Point-Counterpoint: Are Locking Plates Necessary For First MPJ Fusion?

Author(s): 
Patrick DeHeer, DPM, FACFAS, and Shannon Rush, DPM, FACFAS

Yes.

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.

Fixation Considerations With First MPJ Arthrodesis

A significant consideration for first MPJ arthrodesis fixation is the requirement of bicortical screw fixation in conventional plating and the inability to achieve bicortical screw purchase in the area of the first metatarsal head due to the sesamoid apparatus. Bicortical purchase in this area would result in direct irritation of the sesamoids. Bicortical fixation along the plantar surface of the proximal phalanx could cause pressure pain and/or flexor hallucis brevis and longus tendonitis. Although the hallux dorsiflexes between 5 and 15 degrees with an arthrodesis, the weight of the body rolling forward off the hallux at toe-off could cause symptomatology.

   The alternative method to any plating fixation is a crossed screw technique, which researchers have repeatedly shown to be inferior fixation in comparison to dorsal plating with the lag screw technique. This type of fixation is usually limited to smaller cannulated screws such as a 3.0 mm screw. It is just common sense that multiple 2.4 mm locking screws (six or seven) and a dorsally placed locking plate would be significantly stronger than two 3.0 cannulated screws. This approach is technically more demanding than dorsal plating with locking screws.

   One could make this argument for two 4.0 screws but this is also fraught with problems. This is even more technically demanding and the amount of bone removed by the screw insertion has always concerned me. I have always felt that more direct raw bone contact with fixation around the fragments instead of through the fragments produces fewer nonunion complications.

   With the advent of the new compression devices associated with locking plates, which allow for compression prior to screw placement, the normal splinting mechanism of locking plates now can provide compression. This eliminates the need for the lag screw that surgeons have traditionally used with dorsal conventional plating. In addition, this has all but eliminated the need for the combi-hole for compression in the earlier models of locking plates. I would still recommend using a lag screw even with the combi-hole technique but now with the compression devices, I have eliminated the lag screw altogether.

   Additionally, the new first MPJ specific plates are pre-positioned to ensure accurate alignment (the single most crucial component other than stabilization). Furthermore, the new plates allow polyaxial locking, providing multi-axial, fixed angle constructs. This is especially important for first MPJ arthrodesis due to architecture of the first MPJ and the irregular surface shapes. Not only is the surgeon able to place the screws at an angle of 15 degrees to the plate with each hole but the plate itself also allows for polyaxial loading.

In Conclusion

For the time being, locking plates and screws are more expensive than other modes of fixation for first MPJ arthrodesis. However, with time, I would expect the competitive marketplace to drive the prices down.

   It is clear that locking plates provide more stable fixation with an easier surgical technique, but does this mean they are necessary for first MPJ arthrodesis? No, locking plates are not necessary for first MPJ arthrodesis. Are locking plates the best type of fixation for first MPJ arthrodesis? Yes.

   Dr. DeHeer is a Fellow of the American College of Foot and Ankle Surgeons, and is a Diplomate of the American Board of Podiatric Surgery. He is also a team podiatrist for the Indiana Pacers and the Indiana Fever. Dr. DeHeer is in private practice with various offices in Indianapolis.

References
1. Smith WR, Ziran BH, Anglen JO, Stahel PF. Locking plates: tips and tricks. J Bone Joint Surg Am. 2007; 89(10):2298-2307.
2. Williams KA, DiDomenico LA. A closer look at locking plates in podiatric surgery. Podiatry Today. 2008; 21(4):46-52.

No.

While the profession has seen the emergence of many new technologies, this author says there is a lack of evidence to suggest better surgical outcomes arise from the use of locking plates.

By Shannon Rush, DPM, FACFAS

Over the last decade, foot and ankle surgery has made significant steps with respect to surgical biomechanics and implant design. The development of locking plate technology has become very popular in general orthopedic practice as well as the foot and ankle surgical market.

   Spine and maxillofacial implants have employed this technology for bridging mandible defects and cervical spine arthrodesis procedures for the past 20 years.1,2 The application of locking plate technology to foot and ankle surgery has become widespread and popular.

