How to Contour and Pitfalls
There is a true art to contouring orthopaedic implants appropriately. The most basic instruments are bending levers, which slide onto the plate and can be used to bend or to apply torsion. For very small plates, benders shaped like a needle driver, but with a specialized grasper to avoid inadvertently damaging the plate, are available. Three-point plate benders are also commonly used to alter plate shape. These are either handheld or stationary (eg, "table top") and provide a post around which the plate can be contoured. Many 3-point benders have functionality to bend both in line and on the flat (Figure 5). The concept of material relief should be considered when applying contour. A plate's moment of inertia, as discussed previously, is dependent on the amount of material present in the plane of the desired contour. Areas of the implant with material relief (ie, less metal) will deform before more solid areas. Early designs for straight compression plates had a flat undersurface, and when contour was introduced, much of the shape change occurred via deformation of the plate holes because this was the weakest area of the implant. Modern compression plates have relief cuts in the plate between each hole, which results in more evenly distributed stiffness throughout the implant and improved contouring in line with the plate holes.
Photograph demonstrating three types of contouring tools. On the left, bending irons have slots that fit onto the plate and provide a lever to impart shape change. In the center, an example of a handheld 3-point bender. This particular bender can produce shape change on the flat or in line (as demonstrated in Figure 6) and features a control knob on its handle (left side) to adjust bender tension for various size plates. On the right, specialized bending graspers for minifragment plates.
If a plate requires significant contour in multiple planes to be effective, a reconstruction plate may be used. These plates have material relief on the sides of the plate between the holes, allowing for easier contouring on the flat. The surgeon should bend on the flat first because too much contour in the plane of the holes can prevent the plate from fitting into the 3-point bender. Often, a plate requires multiple attempts at contouring before the ideal fit is achieved, and it should be recognized that each load introduced to cause shape change results in damage that can weaken the implant. Titanium, in particular, has been shown to exhibit "notch sensitivity," meaning that small imperfections or damage to the implant can result in markedly decreased fatigue strength.[10,30] When feasible, contouring directly through plate holes should be avoided. Particular attention should be paid to the locking holes because there is markedly decreased strength for the locking plate constructs with a 5–10 degree bend through a locking hole, and locking screws may not be able to thread into the plate holes if they are deformed.[31,32] If a plate requires particularly complex contouring, as is sometimes the case around the pelvis and acetabulum in particular, the surgeon can use a bone model to contour a plate that can then be sterilized and used during surgery (Figure 6). Although not wide spread in clinical practice, some authors have described using 3-dimensional printers to create a model specific to a particular patient and preoperatively contouring plates to fit the printed model.[33,34]
Photographs demonstrating contouring a reconstruction plate for intrapelvic placement during fixation of an acetabular fracture. The plate is first contoured on the flat (top left) using the handheld plate bender. Next, bend in line with the holes is introduced to fit the shape of the pelvic brim (top middle). Finally, torsion is applied to place the anterior holes over the cranial symphysis. The final plate shape is shown in the bottom left panel. This process can be done intraoperatively, or the plate can be contoured to fit a model and subsequently sterilized (bottom right).
When compression plating, it is most helpful to realize that the amount of prebending required is directly related to the size of the bone: smaller bones require less (eg, in the forearm) then larger bones (eg, the tibia or femur). In addition, although compression is most often generated by placing nonlocking screws eccentrically in the holes of a compression plate, one should remember that alternative techniques exist. In good quality bone, a nonlocking screw can be placed outside of the plate and the articulated tension device or a Verbrugge clamp can be used effectively to generate compression (Figure 2).
Finally, autocontouring plates, as discussed previously, is most often done to generate a buttress or antiglide effect, but it can be done any time a straight (or undercontoured) plate is placed onto a curved surface. The order in which screws are placed should be considered when using this technique. If screws are placed far from the fracture on opposite sides (effectively setting the length), autocontouring can generate compression but also has the potential to create a malreduction. Placing 2 screws on 1 side of the fracture first or placing 1 screw on either side close to the fracture and slowly alternating tightening them can avoid this.
Many times, the type of contour required can be predicted based on the fracture pattern and skeletal region being treated. A list of commonly required contouring methods is presented in Table 1.[25,27,35–42]
J Am Acad Orthop Surg. 2020;28(14):585-595. © 2020 American Academy of Orthopaedic Surgeons