Osteoarthritis of the knee and hip is one of the most common musculoskeletal pathologies among the people from middle age to old age. Advances in surgical techniques and materials have enabled complete joint replacements for knees and hips. However, all friction surfaces in orthopaedic implants experience load dependent wear that ultimately limits the useful lifetime of the device. Total Knee Arthroplasty is a common procedure with low complication rate; however, postoperative joint biomechanics can affect range of motion, implant survival rates and long-term outcomes. These factors depend, in great measure, on the surgical technique and implant design.
Orthopaedic implants are usually passive and effect of implant on the body can only be forecasted. But what if implants could tell whether recovery is going according to plan or the care needs to be adjusted? The answer is “SMART Implants”. Smart implants are the devices that can provide diagnostic capabilities along with therapeutic benefits. Smart implants have embedded sensors that provide real-time information to surgeons for positioning of the implant during the surgical procedure as well as post-operative evaluation for better patient care throughout the treatment pathway. Smart implants have the potential to reduce periprosthetic infection, which is a growing problem in orthopaedic practice. The integration of smart orthopaedic implants into daily clinical practice will provide immense cost savings to the health care system by reducing expensive complications, speed up the recovery and reducing readmissions. Also, data from smart implants can contribute to refinements in implant design, surgical technique and strategies for postoperative care and rehabilitation.
Smart orthopaedic implants find applications in knee arthroplasty, hip arthroplasty, spine fusion, fracture fixation, infection detection, early dislocation detection, bone ingrowth measurement, spine fusion detection, fracture healing measurement, early detection of osteolysis, etc. While technology underlying the smart implants has improved over the last several decades, significant technical challenges continue to exist which need to be overcome before smart implants become part of mainstream health care.
A few interesting products in the smart implants area are presented below.
Verasense is a sensor-based device used in Total knee arthroplasty (TKA). It has been developed by OrthoSensor Inc. The device delivers data wirelessly to an intra-operative monitor that enables surgeons to make informed decisions regarding implant position and quantify soft-tissue balance to improve knee balance and stability through the range of motion. The use of this device does not affect the surgeon’s work flow. Once the knee implant is positioned, the surgeon places VERASENSE into the tibial tray and examines the mediolateral loading values. This real-time data forms the basis for adjustments that the surgeon makes to arrive at a better-balanced knee.
OrthoSensor’s partnership with leading joint replacement companies such as Smith & Nephew, Stryker and Zimmer Biomet has allowed VERASENSE to be utilized in replacement procedures around the world. In 2018, OrthoSensor received FDA clearance to use VERASENSE with the Persona Knee System in Australia. The first successful use was at Bathurst Private Hospital where VERASENSE was used for Persona Knee System.
Using VERASENSE saves money for the patient by lowering variable post-operative and post-acute care.
OrthoSensor is also working on the development of a new intraoperative sensor trial to assist balancing during reverse total shoulder arthroplasty, showing sufficient accuracy and promising insights into impingement, stability and mobility. However, USFDA clearance for this is still pending and it is not available for commercial sale yet.
Intellirod Spine has developed LOADPRO and ACCUVISTA. LOADPRO is an intraoperative Rod Strain Sensor. It is a single-use device that allows spine surgeons to balance strains on implanted fusion rods during operation. ACCUVISTA is a post-operative Rod Strain Sensor, a permanent device that allows rod strains to be tracked after spine fusion. These devices measure spinal rod strain and simultaneously communicate left versus right rod strain asymmetry to an external reader during corrective surgical manoeuvres.
Intellirod Spine obtained FDA De Novo approval for its disposable spinal rod strain sensor, the LOADPRO. Approved on the 1st of April 2019, the device clamps onto a standard 5.5mm rod for use in monitoring rod strain during a kyphotic correction surgery. This initial approval grants the use of LOADPRO with the FORTEX pedicle screw system from Xtant Medical. Intellirod has also entered into a licensing agreement with the Cleveland Clinic to expand its microelectronics, sensing know-how and technology into other parts of the spine with a therapeutic device. containing an integrated sensor. The company is developing a therapeutic device to create a next generation "Smart" implant by leveraging its platform of inductive powering and wireless communication.
