These authors discuss the versatility and unique properties of carbon fiber for fixation in various types of foot and ankle surgery.
There are a variety of metallic internal fixation devices available to the foot and ankle surgeon. Fixation plates, Steinmann pins, Kirschner wires, staples, screws and intramedullary nails can help achieve stable fixation of arthrodesis surfaces, fractures and osteotomies. However, metallic internal fixation devices can create impediments to accurate postoperative imaging. Specifically, radiopacity on plain film radiographs and scatter artifact on computed tomography (CT) and magnetic resonance imaging (MRI) can make assessment of bone healing a challenge.
Accordingly, let us take a closer look at the properties of carbon fiber fixation and practical applications in the foot and ankle. We’ll also share our brief experiences of utilizing carbon fiber fixation in foot and ankle surgery. The radiolucent properties of carbon fiber and the modulus of elasticity are potential advantages to this form of fixation, which could have widespread applications in bone and joint surgery.
Carbon fiber is a versatile material that has unique biomechanical properties that make it an ideal material for internal fixation of osteotomies, arthrodesis sites and fractures. Reported complications of internal fixation for arthrodesis and fracture fixation include nonunion, failure of fixation and infection.1 The carbon fiber ankle arthrodesis nail, distal fibular plate and one-third tubular plate possess many properties that may reduce the risk of complications.
Carbon fiber is radiolucent on plain film radiographs, allowing for unobscured views of cortical and cancellous bone on intraoperative and postoperative radiographs. This quality allows for enhanced visualization of arthrodesis surfaces and fracture sites, and could aid in the achievement of optimal positioning and alignment. Researchers have maintained that enhanced visualization leads to less use of intraoperative fluoroscopy and a decrease in operative time.2 Additionally, the unobscured view can potentially afford an accurate assessment of the progression of fusion or fracture healing during the postoperative course. One can potentially identify nonunions and delayed unions earlier and appropriate intervention can begin sooner.
Unlike metallic intermetatarsal nails, which create artifact on MRI and CT, carbon fiber nails do not exhibit signal pileup or signal loss.3 When viewing an MRI image of a patient with a metallic implant, significant signal loss and signal pileup are present if the implant is not parallel to the magnetic field. One can avoid this impediment to visualization even when a carbon fiber implant is not parallel to magnetic field.3
Carbon fiber possesses physical properties that make it comparable, if not superior, to implant alternatives composed of titanium and cobalt chrome molybdenum. The carbon fiber ankle arthrodesis nail has a similar modulus of elasticity to bone and has the ability to withstand prolonged fatigue strain.4 The similar modulus of elasticity lessens stress shielding and allows for enhanced callus formation and stronger union.
Steinberg and colleagues demonstrated that carbon fiber has significantly less wear debris in comparison to titanium.5 Decreased debris theoretically decreases the risk of local tissue reaction and inflammation. The literature reveals the prevalence of metal allergy ranging from 2.7 to 9.4 percent.6 Currently, the majority of metallic joint implants contain nickel, chromium, cobalt-chromium and titanium-aluminum alloys. Allergic reactions to these components can manifest as dermatitis, impaired wound healing, joint effusions, pain, implant loosening and implant failure.6 Carbon fiber is inert and there are no current reports of allergic reaction.5
This small, preliminary case series of carbon fiber fixation with short term-follow-up aims to stimulate further research on the use of this technology in the foot and ankle as well as other areas of the body.
Practical Examples Of The Use Of Carbon Fiber Technology
In using carbon fiber for first metatarsophalangeal joint (MPJ) arthrodesis, we evaluated an unobscured view of trabeculation across the fusion site in the postoperative period. However, the thickness of the plate is a disadvantage in forefoot procedures and did result in removal of the carbon fiber plate in one of the patients.
In a case series of tibiotalocalcaneal arthrodesis procedures, we utilized the carbon fiber intramedullary nail for fixation with the modulus of elasticity being similar to bone and achieved stable fixation without additional stress risers. The radiolucent property of the intermetatarsal rod requires a precise three-dimensional visualization to achieve proper placement of the proximal and distal screws with the assistance of small radiopaque markers contained within the nail. The advantage of the radiolucent property was the ability to evaluate the fusion site with radiographs or CT.
