| Objective: With the development of high-speed transportation and construction, high-energy injury gradually increases. The incidence of complex tibial plateau fracture is rising. Schatzker VI tibial plateau fractures are bilateral plateau fractures associated with metaphyseal separation, which are extremely unstable and hard to be stabilized. Moreover, the skin is in great tension, severe swelling, and easy to form tension blisters several days after fracture. Most of Schatzker VI tibial plateau fractures comes with skin contusion. If not treated properly, infection, skin necrosis, traumatic arthritis and other complications were easily developed. Fracture's anatomic reduction and stable fixation, the effective protection of soft tissue, early functional exercise would maximize joint function recovery. The current commonly used internal fixation: unilateral plate fixation, with low incidence of skin infection and necrosis, it's use is limited as a result of the instability, prone to loss reduction; The traditional bilateral plate fixation is considered to be reliable with limitation of dramatic surgical trauma and poor blood supply of anterior tibial, and also prone to have postoperative complications such as skin necrosis. Surgeons continue to try other ways. Locking plate is a new type of internal fixation developed in recent years. With the advantage of angle stability, it can provide more stabilization than unilateral ordinary plate. Further more, it does not damage the periosteum and blood supply. It is controversial whether it can replace the ordinary double-plate fixation. The purpose of this experiment is to compare the stability of ordinary bilateral steel and pure lateral locking plate fixation by mechanics, provide a theoretical basis for clinical treatment.Methods: Selected eight pairs of embalmed cadavers of adults around a tibia specimens, including 5 males, 3 females; aged 30-60 years with a mean (40.75±10.38) years of age; all the samples provided by the department of Anatomy, Hebei Medical University. Muscle and soft tissue were removed. The specimen with deformity, bone destruction, tuberculosis, cancer and degenerative changes in osteoarthritis was excluded. no osteoporosis were found through Osteocore 3-EXA-type absorptiometry (Medileink, Inc, FRA) line of bone mineral density measurements. The upper 25cm of tibia and inferior 15cm segment of femur (as a pressure device) were selected. All specimens were kept in isotonic saline for 30 minutes, sealed with plastic film, cryoprotected at -20℃and thaw at room temperature for 24 hours before the experiment. With the pendulum saw, the fracture line were made in accordance with pre-designed production schatzkerVI Tibial plateau fracture model. Eight pairs of specimens were divided into two groups randomly with 4 pairs in each group. The specimens of two groups were fixed separately with LCP or ordinary double plates (4.5mm outside golf plate+3.5mm inside dynamic compression plate, or DP). All specimens were anatomically reconstructed.Axial load applied on specimens of the two groups separately. The ipsilateral distal femur and proximal tibia of all specimens are matched to make sure the angle between the femur axis and tibia axis is about same at 7°, the angle between medial condylar long axis and sagittal plane is about 22°, to keep knee joint matching. The distal tibia and proximal femur were fixed on the self-made fixture by the mixing appropriate typeⅡdenture base polymers, All specimens were installed in the CSS-44020 biomechanical testing machine. Specimens were fixed in the experimental machine base, the femoral stump were fixed on top of the testing machine axial compression test.50 N vertical preload was carried out for 3 times, in order to eliminate the creep effects of specimens. The experiment was carried out using continuous load until 800 N, loading rate is 20 N/s. With the YJY-17-type extensometer, vertical displacement and horizontal displacement of the medial and lateral condyle were measured at load to 400N, 800N separately. Each specimen loaded for six times, calculated the average. DP group were tested and recorded in the same way. SPSS13.0 statistical software were used for statistical analysis, with t-test and P value was set at 0.05 for the statistical significance.Results: Through the bone mineral density measurement, no significant difference in bone mineral density between LCP group and the DP group were shown. with the load of 400N on the lateral side, the LCP allowed an average of (0.250±0.053)mm of subsidence, compared with(0.226±0.056) mm for DP; when 800N load apllied, the LCP allowed an average of (0.615±0.086) mm of subsidence, compared with(0.553±0.103) mm for DP. It shows no significant difference between the two groups (P=0.381 and P = 0.220). On the medial side, with 400N load appllied, LCP allowed an average of (0.515±0.130)mm of subsidence, compared with(0.355±0.091)mm for the DP; when 800N load apllied, LCP allowed an average of (0.942±0.249)mm of subsidence, compared with(0.583±0.145) mm for the DP, which shows statistical difference between the two groups(P=0.013 and P=0.003). As to the horizontal displacement, with the 400N load, the horizontal displacement of LCP group and DP group are (0.090±0.020) mm, (0.079±0.018) mm respectively; when load reach 800N, the horizontal displacement are 0.206±0.027 mm in LCP group and 0.183±0.026 mm in DP group. There was no statistically significance between the two groups (P = 0.266 and P = 0.099).At the load of 800N, the axial rigidity on the lateral side of LCP and DP are (1324.9±197.7)N/mm and (1490.5±287.6)N/mm (P=0.201); and (899.3±227.9) N/mm,(1457.6±409.1) N/mm on the medial side (P=0.003). The shear stiffness is (4463.4±643.6), (3943.2±553.4) N/mm respectively, no significant difference between the two groups (P = 0.105).Conclusions: In this study, the stability of the two ways of LCP and DP to fix Schatzker VI tibial plateau fracture models were compared by bio-mechanics method. our data showed that on lateral side of the plateau, there was no significant difference in fixation strength between LCP and DP group; but on the medial side, DP fixation is better than LCP. The two methods have similar ability to resist platform widened. Only with LCP at the lateral side is not enough biomechanically to stabilize the tibial plateau. In addition to LCP at the lateral side, another compression plate at medial tibial plateau is necessary supplement to stabilize some special Schatzker VI fracture.
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