3D development of the mouse pelvic girdle: Insights into the musculoskeletal system and vasculature

The mouse (Mus musculus) pelvis features an elongated ilium and triangular pubis and ischium characteristic of a small quadruped, whereas humans possess a short, broad, bowl-shaped pelvis specialized for bipedal locomotion and childbirth. Mice are widely used to model osteoporosis, hip dysplasia, and other pelvic pathologies, yet in utero mouse pelvic development has been incompletely characterized, limiting cross-species interpretation. Here, we integrate 3D micro-CT and histology to generate a comprehensive atlas of mouse pelvic development from embryonic days 12.5-18.5 (E12.5-E18.5), focusing on the ilium, hip joint, and sacroiliac joint. We show that E14.5 is a critical stage, when the hip and sacroiliac joints form. We identify a sequential developmental program in mice in which joint cartilage forms first, followed by muscle-cartilage interaction, and, subsequently, extensive blood vessel growth. In contrast to the transversely oriented, developmentally delayed iliac growth and ossification described in recent studies of the human bipedal pelvis, the mouse ilium follows an earlier, centrally initiated, longitudinal ossification pattern. Overall, our atlas provides an essential quadrupedal reference for interpreting human pelvic development, evolution, and disease models.