The DSG-enabled screw (Dynamic Surgical Guidance technology) is a pedicle screw with a unique combination of a bipolar sensor and a pedicle screw in just one device. This technology provides surgeons real time guidance and precision in inserting the screw directly into vertebrae. The sensor differentiates various types of tissues (cancellous bone, cortical bone and soft tissues) and provides real time feedback to the surgeon. This smart screw potentially eliminates the need for preparing a pedicle prior to screw insertion.
BoneTag, a unique and universal RFID device, encapsulated in a biocompatible casing which is about the size of a SIM card. Placed inside knee prostheses, it enables communication with all brands of surgical orthopaedic implants by connecting them and making them smart. The physician has to scan the patient’s knee to read the information transmitted by the device to the dedicated BoneTag software.Bonetag was selected by Bpifrance, the General Commissariat for Investment and SATT Network as a high potential candidate for investment. AXLR SATT under partnership with BoneTag associates developed the said RFID device.
BoneTag fulfils three key functions starting from the moment it is integrated into a knee prosthesis, during the surgical procedure:
Other developments that are in progress include orthopaedic implants with wireless communication capabilities for a) detection of loosening for hip implants, (b) force measurements in knee implants, (c) bone healing assessment, (d) wireless correction of orthopaedic structural deformities, (e) temperature measurements for hip implants, (f) measurement of contact forces and moments in the shoulder joint, (g) diagnosis of orthopaedic implant failures, (h) spinal fusion monitoring, etc.
The Department of Electrical and Computer Engineering at The Ohio State University, in a publication, describes the concept of vibrometry which is employed to unobtrusively detect hip implant loosening. There is an insert containing wireless piezoresistive strain sensors which is tested in a mechanical knee simulator that is mimicked under in vivo condition. To assess the bone healing, load measuring electronics has been integrated into the orthopaedic implants. The study demonstrates the wireless telemetry system to measure the bending load in the internal femur.
Recent advances in wireless health care, miniaturized sensors, and wireless powering have indeed enhanced the capabilities of orthopaedic implants by integrating smart functionalities. However, several challenges still remain to be resolved, such as the reliability of the wireless communication link, miniaturization, unobtrusive powering, the ability to achieve stand-alone operation without requiring constant supervision, good measuring accuracy, affordability, low rates of implant failures, animal testing, etc.
In a recent study, scientists at the Department of Bioengineering and Orthopaedics at the University of California, San Francisco (UCSF), used in vivo mouse fracture models to present primary evidence of microscale smart bone plate implants. These implants were able to monitor post-operative fracture healing with high sensitivity using electrical impedance spectroscopy (EIS) integrated to track the healing tissue. In a first, the scientists fixed long bone fractures in a mouse, with external fixtures and bone plates containing the sensor, in an experimental study in the lab. The results have been published in scientific journals.
In the study, EIS measurements were conducted across two microelectrodes in the fracture gap, to track longitudinal differences in mice with good versus poor healing. The scientists presented an equivalent circuit model that combined the EIS data, so as to differentiate the states of fracture repair. Their measurements, which strongly correlated with standard qualitative X-ray microtomography (microCT) values, allowed the frequency-based technique to validate clinically relevant operating frequencies. The results pointed towards the possibility of EIS being combined into existing clinical fracture management strategies such as bone plating. The process developed in the study can ultimately provide physicians quantitative information on the state of fracture repair in patients to guide clinical decision-making.
Scientists at Binghamton University, University of Western Ontario and State University of New York determined that their new smart, self-powered implant needs 4.6 microwatts to function and preliminary testing showed that the average person’s walk produces six microwatts of power, more than enough to power the sensors. The new implant geometry comprises of two ridge-shaped surfaces which rub against one another when a person walks. The frictional sliding that occurs as a result transfers electron from one surface to another, which provides the self-powered charge to the implant. The sensors allow doctors to guide patients when a certain movement has a high impact on the implant so that patients can quickly adjust and avoid damage to the implant.
