SMART (self- monitoring analysis and reporting technology) and sensor based technology applications in trauma and orthopaedic surgery

Abstract

Background

Innovations in implant designs and computer technology have led to the development of smart implants and prostheses in the field of orthopedics and trauma. Sensor-guided devices enable close monitoring of physical, chemical and biological environment around the implants, which has been purported to meliorate the intra-operative precision and post-operative surveillance of patients.

Objective

We evaluate the current applications of sensor-based technology in the management of patients with a spectrum of musculoskeletal conditions.

Material and methods

A thorough search of literature was performed on May 1, 2023, using the 5 databases (Embase, PubMed, Google Scholar, Cochrane Library and Web of Science) in order to identify suitable studies published between 2000 and 2023. All the studies which reported on SMART implants and Sensor based technology in the diverse sub-specialties of orthopedics like trauma, arthroplasty, spine surgery, infections, arthroscopy or sports medicine and paediatric orthopedics were considered. The keywords used for the search included ‘Sensor technology’, ‘SMART implant’ and “Orthopedics”.

Results

Thirty articles were considered for this narrative review. A generation of SMART implants has been developed due to advancements in the microchip technology. Sensor based technology has been utilised in various subspecialties of arthroplasty (in assessing ligament balancing intra-operatively; or prosthetic loosening and gait analysis during follow-up), trauma surgery (as SMART instruments intra-operatively; or in the assessment of bone healing, distraction osteogenesis and functional recovery during follow-up), spine surgery (identification and protection of neural elements from iatrogenic injuries intra-operatively; and assessment of fusion across the instrumented levels during follow-up), paediatric orthopedics (compliance assessment for foot abduction orthosis in congenital talipes equinovarus), infection (monitoring of infection and biofilm formation), rehabilitation (gait analysis) and sports medicine (rotational stability and ligament compliance in patients with ligament injuries or reconstruction).

Conclusion

SMART implants and Sensor based technology have applications in the surgical planning, intra-operative performance, post-operative monitoring and patient surveillance diverse subspecialties of orthopedics and trauma. Future research in newer designs, cost-effective SMART implants and refinement of Sensor based technology will enhance Patient Related Outcome Measures (PROMs).

1. Introduction

A “sensor” is a device, which can perceive diverse physical stimuli like pressure, volume, force, temperature, acceleration, speed, distance, torque etc.; estimate and interpret the changes in these parameters; as well as convert and transmit them to an electronic device which in turn, helps in gathering and deciphering the signals with the help of a processing computer.¹ In the field of healthcare, sensors are utilised to evaluate diseases, assess patient status in chronic medical disorders; as well as facilitate automatic drug delivery or other medical devices which are capable of measuring diverse biological parameters.^2,3

Traditionally, the patient assessment during the pre- and post-operative follow-up period in trauma and orthopaedic situations is based on clinical evaluation and imaging modalities.^4,5 However, such evaluations are performed at specific time intervals and are impacted by inter-observer variability in the interpretations of individual parameters.⁶ With the advent of various technological advancements like artificial intelligence (AI), deep learning, machine learning, industry 4.0, industry 5.0, and big data analytics, potential for developing SMART (self-monitoring analysis and reporting technology) orthopaedic prostheses and implants has been widely realised.1, 2, 3, 4, 5, 6 The smart sensor devices embedded within such implants can provide the real-time information regarding the changes in the physical (including strain, pressure, force or alignment variations) environment and the alterations in in-vivo biochemical milieu.⁷ The information, thus procured, is transmitted to the exterior in the form of radiofrequency or blue-tooth waves; and further interpreted by the clinicians with the help of processing computers.⁸ Sensor-guided devices, which enable close monitoring of physical, chemical and biological environment around the implants, have been purported to meliorate the intra-operative precision and post-operative surveillance of patients.⁵

Although the prospects of such implants are extremely promising, their use is substantially limited at present owing to the financial, logistic and technical constraints.^1,4,5 A majority of the current evidence on such implants is based upon in vitro biomechanical and animal studies; and the overall, short- or long-term clinical outcome and practical feasibility are still largely unknown.¹ The present narrative review was thus planned to comprehensively analyse the clinical and non-clinical studies; and explore the role of the sensor technology in the field of orthopaedic surgery.

