Bone Plate Design Research Articles

Mechanical Design Optimization of Bioabsorbable Fixation Devices for Bone Fractures

Bioabsorbable bone plates can eliminate the necessity for a permanent implant when used to fixate fractures of the human mandible. They are currently not in widespread use because of the low strength of the materials and the requisite large volume of the resulting bone plate. The aim of the current study was to discover a minimally invasive bioabsorbable bone plate design that can provide the same mechanical stability as a standard titanium bone plate. A finite element model of a mandible with a fracture in the body region is subjected to bite loads that are common to patients postsurgery. The model is used first to determine benchmark stress and strain values for a titanium plate. These values are then set as the limits within which the bioabsorbable bone plate must comply. The model is then modified to consider a bone plate made of the polymer poly-L/DL-lactide 70/30. An optimization routine is run to determine the smallest volume of bioabsorbable bone plate that can perform and a titanium bone plate when fixating fractures of this considered type. Two design parameters are varied for the bone plate design during the optimization analysis. The analysis determined that a strut style poly-L-lactide-co-DL-lactide plate of 690 mm2 can provide as much mechanical stability as a similar titanium design structure of 172 mm2. The model has determined a bioabsorbable bone plate design that is as strong as a titanium plate when fixating fractures of the load-bearing mandible. This is an intriguing outcome, considering that the polymer material has only 6% of the stiffness of titanium.

Stiffness and strength design of composite bone plates

Although the potential of composites used for bone plate implantation has been realized for a long period of time, not much literature has addressed optimal design of composite bone plates upon variation in reinforcing fiber structures, plate thicknesses, and so on. In this paper, we present a preliminary but critical design procedure for composite bone plate with target on both its stiffness and its ultimate strength. While the material system used is the same, i.e. carbon fibers and PEEK matrix, three kinds of fibrous preforms namely unidirectional (UD) prepregs, braided fabrics, and knitted fabrics are considered as reinforcements, constituting six different candidate laminated plates. They are UD [0°] ns , angle plied [±20°] ns , multidirectional [0°/±20°/0°] ns , two braiding angle diamond braid fabrics [5°] ns and [15°] ns , and plain weft knitted fabric laminates. By varying the number of layers ( n) in the lamination, different plate thicknesses can be attained. The structure–property relationship of the composite plates is realized through the use of a micromechanics bridging model. A clinically used stainless steel plate is taken as a design benchmark. It has been found that the composite bone plates with all the considered lamination patterns except for the knitted fabric reinforcement and having a thickness near to that of the stainless steel plate can exhibit required properties of bending rigidity and maximum bending moment. The plate thickness is more controlled by strength rather than by stiffness requirement. However, the 5° braided fabric composite bone plate shows an overall superiority as compared to the other lamination forms, and is thus recommended as the first choice.

Bone blood flow response to surgical trauma

The evolution of bone plate design has been with a view to reducing the interface contact between the plate and the underlying bone thereby limiting the perfusion deficiency that develops. Little consequence, however, has been attributed to the drilling of holes in the steps prior to bone plate application; the work present herein attempts to define the vascular response of bone to the trauma of drilling holes. Anaesthetized sheep underwent the creation of drill holes in both tibiae and metatarsi. Animals were then heparinized and euthanatized. Utilizing femoral cannula, perfusion of the vasculature ensued; spalteholz (India ink), disulphine blue and radiocontrast material (barium sulfate). Decalcified histology was performed and correlated with the perfusion studies. Regions of perfusion deficiency were observed immediately adjacent to, and removed from, the drill hole site. Radiographic images showed substantial haematoma formation and vascular disruption in the vicinity of the drill hole site. Histologically, blood vessels immediately adjacent and distal to the drill hole site, contained a proteinaceous/cellular material occluding the vascular space. Our findings support the proposal of a short-term obstruction in cortical blood flow which may contribute to later adaptational osteopaenia following bone plate application. We have observed an acute vascular insufficiency in cortical bone directly related to the trauma of drilling screw holes.

The influence of screw torque, object radius of curvature, mode of bone plate application and bone plate design on bone-plate interface mechanics

Using Fuji Prescale Pressure Sensitive Film we evaluated the influence of screw torque, object radius of curvature, mode of bone plate application (compression or neutral loading) and bone plate design on bone-plate interface mechanics. Testing was performed using 4.5 mm and 3.5 mm dynamic compression (DC) (stainless steel) and limited contact-dynamic compression (LC-DC) plates (titanium). Plexiglass tubing, having different radii of curvature, was used to simulate bone but having more uniform geometric and structural properties. With the film interposed between the bone plate and the plexiglass, bone plates were applied at predetermined levels of screw torque. The resultant image was digitized and then underwent computer-assisted analysis to yield the interface contact area (%) and the average force (in Newtons N) between the bone plate and the object to which it was applied. In any given object, screw torque had the most significant influence on both interface contact area ( P = 0.0001) and average force ( P = 0.0001) at the interface. The bone plates responded differently to dynamization. The DC plate, when applied in compression loading mode, was lifted off the object between the two central screws when compared to the same plate applied in neutral loading mode ( P = 0.0001). Conversely, in the LC-DC plate, an increase in the overall interface contact area was observed when applied in compression loading mode ( P = 0.0002). At a given level of applied screw torque, the object radius of curvature appeared to be a major determining factor for interface contact area and average force ( P = 0.0001, P = 0.0001). We conclude that variables other than bone plate design also influence the interface contact area and average force between a bone plate and object to which it is applied.