PEEK screws are replacing stainless steel and titanium surgical screws in many instances, and they can be found in various orthopedic and trauma fixation applications. Screws can be used to directly interface with bone, or they can be used in conjunction with other trauma fixation and orthopedic devices. For example, PEEK screws can be installed in bone plates to hold a fracture together. They can also be implanted in cortical or cancellous bone, so PEEK’s versatility is a valuable trait in this regard.
Why are PEEK screws emerging as a frontline option?
Stainless steel and titanium have traditionally been the favored materials for surgical screws. In recent years, the introduction of resorbable materials and high performance polymers like PEEK have given surgical teams additional options. Here’s why those surgical teams are increasingly turning to PEEK screws for their patients:
- Biocompatibility and bioinertness – PEEK’s biocompatibility has been confirmed through USP Class VI testing and through extensive patient reports. In 20 years of medical use, PEEK hasn’t demonstrated any toxic or allergic properties, so it can be trusted for long-term or permanent implantation.PEEK is bioinert in ways that metal implants may not be. For instance, patients can develop sensitivity to certain metals after prolonged exposure, but this hasn’t been seen with PEEK. Further, when PEEK is used as a bearing material, it does not liberate extremely small, potentially toxic particles like some metal implants have done in the past.
In addition to its biocompatibility, PEEK also resists attack in an organic or aqueous setting, so it will not corrode and it will not absorb minimal moisture. PEEK screws can be implanted anywhere in the body and remain intact for years.
- Excellent material properties – PEEK is a high performance polymer, so it possesses an elite array of properties, several of them important for trauma fixation and orthopedic applications. High fatigue strength and an ideal flexural modulus are the standout traits, as they approximate cortical bone well. In short, PEEK ‘micro flexes, compresses and bears weight like bone, so it behaves more like a load-sharing material than a load-bearing one.This load-sharing capacity is especially important for trauma fixation and orthopedic procedures. Because it shares the load, PEEK does not cause stress shielding, a common complication among metal, weight-bearing implants. Research published in the European Spine Journal has shown that titanium implants cause bone subsidence (caving in) at rates that far exceed PEEK implants.
PEEK’s fatigue strength is what makes it an ideal screw, as it can withstand tension and compressive forces without losing shape or integrity. The result is a screw that’s better designed for dynamic areas of the body, like the legs, arms, hands and feet.
Since PEEK screws can be installed in cortical bone or softer cancellous bone, they can be used in additional hip and knee arthroscopic procedures.
- Radiolucency – In its natural state, PEEK is radiolucent, so it will not interfere with any form of medical imaging, whether X-ray, MRI or CT scan. This will allow surgical teams to make more accurate, timely assessments, especially where it concerns osteosynthesis.If radiolucency, or imaging transparency is undesirable, additives like barium sulfate can be incorporated into PEEK to provide radiopacity. The addition of barium sulfate does not adversely affect the PEEK, so it can be added without fear of affecting the implant’s function or durability. In either case, PEEK provides an imaging advantage.
- Processability – PEEK’s extensive processability may not be an obvious advantage to patients or physicians, but it’s still a critical consideration. PEEK is a thermoplastic, so it is converted at extremely high temperatures and while using special equipment. Experienced converters use a variety of methods, like extrusion and machining, to turn PEEK into an array of useful medical components.PEEK is almost endlessly processable when machined, as the polymer retains its strong material properties even when subjected to machining stresses. It is essential, however, that an experienced PEEK converter handle machining, as issues with fiber orientation, for example, may compromise the polymer’s function.
For surgical teams, PEEK’s processability allows for a variety of screw sizes and designs, so it’s easier to produce and find screws for a particular patient or implant. PEEK can also be machined to extremely tight tolerances, making a custom fit possible.
- Easier to adjust – Although infrequent, trauma fixation or orthopedic implants may need to be adjusted after implantation. Some PEEK screw systems have been designed with this potential scenario in mind, and they are easier to remove than stainless steel or titanium screws.
In many areas of medicine, PEEK is so successful that it is pushing other biomaterials into lesser roles. That is also true of fixation hardware like screws, where PEEK’s fatigue strength, pullout strength and all-round durability are valuable properties to have. PEEK’s unmatched processability also ensures component manufacturers can develop a full spectrum of screw and screw system designs.