Motion analysis protocol for the clinical evaluation of playing-related musculoskeletal disorders in violinists, violists, and cellists

Rationale: Instrumentalists often suffer from playing-related (neuro-)musculoskeletal disorders (PRMDs). Most common PRMDs in string players are related to upper-body regions. Motion analysis has proven to be helpful in the evaluation of functional disorders. It was already shown that it is a valid and clinically feasible tool for accurate, repeatable, and objective assessments of functional movement in string players. Thus, it may guide clinicians to improvements in injury prevention, diagnosis, and treatment. Nevertheless, its application in clinical consultation is still very uncommon. For this reason, there is a lack of well-established motion analysis protocols for the examination of PRMDs in string players using advanced biomechanical instruments in clinical settings. Purpose: To demonstrate the development and application of a motion analysis protocol for the evaluation of functional upper-body movements in violinists, violists, and cellists in a clinical setting for the investigation of PRMDs. Approach: The protocol was to be integrated into a clinical reasoning process for testing clinical hypotheses and evaluating treatment outcomes in physiotherapy. As a starting point, a primary clinical question was defined, and then, specific upper-body symptom regions as well as measurement parameters (relative rotation angles and muscle activities over time) were identified. Subsequently, involved segments, joints, and muscles were assorted. For quantification of upper-body kinematics a novel, marker-based method was used which provides multi-segmented shoulder and spine models while providing simple application. Based on that, a comprehensive mechanical model of the upper body as well as the associated coordinate systems and rotation sequences were specified. This further guided both, the definition of a custom-made marker set as well as the selection and placement of surface electrodes. Furthermore, required static and functional calibration trials as well as movement tasks for functional assessment were specified. Finally, advanced approaches, such as a comprehensive kinematic model and functional determination of joint centers and axes were established for extraction. Then, outcome parameters and their form of representation were determined for further analysis and interpretation. The application of the method first includes the selection of segments, joints, and muscles to examine – originating from one or more clinical (working) hypotheses or symptom regions. This drives the configuration and placement of required surface markers and electrodes. Then, the required calibration and functional movement trials are executed. After measurement, the outcome parameters get extracted and analyzed. Based on the results the hypothesis is discarded or verified. Content: The method was applied to a violinist (female; 18 years old; 13 years of experience; practicing 2 to 3 hours per day, 7 days per week) with playing-related demands in the left cervical-shoulder-arm region. Subjective findings indicated that the pain regularly occurred after 30 minutes of playing fast or difficult musical pieces. Physical examination showed that strength testing of left serratus anterior muscle caused pain, lower trapezius muscles seemed weak, forearm muscles were sensitive to pressure, movement of the cervical spine to the left was reduced, and upper limb neural tension test was noticeable. This led to the following working hypothesis: Neck-related arm pain with neurodynamic component and motor control problem in the scapulothoracic region. Thus, left-sided cervical-shoulder-arm region was selected for functional examination. Optoelectronic motion capture system and surface electromyography were used for data collection. Static and function calibration trials as well as functional assessment trials (chromatic scale with different tempi) were conducted. Afterwards, data was further processed, and outcome parameters were extracted. Results showed that greater tempo and pain had an impact on the rotation angles and muscle activities. They led to less overall joint movement and range of motion, to less muscle activity in the forearm muscles, and to greater activity inputs in the scapulothoracic muscles. Overall, greater tempo and pain led to a different motor program which verified the working hypothesis. The procedure was repeated after treatment (four appointments over one week) with manual therapy, training, and education. The pre-/post-interventional comparison showed changes in the motor program. There was noticeable higher mean activity in upper trapezius and deltoid muscles and simultaneously less in the remaining ones. In addition, only marginal differences in ranges of motion and muscle activity inputs were found between tempi. The playing style appeared to be more stable now. Overall, it appeared that nearly the same motor program was used for each tempo. Clinical Implications: Potential applications are intraindividual evaluations of simultaneously joint and muscular function in string players during clinical consultation. It is intended to contribute to the diagnosis of PRMDs in terms of an objective, comprehensive and yet clinically feasible diagnostic assessment as well as pre-post-intervention outcome evaluation. Nonetheless, motion analysis must be used with care in clinical decision making. Motion data is subject to both, intraindividual variations, and measurement errors. In addition, the smallest clinically relevant changes are not clear yet. Therefore, results should only be interpreted together with other clinical findings