Clinical potential of implantable wireless sensors for orthopedic treatments

Functionalized orthopaedic implant as pH electrochemical sensing tool for smart diagnosis of hardware infection

In the orthopaedic surgery field, the use of medical implants to treat a patient's bone fracture is nowadays a common practice, nevertheless, it is associated with possible cases of infection. The consequent hardware infection can lead to implant failure and systemic infections, with prolonged hospitalization, time-consuming rehabilitation treatments, and extended antibiotic therapy. Hardware infections are strictly related to bacterial adhesion to the implant, leading to infection occurrence and consequent pH decreasing from physiological level to acid pH. Here, we demonstrate the new strategy to use an orthopaedic implant functionalized with iridium oxide film as the working electrode for the potentiometric monitoring of pH in hardware infection diagnosis. A functional investigation was focused on selecting the implant material, namely titanium, titanium alloy, and stainless steel, and the component, namely screws and implants. After selecting the titanium-based implant as the working electrode and a silver wire as the reference electrode in the final configuration of the smart sensing orthopaedic implant, a calibration curve was performed in standard solutions. An equation equal to y = (0.76 ± 0.02) - (0.068 ± 0.002) x, R2 = 0.996, was obtained in the pH range of 4-8. Subsequently, hysteresis, interference, matrix effect, recovery study, and storage stability were investigated to test the overall performance of the sensing device, demonstrating the tremendous potential of electrochemical sensors to deliver the next generation of smart orthopaedic implants.

Development of an implantable trapezium carpal bone replacement for measuring in vivo loads at the base of the thumb

Understanding the loads that occur across musculoskeletal joints is critical to advancing our understanding of joint function and pathology, implant design and testing, as well as model verification. Substantial work in these areas has occurred in the hip and knee but has not yet been undertaken in smaller joints, such as those in the wrist. The thumb carpometacarpal (CMC) joint is a uniquely human articulation that is also a common site of osteoarthritis with unknown etiology. We present two potential designs for an instrumented trapezium implant and compare approaches to load calibration. Two instrumented trapezia designs were prototyped using strain gauge technology: Tube and Diaphragm. The Tube design is a well-established structure for sensing loads while the Diaphragm is novel. Each design was affixed to a 6-DOF load cell that was used as the reference. Loads were applied manually, and two calibration methods, supervised neural network (DEEP) and matrix algebra (MAT), were implemented. Bland-Altman 95% confidence interval for the limits of agreement (95% CI LOA) was used to assess accuracy. Overall, the DEEP calibration decreased 95% CI LOA compared with the MAT approach for both designs. The Diaphragm design outperformed the Tube design in measuring the primary load vector (joint compression). Importantly, the Diaphragm design permits the hermetic encapsulation of all electronics, which is not possible with the Tube design, given the small size of the trapezium. Substantial work remains before this device can be approved for implantation, but this work lays the foundation for further device development that will be required.

Current state of the art and future directions for implantable sensors in medical technology: Clinical needs and engineering challenges

Implantable sensors have revolutionized the way we monitor biophysical and biochemical parameters by enabling real-time closed-loop intervention or therapy. These technologies align with the new era of healthcare known as healthcare 5.0, which encompasses smart disease control and detection, virtual care, intelligent health management, smart monitoring, and decision-making. This review explores the diverse biomedical applications of implantable temperature, mechanical, electrophysiological, optical, and electrochemical sensors. We delve into the engineering principles that serve as the foundation for their development. We also address the challenges faced by researchers and designers in bridging the gap between implantable sensor research and their clinical adoption by emphasizing the importance of careful consideration of clinical requirements and engineering challenges. We highlight the need for future research to explore issues such as long-term performance, biocompatibility, and power sources, as well as the potential for implantable sensors to transform healthcare across multiple disciplines. It is evident that implantable sensors have immense potential in the field of medical technology. However, the gap between research and clinical adoption remains wide, and there are still major obstacles to overcome before they can become a widely adopted part of medical practice.

Implants with Sensing Capabilities

Because of the aging human population and increased numbers of surgical procedures being performed, there is a growing number of biomedical devices being implanted each year. Although the benefits of implants are significant, there are risks to having foreign materials in the body that may lead to complications that may remain undetectable until a time at which the damage done becomes irreversible. To address this challenge, advances in implantable sensors may enable early detection of even minor changes in the implants or the surrounding tissues and provide early cues for intervention. Therefore, integrating sensors with implants will enable real-time monitoring and lead to improvements in implant function. Sensor integration has been mostly applied to cardiovascular, neural, and orthopedic implants, and advances in combined implant-sensor devices have been significant, yet there are needs still to be addressed. Sensor-integrating implants are still in their infancy; however, some have already made it to the clinic. With an interdisciplinary approach, these sensor-integrating devices will become more efficient, providing clear paths to clinical translation in the future.

