James B. Koeneman

A canine composite femoral stem. An in vivo study

To evaluate a carbon fiber/polysulfone composite femoral stem, a press-fit unilateral hemiarthroplasty was performed in 17 greyhounds. The implant was designed to have strength and elastic properties commensurate with the proximal canine femur. The implant geometry was such that the naturally occurring internal cancellous structures of the proximal femur would be preserved and participate in load transfer from the implant to the bone. Animals were killed at one, five, ten, 16, and 24 months. At necropsy all the femoral stems were well fixed and functioning. All implants maintained their structural integrity. Radiographs and computed tomography scans showed a constructive bone remodeling response. Histologic analysis revealed a benign host tissue response, with few inflammatory cells observed. Both bone and fibrous tissue were observed at the implant-host tissue interface. Implants fabricated from carbon/polysulfone composites have the potential for use in load-bearing applications. An implant with appropriate elastic properties provides the opportunity for the natural bone remodeling response to enhance implant stability. Naturally occurring internal cancellous structures can be utilized for load transfer by femoral components. Press-fit devices with no physical or chemical bone-bonding mechanisms can attain long-term successful functional performance.

Orthopedic Applications of Carbon Fiber Composites

Carbon fiber (CF) composite materials have unique advantages for use in orthopedic surgery, because of their excellent fatigue characteristics, radiolucency, and high strength: weight ratios. The materials can be easily manipulated into complex composite designs, to take advantage of each material’s biomechanical and biocompatible properties, and minimize their weaknesses in the overall composite design. By allowing individual material properties, mechanical properties, and geometrical design considerations to blend into an overall composite design, composite materials of CF exhibit remarkable versatility for orthopedic applications. This versatility is enhanced by the ability of complex designs or shapes to be manufactured by injection- or compression-molding techniques, to modify the biologic and/or biomechanical composite properties. Surface topography and coatings can be easily applied to permanent CF-thermoplastic composites for use as implant devices, to modify interface conditions with host tissue. The ability to vary stiffness within the composite material allows for matching the biomechanical requirements necessary for long-term periprosthetic implantation, as well as fracture fixation with short-term devices, such as external fixators and plates. Orthopedic radiographic imaging techniques are enhanced because of the relative radiolucency of the CF composites, which also allows for in vitro and in vivo implant imaging analysis, to monitor the structural integrity of the device itself. To enhance their clinical utility, the CF composites can be sterilized by standard techniques; customized to size, shape, and appearance; adjusted to weight requirements; and maintained at reasonable shelf lives. In this chapter the versatility of CF composites is illustrated in a joint reconstructive femoral hip implant and acetabular component, as well as in a unique external fixator device for use in orthopedic trauma fracture care.

An Interface Comparison Between a Press-Fit and Ha-Coated Composite Hip Prosthesis

In an attempt to circumvent the problems of loosening and adverse bone remodeling associated with metal femoral stems, carbon fiber composite femoral implants have been developed. A canine femoral implant was constructed with a carbon fiber core and braid and encased in a thermoplastic polysulfone. A proximal particulate hydroxylapatite coating was used in half of the implants, and the remainder were implanted as a press-fit composite stem. There were no clinical differences between the two groups. Positive bone remodeling responses were seen in both groups at fourteen months. Histological examination showed stable bone/implant interfaces in both groups with a propensity for more bone contact proximally in the HA-coated group. The uncoated implants produced a stable fibrous tissue interface with cortical bone maintenance suggesting constructive bone remodeling.