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Most locked plating failures are due to inappropriate device configuration for the fracture pattern. Several studies cite screw positioning variables such as the number and spacing of screws as responsible for occurrences of locking plate breakage, screw loosening, and peri-prosthetic re-fracture. It is also widely accepted that inappropriate device stiffness can inhibit or delay healing. Careful preoperative planning is therefore critical if these failures are to be prevented. This study examines several variables which need to be considered when optimising a locking plate fixation device for fracture treatment including: material selection; screw placement; the effect of the fracture pattern; and the bone-plate offset. We demonstrate that device selection is not straight-forward as many of the variables influence one-another and an identically configured device can perform very differently depending upon the fracture pattern. Finally, we summarise the influence of some of the key parameters and the influence this can have on the fracture healing environment and the stresses within the plate in a flowchart. [ABSTRACT FROM AUTHOR]

High tibial osteotomy surgery is a widely successful joint-preserving procedure which alters the hip-knee-ankle axis which can delay the progression of osteoarthritis; however, conventional osteotomy surgical procedures do not adequately control the posterior tibial slope. This study aimed to determine the key variables influencing posterior tibial slope during high tibial osteotomy and provide a simple means of implementing the findings during pre-operative planning. A virtual cohort of twenty-eight proximal tibia geometries of knee osteoarthritis patients was used in the study. Firstly, absolute posterior tibial slope values were contrasted using anatomical and posterior mechanical axis measurement approaches. Secondly, the influence of variables affecting posterior tibial slope change during osteotomy surgery was investigated using 3D preoperative planning surgical simulation and analytical modelling. There was a poor correlation (R2 = 0.38) between the different clinical measurements of posterior tibial slope; with an average of 7.0 ± 1.3° and 14.8 ± 2.2° respectively. An analytical solution for the change in posterior tibial slope was derived based on the hinge axis angle and the osteotomy opening angle. For three different opening angles (6°, 9° and 12°) and seven different hinge axis orientations (−30° to +30°), the results obtained were identical for the analytical model and the 3D preoperative planning. This study determined that the key variables affecting posterior tibial slope during high tibial osteotomy are the osteotomy opening angle and the hinge axis orientation. The derived formula provides a simple means of determining the change in posterior tibial slope resulting from a particular surgical approach. • Posterior tibial slope can be difficult to manage during high tibial osteotomy. • The key variables are osteotomy opening angle and the hinge axis orientation. • The presented formula can calculate the change in posterior tibial slope. [ABSTRACT FROM AUTHOR]

Abstract: The effect of screw–bone interface modelling strategies was evaluated in the setting of a tibial mid-shaft fracture stabilised using locking plates. Three interface models were examined: fully bonded interface; screw with sliding contact with bone; and screw with sliding contact with bone in an undersized pilot hole. For the simulation of the last interface condition we used a novel thermal expansion approach to generate the pre-stress that the bone would be exposed to during screw insertion. The study finds that the global load-deformation response is not influenced by the interface modelling approach employed; the deformation varied by less than 1% between different interaction models. However, interface modelling is found to have a considerable impact on the local stress–strain environment within the bone in the vicinity of the screws. Frictional and tied representations did not have significantly different peak strain values (<5% difference); the frictional interface had higher peak compressive strains while the tied interface had higher tensile strains. The undersized pilot hole simulation produced the largest strains. The peak minimum principal strains for the frictional interface were 26% of those for the undersized pilot hole simulation at a load of 770 N. It is concluded that the commonly used tie constraint can be used effectively when the only interest is the global load-deformation behaviour. Different contact interface models, however, alter the mechanical response around screw holes leading to different predictions for screw loosening, bone damage and stress shielding. [Copyright &y& Elsevier]

Millions of non-locking screws are manually tightened during surgery each year, but their insertion frequently results in overtightening and damage to the surrounding bone. We postulated that by calculating the torque limit of a screw hole, using bone and screw properties, the risk of overtightening during screw insertion could be reduced. Additionally, predicted maximum torque could be used to identify optimum screw torque, as a percentage of the maximum, based on applied compression and residual pullout strength. Longitudinal cross-sections were taken from juvenile bovine tibial diaphyses, a validated surrogate of human bone, and 3.5 mm cortical non-locking screws were inserted. Fifty-four samples were used to define the association between stripping torque and cortical thickness. The relationship derived enabled prediction of insertion torques representing 40 to 100% of the theoretical stripping torque (T str) for a further 170 samples. Screw-bone compression generated during insertion was measured, followed immediately by axial pullout testing. Screw-bone compression increased linearly with applied torque up to 80% of T str (R2 = 0.752, p < 0.001), but beyond this, no significant further compression was generated. After screw insertion, with all screw threads engaged, more tightening did not create any significant (R2 = 0.000, p = 0.498) increase in pullout strength. Increasing screw tightness beyond 80% of the maximum did not increase screw-bone compression. Variations in torques below T str , did not affect pullout forces of inserted screws. Further validation of these findings in human bone and creation of clinical guidelines based on this research approach should improve surgical outcomes and reduce operative costs. • No significant further compression generated beyond 80% of the maximum torque. • Pullout force unaffected by variations in sub-maximal screw tightness. • Stripping limits of screw holes can be reliably predicted prior to insertion. [ABSTRACT FROM AUTHOR]