Alternatives In Fixation For Osteoporotic Bone
- Volume 25 - Issue 2 - February 2012
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Zehnder and co-workers, in their comparison of locking plates with four screw angulation fixation methods, found no initial difference in load to failure rates between fixation types.14 However, they did find that with increased loading, the locking plates proved to be superior to the non-locking styles.
In regard to using traditional plating in patients with decreased bone density, the theory is that the screws can loosen more easily and become separated from the plate/bone.14 Yanez and colleagues offer a possible solution to this issue by applying a screw-locking element to a traditional plating system, which functions as a locking nut.15 The authors found that this system provides certain advantages over locking plates, including the ability to contour the plate as well as the ability to replace pulled out screws without having to create new drill holes in the bone.
Another study of 216 patients focusing on postoperative complications of ankle fractures in an elderly population found a higher risk of hardware related complications in patients receiving locking plate fixation in comparison to standard plating.16
Locking plate fixation is advantageous when one applies it in cases of osteopenic bone, comminuted fractures or in circumstances when anatomic reduction is not necessary or possible.17 Screws that lock to plates eliminate screw toggle and create a fixed angle or a single beam construct. Traditional plating can only achieve the single beam effect, if at all, with screws that have solid bicortical purchase in dense, healthy bone. The strength of the locking plate single beam is related to the sum of all screw bone interfaces. A locking plate is strongest with multiple anchoring points or multiple screws.
A locking plate construct is thought of as the ultimate external fixator in that it is a rigid structure one places extremely close to the mechanical axis of the bone.18 This construct has demonstrated strength capacities four times that of traditional systems whereas screws tend to toggle.11 The construct creates stable elastic fixation, allows strains of 2 to 10 percent and promotes callus formation, which leads to secondary bone healing. Secondary bone healing requires some relative motion.8,11,19 Locking plates allow that residual “strain” that inevitably occurs when fixating severely comminuted or osteoporotic bone.
Locking plates also make anatomic reduction unnecessary. Anatomic reductions are paramount when employing traditional plating techniques. However, anatomic reduction involves extensive surgical exposure and soft tissue stripping. When it comes to multifragmentary shaft fractures, precise anatomical reduction is often not possible without a great risk of iatrogenic soft tissue trauma.20 Vigorous soft tissue dissection potentiates the likelihood for nonunion or infection. A shift toward minimally invasive surgical techniques encourages locking plate constructs.
In cases that are difficult to reduce anatomically, one should consider using locking plates. Current locking plate designs do not rely on friction force at the bone-plate interface. Therefore, locking designs do not impair periosteal blood flow to healing bone.19 The combination of mechanical superiority and their biologically friendly nature makes locking plate fixation appealing in the surgical correction of complex foot and ankle deformities.