The Biomechanical Study And Clinical Application Appraisal Of The Extrapedicular Internal Fixation On The Middle And Upper Thoracic Spine

Objective:By biomechanical testing and clinical observation of the extrapedicular internal fixation on the middle and upper thoracic spine,explore the feasibility and validity of the technique, provide the basis for clinical application.Methods:1 Biomechanical experimental study:Four fresh-frozen human specimen of middle and upper thoracic spines(T1-T9)were harvested with the medial 5-6 cm of rib,overlying parietal pleura and the intercostal soft tissue intact,removes the thoracic trauma,degenerative disease,cancer and spinal deformity,etc.Before the experiment,make the specimens thawed to room temperature.Each vertebra was instrumented with 6.0×45 mm screws on one side with extrapedicular screw technique and on the opposite side with 4.5×40 mm screws using standard pedicle screw technique.Biomechanical testing was performed on an WD2000 electronic formula universal biomechanical testing system. The maximum axial pullout of strength(POS) was measured.Appraise the feasibility of extrapedicular internal fixation on the middle and upper thoracic spine through the biological mechanics comparison.2 Clinical application:In clinical work,select the appropriate cases of the middle and upper thoracic spines,treat them by using extrapedicular screw technique,29 cases in all,18 male,11 female,of which 7 cases of scoliosis,thoracic burst fracture in 5 cases,thoracic spine fracture-disclocation in 8 cases,thoracic spinal tuberculosis in 4 cases,thoracic primary tumor in 3 cases,thoracic ossification of yellow ligament and thoracic spinal cord injury with T7 subluxation 1 cases,1cases of thoracic pedicle screw fixation.Spinal cord according to ASIA classification,A grade 9 cases,B grade 3 cases,C grade 3 cases,D grade 6 cases,E grade 8 cases.By measuring Cobb's angle before and after the spine surgery,observing the fixation position after surgery,classifying the spinal cord injury through ASIA,appraise the validity of extrapedicular internal fixation on the middle and upper thoracic spine.Results:1 Biomechanical evaluation:68 thoracic screws underwent biomechanical test including 36 extrapedicular screws and 32 pedicle screws.The average POS for extrapedicular screw fixation was 798.32±64.34N compared to 800.21±106.33N for pedicle screw fixation.there were not statistically significant differences in POS between the two techniques.2 Clinical Evaluation:In the 29 cases,176 screws were penetrated by using extrapedicular technique,all screws were penetrated successfully,and no neurovascular injury,followed by six months to 18 months,no screws loosen,pullout,broken,and no significant loss of correction of degrees.Conclusion:The biomechanical test of the extrapedicular internal fixation on the middle and upper thoracic spine shows that the mechanical property of the surgery is well,and proves the clinical feasibility of the technique.The clinical use proves that the technique is safe,simple, stable in entrance point selection and directional control.The technique is a good and reliable posterior fixation method of the middle and upper thoracic spine,and has more practical value.Especially good for the scoliosis and other spinal deformities cases of which pedicles are small,complex and not fit to the pedicle fixation.