A validation study using inertial sensor technology for knee function during gait analysis

The use of body-fixed inertial sensors to analyze human movement may prove useful in the medical field. Improving orthopaedic device design, diagnosing musculoskeletal disorders, and rehabilitation assessment could all benefit from a mobile gait analysis system based on inertial sensors. More specifically, patients recovering from lower limb corrective surgeries tend to adjust gait patterns to accommodate pain, a condition referred to as antalgic gait. Currently there is no quantitative method available to assess recovery for this patient population during post-operative management. A comparison of an inertial two sensor system with the camera-based industry standard has confirmed it as a viable method for lower limb motion analysis during normal gait.;The inertial sensors consist of multiple accelerometers, gyroscopes and magnetometers used to obtain raw data, which is manipulated to calculate dynamic kinematic parameters, specifically the three-dimensional (3D) knee angles. Two validation studies were conducted to determine the precision and accuracy of the measurement of three-dimensional knee angles of a six-sensor inertial measurement unit system (IMU). The first validation study used a robotic arm to simulate a typical gait cycle that would be seen in a clinical laboratory environment. The purpose was to eliminate the intra- and inter subject variability seen in patients where there can be soft tissue artifact, trial to trial variability, and even stride to stride variability. The robot was programmed with the expected three-dimensional knee angles along with the hip flexion and extension for a more repeatable performance between each trial. The robotic arm joint measurements mimicked the flexion/extension (FE), varus/valgus (VV), and internal/external rotation (IE) of the knee. IMU knee angle measurements were compared to the robotic arm joint measurements at key points of interest in the gait cycle.;In the second study, the six sensor IMU system was compared to the gold standard camera based system in a clinical gait analysis setting. The IMU system allowed for simultaneous measurement of both lower limbs during a each trial of gait analysis. The aim of this study would be to determine the reliability of kinematic parameters of the lower limb, specifically 3D knee angles which are clinically appropriate for assessing knee function of lower limb fracture patients during the post-operative time span critical in normal gait recovery.;The IMU system correlated well with the measured robotic arm positions for the all three angles with less than 1degrees difference for all points during the gait cycle except at toeoff (TO) and the initial swing phase. An overestimation at the local minimum occurred at the TO position for FE and increased with each stride. The average difference at the minimum occurring just before TO for FE was 2.9 degrees. During the initial portion of the swing phase after TO, average differences were 7.0 degrees for IE and 12.0 degrees for VV. Results varied from subject to subject for the camera based system comparison. The mean, standard deviation (SD), and extreme values of the RMS for both the right and left leg are reported in Table I for each subject's 3D knee angles. The RMS maximum mean value for FE, VV, and IE angles were 13.41degrees, 9.83 degrees, and 11.09 degrees respectively. The minimum mean value for FE, VV, and IE angles were 1.59 degrees, 2.98 degrees, and 2.03 degrees respectively.