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Aerospace Materials and Orthopaedic Applications: Opportunities and Challenges

1. Composite use for surgical instruments. Numerous surgical instruments are employed in the practice of orthopaedic surgery, including surgical bone awls, bone-hold forceps, bone tampers and surgical elevators, osteotomes and surgical retractors. Traditionally, these have been manufactured using stainless steel. Since intra-operative fluoroscopy is often desirable during surgery, and essential during many trauma procedures, multiple rounds of removal and reinsertion of all instruments may be required to avoid interference with the interpretation of x-ray imaging. Instrument removal and replacement contributes to extended operating time and could contribute to increased mortality and morbidity. Further, the use of steel instruments in close proximity to hip and knee bearing surfaces runs the risk of surface scratching, even at a microscopic level. Scratches on bearing surfaces can have a devastating effect on wear of the implant biomaterials, with a subsequent reduction of implant life and the concomitant problem of debris-induced osteolysis. CIBOR is developing composite surgical instruments that take advantage of weight reduction, radiolucency and non-marring surfaces that aerospace composite materials provide. A range of issues arise to implement this innovation:

  1. The identification of appropriate x-ray compliant composites appropriate for the development of x-ray transparent or translucent instruments.[6]
  2. Development of design criteria that balance fluoroscopy interference and instrument biomechanics required for surgical procedures.
  3. Retention of mechanical stability and bioburden removal for composite instruments subsequent to multiple cycles of autoclave sterilization.
  4. Identification of potential modes of failure for instruments compared with stainless steel equivalents, and determination of the potential risk for creation of composite shards that might arise from instrument breakage or damage by cutting instruments.

Findings to date indicate that composite materials can be identified that provide either complete radiolucency or engineered to exhibit a “ghosting” effect to allow accurate positioning during fluoroscopic procedures. We have observed significant variations between typical aerospace composites when subjected to repeated autoclaving and mechanical testing, but data is now available to suggest that composite instruments should provide a useful lifetime comparable to their stainless steel counterparts. Short term in vivo tests of inflammation provocation using an animal model developed in our labs have demonstrated that risks due to composite shards and smaller debris particles are within an acceptable material range.

2. Composite applications for rapid fixation devices. Battlefield injuries present a complexity of medical problems in a hostile environment, often at considerable distance from trauma care. Orthopaedic injuries constitute a majority of the combat casualties in recent U.S. military conflicts, and 16% of cases involve segmental bone defects or complex fractures.[7] These injuries are invariably complicated by open wounds, and avoiding increased morbidity and mortality requires rapid and rough patient transportation under difficult conditions. The severity of these injuries in conjunction with demanding logistical considerations contribute to a high probability of vascular and nerve damage due to lack of bone fixation. Medical treatment outcomes for battlefield injuries could be improved using a lightweight composite fixation device that provides limb stability and protection from harsh environmental conditions. The development of modern body armor has resulted in a pattern of battlefield injuries that concentrate trauma to the extremities. This is particularly apparent for IED injuries, which result in extensive tissue damage, high risk of contamination and a requirement for orthopaedic treatment in over half of the casualties.[8,9] Inadequate fixation of unstable fractures can result in further damage to the vasculature and nervous system during transport, which may ultimately result in amputation of an injured limb considered to have reasonable salvage potential.[10] CIBOR is conducting research to develop and design concepts, techniques and materials to improve survivability and ensure better medical treatment outcomes in pre-hospital settings by applying aerospace composite technologies to military medical stabilization devices. The product will be a fast setting composite stabilization device that will initially enable shape manipulation and then harden to create a stiff, protective custom-shaped fracture fixation device. This lightweight, compact, portable device will enable quick fracture stabilization in the field. It will conform closely to the shape of the injury site while providing support for improved patient comfort, thereby reducing risk of soft tissue damage during transport. In addition to improved fixation, it will also improve triage decisions with low interference of x-ray imaging.

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