Sex, Load, And Rotator Cuff Tear Severity Impact Functional Task Performance: A Computational Modeling Study

PURPOSE: Rotator cuff tears (RCT) negatively affect activities of daily living (ADL) for older adults. The influence of RCT severity, the role of sex, or the effect of load in ADL performance is not well known. This study examined the effects of RCT severity, external load and sex during a loaded hair comb task on kinematics of older adult males (OAM) and females (OAF) using a computational model. METHODS: An upper extremity model in OpenSim (v.3.3) software was used to determine hand position throughout the use of a hair comb task. Separate models were developed to represent average adult female and adult male (ages >65y) and modified to represent 4 different RCT severities: none, partial, full, and massive tear. Seven external loads, representing household objects, were applied as a point force at the hand center of mass in the negative vertical direction: 0 N to 66.7 N. Hair comb kinematics from 9 participants in a prior study were used as input to Computed Muscle Control (CMC), followed by point kinematics to determine hand position. All permutations of sex, RCT severity, and load were studied. Root mean square error (RMSE) was calculated for differences in hand position between input kinematics and model predictions. RMSE was computed in each global plane and the resultant direction using MATLAB software. Average ± standard deviation RMSE was compared across sex, RCT severity, and external load groups. RESULTS: There was greater hand deviation for OAF (RMSE 0.228 ± 0.119) than OAM (RMSE 0.144 ± 0.112). The largest hand deviation for OAF occurred in the negative vertical direction with the highest external load (RMSE 0.132 ± 0.088) and massive RCT severity (RMSE 0.228 ± 0.119). CONCLUSIONS: OAF have greater hand deviation than OAM during a hair comb task. These differences increase during simulations with higher loads and greater RCT severity. These results will help direct the rehabilitation approach of older adults with RCT, including activity modification and secondary muscle strengthening exercises. Ongoing work is studying muscle compensation strategies during other ADLs to identify possible rehabilitation targets.