In a comparison of CT scans of a traditional intermetatarsal nail and a carbon fiber intermetatarsal nail, there was no artifact obscuring the fusion site and it was clearly projected with the carbon fiber intermetatarsal nail.
What You Should Know About Carbon Fiber Technology
For years, orthopedic surgeons have used carbon fiber technology in the treatment of osseous tumors. Carbon fiber technology provides the surgeon with an unobscured view of the underlying pathology or trauma. The carbon fiber reinforced polyetheretherketone (CFT-PEEK) allows for the use of MRI and CT with little to no artifact.1 Carbon fiber technology provides strength and durability with ease of placement in comparison to stainless steel and titanium.7 The modulus of elasticity of the carbon fiber technology is closer to that of cortical bone than stainless steel or titanium implants, allowing the surrounding bone to function without undue stress from the internal fixation. The implants are composed of longitudinal and diagonally-oriented fibers of carbon, allowing for strength in multiple planes.7
Surgeons have used carbon fiber technology in the treatment of infected nonunions. The radiolucency of the construct allows unparalleled visualization of an osteotomy or arthrodesis site, aiding in the ability to assess bone healing.2 The addition of antibiotic cement coating to the fixation may be a useful option in cases involving infection. Carbon technology also provides an inert biochemical profile, allowing surgeons to use the technology in those patients with documented metallic allergies.4
Carbon technology plating and nails have been designed for both the tibia and fibula. Researchers have demonstrated that the carbon fiber ankle arthrodesis intermetatarsal nail has a lower rate of revision at five years in comparison to other intermetatarsal nails.3
The ability to visualize an arthrodesis site or fracture progression potentially can facilitate more precise management of patients postoperatively. In addition, obtaining advanced imaging (CT and MRI) with little to no artifact is beneficial.
One can apply carbon fiber technology to the treatment of a myriad of pathologies in the foot and ankle, but it is not without complications or difficulties. Some of the initial challenges are due to the characteristic radiolucency on intraoperative fluoroscopy. This can be a challenge for blind screw placement. The placement of cortical screws in close proximity to interfragmentary screws can be especially problematic. The difficulty is due to an inability to visualize the holes within the plate relative to the interfragmentary fixation while looking at intraoperative fluoroscopy. This may lead to potential collision of cortical screws with interfragmentary screws.
In the case of intramedullary fixation, even when the surgeon utilizes a jig, if the drill bit is torqued in the slightest, it can lead to collision of the drill bit with the implant. Placement of the intramedullary nail end cap, which has no embedded metallic identifiers to clue the surgeon in on the exact position relative to the intramedullary nail, has proven to be difficult. The carbon fiber plates cannot bend and are brittle, and the primary author has experienced shattering of a plate, which had already been implanted.
Another drawback is the inability to contour the plates to the bone, leaving the surgeon unable to modify the plate if necessary. These are some of the initial challenges facing this carbon fiber technology, which make it an imperfect alternative to traditional internal fixation materials.
That being said, the carbon fiber technology has shown to be a useful tool in the primary author’s repertoire. However, further research is required to elucidate all the potential applications in foot and ankle surgery as well as other areas of the body.
Dr. Canales is the Chief of the Division of Podiatry and the Director of the Podiatric Residency Program at St. Vincent Charity Medical Center in Cleveland.
Dr. Mandela is a third-year resident at St. Vincent Charity Medical Center in Cleveland.
Dr. Fisher is a second-year resident at St. Vincent Charity Medical Center in Cleveland.
Dr. Benson is a second-year resident at St. Vincent Charity Medical Center in Cleveland.
Dr. Khangura is a first-year resident at St. Vincent Charity Medical Center in Cleveland.
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7. Anderson RT, Pacaccio DJ, Yakacki CM, Carpenter RD. Finite element analysis of a pseudoelastic compression-generating intramedullary ankle arthrodesis nail. J Mechan Behav Biomed Mat. 2016; 62, 83-92.