The accuracy of subacromial injections: a prospective randomized magnetic resonance imaging study.

Abstract

To assess the accuracy of shoulder infiltrations in the subacromial bursa (SAB) by a posterior or an anteromedial approach. Magnetic resonance imaging (MRI) and clinical outcome were used for evaluation. A prospective randomized study. Thirty-three patients (22 women, 11 men; average age, 46 years; range, 25 to 64 years) with clinical signs of subacromial impingement were infiltrated with a mixture of bupivacaine, methylprednisolone, and gadolinium-DTPA directly followed by MRI to determine the actual site of injection. The SAB was randomly infiltrated posteriorly (n = 17) or anteromedially (n = 16). Injection confidence of the surgeon and body-mass index of the patient were recorded. Follow-up consisted of the Constant Score, Simple Shoulder Test, and visual analog scale score for pain taken within 24 hours and 6 weeks after infiltration. Thirteen injections (76%) were in the SAB with a posterior approach and 10 (69%) with an anteromedial approach. Many surrounding structures were hit as well, especially the rotator cuff. A positive correlation between the injection confidence of the orthopaedic surgeon and the MRI was found in 66%. Only injection of the SAB alone resulted in a significant decrease of the pain (P = .004) and an increase in the functional scores. Injection in the bursa and rotator cuff muscle showed a significant increase in pain (P = .032) but no change in clinical scores. The body mass index had no influence on the scores. Injections in the SAB are inaccurate, despite the confident feeling of the clinician. The finding that many different structures can be infiltrated with 1 injection can create both false-positive and -negative results. Level II.