Comparison of tibial fracture plate length, placement, and fibular integrity effects on plate integrity through finite element analysis.

Minimally invasive plate osteosynthesis is the most commonly used minimally invasive surgery technique for tibial fractures, possibly involving single or dual plate methods. Herein, we performed a finite element analysis to investigate plate strength according to the plate type, length, and presence of a fibula by constructing a three-dimensional tibia model. A thickness of 20 mm was cut 50 mm distal from the lateral plateau, and the ligaments were created. Plates were modeled with lengths of 150, 200, and 250 mm and mounted to the tibia. Screws were arranged to avoid overlapping in the dual plating. The von-Mises stress applied to the plates was measured by applying a load of 1 body weight. Dual plates showed the least stress with low displacement, followed by medial and lateral plates. As the plate length increased, the average stress gradually decreased, increasing plate safety. The difference in the influence of the fibula depending on the presence of proximal fibula osteotomy showed that the average stress increased by 35% following proximal fibula osteotomy in the D1(Plate type: Dual plate, Medial plate length: 150 mm, Lateral plate length: 200 mm, Non Proximal fibula osteotomy) and D1P(Plate type: Dual plate, Medial plate length: 150 mm, Lateral plate length: 200 mm, Proximal fibula osteotomy) models, confirming the necessity of the fibula model. There is no consensus guideline for treatment of this kind of fracture case. A single fracture plate can decrease the risk of skin damage, ligament damage, and wound infection, but because of its design, it cannot provide sufficient stability and satisfactory reduction of the condylar fragment, especially in cases of comminution or coronal fracture. So, these results will help clinicians make an informed choice on which plate to use in patients with tibial fractures.

Stress Effect in the Knee Joint Based on the Fibular Osteotomy Level and Varus Deformity: A Finite Element Analysis Study.

Proximal fibular osteotomy (PFO) was found to relieve pain and improve knee function in patients with medial compartment knee osteoarthritis (OA). Therapy redistributes the load applied from the inside to the outside and alleviates the load applied on the inside through fibula osteotomy. Therefore, the clinical effect of fibular osteotomy using the finite element (FE) method was evaluated to calculate the exact change in stress inside a knee joint with varus deformity. Using CT and MRI images of a patient's lower extremities, 3D models of the bone, cartilage, meniscus, and ligaments were constructed. The varus angle, representing the inward angulation of the knee, was increased by applying a force ratio in the medial and lateral directions. The results showed that performing proximal fibular osteotomy led to a significant reduction in stress in the medial direction of the meniscus and cartilage. The stress reduction in the lateral direction was relatively minor. In conclusion, the study demonstrated that proximal fibular osteotomy effectively relieves stress and redistributes the load in the knee joints of patients with medial compartment knee osteoarthritis. The findings emphasize the importance of considering force distribution and the position of fibular osteotomy to achieve optimal clinical outcomes.

Shape suitability and mechanical safety of customised hip implants: Three-dimensional printed acetabular cup for hip arthroplasty.

Background: Owing to an increase in the number of hip arthroplasty surgeries, the number of implant replacement surgeries is increasing rapidly as well. This necessitates the study of hip joint conditions. Therefore, Paprosky defined a classification system to indicate the degree of damage to the hip joint. In this study, a customised hip implant suitable for Paprosky classification Type ⅡC and over was designed. The shape, suitability, and mechanical safety of the worst-case model for the implant were evaluated. Materials and methods: To identify the implant size depending on states over Type ⅡC acetabulum bone loss, a size range was selected and a customised implant was designed according to the computed tomography data within the size range. The implant was designed for the flange, hook, and flattened model types. The worst-case selection test was conducted using finite element analysis. The von Mises stresses of the flange, hook, and flattened models were found as 76.223, 136.99, and 80.791 MPa, respectively. Therefore, the hook-type model was selected as the worst case for the mechanical performance test. Results: A bending test was conducted on the hook-type model without fracture and failure at 5344.56 N. The proposed customised implant was found suitable for Type ⅢA acetabulum bone loss, whereas the shape suitability and mechanical safety were verified for the worst case. Conclusion: The shape of a customised implant suitable for Paprosky ⅢA type was designed. The shape suitability and mechanical safety were evaluated using finite element method analysis and bending tests. Clinical validation is required through subsequent clinical evaluation.

