A Novel Tool for the Detection of Osteochondral Defects in the Ankle Joint

Abstract

Introduction. Ultrasound is known for cheap, fast and non-invasive diagnosis of numerous injuries. Sport-related injuries in the ankle joint and rehabilitation after surgical intervention are badly diagnosable using traditional ultrasound. Bones surrounding the surface of the articular cartilage blocks the ultrasound pulse and hides the talar surface where most injuries occur. Ultrasound wave propagation shows potential to be used in cheap, fast and non-invasive diagnosis of the cartilage regeneration after surgical intervention. The proposed technique uses a transmitter to send a pulse into the ankle joint whereas a transceiver records the propagated pulse on the other side. The recorded ultrasound wave contains information about the size and location of a lesion in the articular cartilage. Aim of this study is to collect the boundary conditions needed for ultrasound wave propagation through the ankle joint and quantify background noise, system noise and minor deviations of the transceiver on the recorded signal. Finally a novel coordinate system is proposed for the reliable recording of a propagated ultrasound pulse. Methods. Three sets of experiment were performed. Experiment 1 aimed to develop a procedure for consistent recording of an ultrasound wave propagated through the ankle joint. Using traditional ultrasonography the angle of the lower leg and the location of the transmitter and transducer was selected. Experiment 2 aimed to quantify the influence of background noise, system noise, and minor deviations of the transceiver on the recorded pulse. Influence was expressed in the normalized root of the mean square error (NRMSE) and the normalized mean cross correlation (NMCC). Using a robotic arm, displacements up to ±0.5 mm and rotations up to ±0.5° were made from the initial position. Experiment 3 aimed to test a novel coordinate system for the reliable recording of the propagated pulse in multiple recording sessions. Results. All three experiments were successful. The procedure resulting from experiment 1 is: angle of the tibia must be 73° relative to horizontal, ultrasound transmitter must be positioned on the posteromedial portal, and the ultrasound transceiver on the anterocentral portal, the forces of the probes on the skin must not exceed 15 Newton. This procedure has successfully been used in experiment 2 and 3. Experiment 2 quantified the background noise in the system to be white with a maximum value of -158 dB. System noise expressed in the NRMSE was between 0.2% and 4.9%. NMCC was between 0.9994 and 0.7147. Influence of displacements of the transceiver was up to a NRMSE of 5% and a NMCC of 0.6941. Rotation influence expressed in the NRMSE was up to 13%, NMCC was 0.7010. The novel coordinate system tested in experiment 3 repeated the recording with a NRMSE up to 34.1% and a NMCC as low as 0.2050. Conclusion. Background and system noise of ultrasound wave propagation through the ankle joint has been quantified. The influence of minor displacement and rotations of the transceiver on the recording of the propagated ultrasound pulse have been quantified. It provides us with knowledge of the position error needed to reproduce the results. Increased signal transfer between the transmitter and transceiver is needed for better signal analysis and assessment of the cartilage diagnosis. Ultrasound wave propagation through the ankle joint is possible and could be a new area of diagnosing and monitoring cartilage damage or regeneration.