Anatomical Variability of Gluteal Region Muscles in the Perinatal Period of Human Ontogenesis

The study of anatomical peculiarities of organs, in particular muscles, and their topographic variants from the standpoint of a macroscopic view is considered topical and perspective in modern anatomy, since micro- and ultramicroscopic anatomy does not provide an exhaustive answer and does not fully reveal the multifaceted nature of anatomical variability. The purpose of the study was to determine the age and individual anatomical variability of the gluteal region muscles in human 6-10-month-old fetuses and newborns. Material and methods. The macroscopic study of typical and variant anatomy of the gluteal region muscles involved 82 specimens of 6-10-month-old fetuses of 186.0-375.0 mm of crown-rump length (CRL) and 10 stillborns without external signs of anatomical deviations or developmental abnormalities, examined by the means of anatomical preparation and morphometry. Results and discussion. At the beginning of the perinatal period of human ontogenesis gluteus maximus muscle usually has a rhomboid flattened form (61%), more rarely it is triangular and elongated-oval. The left gluteus maximus muscle typically has a round-oval shape (45%), rarer it can be rhomboid, trapezoid and rectangular. In 7-month-old fetuses rhombus-shaped right gluteus maximus muscle was detected in 38% of cases, its rectangular, oval, square and triangular forms were more rarely observed. The left gluteus maximus muscle is often rectangular in shape (33%), rarely it can be elongated-oval, rhomboid, triangular and square. In 8-month-old fetuses, there is predominantly a convex quadrangular shape of the gluteus maximus muscles, or such varieties of it as trapezoid, rectangular and square. At the end of the fetal period of ontogenesis, the gluteus maximus muscles tend to have the shape of a scalene quadrilateral or its types: rectangular, trapezoid, and square. In 7 out of 10 researched newborns, the right and left gluteus maximus muscles were quadrilateral in shape; their rhomboid and trapezoid forms were rarer. The gluteus medius and piriform muscles tend to have a triangular shape. In rare cases, the piriform muscle was conical and spindle-shaped. The left piriform muscle is divided into the superior and inferior portions in the fetus of 320.0 mm of CRL. The left piriform muscle is absent in the fetus of 195.0 mm of CRL. The length and width of the right gluteus maximus muscle prevails over the size of the left gluteus maximus muscle in 6-8-month-old fetuses. At the end of the fetal period and, a slight predominance in the length of the right gluteus maximus muscle over the length of the left gluteus maximus muscle is also detected in the newborns, while the left gluteus maximus muscle is slightly wider than the right one. Conclusions. During the perinatal period of ontogenesis, the variability and asymmetry of the shape of some muscles of the right and left gluteal regions are observed. In particular, the gluteus maximus muscle in 6-month-old fetuses is mostly rhomboid, flattened and round-oval in shape, in 7-month-old fetuses it is rhomboid and rectangular in shape, and starting from the 8th month it predominantly acquires a quadrangular shape; the gluteus medius and piriform muscles tend to have a triangular shape, and the quadratus femoris muscle is usually quadrangular in the perinatal period of ontogenesis.