Evaluation Of Sound Pressure Discrimination In The Posterior Spinal Decompression And Fixation Surgery

Object:The high-speed burr is an irreplaceable power device for cutting bone in posterior spinal surgery,but facing a high risk of postoperative neurological complication.Safety operation of the high-speed burr is the most challenging skill which must be overcome for spine surgeons,with a long learning curve.Based on previous work,in this study,the sound pressure characteristics were collected and analyzed during the bone cutting process of posterior spinal decompression and fixation surgery.The sound pressure characteristics were used to identify tissues being cut(cancellous bone,cortical bone,and facet joint surface),detect cortical bone penetration,and realize risk early warning.This study also provides experimental basis for clinical application of sound pressure characteristics in posterior spinal decompression and fixation surgery.Methods:1.The cervical spine specimens of mini-pig were fixed on the operating table in the prone position.Every specimen was dissected carefully to expose the posterior bony structures.The laminae(C3-C7)were drilled by the high-speed burr along the laminafacet junction or the pyramidal-shaped dome,in the way of hole by hole.First,a 5mm melon burr was applied to drill the dorsal cortical bone and cancellous bone of the lamina while the ventral cortical bone was preserved,then bony troughs of 5 mm in width were formed;second,the bony troughs mentioned above were drilled using a 2mm melon burr until the ventral cortical bone was penetrated;then bony troughs of 2 mm in width were formed which could be used as the open side of laminoplasty or laminectomy.Hole by hole means continuous vertical drilling.The vertical hole from dorsal cortical bone to cancellous bone,ventral cortical bone until penetration makes the trough deeper;the burr feed from caudal side to cephalic side with a step distance of radius of the burr,making the trough longer.2.The thoracic and lumbar specimens of mini-pigs were fixed on the operating table in the prone position.The posterior bony structures such as spinous process,lamina,and articular process were exposed and the adjacent soft tissues should be preserved as much as possible.With the engagement of high-speed burr,in the way of hole by hole,the laminae(first and fifth sides)and inferior facet joints(second the eighth sides,upper pedicle-ossification tunnel)of the involved segments were removed;the bony junction between the pedicle and upper facet joint(fourth and sixth sides,lower pedicle-ossification tunnel)was cut off(upper facet joint en bloc resection);the paravertebral muscle,intercostal fascia,and suspensory ligament of nerve root(third and seventh sides)were resected from the upper facet joint;then the upper facet joint en bloc resection via pedicle-ossification tunnel of T8-L5 segments were completed.In the way of hole by hole,longitudinal troughs were made bilaterally along the laminafacet junction;the lamina located on the medial side of the pedicle and medial inferior articular process were cut off;a transverse trough was made between the laminae of involved levels to cut off the bony junction between the pedicle and lamina;the lamina was lifted gently and the traditional posterior laminectomy of T8-L5 was completed.3.The spine specimens of mini-pigs were fixed on the metal table in the prone position.All unnecessary soft tissue was removed and the anatomical landmarks were exposed to make sure the entry points.The junction of the lateral margin of the superior articulating process and the lateral mass was determined;the entry point was chosen at 1 mm caudally and medially to this junction for cervical spine.The entry point of thoracic spine was identified in the middle of the triangle formed by the pars interarticularis,the lower border of the superior articular facet and the medial border of the transverse process.The entry point of lumbar spine was located at the junction between the pars interarticularis and the transverse process.With the application of 2 mm burr,the screw insertion should be parallel to the cranial endplate in the sagittal plane,with angle of 25°–45° from the sagittal plane for the pedicle from C3-C7,15° for T8-T12,and 5-10°for L1-L5.The entry point of translaminar facet screw from L1 to L5 was located at the cranial one third of the base of the spinous process.A 2 mm burr was applied to drill from the entry point toward the opposite pedicle of the lower vertebra,passing the lamina and the facet joint.The lateral angle and caudal angle were 40-50° and 45-60°,respectively.4.Informed consent was obtained from all participants,and the study was approved by the Tianjin Medical University