Mechanical performance of standard and cannulated 4.0‐mm cancellous bone screws

Abstract

The mechanical performance of bone screws is determined by their pull-out strength (holding power), compressive force, stripping torque, yield bending moment, ultimate bending moment, and fatigue strength. These parameters are related to the parameters of the screw design, including major thread diameter, minor thread diameter, thread length, pitch, shaft diameter, cannulation diameter, and material properties. The goal of the study was to theoretically predict the static performance of five 4.0-mm, 45-46-mm-long, cancellous, partially threaded standard and cannulated bone screws and compare the predictions with experimental measurements. A secondary goal was to determine if cannulation of the bone screw diminished its mechanical performance. The predicted values for pull-out force, compressive force, and stripping torque were determined by the thread length, major thread diameter, and thread shape factor. The screws with the largest major thread diameter and longest thread length had the greatest pull-out force, compressive strength, and stripping torque. However, when correcting for the thread length, a higher thread shape factor compensated for a smaller major diameter. The coefficient of determination (r2) for the correlation between the predicted and measured pull-out force improved from 0.75 to 0.90 when the theoretical model included the thread shape factor. The yield and ultimate bending moments are a function of the section modulus and material properties of the screw. The Ace solid screw had the greatest section modulus and yield and ultimate bending moments. The experimental data support the theoretical models for predicting the mechanical performance of bone screws. The design of the bone screws can be optimized on the basis of theoretical modeling. The strong correlation between the predicted and measured parameters allows comparison between bone screws without repeated experimental tests. Theoretical and experimental results show that cannulation of the bone screw did not inherently diminish its mechanical performance.

The Fixation Strength of Scaphoid Bone Screws: An In Vitro Investigation Using Polyurethane Foam

“…Brown et al suggested that predicted values for pullapart force were determined by the thread length, major thread diameter, and thread shape. 10 The Kompressor screw has a trailing thread diameter of 5.0 mmgreater than the trailing thread diameter of other screws Little Grafter 27…”

“…Wheeler et al used a push-out test to quantify the specific resistance of a screw to axial loading and found that the Acutrak screw showed significantly greater push-out force than the AO or Herbert screw. 6 Other studies 3,9,10 have investigated the pullout strength. Brown et al suggested that predicted values for pullapart force were determined by the thread length, major thread diameter, and thread shape.…”

Comparison of the bending performance of solid and cannulated spinal pedicle screws using finite element analyses and biomechanical tests

“…This finding was the same as the results of the past studies mentioned above. Brown et al [20] concluded that simple-beam theory is capable of providing enough evidence to support the optimization of the design of cylindrical bone screws. In the present study, the area moment of inertia for each spinal pedicle screw was calculated to validate this finding.…”

Comparison of two tools for the measurement of interfragmentary movement in femoral neck fractures stabilised by cannulated screws

“…In intramedullary nail [25] the introduction of a slot in a lag screw increases deformation and reduces stress, while the displacements in a trochanteric fracture were similar between a Gamma nail and a PFN [26]. The same finite element model of a femur with a Gamma nail implant produced greater deformation of a subtrochanteric fracture than a femoral neck fracture [27] and the deformation was reduced with the inclusion of an iliospoas force. These studies highlight the strength of finite element analysis in producing a wide range of findings that can be transferred to the clinical application of fixation techniques.…”

“…In healthy patients with a long life expectancy and with the likelihood for the return to everyday activities, the most app1ropriate treatment for fractures of the femoral neck is minimally invasive surgery to reduce the fracture and provide adequate stabilisation [5]. For undisplaced intracapsular fractures of the femoral head and neck, the use of cannulated hip screws to achieve adequate fixation is advocated [3][4][5][6][7][8][9]. Achieving immobilization of the fractured surfaces to allow adequate callus formation during the immediate post-operative period is an important factor for satisfactory bone healing [10].…”