   The practice of locking plate technology in fracture care was driven by the need for better treatment of periarticular and osteoporotic fractures. Locking plate technology affords two desirable benefits to fracture management when properly applied. The first benefit is preservation of the circulation to the periarticular soft tissue envelope and periarticular fracture fragments, which is critical in the healing of these injuries. The second benefit is superior biomechanical stability with respect to screw pullout.

   The biomechanical requirement of plate compression to the bone with conventional plating techniques results in vascular embarrassment to periosteal blood supply beneath the plate and impaired fracture healing. Locked plate technology theoretically allows the application of the implant like an external fixator without compromise to periosteal circulation. Application of a plate with fixed angle screws close to the bone but not compressed against bone affords excellent stability without vascular compromise, which is favorable to bone healing.

   Furthermore, there have been significant advances in surgical philosophy and implant design, giving seed to minimally invasive plate osteosynthesis techniques and anatomy or fracture specific implants. Minimally invasive plating techniques have added another essential surgical tool to treat fractures of the distal femur and tibia. The most common application of locked plating involves bridge plating of comminuted periarticular fractures in which direct anatomic reduction of fracture fragments is either impossible or inappropriate.

   There is no argument that locking plate fixation does afford improved biomechanical performance and less potential fixation construct failure with respect to shear loading and screw pullout.3 These favorable biomechanical properties have led to the widespread use of these implants for various fracture and arthrodesis procedures in foot and ankle surgery. In many instances, these contemporary devices have replaced conventional fixation devices and techniques.

Raising Concerns About ‘Hybrid Techniques’

The expanding indications for the use of such technology have little evidence to support the expanded verve for their use. Much of the expanded use of locking plates has been driven by industry influence and attractive marketing in addition to the new technology being appealing to surgeons. The emergence of anatomically designed plates or procedure specific plates has added to the technology’s popularity. Foot and ankle surgeons have applied these new and expensive implants to procedures such as metatarsophalangeal joint (MPJ) arthrodesis that have historically had very favorable and predictable outcomes.4

   Biomechanically, locking plates take advantage of some of the same fixation principles that external fixators do. Locking plates do not require compression against the bone for stability. Unfortunately, the surgical philosophy of conventional plate fixation and new locking plate technology is often meshed into a “hybrid technique.” Once one applies a locking plate to a bone and compresses the plate in a traditional fashion, the favorable aspect of preserving the periosteal blood supply is lost. In addition, the rigid stability afforded by locking plates and the compromise of the periosteal blood supply beneath the plate is a detriment to bone healing based on current understanding of bone and fracture healing with plate fixation.5

   Alternatively, application of a locking plate that is not directly compressed to the bone results in a dorsally prominent implant that is likely to irritate the soft tissues clinically. This type of application is less problematic in subcutaneous plating of the distal tibia or femur, but often results in hardware irritation over the first MPJ. Poor technique and misunderstanding of locking plate concepts can result in less than optimal plate application. Clearly, more clinical evidence is necessary with respect to dorsal locking plates.

   Furthermore, there is abundant evidence to suggest dorsal plate fixation using conventional implants affords predictable arthrodesis rates and high patient satisfaction.6-8

   When one examines the biologic basis for locking plate technology in first MPJ arthrodesis, it is clear the physiologic basis of the technology’s use is questionable. Further, if the surgeon employs a “hybrid” application of the plate across the MPJ, the favorable biologic environment for healing is compromised. Applying a biomechanically superior fixation construct while ignoring the biological principles of bone healing is a pitfall that the surgeon must avoid.

Other Considerations With First MPJ Arthrodesis

The next analysis of locking plates for first MPJ arthrodesis is one of surgical biomechanics. The forces acting across the MPJ during healing are primarily bending and, to a lesser magnitude, shear. Historically, transarticular screw fixation has shown very favorable arthrodesis rates dating back 30 years.4,9 There is little evidence to suggest locking plates are any better or even comparable to traditional fixation methods with respect to MPJ arthrodesis. A study presented at the American Academy of Orthopaedic Surgeons showed that there was a higher nonunion rate with locking plates for MPJ arthrodesis.10

   Another technical consideration in MPJ arthrodesis, which I feel has significantly improved the technique, is the introduction of conical reamers to prepare the joint. The reamers remove the articular cartilage and subchondral bone, which is critical to healing. The reamers also create a machined fit with the hallux in variable positions.11 The favorable joint debridement and congruent “machined” fit of the arthrodesis interface influences arthrodesis rates as much as the type of fixation one employs.

