Point-Counterpoint: Are Locking Plates Necessary For First MPJ Fusion?
While there are a variety of fixation options for first MPJ fusion, this author explains why locking plates provide superior fixation and a reduced risk of complications.
By Patrick DeHeer, DPM, FACFAS
Are locking plates necessary for first metatarsophalangeal joint (MPJ) arthrodesis? This is the debate at hand. However, I do not think this is the correct question. The more relevant question would be: Are locking plates the best type of fixation for first MPJ arthrodesis?
Of course, locking plates are not necessary for this procedure. There are a multitude of acceptable types of fixation. Locking plates are the superior type of fixation for first MPJ arthrodesis and nobody who fully understands the biomechanics of locking plates could logically dispute this fact. Locking plates have been described as the best of both external and internal fixation. They provide the stable, rigid construction of ex-fix internally. They have also been described as the most significant advancement in orthopedic surgery in the past 20 years or more.
So my question would be, if this were your first MPJ being fused, would you want a locking plate or a lesser form of fixation? I know I would want the most advanced type of fixation with evidence-based medicine used on my foot and I refuse to use anything less on my patients.
Understanding Key Differences Between Conventional Plating And Locking Plates
The goal of locked plating is to increase functional performance of the plate, screw and bone connection in order to improve healing. Locking plates and screws consist of threaded screw heads and plate holes that allow one to insert the screw into the plate itself, thereby facilitating a form of cortical purchase. The penetration of the screw through the near cortex to the plate serves as the second cortex. One can achieve further stability via bicortical screw purchase but this is not a requirement.
Each screw then forms a fixed right angle and this eliminates the potential for toggle. These multiple fixed, right angle anchors provide excellent fixation. Therefore, locking plates function similarly to external fixation by not requiring friction between the plate and bone to provide stabilization. Locking plates have a shorter distance between the plate and bone construct than an external fixator does, thus making locking plates more stable.
The biomechanics of conventional plating rely on friction between the plate and bone, which results in compression of the fragments. The construct is stable if the patient load is less than the frictional force. However, if the patient load exceeds the frictional force, the construct is unstable. The screw-plate interface in traditional plating allows for toggle and therefore failure. When it comes to the biomechanics of locked plating, if the patient load is less than the compressive strength of bone, then the construct is stable. Conventional plating requires the bicortical fixation. Otherwise, the screws will only have a single point of fixation and will toggle with a very small load. Unicortical fixation with locking plates still provides two points of fixation.
The surgical technique for conventional plating requires a well contoured plate to help reduce fragments. Then the plate maintains the reduction as compression occurs between the plate and bone. If one attempts the same technique with a locked plate and locking screws, anatomical reduction will not occur. Locked plating requires reduction of fragments first. Then one applies locking screws to the plate to secure fixation and maintain the reduction of fragments. The combination hole type of locking plates allow the use of lag screws, which can help reduce the fragments, with locking screws adding fixed-angle stability. The surgeon must implant the lag screw before placing locking screws in each fragment. Otherwise, reduction will not occur.
Locked plating does not rely on plate/bone compression and precise plate contouring is not critical. Therefore, in contrast to the use of conventional plating, one can implant locked plating without compressing the periosteum. With conventional plating, the bone is pre-stressed. With locked plating, the plate and not the bone is pre-stressed. Unicortical fixation helps preserve the blood supply and reduces screw-induced stress in bone.