Biomechanical characteristics of different types of laminectomy replantation: a three-dimensional finite element analysis

English Keywords:Laminectomy replantation  Posterior ligament complex  Biomechanics  Finite element analysis

English Abstract:

  【Abstract】 Objectives: To compare the biomechanical characteristics between three types of laminectomy replantation(LMRP) in the lumbar spine utilizing three-dimensional finite element analysis and to provide a relevant biomechanical basis for the selection of LMRP. Methods: The whole lumbar spine CT image data of a 35-year-old healthy male volunteer was extracted to establish finite element models of L1-L5, and the normal whole lumbar spine model M0 was obtained and validated. Referring to the clinical surgical methods, the L3 vertebral body was used as the surgical segment to establish various LMRP models according to different surgical methods and ligament severing conditions, including en-bloc LMRP model M1, head-side flipped LMRP model M2a, tail-side flipped LMRP model M2b, and rotational LMRP model M3 preserving the continuity of the interspinous and supraspinous ligaments. The lower surface of L5 vertebral body was fixed and restrained, and a vertically downward pressure load of 500N and a 10N·m moment load were applied to the upper surface of L1 vertebral body, and the range of motion(ROM) and the maximum Von Mises stress in each segment of lumbar spine of all models under the six motion conditions such as flexion, extension, left and right lateral bending, and left and right axial rotation were analyzed. Results: The validity of M0 was verified since each segment ROM and total ROM from L1 to L5 were similar to the results of previous studies. Of M1-M3 models, under flexion condition, comparing with M0, the overall ROM of L1-L5 increased in percentage as M1(21.6%)>M2b(15.6%)>M2a(12.1%)>M3(3.6%)>M0; ROM of L2/3 segment increased in percantage as M1(52.8%)>M2b(51.8%)>M2a(11.7%)>M3(10.5%)>M0； ROM of L3/4 segment increased in percantage as M1(50.0%)>M2a(46.7%)>M2b(17.1%)>M3(7.9%)>M0; The maximum Von Mises stress on L1/2 disc increased by 19.0%-23.0%; The maximum Von Mises stress on L2/3 disc increased in percantage as M1(29.42%)>M2b(29.41%)>M2a(6.1%)>M3(5.2%)>M0; The maximum Von Mises stress on L3/4 disc increased in percantage as M1(26.6%)>M2a(26.2%)>M2b(7.5%)>M3(2.5%)>M0; The maximum Von Mises stress on L4/5 disc decreased by 10.0%-11.5%; The maximum Von Mises stresses on articular cartilage from L1-L5 increased in percantage as M2a(63.6%)>M1(61.3%)>M2b(9.2%)>M3(3.5%)>M0; The maximum Von Mises stress on the titanium screw at the vertebral body and the pedicle of the surgical vertebrae was not significantly different between models and M3 was the smallest; The maximum Von Mises stress on the titanium screw of the spinous process of the surgical vertebrae and spinous process was M2a>M3>M1>M2b; The maximum Von Mises stress on titanium plates on both sides was M2a>M3>M1, which in M2b was not consistent with the patterns on the surgical vertebrae and other internal fixation devices; The overall stress of M1 and M3 titanium plates was significantly lower than that of M2a and M2b and the stress distribution was relatively uniform. In the left and right rotations, the ROM of L3/4 segment in M1-M3 models increased by about 40% compared with M0, and there was no significant difference in the ROM and the maximum Von Mises stress between models in other states. Conclusions: Comparing with en-bloc LMRP and flipped LMRP, the rotational LMRP preserves the continuity of the interspinous and supraspinous ligaments, which is close to normal model in the ROM of each segment with good postoperative stability, changes little in the stresses of all structures, and features uniform distribution of the stresses of the internal fixations.