Background: The subscapularis muscle originates from the medial two-thirds and from the lower two-thirds of the groove on the subscapular fossa of the scapula and inserts into the lesser tubercle of the humerus. Our initial hypothesis is that it shows little morphological variation. The aim of this study is to demonstrate and classify the morphological variability of the subscapularis muscle.
Methods: Classical anatomical dissection was performed on 64 upper limbs (44 females, 20 males, 30 left and 34 right, fixed in 10% formalin). The mean age "at death" of the cadavers was 75.6 years (range 48-95), and the group comprised equal numbers of female and male adults (Central European population). Upon dissection, the following morphological features were assessed: the number of tendons of the SM, the type of insertion of each tendon of the SM, morphometric measurements of the SM.
Results: Four types of morphology (based on number of tendons) were observed in the cadavers. Type I was characterized by a single band. This was the most common type, occurring in 43.7% of all cases. Type II was characterized by a double tendon (superior and inferior); it occurred in 9.4%. Type III had three tendons (superior, middle, and inferior). It was the rarest type (7.8% of cases). Type IV, called "multiband", was the second most common (39.1%) and was divided into five subtypes.
Conclusions: The subscapularis muscle is highly morphologically variable. Knowledge of particular types of insertion is essential for both clinicians (for example orthopedists, physiotherapists) and anatomists.
Keywords: Accessory subscapularis muscle; Anatomical study; Cadaveric study; New classification; Ontogenesis; Phylogenesis; Subscapularis muscle.
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