The targeting accuracy of subacromial injection to the shoulder: an arthrographic evaluation.

PURPOSE The study goal was to examine the targeting accuracy of subacromial injection to the shoulder and the influence of the location of the injected structure. TYPE OF STUDY A prospective nonrandomized study. METHODS Fifty-three patients (56 shoulders; 34 women and 19 men; mean age, 74.5 years; range, 49 to 91) with impingement signs (Neer, Hawkins) of at least 2 months' duration received a subacromial injection of a mixture of 0.5 mL (2.5 mg) betamethasone acetate and 3 mL of radiographic contrast material (iotrolan) and 7 mL of 1% lidocaine using a lateral approach. Radiographs of the shoulder joint were taken immediately after the injection to determine the structure reached by the injection. Details of pain expressed as Neer and Hawkins impingement signs were obtained before and 15 minutes after the injection, and subjectively assessed using a 4-point self-administered pain score. Pain reduction resulting from subacromial and intradeltoid injection was compared. RESULTS Thirty-nine of the 56 injections (70%) were judged to have reached the subacromial bursa. Twelve (21%) were seen to have entered the deltoid muscle; 2 (4%) were in the glenohumeral joint; and 3 (5%) were subcutaneous. A comparison of subacromial bursal with intradeltoid injection showed no significant differences in pain reduction expressed as impingement signs (1.5 vs 1.7 in the Neer impingement sign and 1.6 vs 1.6 in the Hawkins impingement sign, respectively). CONCLUSIONS This study showed that subacromial injection was a relatively difficult procedure. A high incidence of injections that missed the subacromial bursa would be a sufficient reason to refrain from repeated usage of corticosteroids. These results also suggest that pain relief could be attained whether the injected material reached the subacromial bursa or the deltoid muscle. Successful pain relief after intradeltoid injection seems to call into question the diagnostic value of a positive Neer impingement test.