2. Methods

2.1. Strategy for literature search

• •A thorough literature search was conducted on May 1, 2023 using the 5 databases (Embase, PubMed, Google Scholar, Cochrane Library and Web of Science) in order to identify studies published between 2000 and 2023. The search was conducted with the keywords in combination with Boolean operators, namely (((Sensor technology) OR (SMART Sensor) OR (artificial intelligence) OR (AI) OR (machine learning) OR (ML)) AND ((orthopedics) OR (trauma) OR (arthroplasty) OR (arthroscopy) OR (paediatric orthopedics) OR (orthopedics and trauma))). The strategy for literature search has been depicted in Fig. 1.

Fig. 1.

Flowchart of the literature search strategy for Sensor Technology applications in Trauma and Orthopaedic Surgery.

2.2. Eligibility criteria

• •All the studies which reported on sensor-based implant and prosthetic technology in the diverse sub-specialties of orthopedics like trauma, arthroplasty, arthroscopy or sports medicine and paediatric orthopedics were considered. Among these studies, systematic or narrative reviews, letters to the editor, opinions, and articles published in non-English literature were excluded (Table 1).

Table 1.

Table highlighting the Inclusion and exclusion criteria set the parameters for eligibility for this study.

	Inclusion Criteria	Exclusion Criteria
Study Design	Randomized Control Trials, Observational studies, Clinical trials	Letters to the editor, reviews, grey literature
Patient Population	Patients with Orthopaedic Trauma, Spine and Orthopaedic pathologies
Language	English language	Non-English language

2.3. Article selection and data extraction

• •All the search outputs from the aforementioned databases were downloaded, extracted onto End-note web, de-duplicated and manually selected. The titles were screened first by two of the authors (VK, GP); following which individual abstracts were individually screened by the aforementioned criteria (Table 1). During the second round of screening, the individual, complete manuscripts were reviewed by the two authors (VK, GP) and the final selection was completed. All the discrepancies at the time of article selection were settled after discussion with the senior-most author (VJ).

2.4. Research objective (RO)

The main research objectives of the study include.

• RO1: Sensor-based technology in orthopaedic surgery

• RO2: Problems encountered with sensor-based SMART implants and prosthesis

• RO3: Complications associated with sensor-based SMART implants and prosthesis

• RO4: Biomechanical properties of sensor-based SMART implants

• RO5: Clinical outcome following sensor-based SMART implants and prosthesis

3. Results

Results of literature search: The literature search yielded 714 articles on all the aforementioned databases. Following manual de-duplication and compilation with Endnote, 232 manuscripts were selected. After screening of titles, 75 manuscripts were considered for further screening. Following the screening of abstracts and full manuscript texts, 30 manuscripts were finally chosen (Fig. 1; Table 2).

Table 2.

Description of the individual studies.

