Biologic fixation and bone modeling with an unconstrained canine total knee prosthesis

Area of Science:

• Biomaterials Science
• Orthopedic Surgery
• Biomechanical Engineering

Background:

• Biologic fixation is crucial for long-term success of joint replacement prostheses.
• Understanding dynamic loading effects on fixation is essential for implant design.
• Current methods often rely on cement fixation, which can have limitations.

Purpose of the Study:

• To evaluate the effects of dynamic loading on the biologic fixation of an unconstrained knee prosthesis in dogs.
• To assess the stability and functionality of canine knee replacements over an extended period.
• To investigate the bone-implant interface characteristics under physiological loading conditions.

Main Methods:

• Designed and fabricated an unconstrained knee prosthesis with a cobalt-based alloy femoral component and a polyethylene tibial component.
• Incorporated porous surfaces on the femoral component and grooved stems on the tibial component to promote tissue ingrowth.
• Performed total knee arthroplasty on six beagles and monitored prostheses for up to 20 months.

Main Results:

• Demonstrated excellent overall stability and functionality of the prostheses.
• Observed osseous tissue formation stabilizing each tibial component, with a thin fibrous layer indicating micromovement.
• Confirmed solid fixation of femoral components through bone ingrowth into porous surfaces.
• Documented reactive bone modeling, including formation and resorption, along the implant length due to altered stress states.

Conclusions:

• Dynamic loading effectively promotes biologic fixation in canine knee replacements.
• Porous and grooved implant designs facilitate bone and tissue ingrowth for stable fixation.
• The study provides valuable insights into the biomechanical interactions influencing long-term implant success.