| Objectives Pelvic specimens were used to conduct biomechanical experiments to investigate the biomechanical stability of three kinds ofinternal fixation through K-L approach for the transverse acetabular fracture, including single reconstruction plate, single locking reconstruction plate, double reconstruction plate. And by using pressure sensitive film technology, this research investigated the contact characteristics of hip joint by the changes on the loading area, mean pressure and peak pressure in the dome region after three kinds of transverse acetabular fracture internal fication.Methods Nine adult embalmed pelves were harvested for this study,aged 21-47 years old, average 35.5. Since the level of the fourth and fifth lumbar specimens and two thighs 1/3 at the junction of the body transected specimens. Remove the skin of the specimen, carefully peel the muscle, fascia and other soft tissue attached to the pelvis andthe femoral shaft, remove the ligaments around the acetabulum and the hip joint capsule. Visual observation and X-ray confirmed the pelvis and femur samples were not rheumatism, tuberculosis, tumors, fractures, osteoporosis and other diseases and anatomical variations. Saw specimens from the middle of the pelvis and sacrum pubic symphysis median sagittal, trim sections, made 18 hemipelvic specimens, which were numbered 1 to 18 using random number table, and divided into SP, SL, DP three groups(n=6). At the ischial tuberosity respectively perpendicular to the sagittal, coronal, horizontal each scored a Kirschner, represents the body axis in three-dimensional coordinate system by standing position.Mark acetabular weight-bearing areawith a, b, c, d.Specimens were fixed with denture powder in the inverted one foot standing position.The pressure sensitive film attached to the femoral head, upper and lower covered moisture latex sheath. Connect the femoral shaft with mechanical testing machinewith the speed of 20N/S loaded to 5/6 of bodyweight,and maintained for 2 minutes. when loading, the blunt end of the 1.5mm's Kirschner was inserted into the a and b two holes, leaving the mark on the pressure sensitive film, and at the same time marked on the c and d points. The pressure sensitive film data of 18 specimens from the pelvic specimen were defined as I group data. In the neutral position of the pelvis specimens, between acetabular apex and lunate apex drawing atransverse fracture line through the top of the acetabular, so that the line extends to thethe posterior column greater sciatic notch apex, anterior column through the iliopubic eminence posterior iliopsoas central sulcus.Alongthis linewith a saw(blade thickness of about 0.5mm) cut off acetabular,therebyproducing atransverse acetabular fracturemodels. There were three methods using to get to anatomical reduction of fracture under direct vision. SP group: single reconstruction plate fixation; SL group: locking reconstruction plate fixation; DP group: double reconstruction plate fixation. Pressure sensitive film was pastedon femoral head to measur contact characteristics after fixation, with a incrementally continuous load, at the speed of 20N/S.Messure displacement of the fracture site with grating displacement sensor, and recordinternal fixation failure load.Calculate the average stress, peak stress of the acetabular dome region loading area, and fracture displacement and internal fixation stiffness. Using SPSS 13.0 statistical software for data analysis, using the LSD method for comparison between groups, P < 0.05 was considered statistically significant.Results 1 All of the plates were not damaged. All of the screws were not pulled out. The lag screws were not bent. All of the hemipelves did not have fractures. There were not dislocation of joints during loading.Pressure sensitive film worked out rightly. 2 For the Group I(Intact), the loading area,mean pressure, and peakpressure were as follows: 4.31±0.36cm2, 1.32±0.24 MPa, 2.08±0.19 MPa. For the Group SP(single reconstruction Plate), the loading area,mean pressure,and peak pressure were as follows: 2.61±0.32cm2,2.96±0.48 MPa, 3.48±0.31 MPa. For the Group SL(locking reconstruction plate), the loading area,mean pressure,and peak pressure were as follows: 3.00±0.18cm2,2.43±0.38 MPa,2.8±0.25 MPa. For the Group DP(double reconstruction plate), the loading area, mean pressure, and peak pressure were as follows: 3.53±0.17cm2,1.92±0.23 MPa,2.3±0.15 MPa. For the loading area, mean pressure, and peak pressure, the variances of each group was equal(P>0.05). Through LSD multiple comparison, there was significant difference between groups on the loading area, mean pressure, and peak pressure(P<0.05). The loading area: Group SP< Group SL< Group DP< Group I; Mean pressure: Group SP> Group SL> Group DP> Group I; Peek pressure: Group SP> Group SL> Group DP> Group I. 3 Withthe increasing load, there were increased longitudinal displacement trend in the three groups. Under different loads there were significantly different(P<0.05) between 3 groups about longitudinal displacement. Under the same load, the single reconstruction group of longitudinal displacement significantly larger than a single locking reconstruction group and the double reconstruction group, single locking reconstruction group was significantly greater than the double reconstruction group(P<0.05). Single reconstruction group, single locking reconstruction group, double reconstruction group fixation turn to fail respectively at the loading of 1 000 N, 1 400 N,2 000 N. 4 Under a load of 1400 N, SP group axial stiffness was(93.08 ± 4.26) N/mm, SL group axial stiffness was(135.75 ± 9.80) N/mm, DP group axial stiffness was(266.88 ± 25.72) N/mm. Through Dunnett's T3 multiple comparison, there was significant difference between groups on the stiffness, and Group SP < Group SL < Group DP(P<0.05).Conclusions 1 The high transverse acetabular fracture made the loading area decreased, the mean stress and peak stress increased significantly, it significantly changed the biomechanical behavior of hip joint even after anatomical internal fixation. 2 When acetabular transverse fracture fixed within K-L approach, double reconstruction plate fixation provided more stability than single locking reconstruction plate, and the least influence on contact characteristics of the acetabular. The single reconstruction plate was the most unstable, and had the greatestimpaction to biomechanical behavior of hip joint. |
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