Anterior Internal Impingement
March 1, 2002 4 minutes read
Anterior Internal Impingement
Abstract & Commentary
Synopsis: Partial thickness undersurface rotator cuff tears were identified with anterior internal impingement between the rotator cuff and the anterior superior glenoid in the absence of any evidence of subacromial impingement. Treatment was simple debridement without acromioplasty.
Source: Struhl S. Anterior internal impingement: An arthroscopic observation. Arthroscopy. 2002;18(1):2-7.
Classical outlet impingement as described by Neer refers to pinching of the bursa and rotator cuff under the coracoacromial arch and is associated with rotator cuff tears that occur by attrition. Subacromial decompression has been a standard of care for this outlet impingement with good results. At times, partial thickness tears are observed that seem to originate on the undersurface. Dr. Struhl has made an association with this entity and a new type of impingement that he terms anterior internal impingement. He makes the case that this is different than outlet impingement and should be treated differently as well.
Ten patients who presented clinically in much the same way as patients with classic impingement were identified as having undersurface or articular-sided partial thickness rotator cuff tears. In all of these cases that he took to arthroscopy there was no evidence of subacromial bursitis or outlet impingement. The undersurface rotator cuff tear was a flap or frayed tissue that he noted to come in contact with the anterior superior labrum and glenoid when the arm was in a flexed, internally rotated position. This is the same position the shoulder is placed for the Hawkins test for impingement. In many cases, the patients also had associated glenoid labral fraying in the anterior superior position where impingement occurred. Interestingly, the MRI correctly diagnosed the partial thickness cuff tear in only 20% of the cases. Dr. Struhl used low volume gas arthroscopy through a single posterior portal at the beginning of each case to help identify these partial thickness tears before distortion with large volumes of arthroscopic fluid.
He treated each of these cases by simple debridement of the rotator cuff partial tear. No acromioplasty was performed. The follow-up was brief at only 6 months, and 6 of 9 were pain free with full motion. One patient had basically no improvement who also had coexisting osteoarthritis. The point of the study was not the clinical outcome as much as the clinical correlation with this new diagnostic entity.
Comment by David R. Diduch, MS, MD
Just when we think we understand something here comes another curve ball. Classic outlet impingement as described by Neer is well understood and is a relatively common clinical finding that responds well to subacromial decompression when nonoperative measures fail. Previously, the concept of internal impingement was identified with a partial thickness posterior rotator cuff tear in high level athletes engaged in overhead sports. In an abducted, externally rotated position with the arm cocked back, the undersurface of the rotator cuff was noted to impinge between the posterior head and glenoid margin creating partial thickness cuff tears. This diagnosis is associated with subtle shoulder instability, allowing the shoulder to slide anteriorly while pinching posteriorly.
This concept presented by Dr. Struhl represents a new flavor of internal impingement. None of these patients was noted to have instability or laxity. Rather, he was able to demonstrate using low pressure gas arthroscopy that the anterior portion of the supraspinatus impinged against the anterior superior glenoid labrum when the arm was forward flexed and internally rotated, equivalent to the Hawkins impingement position. He noted that none of these patients had associated subacromial impingement findings at the time of arthroscopy. The photographs in the paper are quite nice and I recommend that the reader review these to better understand the concept.
Dr. Struhl felt that simple debridement of the partial thickness cuff tear and associated labral damage was sufficient treatment. The concept here is removal of the mechanical irritant, avoiding an acromioplasty with its associated morbidity. The major problem I have with this paper is that we don’t have any long-term follow-up or sufficient numbers to determine if his treatment is indeed effective. I agree that his clinical correlation with the arthroscopic images is compelling. I would also agree that this appears to be a variety of partial thickness rotator cuff tear with a different etiology than classic impingement. However, long-term studies must be presented before we can adopt simple debridement as sufficient treatment in the absence of acromioplasty and know that pinching of the cuff without associated laxity is responsible for its diagnosis. The problem is this portion of the cuff has a watershed vascular supply and is associated with outlet impingement as well, possibly predisposing this area of the cuff to undersurface tear from internal impingement. I suspect that we will see a lot more about this in the future.
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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