Functional 3-D reach measurement for shoulder impairments

Purpose: Reach is an important human capability that is used in the design of workspaces as well as a measure of human function during activities of daily living and becomes even more critical in the presence of injury and physical challenges. The presence of an injury or a disease to the joint can require design accommodation which is related to reach. While there are many known factors that affect human maximum reach in industrial applications, little is known about the effects of joint disease and medical treatments (surgery) of joint disease. Our lab has developed a 3-D motion capture methodology to quantify these effects on the maximum reach envelope. The data capture system also allows for the extraction of the typical clinical measures of ab-adduction, horizontal flexion-extension and sagittal plane flexion-extension. Specifically the study examined the maximum reach envelope between asymptomatic and participants with full-tear shoulder injuries. Methods: Reach envelope data has been collected asymptomatic and symptomatic participants using the Computerised Potentiometric System for Anthropometric Measures (CPSAM) (Das, Kozey et al. 1994). The system uses the linear measurement of 4 recording devices to calculate the position of a single point in a 3-D volume. Each participant completed 3 side and front facing trials for each of 3 handheld load conditions; 0, 0.5 and 1.0kg. The 3-D data were collected at 20 Hertz and during a series of trials generating 5400 data points describing the reach envelope for each load condition. For both coordinate systems (Cylindrical and Spherical) a total of 54 equally sized reach panels in were created (Figure 1) and in each case the median R (length) for each bin was calculated to represent the reach. The main effects of reach direction (panel) was determined using a General Linear Model (GLM) Analysis of Variance. The critical alpha was set to be 0.05 and all pairwise post-hoc tests used a Bonferroni correction. Results: For the asymptomatic participants in both spherical and cylindrical coordinate systems, the there was a main effects of load. A Tukey’s Pairwise comparisons show significant decrease in reach compared to the 0 load condition for both load conditions, with no difference between the two load conditions. The reduction in reach with load was approximately 30mm. The analysis pattern for load was the same for absolute and normalized (to arm length) reach lengths. Symptomatic participants had a reduced reach envelope compared to the asymptomatic participants most noticeable at measures close to and above shoulder height. Preliminary comparisons in testing methodology also demonstrated that the symptomatic participants require a greater number of shorter duration collection trials. Symptomatic participants also had small basic range of motion measures. In addition to the median reach lengths for each bin a colour map of typical reach areas was created to provide a simple tool to express reach characteristics for individuals as well as between experimental conditions and groups. Shown in Figure 2 is an example of these colour maps for the asymptomatic participants due to load. If a subject was able to reach a bin, they were added to the count. Red areas indicates where no one reached while green indicates 100% of the participants were able to reach to the panel with a spectrum in between as shown (Figure 2). Similar knowledge translational tools were developed to compare the two groups. Conclusions: Discussion and conclusions: The impact of handheld load on the reach abilities of participants is significant regardless of coordinate system. Normalization of reach data to arm length allowed for better comparison between subjects in terms of range of motion. Spherical coordinates initially show more regions in which the participants were unable to reach compared to the cylindrical bins. Normalization will be required to allow for comparisons of the overall reach envelope for persons of different arm lengths (Delangle, Petiot et al. 2015). With current data there are no issues with arm length limiting reach to the outer z levels in cylindrical coordinates, however as focus is shifted to the outer regions of reach this may change. Many of the participants reach lengths fall just above the greater than 500mm band, so further division would be limiting. Clear differences between the two groups were obtained and the colour maps allow for a simple method to demonstrate these differences.Figure 2Cylindrical and Spherical Colour Maps for 0.0kg Load Conditions.View Large Image Figure ViewerDownload Hi-res image Download (PPT)