Reachout Orthopedics - Issue 1

criterion. A three-dimensional finite element analysis was carried out to investigate the effect of varying the high tibial osteotomy correction angle on the stress distribution in both compartments of the human knee joint by Trad et al . [35]. The maximum von Mises stresses in articular cartilages were obtained to see overall stress distribution. Atmaca et al . [36] analyzed the loading on the tibial articular cartilage following medial meniscectomy performed in various locations and extents, as well as in the healthy knee, via finite element analyses on the solid models. von Mises was selected as damage criteria for cartilage. Wang et al . [37] compared the stress distributions on knee joint cartilage between kneeling and standing positions. The finite element models for both postures were presented, and the mechanical status of the cartilage was investigated. The models were established from magnetic resonance (MR) images of the same subject and assigned with identical material properties. In many papers in the literature, von Mises damage criteria were used because meniscus and soft tissues exhibit ductile material properties. After entering the loading and boundary conditions, FE analyses were solved. The maximum stresses are given in Table 3 for different damage criteria. These stresses were presented as image in Fig. 5 (von Mises), Fig. 6 (Tresca) and Fig. 7 (minimum principal). The maximum von Mises stress in physeal plate was calculated as 1.30 MPa. The maximum von Mises stress in screw and fragments was calculated as 12,931 MPa and 190.31 MPa, respectively. The maximum Tresca stress in physeal plate was calculated as 0.749 MPa. The maximum Tresca stress in screw and fragments was calculated as 6862.80 MPa and 105.01 MPa, respectively. The maximum/minimum principal stress in physeal plate was calculated as 0.36 MPa. The maximum/minimum principal stress Table 2: Mechanical properties of screw, bone and physeal plate used in FEA [32–34]. Parameters Bone Physeal plate Stainless steel Density (kg m −3 ) 2100 1000 7750 Young’s modulus (MPa) 17,000 5 193,000 Yield strength (MPa) 135 207 Ultimate strength (MPa) 148 586 Poisson’s ratio 0.35 0.46 0.31 Table 3: The stress values in different damage criteria. No. Damage criteria Stress distributions Physeal plate (MPa) Screw (MPa) Fragments 1 von Mises 1.30 12,931 190.31 2 Tresca 0.749 6862.80 105.01 3 Minimum principal stress 0.36 492.28 29.44 Fig. 5: von Mises stresses. in screw and fragments was calculated as 492.28 MPa and 29.44 MPa, respectively. As seen in Table 3, stresses in physeal plate are smaller than stresses in screw and fragments. This indicates that a great majority of the stresses on the physeal plate are absorbed by screws. Even if these stress values in physeal plate are very small, physeal plate is affected by stresses. Williams et al . [38] researched physis properties for 5-month bovine. They found ultimate stress value to be 1.36 MPa. We found the maximum von Mises stress in physeal plate to be 1.30 MPa. Even at these values, the epiphyseal plate is likely to be damaged. Also you can see minimum principal stresses in Fig. 7. The minimum principal stresses show compressive stress better. The compressive stresses occur on the wavy surface of the epiphyseal plate. This confirms our analysis, and minimum principal stresses show the compression stresses better than von Mises. According to the SH classification, while type I and II fractures can be treated According to the Salter-Harris classification, while type I and II fractures can be treated by closed methods, type III and IV fractures mostly need open reduction and internal fixation. 5 reachOut Orthopedics