Biomechanical Effect of Coronal Alignment and Ligament Laxity in Total Knee Arthroplasty: A Simulation Study.

The purposes of this study were to develop a cruciate-retaining total knee arthroplasty musculoskeletal model, which enables the adjustment of ligament length and implant alignment; validate the model; and evaluate the effects of varus/valgus alignment adjustment and unbalanced medial/lateral ligament laxity during gait. A cruciate-retaining total knee arthroplasty musculoskeletal model was constructed and validated against the in vivo contact forces. This model was transformed to 2° varus/valgus alignment of femoral or tibial replacement models and 2° medial/lateral laxity models. The contact forces and ligament tensions of the adjusted models were calculated. The contact forces in the model showed good agreement with the in vivo contact forces. Valgus replacement alignment with balanced ligament models showed a lower contact force at the medial compartment than at the neutral alignment model, whereas the varus replacement alignment with balanced ligament models showed a greater contact force at the medial compartment and medial/posterior cruciate ligament tension. The medial laxity with neutral alignment model showed a similar contact force with decreased medial ligament tension compared to the balanced neutral alignment model, whereas the lateral laxity with the neutral alignment model showed a greater contact force and decreased lateral ligament tension. The cruciate-retaining total knee arthroplasty model was validated using in vivo contact forces (r = 0.939) Two degrees of valgus alignment adjustment with balanced ligament or neutral alignment with 2° of medial laxity can be safe without increasing contact force or ligament tension compared to neutral alignment with a balanced extension gap. However, 2° of varus alignment adjustment with balanced ligament or neutral alignment with 2° of lateral laxity may be unfavorable due to the overloading of the joints and knee ligaments.

Evaluating the validity of lightweight talar replacement designs: rational models and topologically optimized models.

BACKGROUND: Total talar replacement is normally stable and satisfactory. We studied a rational scaffold talus model for each size range created through topology optimization (TO) and comparatively evaluated a topologically optimized scaffold bone talus model using a finite element analysis (FEA). We hypothesized that the rational scaffold would be more effective for application to the actual model than the topologically optimized scaffold. METHODS: Size specification for the rational model was performed via TO and inner scaffold simplification. The load condition for worst-case selection reflected the peak point according to the ground reaction force tendency, and the load directions "plantar 10°" (P10), "dorsi 5°" (D5), and "dorsi 10°" (D10) were applied to select worst-case scenarios among the P10, D5, and D10 positions (total nine ranges) of respective size specifications. FEA was performed on each representative specification-standard model, reflecting a load of 5340 N. Among the small bone models selected as the worst-case, an arbitrary size was selected, and the validity of the standard model was evaluated. The standard model was applied to the rational structure during validity evaluation, and the TO model reflecting the internal structure derived by the TO of the arbitrary model was implemented. RESULT: In worst-case selection, the highest peak von Mises stress (PVMS) was calculated from the minimum D5 model (532.11 MPa). Thereafter, FEA revealed peak von Mises stress levels of 218.01 MPa and 565.35 MPa in the rational and topologically optimized models, respectively, confirming that the rational model yielded lower peak von Mises stress. The weight of the minimum model was reduced from 1106 g to 965.4 g after weight reduction through rational scaffold application. CONCLUSION: The rational inner-scaffold-design method is safer than topologically optimized scaffold design, and three types of rational scaffold, according to each size range, confirmed that all sizes of the talus within the anatomical dimension could be covered, which was a valid result in the total talar replacement design. Accordingly, we conclude that an implant design meeting the clinical design requirements, including patient customization, weight reduction, and mechanical stability, should be possible by applying a rational inner scaffold without performing TO design. The scaffold model weight was lower than that of the solid model, and the safety was also verified through FEA.