Motion Artifact Resistant Mounting of Acoustic Emission Sensors for Knee Joint Monitoring

Abstract

Among the many diverse methods of recording biological signals, sound and acoustic emission monitoring are becoming popular for data acquisition; however, these sensors tend to be very susceptible to motion artefacts and noise. In the case of joint monitoring, this issue is even more significant, considering that joint sounds are recorded during limb movements to establish joint health and performance. This paper investigates different sensor attachment methods for acoustic emission monitoring of the knee, which could lead to reduced motion and skin movement artefacts and improve the quality of sensory data sets. As a proof-of-concept study, several methods were tested over a range of exercises to evaluate noise resistance and signal quality. The signals least affected by motion artefacts were recorded when using high-density ethylene-vinyl acetate (EVA) foam holders, attached to the skin with double-sided biocompatible adhesive tape. Securing and isolating the connecting cable with foam is also recommended to avoid noise due to the cable movement.Clinical Relevance-The results of this study will be useful in joint AE monitoring, as well as in other methods of body sound recording that involve the mounting of relatively heavy sensors, such as phonocardiography and respiratory monitoring.

Test-Retest Reliability of Acoustic Emission Sensing of the Knee during Physical Tasks

“…While the findings described are potentially applicable to a wide range of AE monitoring applications for joint assessment, it should be taken into account that measurements were taken using custom sensor-mounting techniques that were previously optimized by the authors [ 27 ] in a cohort of healthy young volunteers. Additionally, an AE sensor with specific characteristics and explicit hit-detection parameters (as outlined in Section 2.1 ) was used to record and define AE events.…”

“…While smaller and more lightweight sensors exist (e.g., Nano30, Physical Acoustics [ 26 ]), they are generally less sensitive (−72 dB Ref V/µbar for Nano30 vs. −36 dB for PK151) and their frequency response is generally higher than that which was previously used for joint AE monitoring [ 10 ].The selected sensor was attached to the right medial tibial condyle area [ 14 ] using ethylene-vinyl acetate (EVA) foam holders with a density of 100 kg/m 3 and double-sided skin-safe tape (Arcos, transparent tape) ( Figure 3 , left). This configuration employing the high-density EVA foam holder with a diameter of 4.5 cm produced the most stable fixation, external noise isolation, and little to no noise during straight-leg motions during preliminary trials [ 27 ].The connecting cable was secured with a plastic holder with cross-linked polyethylene foam (25 kg/m 3 ) isolation ( Figure 3 , center) and was additionally taped to the leg to reduce noise from unwanted cable movement. A further detailed description of the utilized motion artifact-resistant sensor attachment is available in [ 27 ].…”

“…This configuration employing the high-density EVA foam holder with a diameter of 4.5 cm produced the most stable fixation, external noise isolation, and little to no noise during straight-leg motions during preliminary trials [ 27 ].The connecting cable was secured with a plastic holder with cross-linked polyethylene foam (25 kg/m 3 ) isolation ( Figure 3 , center) and was additionally taped to the leg to reduce noise from unwanted cable movement. A further detailed description of the utilized motion artifact-resistant sensor attachment is available in [ 27 ].…”

“…Coefficient of variation (CV) was also used to assess the dispersion of measurements around their mean between participants. Exercises involving straight-leg movements (SLA, SLF) were excluded from a further reliability assessment as the AE hits that were captured during these recordings can be attributed to either noise or acoustic AE events originated from the hip joint during movement [ 27 ].…”

Non-Invasive Assessment of Cartilage Damage of the Human Knee Using Acoustic Emission Monitoring: A Pilot Cadaver Study

“…For instance, the work by Ozmen et al [31] discusses mounting methods to improve accelerometer sensing performance in the 50 Hz-10 kHz frequency band for sound recordings of the knee. In our previous work [32], [33], we presented a procedure to mitigate motion artefacts and improve the repeatability of AE recordings in the broad frequency range of 20-500 kHz. Finally, different positions for the placement of AE sensors were considered for OA knees [21] and wrist joints of healthy volunteers [30].…”