| Objectives:In this study,the stability and internal fixation stress of anterior subcutaneous internal fixation scaffold and bridging combined internal fixation system(subcutaneous double rod,subcutaneous single rod,and bone surface single rod)in the treatment of pelvic anterior ring fracture were analyzed by finite element method,providing theoretical basis for verifying that ortho-bridge systems can effectively treat pelvic anterior ring fracture.Method:Based on the CT data of a healthy volunteer,the finite element model of the normal pelvis was established,and its validity was verified.Then,the anterior subcutaneous internal fixation(group A),bone surface single-rod group of ortho-bridge system(group B),subcutaneous double-rod group of ortho-bridge system(group C)and subcutaneous single-rod group of ortho-bridge system(group D)were simulated to treat the anterior pelvic ring fracture.The biomechanical properties of each group were evaluated by finite element analysis of different internal fixation methods under 500N vertical load,which simulated the standing position of human body.Evaluation indicators:(1)Calculate the displacement of the pelvis and the internal fixation device(global displacement and horizontal displacement).The greater the maximum displacement,the worse the overall stability of the pelvis.The greater the maximum horizontal displacement of the connecting rods in each group is,the easier the connecting rods are to break out and the easier the internal fixation is to fail.(2)Calculate the stress concentration site and the maximum stress value of the pelvis and the internal fixation device,and compare the stress distribution of the left and right sides of the pelvis.The greater the maximum stress of the stress concentration site,the more likely the internal fixation failure will be.(3)Measure the displacement of the two fracture ends.The larger the displacement,the more difficult the fracture is to heal.Result:All four sets of internal fixation devices can effectively restore the biomechanical integrity of the pelvis.After the treatment of anterior pelvic ring fracture with four internal fixation methods,the overall stress distribution and transmission of the pelvis were approximately the same as that of the complete pelvis model.The stress mainly distributed in the anterior margin of each vertebral body of the sacrum,the sacrum wing,the sacroiliac joint,the arched margin of the ilium,the ischium notch and the medial femur.Under the four internal fixation methods,the maximum displacement between the pubic fractures ranged from 0.55 mm to 0.99mm,and the displacement between the ischial ramus fractures was far less than 2cm.Therefore,in the treatment of pelvic anterior ring fracture,all of the four internal fixation methods can achieve stable fixation,and can promote the healing of pubic fracture through appropriate micromotion.Group A and Group D have similar fixation principles,but different locking structures.The maximum horizontal displacement of Group A is about 1.6 times that of Group D.Therefore,the connecting rod slip risk of ortho-bridge system is lower and the locking structure is more stable.The stress shielding effect of subcutaneous single-rod of ortho-bridge system in group D was the smallest,while the stress difference of bone surface single-rod of ortho-bridge system in group B was the largest,and the stress shielding effect was the most obvious.The subcutaneous connecting rod has a certain radian,which can restore the physiological reconstruction of the anterior pelvic ring and has better mechanical compatibility.The maximum stress of each model is far lower than the yield stress of titanium alloy and bone,and the risk of internal fixation fracture and secondary fracture is very low,and the safety is good.Conclusion:1.Both anterior subcutaneous internal fixator and Ortho-Bridge systems can produce appropriate micromotion to promote fracture healing in the treatment of anterior pelvic ring fractures.2.All the four internal fixation methods can restore the stress distribution of the pelvis,and subcutaneous fixation has better biomechanical compatibility than bone surface fixation.3.The ortho-bridge systems has a lower risk of rod slippage than the pedicle screw system. |
