Abstract
Introduction
The use of open wedge high tibial osteotomy (OWHTO) to reduce knee pain by transferring weight-bearing loads to the relatively unaffected lateral compartment in varus knees and to delay the need for a knee replacement by slowing or stopping destruction of the medial joint compartment. To maintain the stability of OWHTO, the most common type of plate was T-Plate as the locking compression plate (LCP) concept. Anterior portion of T-Plate infringe patient's soft tissue resulted in some complications, whereas anatomical L-plate does not. To evaluate the structural stability of the anatomically contoured L-plate in the present study, the effect of weight bearing after osteotomy should be reviewed in the point of the stress of the plate and screws. We hypothesize that its stress path diverge through collateral portion of tibia and the stress level in screws lowered comparing to the result of T-plate presented in existing literature.
Materials and Methods
Based on the postoperative CT data were made from the reconstruction model for finite-element model. The value of Young's modulus and Poisson's ratio were 17,000MPa and 0.36 for cortical bone and 300MPa and 0.3 for cancellous bone. The anatomically contoured L-Plate system, the material of all plate systems were surgical Ti-Alloy were homogeneous and linear properties (Young's modulus = 113,000MPa, Poisson's ratio = 0.33). The screw system were the same as the material properties of the anatomically contoured L-Plate system. For finite element analysis, both the bone and screws were contacted as general condition. And the screws and plate were contacted as tie contact(Figure 1). The load conditions were applied to the top of the tibia based physiological (=1400N) and surgical loads (=200N). In this study, the compressive-bending load was applied to the two nodal points corresponding to the centers of each tibial condyle and divided into 60% and 40% to the medial and lateral sides, respectively. The physiological loads applied in the quadrant section on the proximal tibia.(Chu-An Luo, 2013)
Results
Forlocking screw, it was calculated as 134%, 88.2%, 92.7%, 97.3%, 100%, 88.7%, 80.8%, 112.4% compared to cortical screw (No.05) in each of the portions (No.01∼08) (Figure 2). The maximum stress of the lateral cortex's stress concentration was shown as the anatomically contoured L-Plate 130MPa, it was lower than that reported in the literature T-plate 171MPa. Maximum stress in structurally weak the screw neck was shown in the anatomically contoured L-Plate with 198MPa, T-Plate 200 MPa was similar to that reported in the literature.
Conclusion
The stress path of postoperative bone was found to be formed from at collateral direction in the study. The anatomically contoured L-Plate received a load similar to the T-Plate in the lateral cortex that reported in the literature. But it was confirmed that the maximum stress is more structurally stable enough to appear on the contrast of 76% T-Plate. Although T-Plate is structurally simple with a short moment arm, the anatomically contoured L-Plate is advantage to stress dispersion and more stable than T-Plate.
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