Investigating biomechanical differences in lumbosacral transitional vertebrae among different Castellvi classifications

Different Castellvi classifications of LSTV exert significant biomechanical effects on the lumbar-pelvis complex. Among them, the IIIB and IV types (including the fused left side of the IIIA type) significantly increase sacroiliac joint stress, which may contribute to sacroiliac joint dysfunction or sacroiliac joint subluxation or sacroiliitis. Types IA and IIA may easily lead to discogenic low back pain due to increased local intervertebral disc stress and uneven stress distribution. Types ⅠB and ⅡB induce minimal interference in global displacement, intervertebral disc stress, and sacroiliac joint stress, resulting in a relatively lower risk of low back pain. These results provide a biomechanical reference for the classification-based diagnosis and intervention of LSTV-related low back pain.