Sample entropy (SE) has relative consistency using biologically-derived, discrete data >500 data points. For certain populations, collecting this quantity is not feasible and continuous data has been used. The effect of using continuous versus discrete data on SE is unknown, nor are the relative effects of sampling rate and input parameters m (comparison vector length) and r (tolerance). Eleven subjects walked for 10-minutes and continuous joint angles (480 Hz) were calculated for each lower-extremity joint. Data were downsampled (240, 120, 60 Hz) and discrete range-of-motion was calculated. SE was quantified for angles and range-of-motion at all sampling rates and multiple combinations of parameters. A differential relationship between joints was observed between range-of-motion and joint angles. Range-of-motion SE showed no difference; whereas, joint angle SE significantly decreased from ankle to knee to hip. To confirm findings from biological data, continuous signals with manipulations to frequency, amplitude, and both were generated and underwent similar analysis to the biological data. In general, changes to m, r, and sampling rate had a greater effect on continuous compared to discrete data. Discrete data was robust to sampling rate and m. It is recommended that different data types not be compared and discrete data be used for SE.

The present study aimed at devising a data processing procedure that provides an optimal estimation of the 3-D instantaneous orientation of an inertial measurement unit (IMU). This result is usually obtained by fusing the data measured with accelerometers, gyroscopes, and magnetometers. Nevertheless, issues related to compensation of integration errors and high sensitivity of these devices to magnetic disturbances call for different solutions. In this study, a method based on the use of gyroscope data only is presented, which uses a Weighted Fourier Linear Combiner adaptive filter to perform a drift-free estimate of the 3D orientation of an IMU located on the lower trunk during walking.

Several surgical approaches for total knee arthroplasty (TKA) have been developed to minimize soft-tissue trauma and expedite functional recovery. A group of 61 subjects undergoing computer-navigated, minimally invasive TKA were randomized to receive a mini-parapatellar, standard parapatellar, mini-midvastus (MV), or mini-subvastus approach. Before and after treatment, subjects were asked to negotiate stairs in a self-selected manner. This study used the manner of stair negotiation (i.e., use of handrail, step-over-step, step-by-step) as a proxy for functional ability. Subjects who received TKA through a mini-MV approach demonstrated a significantly lower level of function at 2 and 4 months. If early functional recovery is a goal of TKA, surgeons should be cautious when considering the mini-MV approach, which was found to be inferior to other approaches in this study.