Ectopic tendons of the pectoralis minor muscle as cause for shoulder pain and motion inhibition—Explaining clinically important variabilities through phylogenesis

Abstract

OJECTIVE Clinical consequences of ectopic tendons of the pectoralis minor muscle (PMM) for shoulder pain and range-of-motion limitation have been demonstrated. For better understanding the existence of such ectopic tendons, a phylogenetic hypothesis is proposed. METHODS Forty-five shoulders of anatomical specimens were dissected and examined. Insertions areas of PMM were measured and occurring aberrant tendons were identified. Their relationship with the coracohumeral ligament (CHL) described and samples of the ligament were collected and histologically stained. RESULTS The prevalence of PMM variations was 37.84%. Shoulders with variations showed a statistically significant smaller coracopectoral distance (p<0.001) and larger insertion areas (p<0.003) than shoulders without. A strong negative correlation between these two variables (p<0.001, r = -0.620) was shown. CONCLUSIONS The presented results prompted the conclusion that the CHL may be in fact the remnant of the pectoralis minor tendon (PMT), which migrated from the humerus to the coracoid process through the process of phylogenetic evolution. Variations of PMTs are significantly more common than in previous studies. Imaging techniques appear to be insufficiently sensitive for reliably detecting ectopic tendons. Especially in patients experiencing shoulder pain and stiffness in whom the commoner pathologies have been ruled out the possibility of ectopic PMT should be kept in mind and ruled out.

Association of damage to the coracohumeral ligament with anterosuperior rotator cuff degeneration revealed by anatomical dissection

“…They reported a coracoid insertions size of the ligament of 66.5 ± 23.8 mm 2 and a humeral insertion size of 68.3 ± 18.4 mm 2 . Also, Schwarz and Hirtler 29 in their paper on the ectopic tendons of the pectoralis minor muscle measured the coracoid insertion area of the CHL, which was overall 56.5 ± 36.3 mm 2 , ranging from 54.9 ± 34.4 mm 2 in their group without variation to 66.31 ± 33.8 mm 2 in their group with variation (exemplary image of an ectopic tendon of the pectoralis minor muscle may be found as supplementary material). Although the results of this study showed generally smaller insertion sites compared to the two prior publications, this mainly reflects the interindividual variability of this anatomical structure, which is also mainly supported by the sex-difference reported.…”

“…This is especially important when applying imaging techniques such as MRI in an anatomical setting. As no additional imaging was performed, tissue quality for dissection was acceptable, especially as previous studies also pointed out the disadvantage of formalin-phenol fixation in terms of evaluating ligaments and tendons 29 . Particularly the distinction of different tissue layers was not affected by cryo-preservation.…”

“…Due to the histological similarities of the CHL and the fibrous joint capsule (collagen-type-III) of the glenohumeral joint, the ligament is often described as a thickened part of the joint capsule 23 – 28 . In contrast, however, a more recent publication considers the CHL as a remnant of the tendon of the pectoralis minor muscle, which also would explain the different fiber-composition of this ligament compared to others 29 . The development of the CHL as a distinct structure is also supported by its separate embryological formation from the SGHL, the complex of both ligaments providing for the biceps pully establishing itself much later 30 .…”

Delamination in rotator cuff tears: Explanation of etiology through anatomical dissection

“…Whether this is due to different specimen characteristics or the different fixation methods (fresh‐frozen vs. formalin‐ethanol) cannot be finally clarified. However, Schwarz and Hirtler ( 2019 ) were able to show that the frequency distribution of aberrant pectoralis minor tendons are similar between Caucasians and Mongolians, which might predict similarities in the supraspinatus muscle as well. Our results on the infraspinatus muscle are in accordance with previous results (Mochizuki et al, 2008 ).…”

pooled prevalence estimation of anomalous insertion of pectoralis minor in cadaveric studies

“…A instance of bilateral capsular insertion of a section of PMi was described by Patten [22]. PMi was inserted into the upper part of the glenoidal lip and the surrounding capsule, according to reports [23].…”