ABSTRACT
Objective:To investigate the biomechanical properties of anterior pelvic ring external fixators of two new configurations [iliac crest (IC)+anterior inferior iliac spine (AIIS), anterior superior iliac spine(ASIS)+AIIS] in the treatment of Tile type C1 pelvic fracture.Methods:A 3-dimensional finite element model of Tile type C1 pelvic ring injury (unilateral longitudinal sacral fracture and ipsilateral pubic fracture) was produced. The pelvis was fixed with external fixators of IC, AIIS, combination of IC and AIIS, combination of ASIS and AIIS, and S 1 sacroiliac screw in 5 types of models. In the simulated bipedal standing position and semi-recumbent position, the longitudinal displacement and back rotation angle displacement of the midpoint on the upper surface of S 1 were quantified and compared. Under the simulated left-right compression load state, the lateral displacements of the highest point of the lateral sacral fracture and the highest point of the lateral pubic fracture end were quantified and compared. Under the simulated anterior-posterior shear load state, the backward displacements of the highest point of the lateral sacral fracture end and the highest point of the lateral pubic fracture end were quantified and compared. Results:(1) In the simulated bipedal standing position under the vertical and longitudinal load state, the results of the longitudinal downward displacement of the midpoint on the upper surface of S 1 were consistent with the backward rotation angle displacement, and the order from largest to smallest was IC, AIIS, ASIS+AIIS, IC+AIIS and S 1 sacroiliac screw. The longitudinal downward displacement of IC was significantly larger than that of other models. The longitudinal downward displacement and backward rotation angle displacement of ASIS+AIIS and IC+AIIS were similar, and the latter was smaller. (2) In the simulated semi-recumbent position under the vertical and longitudinal load state, the results of the longitudinal downward displacement and backward rotation angle displacement of the midpoint on the upper surface of S 1 were also consistent, and the order from largest to smallest was IC, AIIS, ASIS+AIIS, IC+AIIS and S 1 sacroiliac screw. (3) Under the simulated left-right compression load state, the results of the lateral displacement of the highest point of the lateral sacral fracture end were consistent with that of the highest point of the lateral pubic fracture end, and the order from largest to smallest was S 1 sacroiliac screw, IC, AIIS, ASIS+AIIS and IC+AIIS. Among them, Among them, The lateral displacement of S 1 sacroiliac screw and IC was larger. The lateral displacement of ASIS+AIIS and IC+AIIS was similar, and the latter was smaller, significantly smaller than that of other models. (4) Under the simulated anterior-posterior shear load state, the results of the backward displacement of the highest point of the lateral sacral fracture end and the highest point of the lateral pubic fracture end were also consistent, and the order from largest to smallest was IC, AIIS, ASIS+AIIS, IC+AIIS and S 1 sacroiliac screw. Among them, the backward displacement of IC and AIIS was larger. The backward displacement of ASIS+AIIS and IC+AIIS was similar, and the latter was smaller. Conclusions:For type C1 pelvic fracture, the biomechanical stabilities of IC+AIIS and ASIS+AIIS are superior to those of IC or AIIS, with ASIS+AIIS being slightly inferior to IC+AIIS. Compared with S 1 sacroiliac screw, IC or AIIS, the lateral stabilities of IC+AIIS and ASIS+AIIS are particularly prominent. The two new external fixator configurations in this study are worthy of clinical application.
