Abstract
OJECTIVEClinical 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.METHODSForty-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.RESULTSThe 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.CONCLUSIONSThe 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.
Highlights
Aberrant tendons of the pectoralis minor muscle (PMM) have been demonstrated to play a role in the genesis of shoulder pain and range-of-motion (ROM) limitation
The presented results prompted the conclusion that the coracohumeral ligament (CHL) may be the remnant of the pectoralis minor tendon (PMT), which migrated from the humerus to the coracoid process through the process of phylogenetic evolution
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
Summary
Aberrant tendons of the pectoralis minor muscle (PMM) have been demonstrated to play a role in the genesis of shoulder pain and range-of-motion (ROM) limitation. [1, 5, 7,8,9,10,11,12] Overall, such variability may among others be explained through embryological, generic or phylogenetic reasons. Trying to explain the muscle’s variability of attachment through its phylogenetic origin, two main hypotheses may be mentioned: (1) The primary attachment of the PMM has been at the coracoid process. Depending on its function in the corresponding species, its tendon migrated either to the humerus (carnivorous), the clavicle (rodent), or the scapula and fascia of the supraspinatus muscle (ungulate). Due to its change of function over the course of evolution, its tendon migrated to the coracoid process, and the coracohumeral ligament (CHL) was determined to be its remnant. Due to its change of function over the course of evolution, its tendon migrated to the coracoid process, and the coracohumeral ligament (CHL) was determined to be its remnant. [16]
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