Implantable biosensors for musculoskeletal health

PURPOSE

A healthy musculoskeletal system requires complex functional integration of bone, muscle, cartilage, and connective tissues responsible for bodily support, motion, and the protection of vital organs. Conditions or injuries to musculoskeeltal tissues can devastate an individual's quality of life. Some conditions that are particularly disabling include severe bone and muscle injuries to the extremities and amputations resulting from unmanageable musculoskeletal conditions or injuries. Monitoring and managing musculoskeletal health is intricate because of the complex mechanobiology of these interconnected tissues.

METHODS

For this article, we reviewed literature on implantable biosensors related to clinical data of the musculoskeletal system, therapeutics for complex bone injuries, and osseointegrated prosthetics as example applications.

RESULTS

As a result, a brief summary of biosensors technologies is provided along with review of noteworthy biosensors and future developments needed to fully realize the translational benefit of biosensors for musculoskeletal health.

CONCLUSIONS

Novel implantable biosensors capable of tracking biophysical parameters in vivo are highly relevant to musculoskeletal health because of their ability to collect clinical data relevant to medical decisions, complex trauma treatment, and the performance of osseointegrated prostheses.

'SMART' implantable devices for spinal implants: a systematic review on current and future trends

Background

'SMART' implants refer to modified orthopedic implants that combine the biomechanical safety and efficacy of traditional devices with the intelligence of data-logging sensors. This review aims to systematically assess the available literature on SMART spinal implants and present these findings in a clinically relevant manner.

Methods

A search of PubMed, Scopus, and Google Scholar databases was conducted by two separate reviewers. Information including sensor type, intended application, and sample size, was extracted from included studies. Risk of bias assessment was conducted using the Office of Health Assessment and Translation (OHAT) risk of bias tool.

Results

Eighteen studies were included for analysis. Eight studies involved SMART rods and ten studies used SMART vertebral body replacements (VBR). No more than 20 patients are reported to have received a SMART spinal implant. Including non-primary evidence, seven unique designs for SMART spinal implants were found. The majority of these used strain gauges with recent designs including thermometers and accelerometers.

Discussion

At present, SMART spinal implants have primarily focused on utilising strain gauges to report loading on the implant itself. This is a logical first step as it allows quantification of real-world requirements of an implant, detection of catastrophic failure, while also allowing researchers and clinicians to estimate changes in load sharing between newly forming bone and the implant itself, providing real-time information on the progression of healing and fusion. Future work includes documenting the correlation between data provided by these SMART implants and clinical findings, including complications such as pedicle screw loosening and interbody cage subsidence.

Osseosurface electronics-thin, wireless, battery-free and multimodal musculoskeletal biointerfaces

Bioelectronic interfaces have been extensively investigated in recent years and advances in technology derived from these tools, such as soft and ultrathin sensors, now offer the opportunity to interface with parts of the body that were largely unexplored due to the lack of suitable tools. The musculoskeletal system is an understudied area where these new technologies can result in advanced capabilities. Bones as a sensor and stimulation location offer tremendous advantages for chronic biointerfaces because devices can be permanently bonded and provide stable optical, electromagnetic, and mechanical impedance over the course of years. Here we introduce a new class of wireless battery-free devices, named osseosurface electronics, which feature soft mechanics, ultra-thin form factor and miniaturized multimodal biointerfaces comprised of sensors and optoelectronics directly adhered to the surface of the bone. Potential of this fully implanted device class is demonstrated via real-time recording of bone strain, millikelvin resolution thermography and delivery of optical stimulation in freely-moving small animal models. Battery-free device architecture, direct growth to the bone via surface engineered calcium phosphate ceramic particles, demonstration of operation in deep tissue in large animal models and readout with a smartphone highlight suitable characteristics for exploratory research and utility as a diagnostic and therapeutic platform.

Simple Smart Implants: Simultaneous Monitoring of Loosening and Temperature in Orthopaedics With an Embedded Ultrasound Transducer

Implant failure can have devastating consequences on patient outcomes following joint replacement. Time to diagnosis affects subsequent treatment success, but current diagnostics do not give early warning and lack accuracy. This research proposes an embedded ultrasound system to monitor implant fixation and temperature - a potential indicator of infection. Requiring only two implanted components: a piezoelectric transducer and a coil, pulse-echo responses are elicited via a three-coil inductive link. This passive system avoids the need for batteries, energy harvesters, and microprocessors, resulting in minimal changes to existing implant architecture. Proof-of-concept was demonstrated in vitro for a titanium plate cemented into synthetic bone, using a small embedded coil with 10 mm diameter. Gross loosening - simulated by completely debonding the implant-cement interface - was detectable with 95% confidence at up to 12 mm implantation depth. Temperature was calibrated with root mean square error of 0.19°C at 5 mm, with measurements accurate to ±1°C with 95% confidence up to 6 mm implantation depth. These data demonstrate that with only a transducer and coil implanted, it is possible to measure fixation and temperature simultaneously. This simple smart implant approach minimises the need to modify well-established implant designs, and hence could enable mass-market adoption.

