Abstract
Anomalous muscular variants of pectoralis major have been reported on several occasions in the medical literature. Among them, chondroepitrochlearis is one of the rarest. Therefore, this study aims to provide a comprehensive description of its anatomy and subsequent clinical significance, along with its phylogenetic importance in pectoral muscle evolution with regard to primate posture. The authors suggest a more appropriate name to better reflect its proximal attachment to the costochondral junction and distal attachment to the epicondyle of humerus, as “chondroepicondylaris”; in addition, we suggest a new theory of phylogenetic significance to explain the twisting of pectoralis major tendon in primates that may have occurred with their adoption to bipedalism and arboreal lifestyle. Finally, the clinical significance of this aberrant muscle is elaborated as a cause of potential neurovascular entrapment and as a possible hurdle during axillary surgeries (i.e., mastectomy).
Highlights
There are many anatomical variations in human musculature
chondroepitrochlearis muscle (CEM) is a muscle that originates from the cartilages or costochondral junctions of the thorax and inserts into the distal brachium (Figure 1); the most common name that has been used for this variation is chondroepitrochlearis
As a muscle that arose from the cartilages or costochondral junctions, with an insertion into the distal humerus, the most common name for this pectoralis major (PM) variation has traditionally been the CEM (Table 1) which was first named by Duvernoy as cited by Wood in 1966 [4]
Summary
There are many anatomical variations in human musculature. Some variations are common while others have been infrequently reported. Anatomical variations of pectoralis major (PM) muscle are noteworthy, because of their extreme rarity and for their phylogenetic and clinical significance. Many different anomalies associated with PM have been extensively described by Bergman and colleagues, such as chondroepitrochlearis muscle (CEM); chondrofascialis; pectoralis quartus; sternalis; and axillary arch muscle (Achselbogen of Langer) [1] out of which the latter is the most frequently reported anomaly [2]. CEM is a muscle that originates from the cartilages or costochondral junctions of the thorax and inserts into the distal brachium (Figure 1); the most common name that has been used for this variation is chondroepitrochlearis
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