Abstract: BACKGROUND: A comparative study based on finite element modeling suggests that for the degenerative anterior lumbar spine structure, the traditional oblique lever has an advantage in mechanical effect strength, but the modified oblique lever performs better in stress distribution rationality and operational safety indicators. There is still a lack of systematic research data on the mechanical mechanism of supine rotation lever and its specificity of efficacy compared with sitting fixed-point rotation lever under divergent bone mineral density conditions.
OBJECTIVE: To comparatively analyze the biomechanical characteristics of these two manipulative modalities of sitting/supine rotation across heterogeneous bone mineral density states.
METHODS: A 26-year-old female patient with L4/5 intervertebral disc protrusion who met the inclusion criteria was selected. After signing the informed consent form, CT data of her lumbar vertebrae were acquired. Based on these CT data, a three-dimensional finite element model of L4/5 intervertebral disc protrusion was constructed and validated. By modifying the material properties of the model, three-dimensional finite element models representing normal bone mass and osteoporosis conditions were developed. Different loading scenarios were applied to simulate two manipulation techniques (supine rotation manipulation and sitting fixed-point rotation manipulation). The range of motion, peak stress, pressure difference between the annulus fibrosus and nucleus pulposus, as well as deformation of the lumbar vertebrae model under each technique were calculated. These data were subsequently imported into statistical software for analysis, generating corresponding statistical charts and evaluating the differences in therapeutic effects between the two manipulation techniques.
RESULTS AND CONCLUSION: (1) Under the conditions of the same torque and bone mineral density, the seated fixed point rotation technique could obtain a larger range of joint motion than the supine rotation manipulation, and showed a more significant safety advantage when the equivalent rotation angle was implemented. (2) There was a significant negative correlation between bone mineral density and manipulation range. (3) Both modalities significantly augmented annulus fibrosus/nucleus pulposus pressure difference (negative pressure within the intervertebral disc), facilitating herniated nucleus pulposus repositioning. (4) Annulus fibrosus strain gradients governed coordinated nucleus pulposus displacement. (5) High-torque supine rotational protocols demonstrated superior lumbar disc herniation reduction efficacy under equivalent bone mineral density constraints. 

Key words: lumbar disc herniation, osteoporosis, supine rotation manipulation, seated fixed-point rotation manipulation, finite element, biomechanics, mechanism