Biomechanical effects on sacroiliac fusion for treating low back pain / 医用生物力学

Objective Based on the finite element method, both sacroiliac fusion and sacroiliac contact models were built to compare the biomechanical differences between the two models and to explore the biomechanical mechanism in the treatment of low back pain by sacroiliac fusion. Methods Two pelvic finite element models were constructed, including the pelvic ring, sacrum, part of the femur, ligaments, cartilage and joint contact. The sacroiliac joints were set to be contact in one model and fusion in the other, respectively. Differences in mechanical conduction on the pelvic ring and the stress on the sacroiliac cartilage under 500 N load between the two models were explored. Results For the fusion model, stresses and displacement on the sacroiliac joint were significantly lower than that of the contact model, especially on the sacroiliac cartilage, where the displacement was reduced by 261% from 0.83 mm to 0.23 mm, and the stresses reduced by 32% from 6.6 MPa to 5.0 MPa. However, the transfer of stress on the pelvic ring was relatively more concentrated in the fusion model. Conclusions Sacroiliac fusion may provide better therapeutic effects on the treatment of low back pain, but the risk of disc herniation and femoral head necrosis must be assessed seriously in advance.

Testing of axial stiffness of human pelvis under gradient vertical loads / 医用生物力学

Objective To analyze the axial stiffness of human pelvis that were set with the double support standing posture and subjected to gradient vertical loads. Method Nine intact embalmed cadaver specimens were marked from 1# to 9# according to the test sequence, and then subjected to vertical static loads in the gradient of 100 N from 0 N to 500 N. The load displacement data were collected by using the beam sensor of electronic universal testing machine to calculate the axial stiffness of human pelvis. Results The differences of axial stiffness among individual pelvis were large (P=0.815), ranging from 240 N/mm to 776 N/mm. All the pelvic specimens were divided into three groups by cluster analysis (the first group: 1#、2#、3#、5#、9#, the second group: 4#、6#、8#, the third group: 7#). According to the processed results, there were statistical differences among the groups (P<0.05). The trends of pelvic axial stiffness were different under gradient loads. The axial stiffness of the first and third group, totally six specimens, increased with loads increasing; while the axial stiffness of the second group including three specimens increased first, but then decreased with the loads increasing. Conclusions There are significant individual differences in pelvic axial stiffness and its changing discipline within the physiological range; the cluster analysis can be used to analyze the changing discipline between the load and stiffness of human pelvis; as a whole, the pelvic axial stiffness increased with the loads increasing.