Effect of Shoulder Arthroscopy on Deltoid Muscle Function
Abstract & Commentary
Synopsis: Because loss of anterior deltoid is a most disabling complication and a very difficult one to reconstruct and reestablish, even using the arthroscopic techniques, the surgeon must minimize the amount of bone resection and realize that at least a partial release of the deltoid muscle fibers will, in all likelihood, occur.
Source: Torpey BM et al. The deltoid muscle origin: histologic characteristics and effects of subacromial decompression. Am J Sports Med 1998;26(3):379-383
In this article, the authors take an important histological look at the deltoid muscle insertion onto the acromion in an attempt to define its attachments to its anterior and lateral aspects. The authors performed histologic sections in cadaver shoulders of the anterior acromion and showed direct and indirect attachments of the deltoid muscle to the acromion. The direct tendinous attachment inserts into the acromion at right angles to the bony surface and is characteristic of Sharpey's fibers histologically. The indirect tendinous attachment of the deltoid onto the acromion has a predominance of collagen fibers that blend obliquely into the surrounding periosteum of the acromion. After identifying the two fiber attachment types, the authors performed a hypothetical arthroscopic acromioplasty of the anterior acromion in cadavers. They found that after removal of 4 mm of bone, 41%of the direct fiber attachment of the deltoid had been released. With a 6 mm acromioplasty, 69% of the deltoid had been released.
Comment by Robert C. Schenck, Jr., MD
Shoulder arthroscopy has revolutionized both the treatment and diagnosis of sports and degenerative shoulder injuries. The technology of shoulder arthroscopy, through direct visualization, has identified pathologic shoulder conditions previously unrecognized,1,2 and these arthroscopic techniques allow shoulder reconstructive techniques without extensive surgical exposure. One particular advantage of arthroscopic techniques has been to avoid the need for deltoid release and repair. Certainly hypothetically, there is a significant advantage to protecting the deltoid muscle origin on the acromion.3,4,5 Historically, an open acromioplasty has been performed with excellent results; however, this procedure requires exposure of the acromion with release of the deltoid subperiosteally, performing the acromioplasty and then subsequently repairing the deltoid origin.6,7 Open acromioplasty has excellent long term follow-up and results; however, a small but significant complication of open acromioplasty is rupture of the deltoid repair with loss of the most important forward flexor of the shoulder - the anterior deltoid muscle. Thus, using arthroscopic techniques to perform an acromioplasty without release and subsequent repair of the deltoid muscle theoretically should be advantageous. Nonetheless, many shoulder surgeons have suspected that acromioplasty alone would release a portion of the deltoid muscle. While Torpey et al acknowledge that the exact clinical relevance of their findings in this paper is not clear, it appears that even the arthroscopic technique of acromioplasty with resection of as little as 4 mm of bone may lead to detachment of a percentage of the deltoid fibers attaching to the acromion. Therefore, at least theoretically, a subacromial decompression even with minimal bony resection will result in some degree of deltoid release. Overzealous arthroscopic decompression certainly could lead to a substantial amount of deltoid muscle release in light of these findings. Clinically, after an arthroscopic acromioplasty performed in a standard fashion, patients appear to have a functional anterior deltoid. Perhaps, partial release of the deltoid through the arthroscopic approach does not change the envelope of indirect and direct fiber attachments and allows preservation of a properly functioning anterior deltoid. Nonetheless, because loss of anterior deltoid is a most disabling complication and a very difficult one to reconstruct and reestablish, even using the arthroscopic techniques, the surgeon must minimize the amount of bone resection and realize that at least a partial release of the deltoid muscle fibers will, in all likelihood, occur.
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