Quantitative anatomy of the growing quadratus lumborum in the human foetus

Purposes The purpose of the study was to quantitatively evaluate the size of the quadratus lumborum and to precisely display its growth dynamics in the human foetus. Materials and methods Using anatomical dissection, digital-image analysis (NIS Elements AR 3.0) and statistical analysis (Student’s t test, regression analysis), the length, width, surface area, and cross-sectional area of the quadratus lumborum were measured, and the width-to-length ratio was calculated in 58 human foetuses of both sexes (26♂, 32♀) aged 16–27 weeks. Results Neither sex nor right-left significant differences were found in relation with the numerical data of the growing quadratus lumborum. The length, width, and cross-sectional area of the quadratus lumborum muscle increased logarithmically, while its surface area increased proportionately to fetal age. The following growth models were computed for the quadratus lumborum: y = −70.397 + 68.501 × ln(age) ± 1.170 for length, y = −20.435 + 8.815 × ln(age) ± 0.703 for width, y = −196.035 + 14.838 × age ± 13.745 for surface area, and y = −48.958 + 20.909 × ln(age) ± 1.100 for cross-sectional area. Conclusions The fetal quadratus lumborum reveals neither sex nor bilateral differences. An increase in length and width of the growing quadratus lumborum follows in a commensurate fashion. The quadratus lumborum grows logarithmically with respect to its length, width, and cross-sectional area, and proportionately to age with respect to its surface area.