	Study Authors	Year of Publication	Country	Journal	Type of Study Major findings
ARTHROPLASTY
1	Gustke (TKA)	2013	USA	The Journal of Arthroplasty	Case series Balanced joints using sensor technology: Significant improvement in WOMAC, KSS and activity level
2	Gharaibeh (TKA)	2018	Australia	ANZ J Surg	Prospective Learning curve with sensor-guided assessment in achieving knee balancing
3	Golladay (TKA)	2019	USA	Journal of Arthroplasty	Prospective Using sensor feedback during TKA: More reproducible, higher percentage of balanced patients, superior clinical outcomes
4	Ismailidis (THA)	2020	Switzerland	Gait and Posture	Case Control Rehagait system: Measures gait kinematic characteristics for osteoarthritis of hip; and is well-suited for clinical practice
5	Indelli (TKA)	2020	USA	Orthopaedic reviews	Surgical technique Intraoperative knee balancing real-time sensors – providing continuous feedback about joint stability or tibio-femoral loading
					Sensor-derived kinematic data: Analysis of gait
6	Livermoore (TKA)	2020	USA	Bone and Joint J	Retrospective Combination of navigated distal femoral cut and sensor-assisted ligament balancing – Did not improve functional, clinical, radiological outcome and complication rates
					Significant increase in expenditure
7	Law (TKA)	2020	USA	Surg Tech International	Prospective Substantial cost reduction with ninety-day bundle payment model for sensor-guided TKA
8	Cochetti (TKA)	2020	USA	J Orthopaedic Surgery	Prospective Sensor technology: No improvement in clinical outcome
					Enables multiple intraoperative modifications for replicating the medial pivot kinematics of native knee joint
9	Thompson (TKA)	2020	Australia	The Knee	Prospective Computer-assisted TKA: Excellent interobserver agreement of sensor pressure measurements (at knee flexion of 10°)
10	Sabatini (TKA)	2021	Italy	Sensors	Retrospective Sensor-assisted pressure evaluation during TKA: Enables reproduction of balanced knee
11	Chang (TKA)	2021	UK	Bone Joint J	Prospective Functional alignment during TKA: Enables achievement of good mediolateral soft tissue balancing
12	Wood (TKA)	2021	Canada	Journal of Arthroplasty	Prospective randomized clinical study Sensor-guided TKA: No improvement in clinical outcome or patient satisfaction
13	Misu (TKA)	2022	Japan	The Knee	Case Control Inertial sensors attached to lower trunk: Enable good assessment of gait performance during TKA
14	Sharma (THA)	2022	USA	Arthroplasty today	Prospective Wearable sensors are accurate in replication pelvic tilt movements pre- and post-operatively in patients undergoing THA
15	Sarpong (TKA)	2022	USA	Clinical Ortho Related Research	Prospective randomized clinical study Sensor-guided balancing did not confer any benefit with regard to clinical or functional outcome; and was associated with enhanced costs and increased operative time
16	Indelli (TKA)	2023	USA	Journal of Experimental Orthopedics	Retrospective Sensor-embedded tibial inserts: Did not replicate normal knee kinematics
TRAUMA
17	Borchani	2015	USA	IEEE	In-vitro Piezo-floating gate sensors: Enable reliable, objective assessment of bone/fracture healing
					Enables decision making regarding implant removal
18	Zens	2016	Germany	Technol Health Care	In-vitro Polydimethylsiloxane-fabricated pressure sensors: To evaluate force (compression versus tension forces) distributions intra-operatively across TBW in olecranon fractures
19	Najafzadeh	2020	Australia	Bio engineering	In-vitro Fibre Bragg Grafting (FBG) sensors: To assess bone strength and strain across fracture ends during various stages of healing, and determine optimal point to resume weight-bearing
SPINE
20	Szivek	2005	USA	Journal of Biomedical materials Research	Case report
					Sensor technology: Allows continuous monitoring of strain across the fusion construct
21	Aebersold	2007	USA	J. Med. Devices	Sensor design report
					Sensor technology: Utility in spine fusion assessment
22	Windolf	2022	Switzerland	Medicina	In vivo animal study
					Sensor technology: Continuous measurement of the load on the rod to evaluate the spinal fusion process
PAEDIATRIC ORTHOPEDICS
23	Morgenstein	2015	USA	J Paed Ortho	Prospective randomized clinical study Sensor technology: For objective measurement of foot abduction orthosis in patients undergoing Ponseti treatment
24	Sangiorgio	2016	USA	JBJS	Prospective Sensor technology: For objective measurement of foot abduction orthosis in patients undergoing Ponseti treatment
25	Richards	2020	USA	J Am Acad Orthop Surgery	Retrospective Sensor technology: For objective measurement of foot abduction orthosis in patients undergoing Ponseti treatment
					There is a gradual decline in the orthosis wear beyond the age of 2 years
					Approximately 50% of children wear the FAO for 8 h or less by their second year.
INFECTION
26	Saccomano	2021	USA	Sensors and Actuators Reports	In-vitro Nanosensors incorporated into biofilms: To determine the minimum biofilm inhibitory concentrations (MBIC) of antibiotics
REHABILITATION
27	Suk Oh	2021	USA	Nature Communications	Sensor design and clinical trial Wireless sensors: For continuous pressure and temperature monitoring in patients with neurological conditions for assessment of pressure sores
28	Kao	2021	Taiwan	Sensors	In-vitro Described sensor technology in bracing/orthotic appliances
ARTHROSCOPY
29	Araki	2011	Japan	International Orthopedics	Prospective Electromagnetic system: Evaluation of knee acceleration during pivot shift
30	Kuroda	2016	UK	Curr Rev Musculoskeletal med	Sensor design Electromagnetic measurement system (EMS): Evaluation of rotational laxity of knee

