Unobtrusive ambulatory estimation of knee joint angles during walking using gyroscope and accelerometer data - a preliminary evaluation study

Osteoarthritis has the highest prevalence in the elderly population, with a rising tendency. Currently often special gait labs are used for objective diagnostic assessment of functional motion deficits or treatment outcome, e.g in patients suffering from gonarthrosis. The artificial lab setting and short measurement periods affect the explanatory power of this method. Inertial multi-sensor systems in contrast allow for monitoring human gait independent of a lab setting. However, recent approaches concerning important knee function parameter analyses have not been validated for long-term monitoring yet.The aim of our research for this paper is to evaluate our wearable joint kinematics measurement system (KINEMATIC-WEAR) for assessing maximum knee joint angles during extended periods of normal walking. Our prototype consists of small multi-sensor nodes with combined tri-axial accelerometer, gyroscope and magnetometer which were attached with kinesiotape to the thigh and shank of a subject while walking at different speeds on a treadmill. The computed maximum knee joint angles were compared with reference measurements performed by a physician on video frames captured during walking, as was the correlation between both value sets. Our results show an excellent correlation of 0.96 between clinical reference measurements and our computed angles. While the accuracy is good for slow walking speeds of 0.28 m/s (lkm/h, mean error: 2.6 deg±1.5) and 0.56 m/s (2km/h, mean error: 2.0 deg±1.6), our algorithm over-estimates the angles by 6.3±3.6 degrees at 0.83 m/s (3 km/h), likely induced by soft tissue motion during heel-strike. Our preliminary results show that our system allows for unobtrusive, long-term out-of-Iab monitoring of knee joint motion parameters. Further studies are necessary to evaluate the system for arthritis patients.