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High Precision Radiostereometric Analysis (RSA) System for Monitoring Micro-Movement in Orthopedic Implants


Over 400,000 people per year in the United States undergo joint replacement surgery comprising a range of implant types and locations. These surgeries include the hip, knee, spine and digital/wrist. It has been well established that short-term micromotion at the implant-bone interface can be a strong predictor of long-term implant loosening and is a consideration both in recipients post-surgery and for the evaluation of new implantation technologies. In order to bring a new implant or surgical methodology (i.e. cement) to market, a product must satisfy the criteria of longevity and stability. Though there are a number of methods to evaluate stability of an implant, the most recognized technique is the X-ray based Roentgen stereophotogrammetric analysis (RSA). In RSA, tantalum reference points are implanted within the bone adjacent to the implant and stereo X-ray images produced to define a global coordinate system. A 3D reconstruction of the interface and the implant is generated and implant displacement monitored over time at the micron level. RSA has been employed to evaluate such orthopedic applications as prosthetic fixation, joint stability and kinematrics, fracture stability, skeletal growth, vertebral motion and spinal fusion.

Since the identification of a strong relationship between short-term RSA results and future risk of loosening of implants following surgery, there has been a strong initiative under the International Organization for Standardization (ISO) to establish a standardized protocol requiring RSA analysis for implant testing prior to market release. One limitation to adoption of this initiative is a need for a different RSA box and analysis system for the different skeletal elements. Similarly there is a need to standardize the method of analysis and accuracy requirements between systems and orthopedic applications.

Description of the Invention:

Researchers at the Robarts Research Institute have developed a new universal RSA calibration system that eliminates the need for joint-specific calibration boxes and analysis. It has been optimized to be 40% and 70% more accurate than other existing technologies (Biplanar and Uniplanar respectively) and is readily adaptable to RSA suites already in use. Finally, the analysis software, which has been optimized to the system, is modular and fully complements existing X-ray detection systems and data formats. The new RSA system has been validated, satisfies the need for universality and provides the best accuracy available in radiostereometric monitoring of implant micro-motion.

Potential Advantages:

• Opportunity in patient-based early stage monitoring of implant stability or orthopedic implant clinical trials
• Represents most accurate and sensitive RSA system available
• Single system applicable to any type and size of skeletal element
• Easily integrated into existing RSA suite
• Comprises hardware and analytical software
• Hardware applicable to any orthopedic area

Patent / Development Status:

US Patent 7,873,147 issued.

Patent Information:


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