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.