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Carbon fiber implants aid fixation of extremity fractures in oncology cases
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Carbon fiber-reinforced polyethertherketone or CFR-PEEK implants have been used in orthopedic surgery, and spine surgery in particular, for almost 2 decades. However, the increased use of these carbon-reinforced implants has recently occurred in orthopedic traumatology, sports medicine and oncology.
Carbon-reinforced implants are made of composite materials that consist of carbon fiber sheets inlayed within a PEEK resin, the mechanical properties of which confer several advantages compared to traditional metal orthopedic implants. Carbon-reinforced implants have a modulus of elasticity of 3.5 GPa, which is closer to the modulus of elasticity of cortical bone (12 to 20 GPa) and cancellous bone (1 GPa) than stainless steel (230 GPa) or titanium (106 to 155 GPa). This modulus may create an optimal loading environment to promote healing in the setting of fractures and it theoretically decreases stress-shielding and the risk of periprosthetic fracture that is associated with more rigid implants.
In orthopedic oncology, the fixation of primary and/or metastatic bone tumors often requires spanning large bone defects that have poor healing capacity and may worsen after the administration of radiation therapy. As these are load-sharing devices, perhaps the greatest advantage of carbon fiber implants in this setting is their durability, which is due to impressive fatigue and bending strength. Reportedly, no material failures have occurred with one of these devices after 1 million cycles.
CFR-PEEK implants are also radiolucent. When used in the prophylactic fixation of benign or low-grade bony lesions following curettage, these implants allow for finer radiographic detail on plain radiographs and decreased artifact on CT and MRI during surveillance for tumor recurrence or progression, as discussed in case 1 of this article.
The absence of backscatter on imaging makes the use of carbon-fiber-reinforced implants attractive when post-fixation administration of adjuvant radiation therapy is indicated to prevent disease progression (eg, metastatic disease).
Several of these implants are available for use in the upper and lower extremity. Their main disadvantage, however, is the inability of these implants to be contoured at the time of surgery.
The following case examples illustrate CFR-PEEK implants used for orthopedic oncology applications.
Case 1
A 67-year-old man presented to our clinic with worsening left leg pain. Plain radiographs (Figure 1a) revealed a lytic lesion within the distal tibia metaphysis with an impending fracture, with concordant lesions within the proximal tibia seen on MRI (Figure 1b). Preoperative workup revealed the lesions were consistent with lymphoma. Due to the impending fracture, operative stabilization was recommended.
The patient was brought to the OR and placed supine on a radiolucent table. The distal lesion was targeted fluoroscopically, and a burr was used to make a small corticotomy. The lesion was curetted (Figure 1c) to reduce tumor volume. A Carbofix Piccolo Tibia Nail (Carbofix Orthopedics Ltd.) was used to stabilize the impending fracture. A patellar-splitting approach was used proximally to establish a starting point using a starting pin, after which an opening reamer was introduced. A beaded-tip guidewire was passed to the distal tibial physeal scar and reaming was performed sequentially until adequate endosteal fit was observed. A nail of correct length was selected and advanced over the guidewire while cement was mixed on the back table. Once the guidewire reached the level of the distal lesion it was removed, the cement was impacted into the defect and the nail was advanced to its distal position as the cement cured. Proximal interlocking screws were placed with the aid of a targeting jig. Distal interlocking screws were placed using freehand perfect-circle technique. These interlocking screws were placed with the aid of radiopaque markers that outlined the interlocking slots within the nail. The radiolucent nail with a radiopaque marker identifies the contour of the intramedullary (IM) nail (arrows), as well as the radiopaque markers that outline the position of the interlocking holes within the nail (arrows) (Figure 1d). Placement of these distal interlocking screws requires that the radiopaque markers appear as “dots” (arrows), which indicate a correct trajectory for placement of the screws. Postoperative radiographs are shown (Figure 1e). The patient was allowed to weight-bear to tolerance postoperatively and radiation therapy was administered to the tibia after the surgical wounds were healed.
Figure 2. An AP radiograph of a lytic lesion is seen within the proximal humerus in a patient with known metastatic lung cancer (a). The lesion was curetted under fluoroscopic guidance; sharp edges at the border of the corticotomy were avoided intraoperatively (b). A CFR-PEEK proximal humerus plate was secured to the bone provisionally with K-wires (c). Locking screws were placed into the humeral head after cementation of the defect (d). Nonlocking screws were placed into the diaphysis for fixation distally (e).
Source: Matthew J. Thompson, MD
Case 2
A 64-year old man with known metastatic lung carcinoma presented to our clinic with arm pain that was present at rest, as well as with activity. Radiographs were obtained (Figure 2a), which showed a large lytic lesion with cortical discontinuity within the medial proximal humerus. Operative stabilization was recommended.
The patient was placed supine on a radiolucent bed with a bump placed under the scapula. An incision was made and the deltopectoral interval was used to expose the proximal humerus. A cortical window was made using a burr, which ensured rounded edges were created that helped prohibit the formation of stress-risers. The lesion was removed using curettes and cement was placed to fill the defect (Figure 2b). A Carbofix Piccolo Proximal Humerus Plate (Carbofix Orthopedics Ltd.) was used for stabilization. It was placed lateral to the bicipital groove and secured in the proper position using provisional fixation (Figure 2c). Locking screws were placed into the proximal humerus via implant-specific locking towers and some of these screws gained additional purchase in the previously placed cement (Figure 2d). Nonlocking titanium screws were placed into the diaphysis with appropriate screw spread, which helped with stress distribution (Figure 2e). Postoperatively, the patient was allowed full range of motion and weight-bearing. Adjuvant radiation therapy was also administered.
In the prophylactic fixation of long bones at risk for necrosis and fracture secondary to high doses of in-field radiation and periosteal stripping (eg, in the treatment of soft tissue sarcoma as addressed in Figure 3), carbon fiber offers durability when healing is unlikely without exerting a significant negative effect on the necessary surveillance for secondary malignancy.
Conclusion
CFR-PEEK implants represent a useful tool in orthopedic oncology. The ability to use an implant with a modulus of elasticity similar to bone, which has superior fatigue strength, allows for a durable construct that can be used for setting weakened bone that is not expected to heal. These implants also improve the sensitivity of surveillance imaging with CT and MRI secondary to reduced artifact, which may enable finer characterization of fracture healing or disease recurrence or progression. Further studies are needed to fully define the performance of these implants over time.
- References:
- Hak DJ, et al. Orthopedics. 2014;doi:10.3928/01477447-20141124-05.
- Hillock R, et al. JISRF Reconstructive Review. 2014;doi:10.15438/rr.v4i1.55.
- Zimel MN, et al. Skeletal Radiol. 2015;doi:10.1107/s00256-015-2158-9.
- For more information:
- Richard W. Gurich Jr., MD; and Matthew J. Thompson MD, can be reached at Department of Orthopaedics and Sports Medicine, University of Washington, 1959 NE Pacific St., Box 356500, Seattle, WA 98195; Gurich’s email: rgurich@uw.edu. Thompson’s email: mthomp2@uw.edu.
Disclosures: Gurich and Thompson report no relevant financial disclosures.