Is Dorsal Plate Fixation Cost-Effective?

In addition, one must consider cost analysis when choosing new technologies. The additional cost of technology and implants without proven surgical results must be questioned until the profession can answer two essential questions: Does the new technology result in better surgical outcomes and does that translate into better patient outcomes?

   There is evidence showing dorsal plate fixation to be significantly more expensive.12 Further buttressing this argument is that there was no significant difference in fusion rates between screw fixation and more expensive plate fixation.

In Conclusion

Clearly, the foot and ankle market has been overrun in the past decade with “newer and better” technology. There is little evidence to suggest there has been any advance in surgical outcomes with locking plates. If the better surgical results and patient satisfaction are justified by employing more expensive implants, then the technology is relevant.

   Metatarsophalangeal joint arthrodesis is a valuable procedure available to the foot and ankle surgeon. The procedure has historically high union rates and patient satisfaction rates. The application of locking plate fixation must address the following questions to be a long-term safe and cost-effective surgical technique. Does the additional soft tissue exposure needed for plate fixation justify the use? What is the rate of union with locking plates in comparison to conventional transarticular screw fixation? What is the rate of implant removal compared to conventional methods of fixation? Does the additional cost justify the use of the implant?

   It is my opinion that a humble and academically honest appraisal of locking plate fixation aside from industry influence for MPJ arthrodesis would find locking plates routinely unnecessary for primary uncomplicated MPJ arthrodesis.

   Dr. Rush is affiliated with the Department of Orthopedics at the Palo Alto Medical Foundation in Mountain View, Calif. He is a Fellow of the American College of Foot and Ankle Surgeons.

References
1. Morscher E, Sutter F, Jenny H, Olerud S. Anterior plating of the cerical spine with the hollow screw-plate system of titanium. Chirurg. 1986; 57(11):702-7.
2. Soderholm AL, Lindqvist C, Skutnabb K, Rahn B. Bridging of mandibular defects with two different reconsttruction systems: an experimental study. J Oral Maxillofac. Surg. 1991; 49(10):1098-105.
3. DeTora M, Kraus K. Mechanical testing of 3.5 mm locking and non-locking bone plates. Vet Comp Orthop Traumatol. 2008; 21(4):318-22.
4. Wassink, S, VAn Den Oever M. Arthrodesis of the first metatarsophalangeal joint using a single screw: retrospective analysis of 109 feet. J Foot Ankle Surg. 2009; 48(6):653-61.
5. Ganesh VK, Ramakrishna K, Ghista DN. Biomechanics of bone-fracture fixation by stiffness-graded plates in comparison with stainless-steel plates. Biomed Eng Online. 2005; 4:46.
6. Kumar S, Pradhan R, Rosenfeld PF. First metatarsophalangeal arthrodesis using a dorsal plate and a compression screw. Foot Ankle Int. 2010; 31(9):797-801.
7. Berlet GC, Hyer CF, Glover JP. A retrospective review of immediate weightbearing after first metatarsophalangeal joint arthrodesis. Foot Ankle Spec. 2008; 1(1):24-8.
8. Goucher NR, Coughlin MJ. Hallux metatarsophalangeal joint arthrodesis using dome-shaped reamers and dorsal plate fixation: a prospective study. Foot Ankle Int. 2006; 27(11):869-76.
9. Brodsky JW, Passmore RN, Pollo FE, Shabat S. Functional outcome of arthrodesis of the first metatarsophalangeal joint using parallel screw fixation. Foot Ankle Int. 2005; 26(2):140-6.
10. Hunt KJ, Ellington K, Anderson RB, et al. Locked versus non-locked plate fixation for hallux MTP arthrodesis. Presented at the 25th Annual Summer Meeting of the American Orthopaedic Foot and Ankle Society, July 15-18, 2009. Vancouver, British Columbia.
11. Sage RA, Lam AT, Taylor DT. Retrospective analysis of first metatarsal phalangeal arthrodesis. J Foot Ankle Surg. 1997; 36(6):425-9; discussion 467.
12. Hyer, CF, Glover JP, Berlet GC, Lee TH. Cost comparison of crossed screws versus dorsal plate construct for first metatarsophalangeal joint arthrodesis. J Foot Ankle Surg. 2008; 47(1):13-8.

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