Use of the Impingement Test to Predict Outcome Following Shoulder Surgery
Abstract & Commentary
Synopsis: The classic impingement test, relief of pain with injection of anesthetic into the subacromial space with the impingement position, was not useful to predict clinical outcome following arthroscopic subacromial decompression.
Source: Kirkley A, et al. Arthroscopy. 2002;18:8-15.
The classic impingement test is defined as significant relief of shoulder pain following a subacromial injection of local anesthetic as the arm is then placed into the Neer impingement position. This has been used for years to help confirm the diagnosis of impingement as the source of pain. Many physicians, including myself, have taken a positive test result to suggest a positive outcome should the patient undergo subacromial decompression surgically. Kirkley and colleagues have challenged this assumption with the present study.
Thirty patients who had failed at least 6 months of conservative treatment were enrolled in this study. Patients having rotator cuff tears by ultrasound or arthroscopy, as well as glenohumeral or acromioclavicular arthritis, were excluded. They were left with patients with classic impingement and rotator cuff tendonosis or partial, insignificant tears. On the day of surgery immediately prior to the procedure, 1 of the 2 surgeons performed the impingement test by injecting 5 mL of 1% Lidocaine into the subacromial space using fluoroscopy to confirm needle location. Ten minutes following the injection, the arm was placed into the impingement position and pain relief was assessed using a visual analogue scale. Both the Neer and the Hawkins impingement positions were used, as well as an assessment of pain at rest and pain with resisted abduction of the shoulder. The outcome following the ensuing arthroscopic subacromial decompression was assessed with a Western Ontario Rotator Cuff Index and the scoring system of the American Shoulder and Elbow Surgeons at 3, 6, and 12 months postoperatively.
Kirkley et al found that pain relief with the impingement test was not a useful predictor of outcome following surgery. Similarly, they found that pain relief with the aggregate impingement test, that is, pain at rest + Neer impingement sign + Hawkins impingement sign + resisted abduction, also is not a good predictor of outcome following surgery.
Comment by David R. Diduch, MD
Kirkley et al challenge a common assumption in orthopaedics. That is, that pain relief with a subacromial injection will predict pain relief once surgical decompression is performed. They carefully constructed a prospective, randomized study that confirmed that both pain relief with the classic Neer impingement test following injection, as well as relief following the Hawkins impingement test and resisted abduction, really had no bearing on whether the patients would improve following surgery. Potential confounding variables that may dilute their findings included that a third of the patients were Workers Compensation and perhaps less motivated to show any improvement and that 43% of their patients had partial thickness rotator cuff tears less than 50% of the cuff thickness. The vast majority of these were on the undersurface of the tendon that is not likely to see the local anesthetic that was injected into the subacromial space. Although this is a confounding variable, that is often the case clinically as well.
Kirkley et al present 6 assumptions that would need to be met in order for the impingement test to be a positive predictor of outcome. They state that if any of these 6 assumptions are not met, then the correlation does not hold true. The first is that the impingement sign of pain with forward flexion overhead may not be sensitive to detect impingement. Next, the injection must be placed into the subacromial space within the bursa at the site of the impingement. The rotator cuff and corresponding bursa would have to be the only structures affected by the anesthetic to make the test valid. The entire thickness of the rotator cuff tendon would have to be anesthetized to provide pain relief for partial thickness tears on the articular surface. Surgery must address the source of pain in terms of the decompression. This is also important in terms of treatment of partial thickness rotator cuff tears. Whether to excise and repair vs. debride alone can be very difficult to determine at the time of surgery. And lastly, as always, the surgery must be done correctly.
This is a very thoughtful paper that really helps us understand the limitations of the impingement test. While it does not discredit the usefulness of the impingement test in the clinical setting, it does help us better understand what to do with the results.
Dr. Diduch, Associate Professor, Department of Orthopaedic Surgery, University of Virginia School of Medicine, Charlottesville, VA, is Editor of Sports Medicine Reports.
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