Objective To investigate the biomechanical differences of three internal fixation approaches, namely improved Galveston (IG), reconstruction plate (RP), and il iosacral screw (LS) to the posterior pelvic ring fracture dislocation and provide experimental evidence for the cl inical appl ication of proper internal fixation method. Methods Six donatedfresh adult cadaver pelvic specimens (age averaged 45 years old) were numbered randomly and their normal biomechanics were tested by the measure instrument (MTS855 Mini-Blonix). The displacement values of normal pelvis were measured under the vertical compression (800 N) and reverse direction compression (8 N·m). Then they were made into left Denis I pelvic fracture and fixed with the IG, RP, and LS, respectively, in different orders. Biomechanics test was conducted on the fixed pelvis from both the vertical and the reversed directions. Results Concerning the direction of vertical ity and torsion, the order of fracture displacement from small to large was the normal pelvis, LS, IG and RP. There was no significant difference between LS and the normal pelvis (P gt; 0.05), and the differences between other tow groups were significant (P lt; 0.05). Conclusion The LS fixation can provide better stabil ity for posterior pelvic ring fracture dislocation when compared with IG and RP.
Objective To investigate the detailed biomechanics of TiNi shape-memory sawtooth-arm embracing plate (TiNi SMA) by comparing with l imited-contact dynamic compression plate (LC-DCP) and static interlocking intramedullary nail (SIiN), so as to provide theoretical evidence for cl inical appl ication. Methods Eight paired cadaveric femurs immersed in formaldehyde were harvested from eight specimens of adults. After making X-ray films and modeling midpiece transverse fracture, one side randomly was fixed by TiNi SMA (group A) and SIiN (group C) orderly, the other side was fixed by LC-DCP (group B). The axial compression, three-point bending (pressed from plate side and opposite side both of group A and group B, from inside of group C), and torsion were tested, and the stress shielding rate was compared. Results At every classified axial compression load, the strains of group A were greater than those of group B and group C (P lt; 0.05), the displacements of group A were greater than those of group B and group C (P lt; 0.05) except 100 N. At every classified three-point bending moment, the displacement of group A were greater than those of group B and group C pressed both from two sides, but there was no difference when pressing from two sides under the same load of group A (P gt; 0.05). At every torsion moment, the torsion angels of group A were greater than those of group B (P lt; 0.05), but equal to those of group C (P gt; 0.05). At 600 N of axial compression load, the stress shielding rates of groups A, B, C were 48.30% ± 22.99%, 89.21% ± 8.97%, 95.00% ± 3.15%, respectively, group A was significantly less than group B and group C (P lt; 0.01). Conclusion The anti-bending abil ity of TiNi SMA is weaker than LC-DCP and SIiN; the anti-torsion abil ity of TiNi SMA is weaker than SIiN, but TiNi SMA is a center-type internal fixation, the superior stress shielding rate and micromovement promote the stress stimulation of fracture, which makes it an ideal internal fixation device.
Objective To evaluate the effect of polymethylmethacrylate (PMMA) augmentation on cervical stabil ity after anterior cervical interbody fusion (ACIF) before and after fatigue. Methods Twelve porcine cervical spines (C3-7) were subjected to testing angular displacement parameters, including the range of motion (ROM), neutral zone (NZ), and elastic zone (EZ), in nondestructive flexion and extension, right/left lateral bending, and left/right rotation on Motion Analysis motion capture system and MTS-858 servo-hydraul ic testing machine. Intact cervical spines served as control group (group A); oneleveldiscectomy and fusion was performed with anterior plate fixation based on group A as group B; flexion and extension,left/right lateral bending (5 000 cycles) fatigue testing based on group B as group C; the augmentation screw channel was used based on group C as group D; and flexion and extension, left/right lateral bending fatigue testing were performed based on group D as group E. Results The ROM, NZ, and EZ in group A were significantly different from those in other groups (P lt; 0.05) at flexion/extension, left/right bending, and left/right rotation. The ROM, NZ, and EZ in group B were significantly smaller than those in group C (P lt; 0.05) in flexion/extension, left/right bending, and left/right rotation, but there was no significant difference when compared with group D (P gt; 0.05). The ROM and NZ in flexion/extension and the EZ in flexion in group B were significant smaller than those in group E (P lt; 0.05), but there was no significant difference in the other indexes (P gt; 0.05). The ROM, NZ, and EZ in group C in flexion and extension, left/right lateral bending, and left/right rotation were significantly higher than those in groups D and E (P lt; 0.05). The ROM and NZ in flexion and extension and left/right lateral bending, and the ROM in left/right rotation, and the EZ in flexion and extension, right bending, and left/right rotation in group D were significantly smaller than those in group E (P lt; 0.05), but there was no significant difference in the other indexes (P gt; 0.05). Conclusion PMMA augmentation can significantly increase the instant cervical stabil ity and provide a biomechanics basis in cervical anterior plate fixation.
Objective To research the biomechanical effect of different length bone plates on treatment of tibial shaft fracture. Methods Forty-five tibia specimens from fresh adult corpse (20-40 years old) were donated (30-38 cm in length, 34 cm on average) and were divided into 3 groups randomly (n=15). Under the following three conditions, the experiment was made separately. Compression stress-strain indexes of whole tibia were determined under the reverse, three spots curving and compression. The vertical elastic strain was 0-1 000 N, the reverse angle was 0-3º, and three bending stresswas 0-400 N. Then the center-section squint non-damage bone fracture model was made, fracture was fixed by 6, 10, 14stainless steel AO LC-DCP, respectively. The compression stress-strain indexes were determined under reverse angle, three spots curving and compression, statistical analysis was done. Results The vertical direction strain value of 6, 10 and 14 hole steel plate under vertical compressions, was 0.449 ± 0.241, 0.093 ± 0.003, 0.139 ± 0.005, respectively ; showing significant difference between 10 and 14 hole steel plates and 6 steel plate (P lt; 0.01) and no significant difference between 10 and 14 hole steel plate (P gt; 0.05). The lateral strain value of 6, 10 and 14 hole steel plate was 0.120 0 ± 0.000 4, 0.127 5 ± 0.010 0, 0.237 0 ± 0.000 6 respectively, indicating a significant difference between stell plates of 6 and 10 hole and 14 hole steel plate (P lt; 0.01) and no difference between 6 and 10 hole steel plate (P gt; 0.05). The torque of 6, 10 and 14 hole steel plate was (5.066 ± 2.715) × 10-3, (5.671 ± 2.527) × 10-3 and (4.570 ± 2.228) × 10-3 Nm, respectively and three spot curving vertical direction strain value was 0.049 ± 0.009, 0.124 ± 0.017, 0.062 ± 0.009, respectively. There were significant differences between various steel plates (P lt; 0.01). Conclusion For the fixation of tibial obl ique fracture, 14 hole steel plate’s stabil ities of anti-vertical compression, anti-reverse and anti-curving are better than those of 6 hole steel plate under the condition of the same material qual ity, thickness, width and screw quantity used.