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Objective To evaluate the biomechanical stability of pectin/polyvinyl alcohol composite （CoPP）hydrogel and to assess the range of motion(ROM) and intradiscal pressure (IDP) changes at the above adjacent segment after the anterior implantation of CoPP hydrogel and cage. Method Six fresh cadaveric lumbar spine specimens（L3～L5）were biomechanically tested on the robotic testing machine. ROM at L3/4 and L4/5 and intradiscal pressure at L3/4 were measured. All measurements were made with initially intact and followed by both CoPP and cage implantations. Results At the implanted level (L4/5), the CoPP spine showed no significant change in the other five motion directions except left lateral bending motion compared with the intact spine (P>0.05), whereas the cage spine decreased significantly in all motion directions when compared with the intact spine or CoPP spine (P0.05), whereas the ROM of cage spine significantly increased in all motion directions compared with the intact spine (P0.05). While the IDP of cage spine significantly increased in flexion/extension and left/right lateral bending compared with the intact spine or CoPP spine (P0.05). Conclusions The implantation of CoPP prosthetic nucleus can preserve the motion function at the operated level and maintain the lumbar stability. Compared with the lumbar fusion, the nucleus replacement has no significant effect on the ROM and IDP at adjacent level, which may decrease or avoid the adjacent segment degeneration.
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PURPOSE: To assess the biomechanical effects and effectiveness of an interspinous spinal spacer (ISS) on the intradiscal pressure using in vitro biomechanical tests. MATERIALS AND METHODS: Six calf spine specimens (less than 2 weeks of age, L1-L5) were divided to two groups the intact and the surgery groups (n=3 each). For the surgery group, an ISS made from PMMA (Greek pi=12-mm) were inserted into the space between the spinous processes of L3-L4. The intradiscal pressures at the various regions of the annulus (anterior, posterior, and posterolateral locations) and the nucleus pulposus were measured using the four pressure transducers under pure compression (700 N) and extension loads (700 N+7.5 Nm). RESULTS: An increase in pressure was observed from neutral to extension at the posterior and posterolateral annulus. After inserting the ISS, the changes in pressure at the adjacent disc levels (L2-L3, L4-L5) were negligible regardless of the loading conditions (p>0.05). However, at the implanted level (L3-L4) statistically significant changes in the pressure were found under extension loading at the nucleus pulposus, posterior and posterolateral regions of the annulus with a pressure drop from 1.48 MPa, 1.42 MPa, 1.71 MPa to 1.11 MPa, 0.961 MPa, 1.08 MPa, at the respective locations (p<0.05). The relative percentage decrease were 25%, 31.7%, and 36.8%. CONCLUSION: On the implanted level, these results showed that the insertion of the ISS with PMMA can effectively reduce the intradiscal pressures by at least 25% quite uniformly over the intravertebral disc during extension. More effective reduction was observed at the posterolateral location. The pressure changes at the adjacent levels were negligible in contrast to the abnormal pressure changes that are frequently reported after conventional rigid fusion. This suggests that the likelihood of adjacent level degeneration after surgery can be minimized using the ISS insertion.
Subject(s)
Polymethyl Methacrylate , Spinal Stenosis , Spine , Transducers, PressureABSTRACT
Objective To compare the effect of pulling and rotating manipulation in different cervical postures on intradiscal pressure of the cervical spinal cord.Methods Quantitative simulation of pulling and rotating manipulation was performed on 6 fresh corpse cervical samples by Mechanical Testing & Simulation(MTS) system in different cervical postures of 20 degrees of anteflexion,neutral position,and 20 degrees of posterior extension,and the changes of intramedullary pressure of intervertebral C3/4,C4/5 and C6/7 were measured.Results The intradiscal pressure of intervertebral C3/4 and C4/5 in the posture of 20 degrees of posterior extension at the end of pulling manipulation by 200N and when the posture returned to the primary after pulling and rotating manipulation was less than that in the posture of 20 degrees of anteflexion(P
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PURPOSE: The biomechanical responses of degenerative porcine intervertebral disc were compared with those MATERIALS AND METHODS: Two groups were set; Group A (44.0+/-2.8 months old, female) and Group B (6.2 +/-1.3 months old, female). Histological (H&E stain) observations were carried out to see the degeneration for both groups. Then biomechanical responses were investigated by measuring height changes in disc, intradiscal pressure values and relaxation time for each specimen under axial compressive loads. RESULTS: Degenerative changes were confirmed through H&E staining in Group A. The ratios of the nucleus pulposus area to total area were 14.7+/-4.5% and 29.2+/-6.0% in Group A and B, respectively (p=0.000). The decrease rates in disc height were 12.1+/-3.3% and 21.6+/-7.6%, in Group A and B, respectively under the axial compression of 740 N (p=0.000). No significant difference in intradiscal pressure measured in anterior zone between-groups except at axial load of 740N (p> 0.05). However, significant difference in pressure was found in posterolateral zone when the load was 542 N and higher (542 N: p=0.015, 740 N: p=0.010). The average relaxation time for Group A was significantly longer than that for Group B at 740N, i.e., at maximum load (anterior: p=0.010, posterolateral: p=0.014). CONCLUSION: Different biomechanical responses in degenerative disc were confirmed. They are 1) less flexible, 2) slower in energy relaxation under axial loading, and 3) larger portion of the external load were taken up at posterior part of annulus fibrous, especially in degenerative disc.
Subject(s)
Intervertebral Disc , Relaxation , SpineABSTRACT
We studied the intradiscal pressure in order to understand the biophysics of the lumbar intervertebral disk. We evaluated the relationship between disk morphology and intradiscal pressure in 90 lumbar intervertebral disks of 64 patients. The intrinsic intradiscal pressure in the ruptured disks was much lower than that in the normal or bulging disk, but intrinsic intradiscal pressure alone did not correlate in a statistically significant way to the absence, or presence and/or type of disk herniation. The elastance of normal disks was statistically significantly higher than that of the protruded disk(p<0.05) ; however, the elastance of lumbar disk was not affected by type of disk protrusion. Factors affecting disk elastance were the degeneration and the integrity of the annulus fibrosus and the posterior longitudinal ligament. The authors experienced no complication during the procedure. The measurement of the intradiscal pressure to evaluated the biophysical function of lumbar intervertebral disks is only a simple and risk-free procedure. Also it is suggested that patients with bulging disks of high elastance may be treated by reducing intradiscal pressure with percutaneous procedures such as chemonucleolysis, and automated discectomy using Nucleotome.