Reach the PEEK: How polymer implants can be used for trauma
John Devine, Invibio Biomaterial Solutions, explains why composite polymer implants are poised for accelerating take-up in trauma fixation.
High-performing polyetheretherketone (PEEK) polymer has for some time now been adopted by innovative medical device companies as an alternative to metal implants. Applications include arthroscopy, joint reconstruction, trauma, dental, and cranio-maxillofacial procedures. In interbody fusion, PEEK is the material of choice, used in over 70% of devices. PEEK Optima is one of them and the recent development of an enhanced grade with hydroxyapatite (HA) fully integrated into this polymer has become a further material option for applications where early bone on-growth is required.
With trauma plates and nails, physicians accustomed to such standard options as titanium or stainless steel might regard polymer-based material and design progress with slight scepticism. However, material R&D hasn't stood still in bringing PEEK-based trauma implants closer, in their properties, to human bone and benefits which were experienced and proven in spine seem to be transferable to new emerging technologies. What is more, these advances may have the possibility to change the way forward in trauma treatment.
In particular, PEEK-Optima Ultra-Reinforced, a carbon fibre-reinforced PEEK (CFR-PEEK) has attracted interest. The material can offer the strength of metal in a composite polymer, suitable for trauma plates and nails, while remaining lightweight. With its favourable modulus of elasticity, it seems to provide the potential for enhanced stress absorption and load-bearing by allowing the design of a less stiff construct, which may support the healing process. The results from some early clinical comparative work with metals, which will be released in October, are expected to increase the interest in these materials.
Over time the trauma industry has shown a preference towards titanium plating rather than stainless steel plating to reduce the overall stiffness of trauma constructs. Despite this, complication rates remain significant and some of this may be addressed by continuing the trend towards a lower stiffness construct. In fact, the stiffness of the CFR-PEEK the PEEK biomaterial pioneer, can be ‘tailored’ to suit therapeutic requirements.1 And while the reinforced material has a mechanical strength similar to that of metals1, it has a greater material fatigue life.1 In addition, CFR-PEEK has the potential to result in earlier and greater callus formation.2
From hidden costs to a hidden champion
Healthcare providers may prefer to continue with traditional metal implants for fracture fixations. However, the economics of orthopaedics prove to have hidden costs. Delayed or non-unions cost healthcare providers more than US$2 billion in failed procedures in the US alone.3 Then there is the additional cost burden of revision surgery along with the negative impact on the patient’s quality of life.
The improved fatigue resistance achieved with PEEK-Optima Ultra Reinforced can potentially reduce complications related to implant failure. In cases where implant removal is required, implants made with the carbon fibre composite material eliminate cold welding problems associated with the use of metal components and minimise bone on-growth4-5 on the implant. This can ease implant removal, reducing operating times by as much as 2.3 times and associated revision surgery costs by as much as 50% compared with metal plates.6-7 This is in a situation where non-union rates have been detailed, in the literature, as being as high as 19% for distal femoral plating.8
Demographic challenges: Rising levels of co-morbidities
Meanwhile, the worldwide patient population has become more challenging with increasing co-morbidities, such as obesity, diabetes and osteoporosis. Complications related to non-unions, delayed unions and implant failure are especially challenging when patients present with such co-morbidities.9-11 For healthcare providers, this is a far from trivial issue. The current figure for obesity is 37.5% of the world's population, while for diabetes the percentage is now 9.5% of the global population. The figure for osteoporosis stands at 26.5%.
These factors, combined with a longer life expectancy and a desire to maintain an acceptable quality of life, have driven the need for alternative biomaterials for use in trauma treatment and fracture fixations. As David Hak, an orthopaedic surgeon with Denver Health at the University of Colorado, notes: "There’s a whole host of patients that are slow to heal. The diabetics, the smokers, patients with open fractures, a whole slew of different patient problems that can lead to delayed bone healing."