4. Discussion

Since 2011, the innovations of Industry 4.0 have meliorated healthcare at various levels, such as ensuring timely diagnosis, innovative treatment, and interconnecting health systems. However, a major pitfall of Industry 4.0 is the inability to deliver a “personalised care” of patients. Since 2015, Industry 5.0 has enabled the personalisation of technology and products; and has built upon the sophistication of Industry 4.0 including smart machines and robotic technology.¹ With evolution of Industry 5.0, the role of additive manufacturing, robotic surgeries, augmented reality, holography, Internet-of-Everything and SMART sensor technology have been evaluated in the field of orthopedics.1, 2, 3 Among these modalities, the technology of SMART sensors has been revolutionising the development of orthopaedic implants and prosthesis.4, 5, 6, 7 Overall, SMART implants may include^4,7.

• a.Additive manufacturing (AM): Involves development of custom or patient-specific instrumentation with the help of computer aided design and 3-D printing technologies.
• b.Smart sensor devices: Implants which deliver real time, post-implantation details, which in turn aids in monitoring implant-related and patients' clinical outcome.

The overall applications of this technology in orthopedics may be discussed under the following categories.

4.1. Arthroplasty surgery

4.1.1. Intra-operative applications

In total knee arthroplasty (TKA) surgeries, “SMART” implants embedded with sensors are employed to evaluate biomechanics, component sizing, alignment and balancing intraoperatively8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25; and to plan rehabilitation post-operatively. VERASENSE, a sensor-assisted next-generation TKA, developed by Orthosensor [Stryker (NYSE:SYK)], provides real-time data (regarding intra-compartmental pressures) for excellent ligament balancing (or achievement of functional outcome) and component sizing.⁸

In a recent meta-analysis, it was concluded that in comparison to manual gap-balancing technique, sensor-guided techniques led to reduced rates of “manipulations-under-anesthesia”. Nevertheless, there were significantly increased rates of additional, intraoperative procedures performed to achieve balance. They reported no significant improvement in functional scores, operative time, mechanical axis and re-operation rates following sensor-assisted TKA.¹⁰ In another randomized controlled trial (RCT), Sarpong et al.⁹ concluded that sensor-guided balancing did not confer any benefit with regard to clinical or functional outcome; and was associated with enhanced costs and increased operative time. On the other hand, certain studies have demonstrated substantially more reproducible and precise balancing of the knee ligaments with sensor technology.¹¹ A systematic review by Betailler et al.²⁵ demonstrated that TKA using sensors facilitated reproduction of natural articular stability. In another review, Yapp et al.²⁰ showed that surgeon-defined soft tissue stability was substantially different from the actual pressures recorded by intra-operative sensors. Thus, verdict on the benefit of sensor-guidance in arthroplasty surgeries is still unclear; and the need for large-scale prospective, randomized trials on this subject cannot be understated.

