Neer test: Pain decreased with impingement maneuvers immediately after injection.

All patients were referred for PT provided according to an evidence-based rehabilitation protocol. 14 This program emphasized range of motion with shoulder shrugs, scapular retraction, and pendulum exercises; flexibility

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