Bilateral variation of the pectoralis minor muscle discovered during practical dissection

Abstract

We describe a case of an original insertion of the pectoralis minor on the coracohumeral ligament, supraspinatus tendon and the capsule of the glenohumeral joint. This variation has been described in anatomy textbooks since the nineteenth century. The peculiarity of this case is that the right shoulder presented type 2 and the left type 1 of the three varieties described by Le Double in 1897. Le Double (1843-1913) was a French anatomist who wrote a treaty on anatomical variations, in particular those of the muscle. Lately, only three publications have reported this variation in anatomic studies. Some authors have described the rotator cuff syndrome caused by this variation and an ultrasound study has demonstrated a frequency of 9.57% for the detection of this variation. It is possible to try and find this variation while investigating in order to diagnose impingement, through ultrasound, CT arthrography or MRI. We believe that this variation should be taken into consideration by surgeons during surgical procedures and arthroscopy.

Inter- and Intraspecific Variations in the Pectoral Muscles of Common Chimpanzees(Pan troglodytes), Bonobos(Pan paniscus), and Humans(Homo sapiens)

“…In two of our Homo sapiens specimens, the pectoralis minor inserted at the glenohumeral capsule (Figure 4) after passing over the coracoid process and through the coracohumeral ligament. The pectoralis minor has also been reported to be inserted at the supraspinatus tendon in humans [29, 36–38, 65], which is similar to our findings in Pan troglodytes . Several studies have found that anomalies in the insertion of the pectoralis minor in humans are related to subacromial impingement [66–68], anteromedial subcoracoid impingement [69], and potential compression of the axillary artery and the brachial plexus [35], while others have found no association with clinical symptoms [40].…”

“…The pectoralis minor can also be inserted at the supraspinatus tendon [29, 36–38]. Magnetic resonance arthrography has identified the insertion of the pectoralis minor at the glenohumeral capsule without insertion at the coracoid process in 1.5% of humans [39], while ultrasound has identified this phenomenon in 9.6% of humans [40].…”

“…The study of the pectoral muscles is especially important in bonobos, because their anatomy and variations have been poorly studied since Miller's classic monograph on the anatomy of the muscles of Pan paniscus based on a single specimen [22]. A detailed analysis of the pectoral muscles and their possible variations in common chimpanzees and bonobos will also provide valuable information on the anatomic variations of these muscles in humans, especially the presence of supernumerary muscles, such as the pectoralis abdominis, and the variations on insertion of the pectoralis minor, which have been related to the etiopathogenesis of some diseases such as the subacromial impingement syndrome [35, 37, 38] and to some surgical complications [32, 33, 41]. …”

A case of bilateral aberrant pectoralis minor insertion with absent coracohumeral ligament: Clinical relevance and controversies

“…6 According to authors' knowledge, only four cases have been reported in the literature about bilateral aberrant insertions of pectoralis minor, of which three were noted during cadaveric dissection and one was done radiologically. 4,[7][8][9] We report a case of bilateral PM ectopic insertion over anterior border of supraspinatus tendon with absent coracohumeral ligament (CHL) which was diagnosed during shoulder arthroscopy performed for a painful right shoulder.…”

Pectoralis minor tendon in the rotator interval: arthroscopic, magnetic resonance imaging findings, and clinical significance

“…Furthermore, we are not aware of any study that has evaluated diagnostic performances of magnetic resonance imaging (MRI) for this variation. Uzel et al 16 emphasized that this variation should be taken into consideration by surgeons during the surgical procedure and arthroscopy and that preoperative diagnosis of insertional variation of the pectoralis minor might be of value.…”