Embedded sensing package for temporary bone cement spacers in infected total knee arthroplasty

https://doi.org/10.1016/j.jmbbm.2020.104301Get rights and content

Abstract

The re-infection rate of total knee arthroplasty (TKA) after two stage revision (15%) remains high as it can be challenging to determine whether the infection has been fully cleared between the first and second stage procedures. Temporary embedded sensor systems could be a potential solution to indicate whether the infection has been cleared. In this study a telemetric sensor system to integrate with a bone cement spacer and measure knee joint temperature was designed and evaluated. The sensor package precision, accuracy, hysteresis, and thermal equilibrium were empirically determined. Cadaveric testing was performed with the sensor package implanted inside the femoral notch alongside a pre-formed femoral and tibial bone cement spacer. The limb was tested though 30,000 cycles at 0.5 Hz under a 500 N load. Accuracy and precision of the sensing package were found to be ±0.24 °C and 0.09 °C respectively with negligible hysteresis. Thermal insulation caused by the implant itself was found to produce a thermal time constant of 263 ± 5 s, resulting in a 17 min rise time. Memory capacity enabled data logging every 20 s for a 6 week period before necessitating data transfer. Bluetooth was suitable for data transmission while the package was implanted. Following cyclic loading of the cadaveric specimen, imaging and debridement revealed no issues related to mechanical integrity of the bone cement spacer or encapsulated sensor package. While additional validation is required before use in patients, the concept of temporary embedded sensing technology to aid management of infection treatments is promising.

Introduction

Persistent infection of total knee arthroplasty is an issue resulting in serious long term mobility challenges, exorbitant healthcare expenses, and occasionally, morbidity for >20,000 North Americans annually (Canadian Institute for He, 2018; Foran, 2015). Approximately 1–3% of total knee arthroplasties (TKA) require revision due to infection (Kalore et al., 2011; Martinez-Pastor et al., 2013; Cury et al., 2015; Mallon et al., 2018; Springer et al., 2017; Lu et al., 2017). The gold standard treatment in these cases in North America is a two-stage revision. This involves the surgical removal of the infected implant and temporary installation of an antibiotic bone cement knee spacer for a period of 6–10 weeks while the infection is treated. When convinced the infection is cleared, the surgeon will perform a second procedure to remove the antibiotic spacer and install the permanent “revision” knee replacement. Unfortunately, this procedure has a much lower success rate with ~15% of revision patients maintaining infection after this extremely costly procedure (Pangaud et al., 2019). In these cases, persistent infection was not completely cleared while the antibiotic spacer was implanted before the second stage revision was completed.

The surgical trauma from the first stage of revision surgery coupled with extensive local and systemic antibiotic and anti-inflammatory therapies results in dynamic fluctuation of common infection markers (Mont et al., 2000). Taking temperatures, blood, or serum samples only on occasion after the first stage revision may be insufficient to form a comprehensive picture of the infection status, and may contribute to the comparatively poor re-infection rate after second stage revision. Therefore, diagnostic tools for infection status specifically designed for the dynamic nature of infection symptoms during two stage revision treatment could aid surgeons in correctly determining when to perform the second stage surgery. In other medical fields, commercial implantable sensor systems have already been popularized. Examples include pacemakers, cardiac monitors, and gastrointestinal stimulators. In orthopaedics, instrumented implants have been used for measurements of joint loads in research, but so far there are no commercial products on the market (D'Lima et al., 2005; Bergmann et al., 2014).

We propose to leverage low power embedded electronics to instrument the antibiotic spacer with sensing and logging capability. This device would passively collect and store readings directly from the implant site. When the patient visits the clinic, the surgeon will be able to wirelessly access logged information to observe trends from within the joint space over time. In this pilot study, temperature was used as the primary sensing metric and two hypotheses are tested. First, that the sensing package developed will offer sufficient sensing, power management, and communication performance to be feasibly used for the application of infection diagnostics in a knee spacer. Second, that the integration of the proposed instrumented package adjacent to a bone cement spacer is feasible and does not mechanically interfere with the integrity of the spacer.

Section snippets

Instrumentation package

The sensor package was designed to be a self-contained unit that could be encased in bone cement and installed adjacent to the bone cement spacer within the joint (Fig. 1). While many potential measurements could be relevant for infection, temperature was selected as the primary metric of interest to demonstrate the concept. Elevated temperature is a known indication of infection (Evans et al., 2015). Furthermore, surgical wound temperature changes in correlation with different stages of

Sensing precision testing

Precision was determined to be 0.09 °C with 95% confidence by calculating the standard deviation of the 100 measurements captured at steady state condition.

Sensor accuracy and hysteresis testing

The characteristic equation for sensor calibration was T[°C] = 0.3411 × Measurement – 54.55 with 0.995 R-squared correlation (Fig. 3). Sensor accuracy was ±0.24 °C accuracy with 95% confidence throughout the sensing range (Fig. 4).

Hysteresis was also observed in the validation data set to have a mean value of -0.001 °C across the entire

Discussion

The sensor package met practical goals required for its implementation. Positioning the sensor package alongside the femoral component is perhaps a preferred location to embed this sensor over the tibial component. The femoral notch offers space for increased cement volume relative to the intermedullary canal of the tibia and permits a more thorough coating of the sensor with bone cement. While Bluetooth penetration and signal decreased slightly with implantation, signal stability was excellent

Authorship statement

Michael K. Lavdas: Investigation, Formal Analysis, Visualization, Writing Original Draft.

Ryan Willing: Methodology, Investigation, Writing Review & Editing.

Brent A. Lanting: Methodology, Investigation, Writing Review & Editing.

Matthew G. Teeter: Conceptualization, Methodology, Project Administration, Supervision, Writing Review & Editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

We acknowledge funding from the Western Bone and Joint Institute and a Discovery Grant from the Nautral Sciencs and Engineering Research Council of Canada.

References (34)

  • O.M.E.G.A. Engineering

    OMEGASCOPE™ handheld infrared thermometer

  • S.S. Evans et al.

    Fever and the thermal regulation of immunity: the immune system feels the heat

    Nat. Rev. Immunol.

    (2015)
  • J.R.H. Foran

    Total knee replacement

    OrthoInfo

    (2015)
  • J.R.H. Foran

    Total knee replacement exercise guide

    Orthoinfo

    (2017)
  • P. Garg et al.

    Antibiotic-impregnated articulating cement spacer for infected total knee arthroplasty

    Indian J. Orthop.

    (2011)
  • C. Goumopolus

    A high precision, wireless temperature measurement system for pervasive computing applications

    Sensors

    (2018)
  • Y.-T. Jia et al.

    Antibiotic-loaded articulating cement spacers in two-stage revision for infected total knee arthroplasty: individual antibiotic treatment and early results of 21 cases

    Chin. J. Traumatol.

    (2012)
  • Cited by (0)

    View full text