Instrumented hip joint replacements, femoral replacements and femoral fracture stabilizers

Abstract

This paper reviews instrumented hip joint replacements, instrumented femoral replacements and instrumented femoral fracture stabilizers. Examination of the evolution of such implants was carried out, including the detailed analysis of 16 architectures, designed by 8 research teams and implanted in 32 patients. Their power supply, measurement, communication, processing and actuation systems were reviewed, as were the tests carried out to evaluate their performance and safety. These instrumented implants were only designed to measure biomechanical and thermodynamic quantities in vivo, in order to use such data to conduct research projects and optimize rehabilitation processes. The most promising trend is to minimize aseptic loosening and/or infection following hip or femoral replacements or femoral stabilization procedures by using therapeutic actuators inside instrumented implants to apply controlled stimuli in the bone–implant interface.

Keywords::

• arthroplasty
• energy harvesting
• femoral fixation
• femoral replacement
• hip joint replacement
• instrumented implant
• medical device
• orthopedics
• telemetry
• therapeutic actuator

Acknowledgements

The authors would like to thank the Portuguese Foundation for Science and Technology (FCT) for their financial support under the grants PTDC/EME-PME/105465/2008 and SFRH/BD/78414/2011. The permission for reproduction of Figure 3 by Elsevier is appreciated. Finally, the authors would also like to thank the peer reviewers and R Pascoal for their useful suggestions and constructive remarks.

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Although considerable research efforts have been conducted to optimize the design and materials of hip implants, revision rates are about 6% after 5 years and 12% after 10 years following THR. The number of primary THR at younger ages (less than 65 years old) is increasing. The use of uncemented primary and revision THR is also increasing. Aseptic loosening has been the most important reason for hip revision. An increased risk of revision due to infection after THR has been verified in the last years.

• Instrumented hip joint replacements, instrumented femoral replacements and instrumented femoral fracture stabilizers were proposed for research purposes focused on studying the dynamics of biomechanical and thermodynamic quantities when such implants operate in vivo. They have been designed to: collect data (mainly forces, moments and temperatures) for calibration of models defining the implants’ biomechanical and thermal environment; optimize the mechanical design and materials’ behavior of implants; carry out preclinical testing; track the healing evolution and improve the rehabilitation processes after arthroplasty.

• Twelve architectures for instrumented hip joint replacements, without percutaneous wired connections, were implanted into 24 human patients. Two architectures for instrumented femoral replacements were implanted into four human patients. Two architectures for instrumented femoral fixation implants were implanted into four human patients.

• More than 9 years of successful operation was achieved by instrumented hip joint replacements. Up to 9 years of data were acquired in vivo from these implants. No side effects were reported.

• All instrumented implants were designed with measurement, communication and electric power supply systems. However, no therapeutic actuation systems were embedded in the structure of these instrumented implants in order to maximize their ability to overcome failures in real-time.

• Instrumented implants are being developed as medical devices for advanced therapies toward the minimization of revision rates.

• The most promising trend in this field is focused on the design of instrumented active implants to prevent aseptic loosening and/or infection: implants comprising therapeutic actuation systems with ability to induce trajectories from each state of loosening/infection to states of without-loosening/infection.

• Optimization of electric power supply systems must be conducted toward self-powering. Energy harvesting systems are noteworthy in this scope.

• Measurement systems must be developed toward the characterization of the implants’ biomechanical environment, as well as the design of a network of sensors around critical regions where loosening and infection occur.

• Design of electrical and mechanical stimulation systems for instrumented implants may effectively induce and control bone growth in regions where aseptic loosening occurs.

Notes