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Study links fatty degeneration of the rotator cuff with tear size
Kim HM. J Bone Joint Surg (Am). 2010;92:829–839.
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In a recent study, investigators discovered that shoulders with full-thickness rotator cuff tears were most likely to show evidence of fatty degeneration on ultrasonograms.
For their study, H. Mike Kim, MD, of the Washington University School of Medicine, St. Louis, and colleagues reviewed the ultrasonograms of both shoulders in 262 patients to study the types of rotator cuff tears and the presence of fatty degeneration in the supraspinatus and infraspinatus muscles.
The investigators identified 251 shoulders that had full-thickness rotator cuff tears and evaluated the size of the tear and its location. They then statistically compared the relationship of cuff tear size and location to the amount of fatty degeneration in the rotator cuff muscles.
“Of the 251 shoulders with a full-thickness tear, 87 (34.7%) had fatty degeneration in either the supraspinatus or infraspinatus, or both,” the investigators wrote in their study abstract. They also found that 82 tears (32.7%) were located 0 mm between the biceps tendon and the anterior margin of the tear.
Furthermore, “90% of the full-thickness tears with fatty degeneration of both muscles had a distance of 0 mm posterior from the biceps, whereas only 9% of those without fatty degeneration had a distance of 0 mm,” the investigators wrote.
They also found that the width and length of tears with fatty degeneration was greater than those without fatty degeneration, and that the distance posterior from the biceps was significantly shorter in tears with fatty degeneration. Both these differences were statistically significant.
Fatty degeneration greatly affects outcome of rotator cuff surgery with higher levels of fatty degeneration being associated with higher retear rates and inferior outcomes. The study by Kim identified a striking relationship linking increased tear size with increased fatty degeneration. In addition, the distance of the tear posterior to the biceps was more important than tear length and width in predicting supraspinatus fatty degeneration. In fact, this is the first study to establish an association between tear size and tear geometry.
The mechanism of the fatty degeneration for supraspinatus tears that are preferentially located at the anterior aspect is likely related to regional variation in the tendon-muscle unit anatomy. The anterior supraspinatus tendon is known as the rotator cuff cable, and this portion of the tendon has greater muscle mass attaching to it than the more posterior aspect of the tendon. Therefore, anterior tears functionally detach more supraspinatus muscle.
This work has important clinical implications. First, patients with asymptomatic rotator cuff tears, such as those that responded well to initial nonoperative treatment, need counseling on the risks associated with delayed surgery. Based on the findings of Kim, patients can now be better counseled with knowledge that anterior supraspinatus tears have a greater association with fatty degeneration. Second, when surgical repair is performed on supraspinatus tears, great emphasis must be taken to optimize the repair of the anterior aspect of the supraspinatus tendon.
– Christopher S. Ahmad, MD
Assistant Professor of Orthopedic Surgery
Columbia University, Center for Shoulder, Elbow and Sports Medicine
New York