4.1.2. Post-operative applications

Among the various complications following arthroplasty surgery, prosthetic loosening attributed to aseptic loosening (secondary to mechanical wear) and septic loosening (prosthetic infection) are crucial.⁴ Sensor technology has been reported to be valuable in detecting such loosening effectively.⁵ The mechano-acoustic sensor embedded within implant, when activated by external coil, can detect prosthetic loosening or osteo-integration.^8,22,26,27 This technology can be highly beneficial during the patients’ follow-up. In addition, studies by Indelli⁸ and Ismailidis^26,27 (and a review by Loo.²²) concluded that the sensor-derived data could be utilised for providing real-time gait analysis during the follow-up of patients undergoing TKA and THA.

4.2. Trauma surgery

4.2.1. Intra-operative applications

Magnetic sensor system, consisting of a magnet placed in distal locking hole of intramedullary nail, has been developed to guide sensors on drill to safely insert locking bolt with precision and minimal radiation exposure.28, 29, 30, 31, 32, 33, 34, 35 Polydimethylsiloxane-fabricated pressure sensors have been utilised to evaluate the force (compression versus tension forces) distributions intra-operatively across tension band wiring in olecranon fractures.³⁵ Studies have also reported the use of instrumentations guided by sensor mechanism, which can enhance precision during various trauma surgeries (eg. McGinley Ortho-pedics “Intellisense”™).^31,32 Such SMART drills can provide better direction and depth senses; as well as mitigate radiation exposure to the surgeons.^31,32

4.2.2. Post-operative applications

Sensor technology has been used to monitor bone healing and callus formation during the follow-up.³³ The implants embedded with sensor system (comprised of an external excitation antenna capable of emitting electromagnetic wave based on the architectural features of the adjoining bone) can detect changes in relative load transmissions across the callus and implant. During the natural process of fracture healing, the load transmission gradually shifts from the implant onto the callus; and serial measurements of these load shifts with sensor technology can be helpful in early detection of non-unions.³³ An in-vitro study by Najafzadeh et al.,³³ Fibre Bragg Grafting (FBG) sensors were incorporated within the implant for the assessment of bone strength and strain across fracture ends during various stages of healing, in order to determine the optimal point to resume load-bearing activities.

On a similar note, it has been demonstrated that piezo-floating gate (PFG) sensors can diagnose non-unions much earlier than any other modality (in animal models, non-unions have been detected as early as 21 days).³⁰ It has therefore been purported that sensor-based implants can be routinely employed in the timely diagnosis of fractures which are notorious for poor healing, including distal tibia, scaphoid, neck of femur and talus.^31,33,35 Sensors embedded into illizarov ring fixators and hexapods have been utilised to monitor distraction osteogenesis, strains across the bone ends, quality of callus formation and achievement of angular corrections.^7,29 These sensors can thus enable continuous, reliable and objective monitoring of bone healing, which is impossible with the current modalities.^7,29 These devices can thus help us to decide upon the accurate time for implant removal. In the study by Marmor,²⁹ role of wearable activity monitors (WAM) in determining the patients’ pre-injury and post-injury functions was discussed.