Given these rather alarming statistics, it is little wonder that the frequency of non-union of the fracture has been assessed as up to 10%.12 And complicating the matter further, metal trauma fixation hardware can fail before union occurs. Plates made with PEEK- Optima Ultra Reinforced, on the other hand, may provide 50 times greater fatigue resistance13, increasing the window of opportunity for union and providing a greater likelihood that healing will occur.
For PEEK-Optima Ultra-Reinforced, data13 also indicates that implants manufactured with CFR-PEEK can result in 150% greater callus formation13, which may improve secondary bone healing. Results of pre-clinical testing on an ovine model demonstrate earlier and greater callus formation throughout the 12-week study period – particularly within the initial six-week period including 150% more callus at two weeks.13
Advantages of radiolucency
The radiolucency of CFR-PEEK can also be a decisive factor, enabling 360° of fracture visibility in the post-operative monitoring of therapeutic progress. In contrast to metal implants, complications, including breakages, can be detected much more readily when radiolucent CFR-PEEK implants are used, allowing a faster and more precise response on the part of the physician.
In fact, such implants offer surgeons circumferential visibility of the fracture site during, as well as after, surgery. This assessment of reduction may result in safer procedures since all cortices near a joint are visible, potentially reducing the risk of screw perforation.14 In particular, the radiolucency of CFR-PEEK implants enables the improved capture of MRI and CT diagnostics, with the major advantage that images are artifact-free. Radiolucency also improves the visibility of the surrounding anatomy in polytrauma patients.
Improved visibility of the healing process gives physicians increased confidence that they can make an accurate assessment of when to return patients to load-bearing activities.
A case in point – Olympic sprinter James Ellington
UK Olympic team sprinter James Ellington has been making headlines in the media worldwide. He competed in the 2016 Rio Olympics, but in January 2017 was badly injured in a motorcycle accident. Ellington had sustained multiple trauma injuries, including fractures of the tibia and fibula of the right leg, a broken left ankle, a fractured eye socket, and a broken pelvis. Knowing that the recovery process would be complex James and his physician, James Youngman, University College London Hospitals (UCLH) decided to choose the relatively new treatment option of CFR-PEEK implants, because they were aware of the carbon-fibre reinforced polymer's growing reputation for potentially enabling faster recovery in fracture healing. Surgery included the insertion of a composite nail made with PEEK-Optima Ultra-Reinforced, in the effort to repair the fractures of the right leg. This nail was supplied by CarboFix Orthopedics Ltda company specialising in solutions for the fixation of long bone fractures.
Surgery was performed successfully, and the rehabilitation phase is progressing well. He was able to leave his wheelchair weeks before therapists had anticipated. And in a typical display of passion for his sport, Ellington has even vowed to return to competitive athletics.
Speeding up healing by the use of PEEK-polymer implants can be a crucial clinical advantage, potentially leading to earlier weight bearing, with less muscle loss.
Companies like Invibio partnering with medical device manufacturers and building on its initial research, composites processing knowledge, capital equipment and manufacturing facilities, contribute to expedite medical-device innovation. For a trauma company that normally offers metal implants, that could represent an investment saving of millions of dollars. Invibio can cut start-up costs, help medical device manufacturers quickly assess how the PEEK-based material will work in their devices and help them develop and commercialise products at a greater speed.
The verdict is in – Implantable PEEK polymers are pioneering progress
Worldwide, the goal of achieving the best possible clinical outcomes for patients appears consistent. But for a variety of reasons, the medical device industry will have a difficult task of demonstrating that new product innovations are addressing this challenge and, ultimately, improving patient care.
For certain applications, orthopaedic surgeons are transitioning from stainless steel to less stiff titanium implants. Novel PEEK composites offer the potential to carry on this trend to less stiff solutions that potentially result in improved clinical outcomes and as a consequence contribute to reduce the overall cost of care. UK-based Invibio launched an implantable grade of PEEK in 1999 and, after some time, the adoption of the polymer gained speed. Around nine million devices constructed from grades of the company's PEEK-Optima have been implanted today, potentially improving clinical outcomes – and the polymer continues to be used to actively innovate in the quest for improved patient care.
References 1-18: Supporting information available upon request from Invibio Biomaterial Solutions for all claims.