Humeral and Scapular Kinematics Correction in Patients With Full-thickness Rotator Cuff Tear: Co-contraction Patterns and Muscle Training, Novel Brace With Neuromuscular Electrical Stimulation

Participants Based on the pilot study, a sample size of 30 patients is calculated to provide 80% power with an effect size of 0.5 (acromiohumeral distance difference = 0.9 mm with and without NMES). Rotator cuff tear subjects will be recruited from the Department of Orthopedic surgery or Department of Physical Medicine and Rehabilitation at National Taiwan University Hospital (NTUH). All subjects will be provided written informed consent before inclusion in the experiment. The study is approved by the NTUH Institutional Review Board.

Instrumentation Three-dimensional electromagnetic motion tracking system The Polhemus 3Space FASTRAK® (Polhemus Inc., Colchester, VT, US), an electromagnetic motion analysis system with MotionMonitor software (Innovative Sports Training, Inc., Chicago, IL, US), will be used to track and collect three-dimensional scapular kinematics. Three sensors are attached to the flat bony surface of the acromion and the sternum with adhesive tape, and to the distal humerus between the lateral and medial epicondyles via Velcro straps with adhesive tape (Figure 1). The other sensors are attached by a stylus to digitalize the 3-dimensional positions on bony landmarks including the sternal notch, xiphoid process, C7 vertebrae, T8 vertebrae, T12 vertebrae, anterior and posterior glenohumeral joint, acromioclavicular joint, root of the spine of the scapula, inferior angle of the scapula, and lateral and medial epicondyles to build the shoulder complex model. Each receiver will be sampled at the rate of 120 updates/second divided by the number of sensors.

Ultrasonography (USG) measurements The BenQ T3300 Tablet Ultrasound System (BenQ Medical Technology Corp., Taipei, Taiwan) with a L154BH linear array 4-15MHz broadband transducer will be used for non-invasive evaluation of AHD in 3 actively abducted positions (at 0°, 60°, and 90° of shoulder abduction). Real-time imaging will be performed with rapid B-mode scanning to generate images with the following settings: gain, 66-68; dynamic range, 75; persistence, 3; QScan, 4, for sharpness and smoothing; gray map, 3; Chroma 0; steer angle, 0; and transducer, 5.5 MHz. The minimum measurement distance of this USG is 1 mm with error less than ± 5%.

Neuromuscular Electrical Stimulation (NMES) The GM300TE COMBO NMES (Gemore Technology Co., Ltd., New Taipei City, Taiwan), a portable machine with dual controllable channels and a manual switch, will be applied to the PM and TM. According to a previous study, muscle force generation is modulated by stimulated frequency, pulse width, and intensity. It linearly increases with stimulated amplitude and pulse duration. The electronics of the unit creates the electrical impulses with an output frequency of 50 Hz and a pulse width of 300 microseconds. The synchronous (S) mode and asymmetrical rectangular wave-pulse are used throughout the experiment. The amplitude is set as muscle motor-level contraction with self-perception of maximal tolerable intensity. The time of tetanic stimulation is 7 seconds with 20-second intervals between stimulations to avoid muscle fatigue. The two circular electrodes are used on each adductor to minimize the stimulated interference with the nearby muscles.

Surface electromyography (sEMG) Muscle activation will be collected at 1000 Hz/channel with the resolution of a 16-bit A/D converter to 16-bit D/A analog converter (Model MP 150, Biopac Systems Inc., Aero Camino Goleta, CA, USA). The system includes pairs of silver chloride circular electrodes (diameter: 10 mm; Ludlow Company LP, Chicopee, MA) with an interelectrode distance of 20 mm (center to center). The collected signals are amplified with a Grass AC/DC amplifier (Model 15A12, Astro-Med Inc., West Warwick, RI, USA) with gain of 1000 dB, a common-mode rejection ratio (CMRR) of 86 dB at 60 Hz, and a bandwidth (-3 dB) of 10 to 1000 Hz. Full bandwidth data (captured by the data acquisition and analysis systems software, AcqKnowledge, Biopac, Aero Camino Goleta, CA) are reduced using a root mean square (RMS) algorithm to produce envelopes with an effective sampling rate of 50 samples per second. The mean of the three trials for each task are calculated for data analysis.