Patients with rotator cuff tears experience fatty infiltration increased percentages of most likely caused primarily by muscle atrophy and a single image slice did not capture 3-D muscle measurements, according to recently published data.
“Clinical scores for muscle atrophy and fatty infiltration of the rotator cuff typically use a single image slice, and those single image slices are not actually capturing the 3-D information about fatty infiltration and the size of the muscle,” Katherine R. Saul, PhD, associate professor in the Department of Mechanical and Aerospace Engineering at North Carolina State University, told Orthopedics Today. “[A] related piece of information is the single image slice relies on a clinician’s interpretation of quantitative imaging data. They often report it appears there is more intramuscular fat after an injury, but our work demonstrates, at least in these subjects, what was happening was not so much that there was more fat present, but there was less muscle present.”
Rotator cuff tears
Saul and her colleagues performed a clinical imaging assessment on 10 patients with rotator cuff tears of the supraspinatus and 10 matched controls. Three-dimensional measurements were collected of rotator cuff muscle and of intramuscular fat tissues using MRI.
Single-image assessments had no significant association with 3-D measurements of fatty infiltration for the supraspinatus and infraspinatus muscles. Researchers found significantly increased percentages of fatty infiltration for each rotator cuff muscle in patients with rotator cuff tears vs. matched controls. Patients with rotator cuff tears hadreduced whole muscle volume and reduced fat-free muscle volume for the supraspinatus, infraspinatus and subscapularis muscles. Only the teres minor has significantly increased fatty infiltration volume. These changes were associated with significantly reduced adduction, flexion and external rotation strength for patients with rotator cuff tears. Muscle volume was a significant predictor of strength for all comparisons.
“We need to be considering treatments that try to preserve muscle volume and reduce atrophy rather than explicitly looking at the fat. The loss of muscle is tied to strengths and functional ability, so it is important to maintain that,” Saul said.
Saul said the next step is the development of a quicker clinical method to help physicians better understand where the fat is located and what geometric character the fat has in a rotator cuff tear.
“I know the methods we used for research are time-intensive and to directly apply them to the clinic is probably unrealistic, but if we have a better understanding of where clinicians should be looking for fat content, for example, then we may be able to design a method more appropriate for use in a clinical setting.”
In a study recently published in Annals of Biomedical Engineering, Saul and her colleagues performed a quantitative analysis of the whole muscle to identify where fat is located and how it is clustered.
“We can put a number to it now and found in the supraspinatus, there is both more fat and it is more clustered near the distal end end adjacent to the tendon tear, but this is different in other muscles of the rotator cuff,” Saul said. “Other researchers have qualitatively described it is different for other disease processes, so that gives us an idea it is important to, first of all, characterize the whole muscle. But also, in the specific case of rotator cuff tear of the supraspinatus, we see looking toward the distal end is a better place to look for fat rather than looking in the middle of the muscle, which is what clinical methods do now.” – by Casey Tingle
- Santago II AC, et al. Ann Biomed Eng. 2015;doi:10.1007/s10439-015-1488-z.
- Vidt ME, et al. Arthroscopy. 2016;doi:10.1016/j.arthro.2015.06.035.
- For more information:
- Katherine R. Saul, PhD, can be reached at the Department of Mechanical and Aerospace Engineering, North Carolina State University, 911 Oval Dr., Engineering Building 3, Raleigh, NC 27695; email: firstname.lastname@example.org.
Disclosure: Saul reports this work was supported by the NIH, National Institute on Aging, the National Science Foundation and the Center for Biomolecular Imaging, and the Translational Science Institute Clinical Research Unit at Wake Forest School of Medicine.