A comparison of non-invasive methods for estimating scapular kinematics in typically developing adolescents
Date
2016
Authors
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Publisher
University of Delaware
Abstract
Typical shoulder motion depends on proper contributions of both the scapulothoracic (ST) and glenohumeral (GH) joints. Abnormal scapular kinematics are related to a variety of shoulder pathologies such as impingement syndrome and rotator cuff tears. Identification of scapular dyskinesis and evaluation of subsequent interventions depend on the ability to properly measure ST and GH motion. ☐ In upper extremity literature, the recommended dynamic measurement method is the acromion marker cluster (AMC). While it enjoys widespread use, this approach yields large errors at higher levels of humeral elevation and has also been shown to be inaccurate in populations with pathological upper extremity motion. Recently, an approach that develops individualized regression equations has been proposed as an alternative to the AMC. This technique utilizes the relationship between ST orientation, humerothoracic (HT) orientation and acromion process (AP) displacement derived from a set of static positions to predict ST orientations from HT and AP measures in motion. These individualized regressions demonstrated promising results for healthy adults; however, this method has not been validated on children or in populations with pathological motion. Furthermore, this approach has not yet been compared to the more conventional AMC. ☐ This study compared the AMC to the regression approach in typically developing adolescents performing a series of functional tasks. The accuracy of each method was evaluated against palpated ST angles and error trends were examined for relationships to the amount of HT motion. Following the static accuracy evaluation, measurements by the AMC were compared across both static and dynamic conditions. Finally, the two methods were compared during dynamic execution of the functional tasks, and differences were evaluated in the context of the previous analyses and also with respect to the amount of HT motion. ☐ The results of this study revealed that the regression approach yielded smaller errors than the AMC along each axis of motion and in every position. The performance of the regression approach suffered, however, when applied to positions outside of the range of motion present in the set of positions used to build the equations. The AMC demonstrated significant errors in capturing motion about the ST internal rotation axis and a trend toward overestimation of ST posterior tilt. These directional biases were exacerbated from static to dynamic conditions. In motion, the AMC and regression methods differed considerably in many subjects. On average, the AMC produced higher upward rotation angles, lower internal rotation angles and higher posterior tilt angles than the regression approach. Upon examination of many individual trials with extreme differences, the regression approach was typically within one standard deviation of the corresponding static mean palpated angle, while the AMC often produced angles that exceeded two standard deviations from the static mean. Dynamic differences between methods were found to be related to the amount of AMC error in the corresponding static position. Additionally, the two methods diverged for ST internal rotation and posterior tilt with increased HT displacement. When the dynamic results were examined in the context of the static validation, it appeared that the regression approach outperformed the AMC for functional tasks in the adolescent population. These findings can inform future researchers as to the best choice of scapular kinematic measurement method and provide context for interpretation of scapular kinematics resulting from the use of either approach.