General Hospital Institutional Review Boards and Ethics Committee.From February 2020 to May 2020,6 cervical spinal stenosis patients were treated with traditional laminectomy,single and double open door laminoplasty(2 case for each surgery);2 thoracic spinal stenosis patients were treated with traditional laminectomy and upper facet joint en bloc resection via pedicleossification tunnel,respectively.Every participant was diagnosed by preoperative Xray,CT,and MRI.Under general anesthesia,the patient was placed in the prone position,the surgical processes were as shown in method 1-2.In order to avoid the spinal cord injury,the ventral cortical bone was not penetrated and the related sound pressure signal was also not collected in each surgery.5.In the above specimen and clinical experiments,the sound pressure signals in the cutting process were collected with a miniature microphone.In the specimen experiment,the microphone was fixed on the side of the handpiece of high-speed burr,while in the clinical experiment the microphone was packaged with sterile medical transparent dressing and fixed on the infusion stand.By using the joint time-frequency analysis method,the sound pressure signals were processed with multi-layer wavelet packet decompression until each node contains only one harmonic component,and its frequency is an integer multiple of the spindle frequency of the motor burr.The amplitude of each harmonic component can reflect the cutting states.The amplitude of the harmonic components was calculated to distinguish tissues being cut and detect cortical bone penetration.Result:1?In posterior cervical decompression surgery,on the hinge side,the amplitude of the cancellous bone was lower than that of the ventral cortical bone,and there were significant differences at 1-4 k Hz(p < 0.001),but there was no significant difference at 5 k Hz(p > 0.05);on the open side or cutting zone of laminectomy,the amplitude of the ventral cortical bone was significantly larger than that of cortical bone penetration(1-5 k Hz,p < 0.001).2.In posterior thoracic and lumbar decompression surgery,significant differences in harmonic amplitude could be found between cancellous bone and cortical bone(lamina),cortical bone and cortical bone penetration(lamina and pedicle-ossification tunnel),at the frequency spectrum from 1 k Hz to 5 k Hz(p < 0.001).For the amplitude of cortical bone and cortical penetration of pedicle-ossification tunnel,there were significant differences at 2-4 k Hz(2 k Hz,p<0.001;3-4 k Hz,p<0.05),but there was no significant difference at 1and 5 k Hz(p > 0.05).3.In the pedicle screw insertion process,for both pedicle and vertebral body,the amplitudes of cancellous bone and cortical bone were significantly different over the entire frequency range(1 k Hz,2 k Hz,4 k Hz,and 5 k Hz,p<0.001;3 k Hz,p<0.05);the amplitudes of cortical bone and cortical penetration were also different(1-5 k Hz,p<0.001).In the translaminar facet screw insertion process,differences in amplitudes were statistically significant in every tissue pair at certain frequency: for cancellous bone and cortical bone,p<0.001 at 1-4 k Hz,p<0.05 at 5 k Hz;for cancellous bone and cortical penetration,cancellous bone and facet joint surface,cortical bone and cortical penetration,and cortical penetration and facet joint surface,p<0.001 at 1-5 k Hz;for cortical bone and facet joint surface,p>0.05 at 3 k Hz,p<0.001 at other frequency.4.The results of clinical experiments are as follows: in posterior cervical decompression surgery,the amplitudes of cancellous bone were always lower than that of cortical bone(1-3 k Hz,p<0.001;4 k Hz,p<0.01;5 k Hz,p>0.05);in traditional thoracic laminectomy surgery,there were significance in amplitudes between cancellous bone and cortical bone at 1-4 k Hz(p<0.001),but not at 5 k Hz(p>0.05);in the upper facet joint en bloc resection via pedicle-ossification tunnel thoracic decompression surgery,the amplitudes of cancellous bone was higher than that of cortical bone at 1 k Hz(p>0.05)and lower at 2-5 k Hz(3 k Hz,p>0.05;2,4,5 k Hz,p<0.001).Conclusion:The results of specimens and clinical experiments proved that in posterior spinal decompression and fixation surgery,sound pressure features could be used to identify drilling states(cancellous bone,cortical bone,cortical bone penetration,and facet joint surface)in real time,control the depth and direction of the burr precisely,and realize risk early warning.This study enriches the signal feedback system of spinal surgery,establishes the method of identifying drilling states by sound pressure feedback,and provides experimental basis for the establishment of safe posterior spinal decompression and fixation surgery based on sound pressure characteristics.