Research And Development Of A Minimal Invasive Transiliac Interlocking System(MITIS)for Posterior Pelvic Ring Fixation

Objectives:Posterior pelvic ring injuries,serious injuries of pelvic fractures,mainly caused by high-energy trauma,are always associated with significant high rate of complications and mortalities.Reduction and fixation after Pelvic posterior ring injuries are of great importance for the control of hemorrhage,the stability of pelvic ring,as well as less solft tissue injuries and better prognosis.Currently,there still have not been an secure and efficient method for the fixation of posterior pelvic ring injuries.based on the mechanism of interlocking intramedullary nails,we intend to design a minimal invasive transiliac interloocking system(MITIS)for the fixation of posterior pelvic ring,and further study would be focus on the design and evaluation of this system.the results,including security,minimally invasive effect and biomechanics stability of the MITIS would be the foundation of further clinical studies.Methods:1.The original CT data of 100 Selected healthy adults(50 male,50 female)were imported into the software of Mimics Innovation Suit 19.0 for three-dimensional reconstruction,after standardlizing of the coordinate system,the distance between the the posterior wall of sacral canal to the level of bilateral iliac crest was measured to position the needling point of main nail.Then,parameter was set by measuring the horizontal distance between the bilateral point.According to these data,further procedure was implemented to simulate the placing of main nails on 3D pelvic models with Mimics solftware.After the main nails located,lateral and medial nails were respectively placed.The lateral nail towards the top of Sciatic notch and the medial nail towards to the upper anterior margin of acetabulum.Then the angle was measured and recorded for further analysis,thus providing data for the designing of MITIS.2.Further evaluation of minimally invasive character was based on the surgery simulation with MITIS in cadaver models(3male,3female).Four 2-3cm length incisions were made on the region of posterior ilium and posterior-lateral sacrum.The main nail was placed through the lateral incision after expanding of the hole.Bilateral interlock screws were screwed by a gueder.After that,the length of incisions was recorded.Autopsy was perfromed for identification of inappropriate length and orientation of nails.3.With the help of the software 3-Matic,MITIS model was simulated placing of nails on100 pelvic models.Use the movement and rotation commands to move and rotate the MITIS in the three directions of the xyz coordinate,and the safty margins should be observed and measured to analyse the safe region for surgical mistakes.4.A one leg standing biomechanical model was made with 6(3 male,3 female)adult pelvic specimens.After the 1000 continuous sagittal 100N-350 N load,The Tile C-type pelvic fracture model(Denis ? type sacral fracture with pubic symphysis dislocation)was made.After 6-hole plate fixation of the pubic symphysis,sacroiliac screw,tension band locking plate and continue with MITIS fixation are biomechanical tested.Use an optical motion capture to collect the 3D movement coordinate of 2 points located in bilateral fracture line of the sacrum.We can assess the stability of MITIS and mechanics features.Results:1.The design parameters of the main nail are confirmed by the measurement of the pelvic image data and the statistics of the screw angle vector after the screw simulating.The diameter of the main nail is 11 mm,and the interval length is 98 mm ~ 158 mm,with every 4mm long to produce a specification.The angle of both ends of the lateral interlocking nails to the pelvic of female and male is 24.9°and 20.1°respectively,while the tilt angle to the foot side are 64.2°and 65°respectively.The angle of medial nail to the lateral pelvic are 35°and 34.1°respectively,while the tilt angle to the foot side were46.8°and 46.3°.The aperture of the main interlocking nail is designed as 5.1mm and the diameter of the interlocking nail is 5mm.2.In the simulated operation experiment,all six specimens were successfully placed with MITIS.Both the main nail and bilateral interlocking nails were nailed with two 3cm long transverse incisions and two 2cm long longitudinal incisions according to the established surgical procedure.The incision is long enough not to need to extend again.Examined after anatomy,all 6 specimens were normal pelvis with no significant individual mutation,no screw was inserted into the spinal canal and sacral foramina,no damage was occoured to the sacroiliac joint.The main nail is well located with the end into bilateral iliac crest.3.In the 100 cases of simulated screwing,one case was failed because of the iliac bone dysmorphism,The successfully screwing rate of MITIS was 99%.The safety marginresults showed a enough safty area was in ilium for surgons to implant MITIS.4.One of the six specimens had failed to complete all 1000 cycles of pressurization due to the severe osteoporosis.Biomechanical experiments showed that MITIS fixation is better in the resistance to shear stress on the sagittal plane of the pelvis than SIS and TBP,but is weaker in the resistance in the horizontal direction than TBP fixation.However,in the situation of the relative displacement from bilateral displacement of the fracture,MITIS is as good as SIS,and both better than TBP fixation.Conclusion:MITIS,as an innovative design,can be minimally invasive,safe and stable for pelvic rings,and is expected to be a new option for posterior ring fixation,but further clinical trials are needed to be taken for validation of the advantages.