ABSTRACT
Objective To compare the biomechanical characteristics of lengthened sacroiliac screw and long sacroiliac screw fixated in different ways for the treatment of central vertical sacral fractures to provide reference for clinical practice.Methods A finite element model with three dimensions of Tile type C pelvic ring injury (central type Denis Ⅲ fracture of sacrum) was produced.The central sacral fractures were fixated with lengthened sacroiliac screw or long sacroiliac screw in 7 types of models respectively as follows.(1) One long sacroiliac screw was fixated in S1 segment from the right (C1);(2) One long sacroiliac screw was fixated in S2 segment from the right (C2);(3)Two long sacroiliac screws were fixated in S1 and S2 segments respectively from the right (C12);(4) One long sacroiliac screw was fixated in S1 segment from the right and one long sacroiliac screw was fixated in S2 segment from the left (C12hybrid);(5) One lengthened sacroiliac screw was fixated in S1 segment from the right (J1);(6) One lengthened sacroiliac screw was fixated in S2 segment from the right (J2);(7)Two lengthened sacroiliac screws were fixated in S1 and S2 segments respectively from the right (J12).The shift and angle displacement of the central superior surface of sacrum in the case of standing on both feet were measured and compared.The maximum Von Mises stresses in different positions were measured.And various mechanical indices (including stresses of various parts and stress distribution of screws and pelvis,etc) were also quantified and compared.Results The stability of the posterior ring-screw complex was optimal when the sacrum was fixated with S1 & S2 lengthened sacroiliac screws.The maximum Von Mises stresses of screw were affected by sacral segments,namely,S1 ＞ S2 ＞ S1& S2.The maximum Von Mises stress of screws in S1 and S2 segments were similar.The maximum stress of the lengthened sacroiliac screw was lower than that of the long sacroiliac screw.The maximum Von Mises stress of bilateral sacroiliac joints in the lengthened sacroiliac screw fixation model was similar to that of normal pelvis.The maximum stress in the left sacroiliac joint of the long sacroiliac screw fixation model was larger than that of the normal pelvis.The maximum Von Mises stress of screw-bone interface of the long sacroiliac screw fixation model was larger than that of the lengthened sacroiliac screw fixation model.The screw stress distribution of the lengthened sacroiliac screw was superior to that of the long sacroiliac screw,and the screw stress distribution of the double segment fixation was superior to that of the single segment fixation.There was relatively less difference between the pelvic stress distribution of double segment fixation model and that of the normal pelvic model.Conclusion The fixation of S1 & S2 lengthened sacroiliac screws utilized in central sacral fractures of Tile C pelvic ring injury results in a more stable posterior pelvic ringscrew complex,more dispersed screw stress and better pelvic stress distribution which is closed to normal,and can also reduce the risk of internal fixation failure as well as lower back pain.
ABSTRACT
BACKGROUND:Percutaneous hol ow screw under X-Ray fluoroscopy has been shown to treat fracture of acetabulum of the pelvis, but the time of internal fixation was long, and the amount of radiation exposure to the patients and physicians was large. OBJECTIVE:To test the application of the ISO-C3D METHODS:Thirty-one patients with fracture of the acetabulum were treated with percutaneous hol ow screw under a fluoroscopy-based ISO-C computerized navigational system for fracture of acetabulum. 3D computerized navigational system. The interval from injury to operation was 4 to 13 days. Al patients were fol owed up for one year. RESULTS AND CONCLUSION:The average bleeding volume during operation was only 18 mL, except that the bleeding volume of only one patient, who suffered from the sacroiliacjoint injury and received open reduction and internal fixation, was up to 300 mL. The total number of screws used in the operation was 42, among which 24 were screws for acetabular anterior column fracture and 18 for posterior column fracture. Al screws were implanted once precisely. The average time of internal fixation was 59 minutes, and the mean time for fluoroscopy was 39 seconds. The 31 patients were pain-free one week after the operation and no complication (infection, vascular nerve injury or implant breakage) was noted post-operatively. When the fol ow-up ended, radiography revealed fracture union with satisfactory screw fixation (no screw breakage or loosening). According to Matta functional scoring, results were excellent in 23 cases, good in 8 cases, with an excellent and good rate of 100%. According to Majeed functional scoring, the results were excellent in 22 cases, good in 6 cases and average in 3 cases, with an excellent and good rate of 90%. These results indicated that ISO-C3D computerized navigational system can supply stable internal fixation without an increase of complication.