Fetal development of the thoracolumbar fascia with special reference to the fascial connection with the transversus abdominis, latissimus dorsi, and serratus posterior inferior muscles.

PURPOSE: The three-layered thoracolumbar fascia (TLF) encapsulates the erector spinae and the quadratus lumborum and has been a major concern for physical therapists. However, knowledge of its prenatal development and growth is limited. METHODS: Histological examination of 25 embryos and fetuses at 6-37 weeks (CRLs, 15-310 mm). RESULTS: At the posterior end, the abdominal muscles continued toward an initial posterior layer of the TLF (pTLF) at 6 weeks, but the connection became narrow and limited to the obliquus externus aponeurosis until near term. The middle layer of the TLF (mTLF) appeared as a posterior continuation of the transversalis fascia at 9 weeks and, depending on a mechanical demand for the vertebral column extension near term, it grew as a thick intermuscular septum between the iliocostalis and quadratus lumborum. Thus, the mTLF lateral end changed from the abdominal wall to the back or pTLF. The serratus posterior inferior originated from the pTLF after 9 weeks, but a connection of the latissimus dorsi with the fascia was established much later. Near term, the gluteus maximus was attached to an aponeurosis covering the multifidus behind the sacrum. Therefore, the pTLF extended to cover the gluteal muscles. CONCLUSION: We rejected the hypothesis that the mTLF develops as a marginal tissue between the primitive epaxial and hypaxial muscles. This study seemed to be the first report showing a fact that, within prenatal life, a drastic change is likely to occur in interfascial connections and their topographical relation to muscles; the TLF might be the best sample.

Morphometric properties of the levator scapulae, rhomboid major, and rhomboid minor in human fetuses.

PURPOSE: The main objective of this study is to showcase the growth dynamics of levator scapulae, rhomboid major, and rhomboid minor algebraically, to help plan surgeries on newborns and young infants. METHODS: Twenty-five formalin-fixed fetuses (11 male-14 female) with a mean gestational age of 21.80 ± 2.61 (range 18-27) weeks present in the inventory of Mersin University Faculty of Medicine Anatomy Department were dissected. Surface area of levator scapulae, rhomboid major, and rhomboid minor was calculated using digital image analysis software; width and length parameters were measured using digital calipers. RESULTS: Neither sex nor side significant differences were observed in relation with the numerical data of levator scapulae, rhomboid major, and rhomboid minor (p > 0.05). Algebraic parameters such as surface area, width and length were detected to exhibit a linear growth from 18th to 27th week. Linear functions for levator scapulae, rhomboid major and rhomboid minor surface areas were obtained as y = - 136.871 + 10.598 × age (weeks), y = - 480.567 + 33.147 × age (weeks) and y = - 128.090 + 8.843 × age (weeks), respectively. CONCLUSION: The results and data of this study can potentially be beneficial in planning of surgeries for many infancy diseases such as trapezius paralysis, obstetrical brachial plexus palsy, Sprengel's disease, or winged scapula. Linear functions calculated in this study are expected to provide a better understanding of the growth dynamics of levator scapulae, rhomboid major, and rhomboid minor in fetal term and more precise estimation of muscle sizes.

Morphometric study of the triangle of Petit in human fetuses.

BACKGROUND: The inferior lumbar triangle of Petit is bounded by the iliac crest, lateral border of the latissimus dorsi and the medial border of the external oblique. OBJECTIVES: In the present study, we aimed to quantitatively examine the base, sides, area, and interior angles of the inferior lumbar triangle in the human fetus so as to provide their growth dynamics. MATERIAL AND METHODS: Using anatomical dissection, digital image analysis (NIS-Elements AR 3.0), and statistics (Student's t-test, regression analysis), we measured the base, 2 sides, area and interior angles of Petit's triangle in 35 fetuses of both sexes (16 male, 19 female) aged 14-24 weeks. RESULTS: Neither sex nor laterality differences were found. All the parameters studied increased commensurately with age. The linear functions were computed as follows: y = -0.427 + 0.302 × age for base, y = 1.386 + 0.278 × age for medial side, y = 0.871 + 0.323 × age for lateral side, and y = -13.230 + 1.590 × age for area of the Petit triangle. CONCLUSIONS: In terms of geometry, Petit triangle reveals neither male-female nor right-left differences. An increase in both lengths and area of the inferior lumbar triangle follows proportionately. The Petit triangle is an acute one in the human fetus.

The hypaxial origin of the epaxially located rhomboid muscles.

