Biomechanical Analysis Of Thoracolumbar Denis B Bursting Fractures Treated By Monosegmental And Bisegmental Fusion

Objective: Traumatic fractures of the thoracolumbar spine, especially thethoracolumbar junction (T10–L2), are the most common fractures of thespinal column. The transition from the less mobile thoracic spine with itsassociated ribs and sternum to the more dynamic lumbar spine makes this anarea of great biomechanical stress. The thoracic region kyphosis ranges from18°to51°and the spine transitions to a lumbar lordosis ranging from42°to74°.The thoracolumbar region (T10-L2) is either straight or slightlykyphotic (0°-10°) in the sagittal plane. The thoracolumbar junction isuniquely predisposed to traumatic injuries caused by high energy forces beingtransmitted through this region as a result of the transition from the kyphoticthoracic to the lordotic lumbar region.Disruptions of the thoracolumbar spine are often a result of high-energyinjuries, the majority being the result of motor vehicle accidents and falls. As40%to80%of thoroacolumbar spine injuries are in a setting of high energy,motor vehicle. accidents, falls, and so forth, many are considered unstablefrom either a biomechanical or a neurologic standpoint and often suffer frominjury to more than two other organ systems. Common associated injuries,especially associated with thoraciclevel fractures, reflect the forces of blunttrauma and rapid acceleration and deceleration: pneumothorax, hemothorax,rib fractures, bronchial disruption, myocardial or pulmonary contusion, greatvessel injuries, hemopericardium, cardiac tamponade, and diaphragmaticrupture.Bursting fractures account for10%-20%spinalfracture.Commonly,accompanied by neurological damage. Denis devidedburst fractures into five types, Denis B type fracture is the most common,accounting for49.2%. The purpose of surgical treatment include: nerve decompression, reconstruction of spinal, spinal fusion. The main treatmentoptions include: anterior approach, posterior approach and combined approach.The advantage of the posterior approach include: effective reconstruction,stable fixation, less operation time. For Anterior approach, advantage include:more thoroughly spinal decompression and reconstruction of anterior column.Currently, most scholars support monosegmental fusion(injured vertebraand upper vertebral) for the treatment of Denis B fracture. This method canreduce the amounts of fusion segment, keep the normal disc. However, thereare little research about the stability of this kind of operation. The purpose ofthis experiment is to compare the biomechanical properties of Denis Bfractures treated by monosegmental and bisegmental fusion.Methods: Thoracolumbar spines (T11–L3) of6calves were used. Eachof the six specimens (No. I-VI) underwent the following protocol test steps:1.Specimens tested intact2. Partial corpectomy(L1) and discectomy (T12/L1),Bone graft(T12-L1) with anterior bisegmental fixation (T12/L2)3. specimenswere additionally stabilized by a bisegmental pedicle screw after removing theanterior fixation4. Partial corpectomy(L1)between the caudal and cranialendplate of the adjacent vertebrae,bone graft (T12–L2) stabilized bybisegmental pedicle screw.(T12–L2)5. Bone graft(T12-L2) with anteriorbisegmental fixation (T12/L2) after removing the pedicle screw. Test withmaximum rotation moment of±7.5Nm, maximum compression load of300N.Results: The right/left axial rotation were not stable in the unstable group.ROM was significantly increased in the unstable group compared with theintact group (P＜0.05). The right/left axial rotation ROM were significantlyreduced in the monosegmental fusion and bisegmental fusion compared withthe unstable group (P＜0.05). For the combined approach,axial rotation ROMwas smaller in the monosegmental fusion compared with the bisegmentalfusion (P＜0.05)，and have no significant difference compared with anteriorbisegmental fixation(P＞0.05).For the bisegmental fusion, stability of anteriorfixation is similar with the combined approach(P＞0.05).For the anteriorfixation, ROM was significantly increased in the bisegmental fusion group compared with the monosegmental fusion group.(P＜0.05). Forcompression,there are no significant difference among different kinds offixiations.Conclusion: Combined anterior monosegmental fusion with posteriorinstrumentation provides enough stability. Under the premise of satisfactoryinterbody fusion, removal the pedicle screw after monosegmental fusion canincrease spinal motion, reduce the stress of the adjacent intervertebral disc andbe conducive to delay disc degeneration.