Biomechanical Study Of PLIF Combined With Compression Fixation

IntroductionIt is often seen today that all kinds of lumbar disability associated disease for cataplasis and trauma,for example; lumbar spondylolisthesis, degennerative lumbar scoliosis, lumbar disability sign, lumbar fracture dislocation, et al. It is said that the disease incidence of lumbar spondylolisthesis is 6% among people. In a society composed of increasing numbers of lumbar disability associated disease , the treatment of lumbar disability associated disease is becoming a major challenge for spinal surgeon. Some goals of spinal surgery have been achieved by interbody fusion using a posterior approach popularized by Cloward. However, significant problems including failure of fusion, persistent neurologic compression , and iliac crest donor complication using the classic PLIF remain. The purpose of our study was to introduce and evaluate the biomechanical features of PLIF combined with compression fixation.ObjectiveThe purpose of the current study was to introduce and evaluate the biomechanical features of PLIF combined with compression fixation.Methods36 fresh calf lumbar spines (L₂-5 motion segments) were harvested. Each motion segment was radiographed to ensure that no major structural abnormalities were present (e. g, pars defects, compression fractures). Specimens were thencarefully stripped of soft tissues with the intact of bone membrane, intervertebral disc, facet sac and all ligaments. The end of the each motion segment was fixed to the materials testing machine using the self - made clamp and bone cement (PMMA).Biomechanical Loading SequenceThe current study was to compare the biomechanical stability in calf models of two methods. The specimen was positioned and clamped in a materials testing machine (BIONIX858, Material Test System, Eden, Prairie, MN, USA). The intact specimen was then biomechanically tested as follows: 1) axial compression (500 N) , 2) flexion (10 Nm) , 3) extension (10Nm) , 4) right lateral bending (10 Nm) , and 5) left lateral bending (10Nm). Stiffness values were calculated from the load deflection curves obtained.After the intact specimen had been tested according to the six - step loading sequence, an L₄ laminectomy, a bilateral L₄-5 facetectomy, and a radical dis-cectomy (with resection of both anterior and posterior longitudinal ligaments) were performed. Thus, all the simulated disability specimens were obtained according to Panjabi method.The specimens with different fixational techniques, PLIF combined with compression techniques fixation, traditional PLIF techniques fixation, were tested respectively. All the simulated specimens were biomechanically tested as a-bove, Stiffness values were calculated from the load deflection curves obtained.Load deflection curves were obtained each time, and stiffness values were calculated from the curve. A cyclic compression force was applied as conditioning (500 ± 10 N at 1 Hz for 100 cycles) to remove excess fluid from the disc and return the disc to its predeath height.Load Displacement CurvesThe stiffness of the motion segment was determined each time from the slope of the load displacement curve obtained. To adjust for variations in stiffness between motion segments, a normalized stiffness ratio was calculated by dividing the value of stiffness obtained for the experimental condition (e. g, after PLIF combined with compression fixation techniques fixation, traditional PLIF techniques fixation) by the stiffness value obtained for the intact specimen.