Locking Plates: Do They Prevent Complications?
- Volume 27 - Issue 4 - April 2014
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Offering a closer look at the emergence and evolution of locking plates, these authors provide a thorough review of the literature to gauge the effectiveness of this fixation for first MPJ arthrodesis, calcaneal fractures and distal tibia fractures.
Plates and screws have been in use for bone healing to facilitate osteosynthesis since 1886.1 Researchers have studied these techniques of promoting primary bone healing with rigid stable internal fixation.
The founders of the Swiss American Study of Internal Fixation standardized the use of plates in the 1950s.2 The principles set forth by the American Orthopedic group included direct fracture exposure with anatomic reduction and rigid internal fixation.2 These conventional plating systems and methods have relied on the compressive force of the plate-to-bone interface to provide a stable construct. Ideally, the rigidity with this technique will lead to primary bone healing with no callus formation.
For many years, all the focus has been on the mechanical stability of the bone. Over the past 30 years, this philosophy has changed to addressing the “biology” of the fracture. More and more, attention and priority have shifted to the soft tissue envelope and the vascularity of the injury.
The amount of compression needed at the plate-to-bone interface to obtain stability diminishes the periosteal blood supply. This decreased blood to the injured bone has the potential to cause bone necrosis, delayed union or non-union of the bone, and an increased risk of infection and sequestration.3,4 The torque that surgeons use to insert the screws generates an axial preload and results in friction between the plate-bone interface. Accordingly, one must adequately contour the plate to sit directly against the bone. Within the plate, the screws can still toggle so authors have recommended bicortical screw fixation to prevent this toggling motion.5,6 Since this technique relies on the compression of the plate to bone for stability, good bone quality is required for solid fixation.
Primary bone healing can occur when strain levels at the fracture site are less than 2 percent. The definition of strain is the change in the length of the fracture gap divided by the length of the original fracture gap.7 Strain levels between 2 and 10 percent produce callus formation with bone healing, referred to as secondary bone healing. Strain levels greater than 10 percent result in no bone healing.7
That said, stable internal fixation usually provides less than 2 percent strain, resulting in primary bone healing.7 In contrast, splints, casts, intramedullary nails, bridging plates and external fixation usually lead to strain levels of 2 to 10 percent, leading to secondary bone healing with callus formation.7 Perren noted that “tissues cannot be produced under strain conditions which exceed the elongation at time of tissue rupture.”8
Plate-screw-bone constructs can act as either load-sharing or load-bearing devices. Neutralization plates function as load-sharing devices, neutralizing the effects of bending, rotation and axial forces on the fracture site.9,10 These plates cross a fracture that is already reduced and compressed with lag screws. In contrast to this are load-bearing buttresses and antiglide plates. These plates act as counter shear forces at the fracture site by converting the shear strain to axial compression forces.