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.
Keywords: Petit triangle; area; digital-image analysis; inferior lumbar triangle; side.