Fetal development and growth of the human erector spinae with special reference to attachments on the surface aponeurosis.

PURPOSE: The longissimus (LO) and iliocostalis (IC) of adults consist of myofibers extending from the superolateral to the inferomedial side of the back and, because of the same course, they are fused in the thoracolumbar region. The LO also has a medial attachment to the long myofibers of the transversospinalis (TS) showing a course from the superomedial to the inferolateral side. However, there is apparently no information regarding when and how these similar longitudinal muscles differentiate from a cluster of dorsomedial myotome cells. METHODS: We examined sagittal and horizontal sections of the trunks of 39 human embryos and fetuses (18-330 mm crown-rump length). RESULTS: At 6-7 weeks gestational age (GA), the surface aponeurosis appeared prior to and independent of the thoracolumbar fascia. At 6-9 weeks GA, the LO myofibers had a postero-inferior course, from the transverse process to the initial aponeurosis, whereas the TS myofibers had a postero-superior course, from a lateral extension of the intertransverse ligament to the aponeurosis. However, the IC consisted of supracostal longitudinal myofibers and was distant from the LO until 12 weeks GA. Because of the lack of ligamentous attachments and ribs, myofibers of the TS, LO, and IC took a similar inferior course in the lumbar region. When the early TS was represented by the transverso-aponeurotic muscle, consequently, the LO corresponded to the aponeuro-transversal muscle and was independent from the IC. CONCLUSION: The classical model of TS and LO development does not recognize the essential role of the aponeurosis identified here.

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.

Expression of MMP-1, -2, and -8 in longissimus dorsi muscle and their relationship with meat quality traits in cattle.

The extracellular matrix (ECM) is the major macromolecule in skeletal muscle, which affects meat quality greatly. The remodeling of the ECM is mainly regulated by matrix metalloproteinases (MMPs). The expression patterns of MMP-1, -2, and -8 in longissimus dorsi muscle were explored using quantitative real-time polymerase chain reaction. The results show that the expression of MMP-1, -2, and -8 decreased significantly from 135 days of pregnancy to postnatal 30 months. While the expression of MMP-1, -2, and -8 showed no significant relationships with intramuscular fat contents, MMP-1 and -2 showed significant negative correlations with the shearing force of the longissimus dorsi muscle in cattle. The expression of MMP-1 also showed a significant negative correlation with cooking loss and a positive correlation with water holding capacity. The expression levels of MMP-1 and -2 were usually higher in fat than in skeletal muscle tissue. The expression of MMP-8 was significantly higher in the mammary fat pad and the longissimus dorsi muscle than in all other tissues. This study indicates that the remodeling of the ECM has important effects both on the development of postnatal skeletal muscle and on meat quality.