3D Finite Element Analysis of the Modular Prosthesis with Tooth Mechanism of the Femoral Shaft

Modular intercalary prosthetic reconstruction for malignant and metastatic tumours of the proximal femur

To illustrate the surgical technique and explore clinical outcomes of the reconstruction for the malignant and metastatic bone tumour of proximal femur with metallic modular intercalary prosthesis. Sixteen patients who underwent modular intercalary prosthetic reconstruction after tumour resection were included from April 2012 and October 2020. Prosthesis and screws parameters, resected bone length and residual bone length, clinical outcomes and survivorship were analyzed. All patients were followed up for an average of 19 months (range 1-74). In our series, 12 patients died of the progression of the primary disease at the final follow-up. The cumulative survivorship since the treatment of proximal femoral metastasis was 78.6% (11 patients) at 6 months and 38.5% (5 patients) at 1 year. The mean MSTS score was 22.25 ± 4.55 among all patients. There were no cases of loosening or breakage of the prostheses, plates or screws, despite the various measurements of prostheses and residual bones. Modular intercalary prosthetic reconstruction was an effective method for malignant tumour of the proximal femur, including the advantages of providing early pain relief, quickly restoring postoperative function, required a short operation time, and preserving the adjacent joints.

Identification of screw spacing on pediatric hip locking plate in proximal femoral osteotomy

This study describes a computational analysis technique for evaluating the effect of screw spacing and angle on the pediatric hip locking plate system in proximal femoral osteotomy in pediatric patients having DDH with an aberrant femoral head and femoral angle. Under static compressive load conditions, the stresses of the screw and bone were examined as the screw spacing and angle changed. The spacing and angle of various screws were specifically considered as variables in this study based on the pile mechanism studied in civil engineering. As with the group pile mechanism, the tighter the screw spacing under static compressive loads, the more the overlapping effect between the bone stresses and the screws develops, increasing the risk of injuring the patient's bone. Therefore, a series of simulations was performed to determine the optimal screw spacing and angles to minimize the overlapping effect of bone stress. In addition, a formula for determining the minimum screw spacing was proposed based on the computational simulation results. Finally, if the outcomes of this study are applied to pediatric patients with DDH in the pre-proximal femoral osteotomy stage, post-operative load-induced femur damage will be reduced.

Stress distribution in resin-based CAD-CAM implant-supported crowns

OBJECTIVE

This study aimed to evaluate the influence of new resin-based CAD-CAM implant-supported materials on posterior crown restoration stress and strain concentrations.

METHODS

A previous 3D implant model was edited to receive a cement-retained posterior crown manufactured with different CAD/CAM materials (Estelite P Block, Estelite Block II or Estelite Layered Block). Each solid model was exported to the computer-aided engineering software and submitted to the finite element analysis of stress and strain. Material properties were assigned to each solid with isotropic and homogeneous behavior according to the manufacturer information. A vertical load of 600 N was applied in the occlusal region of the crown, via a simulated food bolus, and stress was calculated in Von Misses (σVM) for the implant, abutment and screw, Maximum (σMAX) Principal Stresses for the crown and microstrain for the bone.

RESULTS

All simulated materials showed acceptable stresses levels with a similar stress pattern among the models. At the crown intaglio region and cement layer, however, differences were observed: Estelite P Block showed a lower tensile and shear stresses magnitude when compared to other resin-based materials with lower elastic modulus.

SIGNIFICANCE

The stress effect of different resin-based CAD-CAM implant-supported crowns is predominant in the crown and cement layer, with Estelite P Block showing 7.4 % versus 9.3 % and 9.2 % for Estelite Block II and Estelite Layered Block of crown failure risk.

Biomechanical analysis of locking plates for fixation of metacarpal shaft fractures: A finite element analysis

BACKGROUND

There appears to be a paucity of knowledge about the biomechanics of locking plates for the fixation of metacarpal shaft fractures. A thorough understanding of the biomechanics of locking plates is needed to apply them correctly, optimize outcomes, and avoid complications. The purpose of this study is to investigate the biomechanics of the fixation of metacarpal fractures using locking plate-screw constructs with different numbers of screws.

HYPOTHESIS

The difference in the number of screws in the locking plate influenced the biomechanical outcome of the metacarpal fracture.

METHODS

Finite element models of third metacarpal fractures with locking plate-screw constructs were established, and the magnitude and distribution of their stresses and displacements were investigated when a vertical load of 100N was applied.

RESULTS

For the metacarpal fracture with a locking plate and screws, the stress in the metacarpal was largely shared by the plate-screw construct. For the plate-screw construct, the stress is concentrated in the area close to the fracture line, and the 6-screw Group has the lowest failure risk since it has the lowest plate stress and the second-lowest screw stress. The implant-bone construct with 8 screws has better biomechanical stability because of minimal displacement, but increased stress on both the metacarpal bone and the screws, leading to increased failure rates.

DISCUSSION

The stresses in the metacarpal were mostly shared by the plate-screw constructs and the screws closest to the fracture line were the most likely to break or loosen. For the implant-bone constructs, the locking plate with 2 screws was the most vulnerable to break or loosen, whereas the locking plate with 6 screws was the least likely to break or loosen. The implant-bone construct with 8 screws had better biomechanical stability, but the stresses in both the metacarpal and the screws were increased, which increased the risk of failure.

LEVEL OF EVIDENCE

IV, basic science study.