ABSTRACT
Objective To investigate the reliability of using the pubic symphysis diastasis of 25 mm and anterior separation distance of sacroiliac joint to differentiate anteroposterior compression (APC) type Ⅰ and Ⅱ injuries as well as assess the injury severity.Methods A total of 11 (seven males and four females) fresh cadaver specimens with 22 hemipelvis were collected.The pelvic APC injury test models including fixed hemipelvis (restricted group) and unfixed hemipelvis (non-restricted group) were established,with 11 hemipelvis in each group according to the random number table method.Meanwhile the specimens were divided into male group (14 hemipelvis) and female group (eight hemipelvis),simulating APC type injury external rotation hemipelvis.The public symophysis interval and anterior interval of sacroiliac joint of the original pelvis,the pubic symphysis diastasis and anterior diastasis of sacroiliac joint after anterior tibiofibular ligament failure,as well as the affected pelvis ligament and sacral ligament injury were recorded and compared between the restricted and non-restricted groups,male and female groups.Results There were no significant differences in the public symphysis interval of the original pelvis and anterior interval of sacroiliac joint between the restricted group and the non-restricted group (P ＞ 0.05).The pubic symphysis interval of the original pelvis was [(5.13 ± 0.61) mm] in male group and (4.03 ± 0.84)mm] in female group (P ＜ 0.05).When the anterior tibiofibular ligament ruptured,the pubic symphysis diastasis distance was (23.36 ± 7.27) mm,ranging from 12 to 41 mm,and the diastasis distance of anterior sacroiliac joint was (9.82 ± 3.25)mm,ranging from 5 to 18 mm.In terms of the public symphysis interval,there were no significant differences between male and female groups,restricted and the non-restricted groups (P ＞ 0.05).In terms of anterior interval of sacroiliac joint,there was significant difference between male and female groups (P ＜ 0.05) but no significant difference between the restricted and non-restricted groups (P ＞ 0.05).In the restricted group,sacrotuberous ligament injuries were found in four patients,and sacrospinous ligament injuries in five,whhile there were no obvious sacrospinous ligament and sacrotuberous ligament injuries in non-restricted group.There were 10 specimens with the pubic symphysis diastasis ≥23.36 mm and 10 specimens with the diastasis distance of anterior sacroiliac joint ≥9.82 mm (46％),and there were 15 specimens with at least the pubic symphysis interval ≥ 23.36 mm or the anterior interval of sacroiliac joint ≥ 9.82 mm (68％).Conclusions The public symphysis interval ≥ 23.36 mm or anterior interval of sacroiliac joint ≥ 9.82 mm can distinguish anteroposterior compression Ⅰ from Ⅱ injuries,and the combination of the two criteria can be beneficial to assessment of pelvic injury severity.
ABSTRACT
Objective To establish a three-dimensional finite element model of pelvic anteroposterior compression (APC) for analysis of mechanisms for related liganentous damages.Methods A finite element model and a laboratory mechanical model of APC were established using the same pelvic specimens.In a finite element model of normal pelvic bones and ligaments,after the right pelvis was fixated the pubic symphysis (PS) was sectioned.Next,a manual external mobile force was gradually applied to the left hemipelvis to make the PS diastasis 10,20,30,40,60,80 and 100 mm apart.The mechanical experiment revealed the anterior sacroiliac ligament (ASIL) was ruptured when the PS diastasis reached 28 mm.After the strain value of ASIL was calculated through the finite element model,it was applied to the other pelvic ligaments.The displacement in front of the sacroiliac joint (SIJ),stress,strain and extent of injury and disruption of sacrotuberous/sacrospinous ligaments (STL/SSL) with a corresponding PS diastasis were observed and recorded.Results ASIL failed at the point when the PS diastasis was 28 mm and the displacement in front of SIJ was 7.41 ± 1.14 mm.The strain and maximum principal stress of ASIL calculated in the finite element model were 259.5％ and 543.24 MPa respectively.The maximum principal stress value of SSL was 35.00 MPa at the point of failure when the PS diastasis and the displacement in front of SIJ were 51 mm and 15.23 ±2.88 mm,respectively.When the PS diastasis and the displacement in front of SIJ were 100 mm and 7.5 mm respectively,the maximum principal stress value of STL was 16.17 MPa but the strained ligament was not ruptured.When the pelvis was rotated externally step by step,the ASIL failure was followed by the rupture of SSL but not necessarily by the STL failure.Conclusion As the finite element pelvic bone-ligament model established in this study can effectively simulate the mechanisms for APC injury,it can be used to evaluate different extents of pelvic ligamentous injury,providing a basis for the biomechanical study of pelvic bones and ligaments.
ABSTRACT
BACKGROUND:A new type of medical titanium alloy Ti2448 (Ti-24Nb-4Zr-7.9Sn) is by far the lowest initial modulus of titanium alloy, with the initial modulus of about 40 GPa, the average Young's modulus<20 GPa, and tensile strength of about 900 MPa;human tissue biocompatibility and mechanical compatibility are excellent. OBJECTIVE:To investigate the biomechanical properties of a new low elastic modulus spinal pedicle screw fixation system and compare it with Ti6Al4V pedicle screw. METHODS:Totally 60 fresh human cadaveric thoracic vertebrae were randomly selected:on one side, pedicle new low modulus Ti2448 pedicle screws, as the experimental group;on the other side, pedicle screw Ti6Al4V, as control group. The maximum bending load and maximum load displacement, maximum torque and maximum axial pul ing force of the two groups were detected. RESULTS AND CONCLUSION:There was no significant difference in the maximum bending load, maximum load displacement, maximum torque and maximum pulling force between the two groups. The results show that the maximum bending strength, the maximum torque and maximum pul out force in low elastic modulus of Ti2448 pedicle screw fixation system are consistent with the Ti6Al4V screws, which can meet the needs of internal fixation on spinal biomechanics strength.