Comparison of rotator cuff muscle architecture among humans and selected vertebrate species

Abstract

In this study, we compare rotator cuff muscle architecture of typically used animal models with that of humans and quantify the scaling relationships of these muscles across mammals. The four muscles that correspond to the human rotator cuff -supraspinatus, infraspinatus, subscapularis and teres minor -of 10 commonly studied animals were excised and subjected to a series of comparative measurements. When body mass among animals was regressed against physiological cross-sectional area, muscle mass and normalized fiber length, the confidence intervals suggested geometric scaling but did not exclude other scaling relationships. Based on the architectural difference index (ADI), a combined measure of fiber length-to-moment arm ratio, fiber length-to-muscle length ratio and the fraction of the total rotator cuff physiological cross-sectional area contributed by each muscle, chimpanzees were found to be the most similar to humans (ADI=2.15), followed closely by capuchins (ADI=2.16). Interestingly, of the eight non-primates studied, smaller mammals such as mice, rats and dogs were more similar to humans in architectural parameters compared with larger mammals such as sheep, pigs or cows. The force production versus velocity trade-off (indicated by fiber length-to-moment arm ratio) and the excursion ability (indicated by fiber length-to-muscle length ratio) of humans were also most similar to those of primates, followed by the small mammals. Overall, primates provide the best architectural representation of human muscle architecture. However, based on the muscle architectural parameters of non-primates, smaller rather than larger mammals may be better models for studying muscles related to the human rotator cuff.

Allometry of the Tendon Enthesis: Mechanisms of Load Transfer Between Tendon and Bone

“…For each species studied, approximately three animals were used. Such sample sizes are not uncommon for allometric studies in which the number of species is of greater importance than the number of individual animals [23,41]. The spread in the variables is quite small with an n ¼ 3; therefore, this value was employed to minimize animal usage.…”

“…Values of pennation angle and fiber length for the supraspinatus muscle of each animal were taken from Mathewson et al [23]. The value of PCSA for a particular muscle is directly proportional to the force generated by that muscle [24][25][26].…”

Muscle Fibers are Injured at the Time of Acute and Chronic Rotator Cuff Repair

“…In rats, the length of individual fibers is approximately 40% of the whole muscle length [19], so changes in fibers located in the distal portion of the muscle may not reflect changes in fibers located in the proximal portion. Although the middistal portion showed widespread damage in the acute tear and chronic tear and repair groups, the midproximal portion was protected from injury for most experimental conditions.…”

“…The degree of shortening and lengthening we observed is similar to what is observed clinically. In humans, the length of an intact supraspinatus muscle is approximately 11 cm [19], and because many patients have chronic tears that are 2 to 3 cm in length [20], surgical repair of a torn rotator cuff may result in sudden 20% or greater changes in length that may induce extensive injury throughout the muscle.…”

The Influence of Partial and Full Thickness Tears on Infraspinatus Tendon Strain Patterns

“…While this does achieve the loading conditions of a tear, it fails to mimic the pathologic and degenerative changes that are usually associated with a rotator cuff tendon tear. Second, we used a sheep infraspinatus tendon, which is frequently used as a model for rotator cuff pathology repair due to its size and geometric similarity to the human supraspinatus tendon; however, it has recently been suggested that smaller mammals or rodents may be a more functionally accurate model [23,24]. In addition, it has recently been reported that collagen fiber organization and alignment are affected by load; however, little work has been done comparing the fibril level architecture between sheep and human rotator cuff tendons, which limits the inferences that can be made [14,17,21].…”