Blind subacromial injection from the anterolateral approach: the ballooning sign

Our aim was to verify the association of fullness over the skin distal to anterior acromion termed "ballooning" in relation to accuracy of subacromial injection and determine its accuracy in terms of sensitivity, specificity, and predictive value. We hypothesized that a positive ballooning was a sign of an accurately placed injection into the subacromial bursa.

Data of 136 shoulders with impingement, which received subacromial steroid injections, were evaluated for presence of ballooning signs, pain, motion, and muscle strength. Injections were performed via anterolateral approach, followed by radiographs to locate the contrast. Data were compared between pre- and post-injections as well as between accurate and inaccurate groups to evaluate the correlations between targeting accuracy and immediate outcomes.

Ballooning signs were positive in 104 shoulders (76.5%), of which majority were inaccurate (58.7%). The accuracy rate was 49.3% with sensitivity of 64.2%, specificity 11.6% and positive as well as negative predictive values of 41.3% and 25% consecutively. Dispersal rate to the surrounding structures was 86.6% with majority infiltrated the deltoid (29.4%). Significant improvement was noted between pre- and post-injections in all parameters except muscle strength, indicating equal pain relief regardless of locations.

The ballooning sign is not a reliable indicator for or against subacromial injection. Blind subacromial injections are frequently inaccurate using the anterolateral approach. Nevertheless, immediate improvement of pain, motion, and muscle strength can be expected regardless of location.