The Biomechanics Analysis Of Different Cervical Minimally Invasive Surgeries For Cervical Spondylotic Radiculopathy

Background:Anterior cervical discectomy and fusion（ACDF）possesses high fusion rates and clinical success rates,and facilitates the remission of the symptoms efficiently,which is regarded as the standard procedure for cervical spondylotic radiculopathy（CSR）.However,the treatment of internal fixation and fusion results in a loss of motion capacity of the operated segment and a compensatory increase of adjacent segment motion,which could accelerate the adjacent segment degeneration.With the popularization of the concept of minimally invasive and the development of equipment,an increasing number of spine surgeries emerge a trend of transformation from open surgery to minimally invasive.Cervical endoscopic minimally invasive surgeries divide into two categories,including posterior endoscopic cervical foraminotomy（PECF）and anterior transdiscal approach of endoscopic cervical discectomy（ATd-ECD）.The two minimally invasive surgeries obtain the same efficacy as fusion surgery and significantly decrease the risk of adjacent segment degeneration.Hence,they have turned into an effective alternative surgery for cervical spondylotic radiculopathy nowadays.The other minimally invasive surgeries,like the anterior transcorporeal approach of endoscopic cervical discectomy（ATc-ECD）and microsurgical anterior cervical foraminotomy（MACF）,also satisfyingly relieve the symptoms of nerve compression,though there are relatively few reports compared with the above-mentioned two surgeries.Minimally invasive surgery is a trend in the treatment of spinal diseases.Nevertheless,because of lack of fusion and internal fixation,this method needs to remove part structure and could cause some changes of the cervical spine in biomechanics,such as stability loss and facet joint pressure increase and so on.Up to now,there is little biomechanical research about minimally invasive surgeries and it is unclear which surgery is closest to the normal cervical physiology.Meanwhile,there is a need for a furthermore study to comprehend uncovertebral joint degeneration or not after minimally invasive surgeries.Purpose:Evaluating the biomechanics changes of operated and adjacent segments after four minimally invasive surgeries by using finite element analysis tool,and exploring which surgery is nearest to the normal cervical physiology and evaluating the biomechanics changes of the uncovertebral joint after surgeries.Method:Based on the computer tomography image of a healthy subject,the C3-C7 standard model was constructed by using finite element software.After mesh precision analysis and model verification,four minimally invasive surgeries were established based on the practical operation of procedures.The standard model was applied 1 Nm moment and 50 N follower force to simulate cervical flexion,extension,lateral bending,and axial rotation.The predicted displacement of the standard model should be calculated in different motions.Afterward,four minimally invasive were applied 1.0 Nm moment and displacement load,which ensured minimally invasive models have the same displacement as the standard model.Finally,the biomechanics results of all models,such as the range of motion（ROM）,intradiscal pressure（IDP）,annulus fibrosus pressure（AFP）,facet joint contact pressure（FJ CPRESS）,and uncovertebral joint contact pressure（UJ CPRESS）,were calculated in the operated and adjacent segments under different motions.Results:In the ATc-ECD model,there were no obvious changes in the biomechanics parameters in the operated and adjacent segments under different motions.In all models,the motion capacity of ATd-ECD increased the most in the operated segment and then was PECF.For intradiscal pressure,the ATd-ECD model represented a significant decrease under different motions in the operated segment,whereas,the MACF model increased the most.For facet joints contact pressure,the operated segment had a significant increase under different motions after the ATd-ECD procedure and did not emerge an obvious increase after MACF.For the PECF model,the facet joint pressure showed a slight decrease under lateral bending motion,while the pressure increased under flexion and axial rotation,and the pressure showed the maximum change during axial rotation compared with the other models.Compared with the change of facet joint CPRESS,all surgical models had a little effect on the uncovertebral joint,and the pressure increase mainly occurred in lateral bending and axial rotation.However,for the MACF model,the uncovertebral joint contact pressure represented a significant decrease under extension because of the posterior part of the uncovertebral joint removing.For adjacent segments,the biomechanics parameters usually show a compensatory tendency in all surgical models.Conclusions:Four surgical models show good biomechanics stability,and the ATc-ECD model is nearest to the normal cervical.However,the ATd-ECD obviously changes the biomechanics of the cervical spine and could cause further degeneration in the operated segment.Four minimally invasive models could accelerate the degeneration of the uncovertebral joint and the facet joint,but the uncovertebral joint could have a lower degeneration risk than the facet joint.