[Finite element analysis of traditional treatment methods for osteoporotic vertebral compression fractures].

Abstract

Objective: To analyze and compare the treatment of osteoporotic vertebral compression fracture by finite element method, and to explore biomechanical feasibility and advantages of traditional manual therapy for osteoporotic vertebral compression fractures(OVCFs).

Methods: A 26-year-old healthy volunteer (heighted 1.8 m, body weighted 85 kg) was selected, simulated and reconstructed OVCFs model (T₁₁-L₂), set the degrees of freedom below L₂ vertebra as "0", and then applied four different simulated working conditions for loading to observe stress distribution of model and displacement of the fractured vertebra. Repositioning in hyperextension position, applied a forward 7.5 N·m torque of positive force to X-axis of model fracture vertebra;simple compression repositioning, applied 400 N load perpendicular to Y-axis to fractured vertebra; compression repositioning in hyperextension position, the simulation of position involved applying 7.5 N·m forward torque to X-axis of the model fracture vertebra and 400 N load perpendicular to Y-axis to fractured vertebra; compound manual repositioning, applied 7.5 N·m forward torque to X-axis of model fracture vertebra, then applied 400 N load perpendicular to Y-axis, removed the previous fixation and load, then set the degrees of freedom below L₂ vertebra to "0", and applied 400 N load to L₁.

Results: Comparison of equivalent stresses under various loading conditions showed compound manual repositioning (124.35 MPa)> compression repositioning in hyperextension position (101.17 MPa)>repositioning in hyperextension position (95.22 MPa)> simple compression repositioning (31.11 MPa). The stress in repositioning in hyperextension position, compression repositioning in hyperextension position, and compound manual repositioning could concentrate on anterior-middle column of the target vertebra. The stress in simple compression repositioning did not concentrate on the target vertebra and showed obvious dispersion. Comparison of stress peak values showed the stress peak of compound manual repositioning (149.41 MPa)>compression repositioning in hyperextension position (120.54 MPa)>repositioning in hyperextension position (111.32 MPa)>simple compression repositioning(27.60 MPa), the stress peaks of repositioning in hyperextension position, compression repositioning in hyperextension position, and compound manual repositioning were concentrated on anterior-middle column of the target vertebra, while the stress peak of simple pressing reduction was significantly dispersed. Comparison of model displacement showed compound manual repositioning (2.24 mm)>compression repositioning in hyperextension position (2.17 mm)>repositioning in hyperextension position (1.89 mm)>simple compression repositioning(1.24 mm), the model displacements in all these repositioning methods were concentrated on anterior-middle column of the target vertebrae. The displacement trend gradually decreased from the upper edge of the fractured vertebra to the bottom. The model displacements were relatively disordered in simple compression repositioning. The model displacements corresponded to the equivalent stress of the fractured vertebrae. The stress distribution of the target vertebral nucleus pulposus and ligaments under different working conditions showed the stress was the greatest in interspinous ligaments and interspinous ligaments during repositioning in hyperextension position, compression repositioning in hyperextension position and compound manual repositioning, while the stress of nucleus pulposus and ligaments was more dispersed without obvious stress concentration area during simple compression repositioning.

Conclusion: Compound manual repositioning is currently the preferred treatment for OVCFs. The extended position and ligament integrity are of great significance for reduction of OVCFs.