Assessment of lower limb prosthesis through wearable sensors and thermography

Abstract

This study aimed to explore the application of infrared thermography in combination with ambulatory wearable monitoring of temperature and relative humidity, to assess the residual limb-to-liner interface in lower-limb prosthesis users. Five male traumatic transtibial amputees were involved, who reported no problems or discomfort while wearing the prosthesis. A thermal imaging camera was used to measure superficial thermal distribution maps of the stump. A wearable system for recording the temperature and relative humidity in up to four anatomical points was developed, tested in vitro and integrated with the measurement set. The parallel application of an infrared camera and wearable sensors provided complementary information. Four main Regions of Interest were identified on the stump (inferior patella, lateral/medial epicondyles, tibial tuberosity), with good inter-subject repeatability. An average increase of 20% in hot areas (P < 0.05) is shown after walking compared to resting conditions. The sensors inside the cuff did not provoke any discomfort during recordings and provide an inside of the thermal exchanges while walking and recording the temperature increase (a regime value is ~+1.1 ± 0.7 °C) and a more significant one (~+4.1 ± 2.3%) in humidity because of the sweat produced. This study has also begun the development of a reference data set for optimal socket/liner-stump construction.

Figure 1.

SHT21S sensors (A) connected to the Seeeduino Datalogger (B) and placed close to the sensing tip of the Amprobe TR300 (C) in the oven.

Figure 2.

Example of (a) temperature raw data; and (b) temperature data after filtering.

Figure 3.

Temperature data after sensor-specific calibration (bias compensation). See Figure 2b for the same data before calibration.

Figure 4.

(a) Bland-Altman plot for S1 vs. TR300 for humidity. There is a clear correlation between the error (y axis, TR300-S1, [RH%]) and the true value estimate (x axis, 0.5 × (TR300 + S1), [RH%]); (b) Humidity signals from Sensirion sensors, pre- and post- calibration.

Figure 5.

The experimental set-up (on the left): (A) the subject and his stump; (B) the IR camera for thermal map recording; (C) the PC for data processing; (D) a rotating platform for controlled image plane projections recording. The wearable sensor setup (on the right).

Figure 6.

The image processing and the identification of the four ROI-hot spots at the human-prosthesis interface (on the right side, i.e., the stump of the left leg).