In vertebrates, skeletal muscles of the body are made up of epaxial and hypaxial muscles based on their innervation and relative position to the vertebral column. The epaxial muscles are innervated by the dorsal branches of the spinal nerves and comprise the intrinsic (deep) back muscles, while the hypaxial muscles are innervated by the ventral branches of the spinal nerves including the plexus and consist of a heterogeneous group of intercostal, abdominal, and limb as well as girdle muscles. The canonical view holds that the epaxial muscles are derived from the medial halves of the somites, whereas the hypaxial muscles are all derived from the lateral somitic halves. The rhomboid muscles are situated dorsal to the vertebral column and therefore in the domain typically occupied by epaxial muscles. However, they are innervated by a ventral branch of the brachial plexus called the N. dorsalis scapulae. Due to the apparent inappropriate position of the muscle in relation to its innervation we investigated its origin to help clarify this issue. To study the embryonic origin of the rhomboid muscles, we followed derivatives of the medial and lateral somite halves using quail-chick chimeras. Our results showed that the rhomboid muscles are made up of cells derived mainly from the lateral portion of the somite. Therefore the rhomboid muscles which lie within the epaxial domain of the body, originate from the hypaxial domain of the somites. However their connective tissue is derived from both medial and lateral somites.

Teres major and latissimus dorsi muscles in human embryos: A reconsideration of the so-called brother muscles.

The teres major and latissimus dorsi muscles (TM, LD) are considered to be the so-called brother muscles. Actually, being similar to the TM, an uppermost part of the LD usually arises from the scapular plate. In embryos of 11 mm CRL, anlagen of the TM and LD appeared to be fused to provide a single mass at an angle between the axillary and radial nerves. However, splitting had already finished in not only the TM and LD but also the other muscles at and around the shoulder in specimens of 14 mm CRL. Thus, muscle splitting at the region appeared to occur simultaneously at a short stage of 12-13 mm CRL.The TM and LD carried a common tendon still at 6 weeks (14-16 mm CRL), but their muscle bellies were separated clearly. A concept of brother muscles might be applied to the TM and LD according to a bias from the gross and comparative anatomy, not from the embryological view.

Quantitative Anatomy of the Trapezius Muscle in the Human Fetus.

BACKGROUND: The trapezius muscle consists of three parts that are capable of functioning independently. Its superior part together with the levator scapulae and rhomboids elevate the shoulder, the middle part retracts the scapula, while the inferior part lowers the shoulder. OBJECTIVES: The present study aimed to supplement numerical data and to provide growth dynamics of the trapezius in the human fetus. MATERIAL AND METHODS: Using methods of anatomical dissection, digital image analysis (NIS Elements AR 3.0), and statistics (Student's t-test, regression analysis), we measured the length, the width and the surface area of the trapezius in 30 fetuses of both sexes (13™ k,17™ … ) aged 13-19 weeks. RESULTS: Neither sex nor laterality differences were found. All the studied parameters of the trapezius increased proportionately with age. The linear functions were computed as follows: y = -103.288 + 10.514 × age (r = 0.957) for total length of the trapezius muscle, y = -67.439 + 6.689 × age (r = 0.856) for length of its descending part, y = -8.493 + 1.033 × age (r = 0.53) for length of its transverse part, y = -27.545 + 2.802 × age (r = 0.791) for length of its ascending part, y = -19.970 + 2.505 × age (r = 0.875) for width of the trapezius muscle, and y = -2670.458 + 212.029 × age (r = 0.915) for its surface area. CONCLUSIONS: Neither sex nor laterality differences exist in the numerical data of the trapezius muscle in the human fetus. The descending part of trapezius is the longest, while its transverse part is the shortest. The growth dynamics of the fetal trapezius muscle follows proportionately.

DUX4 and DUX4 downstream target genes are expressed in fetal FSHD muscles.

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most prevalent adult muscular dystrophies. The common clinical signs usually appear during the second decade of life but when the first molecular dysregulations occur is still unknown. Our aim was to determine whether molecular dysregulations can be identified during FSHD fetal muscle development. We compared muscle biopsies derived from FSHD1 fetuses and the cells derived from some of these biopsies with biopsies and cells derived from control fetuses. We mainly focus on DUX4 isoform expression because the expression of DUX4 has been confirmed in both FSHD cells and biopsies by several laboratories. We measured DUX4 isoform expression by using qRT-PCR in fetal FSHD1 myotubes treated or not with an shRNA directed against DUX4 mRNA. We also analyzed DUX4 downstream target gene expression in myotubes and fetal or adult FSHD1 and control quadriceps biopsies. We show that both DUX4-FL isoforms are already expressed in FSHD1 myotubes. Interestingly, DUX4-FL expression level is much lower in trapezius than in quadriceps myotubes, which is confirmed by the level of expression of DUX4 downstream genes. We observed that TRIM43 and MBD3L2 are already overexpressed in FSHD1 fetal quadriceps biopsies, at similar levels to those observed in adult FSHD1 quadriceps biopsies. These results indicate that molecular markers of the disease are already expressed during fetal life, thus opening a new field of investigation for mechanisms leading to FSHD.