Shoulder MRI after impingement test injection

Objective. To determine how long injected fluid from an impingement test remains in the bursa or adjacent soft tissues after an injection. Design and patients. Six patients prospectively underwent MRI of the shoulder immediately before and after an impingement test injection, and at 3 days, 2 weeks and 4 weeks later. MR images were evaluated and graded for fluid distribution within the bursa and adjacent soft tissues. The rotator cuff was evaluated for signal abnormalities related to the injection. Results and conclusion. Three days after the injection, the soft tissue fluid had returned to pre-injection levels or less in five of the six patients. No patients showed rotator cuff signal abnormalities related to the impingement test injection. We recommend a delay of 3 days before a shoulder MR examination after an injection has been performed, to avoid misinterpretations.