FDA public workshop: Orthopaedic sensing, measuring, and advanced reporting technology (SMART) devices

Traditional orthopaedic devices do not communicate with physicians or patients post-operatively. After implantation, follow-up of traditional orthopaedic devices is generally limited to episodic monitoring. However, the orthopaedic community may be shifting towards incorporation of smart technology. Smart technology in orthopaedics is a term that encompasses a wide range of potential applications. Smart orthopaedic implants offer the possibility of gathering data and exchanging it with an external reader. They incorporate technology that enables automated sensing, measuring, processing, and reporting of patient or device parameters at or near the implant. While including advanced technology in orthopaedic devices has the potential to benefit patients, physicians, and the scientific community, it may also increase the patient risks associated with the implants. Understanding the benefit-risk profile of new smart orthopaedic devices is critical to ensuring their safety and effectiveness. The 2018 FDA public workshop on orthopaedic sensing, measuring, and advanced reporting technology (SMART) devices was held on April 30, 2018, at the FDA White Oak Campus in Silver Spring, MD with the goal of fostering a collaborative dialogue amongst the orthopaedic community. Workshop attendees discussed four key areas related to smart orthopaedic devices: engineering and technology considerations, clinical and patient perspectives, cybersecurity, and regulatory considerations. The workshop presentations and associated discussions highlighted the need for the orthopaedic community to collectively craft a responsible path for incorporating smart technology in musculoskeletal disease care.

Wireless Technologies for Implantable Devices

Wireless technologies are incorporated in implantable devices since at least the 1950s. With remote data collection and control of implantable devices, these wireless technologies help researchers and clinicians to better understand diseases and to improve medical treatments. Today, wireless technologies are still more commonly used for research, with limited applications in a number of clinical implantable devices. Recent development and standardization of wireless technologies present a good opportunity for their wider use in other types of implantable devices, which will significantly improve the outcomes of many diseases or injuries. This review briefly describes some common wireless technologies and modern advancements, as well as their strengths and suitability for use in implantable medical devices. The applications of these wireless technologies in treatments of orthopedic and cardiovascular injuries and disorders are described. This review then concludes with a discussion on the technical challenges and potential solutions of implementing wireless technologies in implantable devices.

Altering the Course of Technologies to Monitor Loosening States of Endoprosthetic Implants

Musculoskeletal disorders are becoming an ever-growing societal burden and, as a result, millions of bone replacements surgeries are performed per year worldwide. Despite total joint replacements being recognized among the most successful surgeries of the last century, implant failure rates exceeding 10% are still reported. These numbers highlight the necessity of technologies to provide an accurate monitoring of the bone–implant interface state. This study provides a detailed review of the most relevant methodologies and technologies already proposed to monitor the loosening states of endoprosthetic implants, as well as their performance and experimental validation. A total of forty-two papers describing both intracorporeal and extracorporeal technologies for cemented or cementless fixation were thoroughly analyzed. Thirty-eight technologies were identified, which are categorized into five methodologies: vibrometric, acoustic, bioelectric impedance, magnetic induction, and strain. Research efforts were mainly focused on vibrometric and acoustic technologies. Differently, approaches based on bioelectric impedance, magnetic induction and strain have been less explored. Although most technologies are noninvasive and are able to monitor different loosening stages of endoprosthetic implants, they are not able to provide effective monitoring during daily living of patients.

Miniaturized Sensors Registering the Long-Term Course of Suture Tension In Vivo under Varying Intra-Abdominal Pressure

BACKGROUND

Failure of laparotomy closure develops after up to 20% of abdominal operations. Suture tension has an influence on the quality of tissue regeneration. No sensors are available to register suture tension dynamics in vivo.

METHODS

In a series of animal experiments, the effect of suture tension on the ultrastructure of the healing incision was examined. Surgeons' ability to suture with target tension was tested. An implantable sensor and data logger were developed and tested experimentally in sutures closing midline laparotomies in pigs both under normal and elevated intra-abdominal pressure.

RESULTS

High suture tension has a negative influence on the regeneration of laparotomy incisions. Running sutures for laparotomy closure lose 45% of their initial tension over periods of 23 h. Intermittent elevation of intra-abdominal pressure to 30 mm Hg leads to a near total loss of suture tension after 23 h.

CONCLUSION

Surgeons are not able to control and reproduce suture tension. Suture tension dynamics can be measured in vivo by the sensor developed. Further research is needed to define a tissue-specific suture tension optimum to reduce the incidence of complications after laparotomy. Techniques for laparotomy closure need to be modified.