4.3. Spine surgery

4.3.1. Intra-operative applications

In the context of minimally-invasive and percutaneous spine surgeries, Raman micro-spectroscopic system which may be embedded within the spinal implants and instruments, can be utilised to protect the nerve roots and other neural elements from iatrogenic injuries.³⁶ The efficacy of such a system has been well-demonstrated in animal models.^37,38

4.3.2. Post-operative applications

SMART spinal implants have been purported to be of significant benefit in monitoring the spinal fusion, especially in situations of long-segment instrumented arthrodesis.36, 37, 38 Strain gauzes have been employed to attach to the laminae of the vertebrae and posterior spinal implants. As the fusion progresses, strain across fusion rod decreases; and peak bone strain gradually increases initially after which it levels off. Such implants have been available in the form of pedicle-based and inter-body systems.³⁷ Fowler-Nordheim sensor-data-logger is an implant, which is battery-free and powers itself using energy harvested by piezo-electric transducer. The same signal is utilised by sensor in order to evaluate progression of spinal fusion.³⁸

4.4. Paediatric orthopedics

Studies have utilised sensor technology for an objective quantification of the daily hours of post-correction foot abduction orthosis (FAO) wear in patients undergoing Ponseti casting for the treatment of congenital talipes equinovarus (CTEV) deformity.39, 40, 41 Richards et al.⁴¹ reported that there was a gradual decline in the orthosis wears beyond the age of 2 years; and approximately 50% of children were wearing the FAO for 8 h or less by their second year. The authors emphasized upon the utility of sensors for monitoring the brace wear during growing years, so as to ascertain good compliance.39, 40, 41

4.5. Infection

Micro-electro-mechanical systems-based sensors, placed within the implants, may detect the bio-chemical changes produced from bacteria like concentration of oxygen, pH, temperature, ions etc.⁴² When stimulated by these signals, the sensors may activate the reservoirs to release biofilm-inhibitory molecules and large doses of antibiotics. Such sensors can thus aid in the monitoring of infection and provide excellent information regarding the characteristics of biofilms.⁴²

4.6. Rehabilitation

The sensor systems have been purported to be helpful in different rehabilitative scenarios of operative and non-operative patients. While Suk Oh et al.³⁴ evaluated the role of wireless sensors in the continuous measurements of temperature and pressure in patients with severe neurological injuries and those at risk for pressure injuries; inertial sensor systems (consisting of seven sensors including 3 accelerometers, 3 gyroscopes and a magnetometer) have been utilised in gait evaluation of patients with hip pathologies. Kao et al.⁴³ described role of sensors in developing braces or orthotic devices. Kuroda et al.²⁸ described the role of electromagnetic tracker, a six-degrees-of-freedom measuring device, which can concomitantly record the orientation of electromagnetic sensors (EMS) attached to diverse body segments via transmitters. Such sensors aid in detailed kinematic assessment, gait analysis and rehabilitative approaches across diverse clinical scenarios.

4.7. Sports medicine and arthroscopy

The sensor technology has been utilised to assess knee stability following ligamentous injuries and reconstructions.^44,45 Araki⁴⁴ and Hoshini⁴⁵ demonstrated an electromagnetic measurement system (EMS), which is capable of evaluating six-degrees-of-freedom of knee kinematics (FASTRAK, Polhemus, USA). The system involves an electromagnetic transmitter and three electromagnetic receivers. Abnormal movement during the pivot-shift is characterised by 2 phases: a. increased anterior tibial translation; b. increased acceleration of posterior tibial reduction. Through the device, knee acceleration during pivot-shift evaluation following anterior cruciate ligament reconstruction may be evaluated. It has also been employed to evaluate the rotational laxity during clinical follow-up.

4.7.1. Limitation of the study

Our review carries the limitations inherent to most narrative reviews. The review has included retrospective, prospective and in-vitro studies. No specific strategy was employed to evaluate methodological quality of reviewed manuscripts. Sample sizes of the included manuscripts were varied. Nevertheless, our study comprehensively reviewed the available evidence in detail; and has summarised our understanding on this subject heretofore.

5. Conclusion

Sensor-guided technology has a tremendous potential across diverse subspecialties of orthopedics and trauma, namely arthroplasty, trauma, spine surgery, paediatric orthopedics, infection, rehabilitation and arthroscopy. It can be beneficial during the surgical planning, intra-operative execution, post-operative monitoring; and patient surveillance.