The vertebral column plays a central role in mechanical support, neural protection, and locomotion. The lumbosacral region is particularly important because it transfers loads between the axial skeleton and the pelvis while maintaining spinal stability during movement. Because spinal morphology is closely related to locomotor mechanics, animal models are widely used in comparative spinal research. Among non-human primates, the rhesus macaque (Macaca mulatta) has become an important translational model; however, detailed morphometric information describing the lower spine remains limited. This study performed a computed tomography (CT)-based morphometric analysis of the lumbar (L۱–L۷), sacral (S۱–S۳), and proximal caudal (Ca۱–Ca۳) vertebrae in five healthy adult female rhesus macaques. CT images were obtained using standardized imaging parameters. Seven morphometric parameters were evaluated, including vertebral body height (VBH), vertebral body length (VBL), spinal canal height (SCH), spinal canal width (SCW), transverse process length (TPL), transverse process width (TPW), and spinous process height (SPH). Measurements were conducted using dedicated imaging software, and statistical comparisons among vertebral levels were performed with significance defined as P < ۰.۰۵. Within the lumbar region, most parameters showed no significant differences across L۱–L۷, indicating relative morphometric uniformity. The only parameter demonstrating significant variation was transverse process width (TPW), which increased significantly from L۲ and remained relatively constant through L۷. In the sacrococcygeal region, vertebral body and spinal canal dimensions at S۱ were comparable to the last lumbar vertebra but decreased significantly at S۲ and remained stable through Ca۳. Transverse processes were largest at S۱ and showed a progressive reduction toward S۳. The rhesus macaque spine demonstrates relative lumbar uniformity and a rapid structural reduction across the sacrococcygeal region, reflecting biomechanical adaptations to quadrupedal locomotion. These findings provide baseline morphometric data that may support comparative spinal studies and translational spinal research.
