Comparative anatomy of the rotator cuff

Abstract

While the evolution of the bony skeleton of the shoulder girdle is well described, there is little information regarding the soft tissues, in particular of the rotator cuff. We dissected the shoulders of 23 different species and compared the anatomical features of the tendons of the rotator cuff. The alignment and orientation of the collagen fibres of some of the tendons were also examined histologically. The behaviour of the relevant species was studied, with particular reference to the extent and frequency of forward-reaching and overhead activity of the forelimb. In quadrupedal species, the tendons of supraspinatus, infraspinatus and teres minor were seen to insert into the greater tuberosity of the humerus separately. They therefore did not form a true rotator cuff with blending of the tendons. This was only found in advanced primates and in one unusual species, the tree kangaroo. These findings support the suggestion that the appearance of the rotator cuff in the evolutionary process parallels anatomical adaptation to regular overhead activity and the increased use of the arm away from the sagittal plane.

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

“…Therefore, the effect of weight-bearing and upper extremity function on muscle size should be considered when choosing an appropriate animal model. Non-human primates are more closely related to humans compared with non-primate mammals, and have many morphological similarities (Sonnabend and Young, 2009). Therefore, it is not surprising that the rotator cuff muscle anatomy of the two primates in this study is more similar to that of humans than the other species, because upper limb functions are more similar to those of humans.…”

“…For this study, we consider muscle architectural parameters such as PCSA, fiber length to muscle length ratio (L fn /L mn ) and L fn /MA as the most important architectural parameters. While some anatomical and architectural characteristics of various shoulder muscles of individual animals have been reported (Oxnard, 1968;Sonnabend and Young, 2009), a comprehensive architectural comparison across multiple species has not been undertaken. Therefore, this study had two aims: (1) to define the architecture of each of the four rotator cuff muscles among humans and 10 species commonly used in rotator cuff research to determine the best models for the healthy human rotator cuff, and (2) to determine how rotator cuff muscle architecture scales with body size.…”

“…Other quadrupeds such as sheep, pigs, cows, rats and mice had tendons that inserted independently (Sonnabend and Young, 2009). This difference is most likely due to the fact that humans and the other primates in the study have a much wider range of forelimb motion, and perhaps less bony stability, compared with the other animals studied and that they lift their forelimbs above their heads in the course of normal motion.…”

“…Because the human glenohumeral joint has little intrinsic joint stability (O'Brien et al, 1990;Turkel et al, 1981), rotator cuff muscles and ligaments play a crucial role in maintaining stability throughout the range of motion. The tendons of the four rotator cuff muscles, while separate at the muscle bellies, come together at the glenohumeral joint and fuse with the fibrous capsule (Clark and Harryman, 1992;Sonnabend and Young, 2009). Architecturally and biomechanically, the muscles complement each other, allowing sarcomere length to vary in a way that maximizes force production over a wide range of joint angles and, therefore, maximizes stability (Ward et al, 2006).…”

Characteristics of Animal Shoulder Models for Rotator Cuff Experiments

“…7). 23) Baboons have a true definite RC with the tendons of SSP and ISP blending well medial to their insertion to the greater tuberosity. As in man, the tendon of TM in the baboon was much shorter than those of the spinati, but it did blend with the posterior margin of the tendon of ISP, completing the RC.…”