The effect of cement on hip stem fixation: a biomechanical study

Biomechanical evaluation of intramedullary retrograde nail and dynamic condylar screw used in unstable distal femoral fractures

Distal femur fractures are a common problem in orthopedics. Intramedullary retrograde nails (IRN) and dynamic condylar screws (DCS) are generally used for the treatment of these fractures. In this study, it was aimed to mechanically evaluate and compare these two implants used for the treatment of distal femur fractures. In this study, an AOOTA 33C1.3 fracture was created on the intact femur obtained from computed tomography images. The fractures were fixed with DCS and IRN. Then the created models were imported into the ANSYS Workbench for finite element analysis to determine the most convenient mechanical fixation type. The distal region of the femur was loaded considering 75 kg-f, and the created models were constrained in all directions from the femoral head. The intact femur was also analyzed to compare it with the DCS and IRN fixation models. The von Mises stress, strain, and displacement results were examined to determine the damage risk. According to the results, the risk of damage is lower in the model of fixation with IRN. The normal strain distribution in the model fixed with IRN is closer to the model of an intact femur. For this reason, the risk of stress shielding in IRN fixation is less than in DCS fixation. However, the fracture lines were more stable in the fixation with the DCS. In conclusion, fracture fixation with IRN is mechanically more suitable for distal femur fractures in terms of fracture healing.

Finite element analysis of the mechanical strength of a new hip Spacer

BACKGROUND AND OBJECTIVE

At present, the influence of the internal metallic endoskeleton of Spacer on the biomechanical strength of Spacer remains unclear. The aim of this study was to analyze the mechanical stability of a novel Spacer applying a annular skeleton that mimics the structure of trabecular bone using finite element methods.

METHEDS

The femur models of three healthy individuals and skeletonless Spacer, K-Spacer, and AD-Spacer were assembled to create 15 3D models. Finite element analysis was performed in an Ansys Bench2022R1. Biomechanical parameters such as stress and strain of the Spacer, internal skeleton and femur were evaluated under three loads, which were applied with the maximum force borne by the hip joint (2100 N), standing on one leg (700 N), and standing on two legs (350 N). The mechanical properties of the new hip Spacer were evaluated.

RESULT

The stresses on the medial and lateral surfaces of the AD-Spacer and K-Spacer were smaller than the stresses in the state without skeletal support. The maximum stresses on the medial and lateral surfaces of the AD-Spacer were smaller than those of the inserted K-Spacer, and the difference gradually increased with the increase of force intensity. When the skeleton diameter was increased from 3 to 4 mm, the stresses in the medial and lateral sides of the AD-Spacer and K-Spacer necks decreased. The stress of both skeletons was concentrated at the neck, but the stress of the annular skeleton was evenly distributed on the medial and lateral sides of the skeleton. The mean stress in the proximal femur was higher in femurs with K-Spacer than in femurs with AD-Spacer.

CONCLUSIONS

AD-Spacer has lower stress and higher load-bearing capacity than K-Spacer, and the advantages of AD-Spacer are more obvious under the maximum load state of hip joint.

Static, fatigue and stress-shielding analysis of the use of different PEEK based materials as hip stem implants

There is a possibility that hip joints may become dysfunctional due to age, wear or some accidents, and in this case they need to be replaced with hip implants. However, after conventional hip stem implantation, the load transferred to the bone usually decreases due to the high stiffness of the metallic (most commonly Ti6Al4V, CoCr or stainless steel) hip stem implant, and as a result, mineral loss occurs in the bone which weakens. On the other hand, PEEK is an advantageous material with its low cost, ease of production, corrosion resistance and biocompatibility. More importantly, it has the potential to be a good alternative to metallic materials in load-bearing bone replacements, thanks to its mechanical properties and density close to that of the bone. In this study, hip stem implants having three different commercial PEEK materials and four different metallic main spar designs were modeled. Their behavior under static and dynamic loading conditions was analyzed according to ASTM-F2996-20 and ISO-7206-4:2010 standard test methods, and the stress-shielding effect of hip stems modeled as implanted into the femur was simulated using ANSYS commercial finite element analysis software. According to the results, it was observed that CFP based hip stem models meet the five million life time criteria and increase the stress on the femur bone by up to 57%.

Health technology assessment through Six Sigma Methodology to assess cemented and uncemented protheses in total hip arthroplasty

The purpose of this study is to use Health Technology Assessment (HTA) through the Six Sigma (SS) and DMAIC (Define, Measure, Analyse, Improve, Control) problem-solving strategies for comparing cemented and uncemented prostheses in terms of the costs incurred for Total hip arthroplasty (THA) and the length of hospital stay (LOS). Multinomial logistic regression analysis for modelling the data was also performed. Quantitative parameters extracted from gait analysis, electromyography and computed tomography images were used to compare the approaches, but the analysis did not show statistical significance. The variables regarding costs were studied with the Mann-Whitney and Kruskal-Wallis tests. No statistically significant difference between cemented and uncemented prosthesis for the total cost of LOS was found, but the cost of the surgeon had an influence on the overall expenses, affecting the cemented prosthetic approach. The material costs of surgery for the uncemented prosthesis and the cost of theatre of surgery for the cemented prosthesis were the most influential. Multinomial logistic regression identified the Vastus Lateralis variable as statistically significant. The overall accuracy of the model is 93.0%. The use of SS and DMAIC cycle as tools of HTA proved that the cemented and uncemented approaches for THA have similar costs and LOSy.