MONITORING AND ANALYSIS OF ACOUSTIC EMISSIONS FROM KNEE JOINTS

MONITORING AND ANALYSIS OF ACOUSTIC EMISSIONS FROM KNEE JOINTS
Ivan Vatolik, Gordon Hunter, Michael Everington, Andy Augousti
Faculty of Science. Engineering and Computing,'Kingston University, KT1 2EE, UK.
1 INTRODUCTION
Many people experience mobility problems as they age,often due to damage to bone joints and to the cartilage between the bones in these joints, which can eventually lead to osteoarthritis and severe pain. Such problems are particularly common in former athletes, since injuries sustained during intensive "high impact" exercise activities can easily lead to cartilage and joint damage. Damage to soft tissues such as cartilage does not show up well on conventional X-rays, and more suitable medical imaging methods (such as MRI) for the detection of such problems. tend to be expensive and require specialist operators and heavy equipment, and are not available in all hospitals or clinics - let alone at a typical sports venue or training facility. Failure to identify problems of this type early can result in a person requiring surgery with no guarantee of success. or having to live with painful disability and reduced mobility.
Several studies have investigated the effects of different types of exercise on the knee cartilage and found that the cartilage undergoes signicant changes in volume during exercise (e.g. Eckstein et al., 2005; Kessler et al., 2008)☝. It has also been reported that healthy cartilage, due to its viscoelastic properties, normally returns back to its natural static state within 90 minutes of the end of exercising. Since the viscoelasticity is temperature dependent, studying the recovery patterns of cartilage under a variety of conditions would be benecial to the medical, athletic and scientic communities, In addition, the study of acoustic emissions from bone joints has recently been shown to be a valuable tool in identifying knee cartilage degeneration and osteoarthritiss-V. Observing, recording and analysing such acoustic emissions can be done non-invasively, and does not require very expensive equipment (compared with, say, MRI). Therefore, a system for doing this could potentially be an inexpensive, accessible and portable tool for monitoring cartilage degradation and spotting the early signs of the onset of osteoarthritis.
In this paper, we report recent work on the development and testing of a system for the detection, monitoring and analysis of acoustic emissions from knee joints, with a view to using these for the early detection of the symptoms of osteoarthritis in sportspeople. Preliminary results are presented, an initial analysis of these is discussed, and modelling the decay of sound oscillations following impulses occurring naturally during knee exion proposed as a means of inferring the state of health of the knee cartila