Rather than using a battery that would add weight to the implants and require periodic replacement, the scientists opted to use an energy harvesting mechanism that powers the knee implant using the patient’s motion. An energy harvesting prototype using triboelectric energy, or energy collected from friction under a mechanical testing machine, was tested to examine its output under equivalent body loads. The harvester prototype was placed between the tibial component and polyethylene bearing of the knee replacement implant. Continual monitoring of knee loads after surgery offers the potential to improve surgical procedures and implant designs.
Nano-Tera projects are cooperatively organised engineering projects that aim to analyse and develop innovative systems featuring small-scale components (micro- and nanoscale) and systems comprising very large data sets (tera). The goal of the select Nano-Tera project was to design a system to measure biomechanical parameters of a knee prosthesis. The system comprises of partly implanted and partly external tools that could help the surgeons during surgery and the rehabilitation and thereby increase the quality of life of the patients. The system helps in estimation of imbalance in medial-lateral ligaments based on force measurements and estimation of loosening of the prosthesis through measurement of kinematics. Also, this would help in measuring the other biomechanical forces acting on the prosthesis, including joint angles and translation motions.
With the participation of the Swiss National Research Fund, CHUV and EPFL, the researchers developed the above-mentioned implant equipped with sensors.
In addition to Intellirod Spine Inc. and Orthosensor Inc., the Pennsylvania-based Ortho-tag, along with the University of Pittsburgh, has developed microchips that are mounted on to orthopaedic implants at the time of surgery. The tags can then communicate wirelessly through the skin with the company's proprietary RFID reader called Touch Probe. Additionally, the company is developing biosensors that can be integrated with these transcutaneous near field tags which can provide feedback to the doctors about the status of the joint infection.
Synergistic Biosensors is a start-up orthopaedic device company developing a diagnostic system that precisely measures orthopaedic implant motion at the micron level without the use of expensive x-rays. The technology can be used for any type of joint replacement. Since a loose implant results in erosion of supporting bone, the sooner pathologic motion is detected, the less bone stock is lost and the greater are the chances for successful remedial intervention by the orthopaedic surgeon. Other diagnostic tools on the market are imprecise for assessing the relative stability of such implants.
Synergistic Biosensors, in collaboration with RTI International in Raleigh/Durham, and North Carolina State University’s Department of Electrical Engineering and Computer Sciences has worked to establish the proof of concept for the sensor’s technology. The system consists of an embedded in vivo wireless multifunctional sensor placed close to (but not in contact with) an orthopaedic implant—such as a hip replacement. The system also includes a wireless interface module (WIM)—no bigger than a cellphone—that powers the sensor from outside the body. Using proximity induction technology, the sensor calculates the distance to the nearby implant and wirelessly transmits this data back to the WIM. The WIM then converts the data into a real-time distance measurement.
Synergistic Biosensors, intending to further the research from the established proof of concept phase through the prototype stage, is currently seeking qualiﬁed investors.
Arthromeda is a private company committed to the development of a simple sensor system which offers cost-effective, patient-specific solutions to improve outcomes in arthroplasty surgeries. It is currently headquartered in Lowell, Massachusetts. Arthromeda uses micro-sensors to wirelessly connect to a software system that’ll help surgeons navigate the implantation process onscreen. Its digital templating software, called ArthroPlan, is meant to be a cost-effective tool that is meant to be compatible with standard work stations, PCs and laptops.
The following examples indicate the type of smart implants we can expect to see in the near future.
The invention from Zimmer Inc. relates to a prosthesis for implantation into a mammalian body with a sensor array comprising multiple sensors mounted to the prosthesis configured to measure pressure of the fluids in the body; and an electronics structure for receiving signals from the sensor array and wirelessly transmitting the same to a remote receiver; the sensors are in communication with fluids bathing the prosthesis to measure the pressure of the fluids.
The invention from Intellirod Spine Inc. deals with medical diagnostic measurements from implanted sensors. A spinal implant-monitoring apparatus that includes: a bridge, strain gauges to provide a signal indicative of strain measured between the legs of the bridge; a second interior with the control circuitry, the housing mounted on the surface of the bridge, etc. The control circuitry is in communication with the strain gauges and are configured to convert the signal into digital data.
The invention from Biomet LLC deals with an implantable sensor configured to be inserted in an intramedullary canal consisting of a primary insert, a secondary insert, and an antenna. The primary insert can include a distal end and a proximal end, and a central bore that can extend from an opening in the distal end towards the proximal end. The secondary insert can include a body and a sensor module. The sensor module can be disposable within the body and can be configured to produce a sensor signal as a function of a parameter indicative of infection. The antenna can be disposed in the central bore and can be configured to transmit a wireless signal as a function of the sensor signal.
The invention from MACQUARIE UNIVERSITY deals with a sensor for monitoring a prosthesis implanted in biological tissue. The sensor transmits a measurement signal towards the prosthesis which is received by a receiver. An antenna transmits data to an external device. A data analyser analyses the transmitted data to obtain monitoring information comprising spatial position of the prosthesis relative to the sensors.
The invention from Just Huajian Medical Device Ltd relates to an intelligent knee joint tibia platform test pad module. The intelligent knee joint tibia platform test pad module comprises test pad body which is provided with an accommodating cavity and a force measurement chip which is arranged in the accommodating cavity in the intelligent knee joint tibia platform test pad module, so that the stress distribution on the inner and the outer side of a knee joint during a moving process can be measured and displayed accurately through pressure sensor probes which are uniformly arranged on a force measurement plate frame. When a movement test is performed on the knee joint, causes are excluded in time in an operation; uniform distribution of the stress is realized; effective cooperation of artificial prostheses of various parts is ensured.
The invention from Zimmer Inc. deals with a system and method for assessing hip arthroplasty component movement. The method includes receiving data from a sensor embedded in a femoral head component, which is configured to fit in an acetabular component, determining information about a magnetic field from the data, and outputting an indication of an orientation, coverage, or a force of the femoral head component relative to the acetabular component.
The invention from Synergistic Biosensors deals with an implantable position detecting system configured to detect a position of an implantable device with respect to a body structure. The system includes one proximity measuring transducer configured to be implanted on the body structure a distance from the implantable device, and another being configured to receive energy from an external electromagnetic field generated by an external sensing interface.
The invention from Arthromeda Inc. deals with systems and methods for providing alignment in total knee arthroplasty operations. It includes multiple sensors coupled to a patient's bones or other surgical tools. The sensors detect their position and orientation in space and communicate this information to a processor. The processor can utilize the information to display data to a surgeon or other user regarding the position, angle, and alignment of a patient's bones, surgical tools, and the reconstructed knee joint.
Smart implants will revolutionize the Orthopaedic sector by reducing the post-operative risks associated with surgeries. A handful of products are out in the market from companies such as Orthosensor, Intellirod spine, SpineGuard, etc. Companies like Zimmer, Smith & Nephew Inc. and Stryker have partnered with Orthosensor for VERSASENSE, however top companies in the space are yet to invest in smart implants technology. Interestingly, small companies seems to be playing an active role in this area and also most of the Universities/Research institutes are engaged in developing prototypes of smart implants, conducting trials with funding from investors. In some cases, the prototype has been successfully developed and some are still in the development stage, down the lane few will be able to complete the clinical trials successfully and some will end up in the middle because of lack of funds
The smart implant area in orthopedics is picking up slowly possibly because of the challenges in the reliability of sensors, biocompatibility of smart implants, also customization of the implants in conjunction with sensors, and also with the site of surgery (Knee, Hip, Shoulder OR spine, etc.). Hence, with smart technologies revolutionizing modern medicine, it is anticipated that more companies will invest in further development of this technology.