A study evaluating differences in 3D upper limb kinematics and surface electromyography measures in adults with and without facioscapulohumeral dystrophy.

Background: Facioscapulohumeral dystrophy (FSHD) is a rare disease that causes progressive muscle wasting and loss of function, with the upper limb being the most affected. Factors leading to loss of arm function are poorly understood. A better understanding of movement profiles determined using 3D movement analysis could help inform treatment selection and development; however, limited evidence is available for combined 3D movement and surface electromyography (sEMG) studies that include the scapula. Our null hypothesis is that there are no differences between the movement and muscle activity of people with FSHD and age- and sex-matched controls (two-tailed). Methods: Adults were recruited into three groups: (1) FSHD with scapulothoracic arthrodesis (scap fix); (2) FSHD and no surgery (no surgery); or (3) age- and sex- matched control group (CG). Participants attended a single session and carried out seven motion tasks in which their movements and muscle activity was measured using 3D movement analysis and sEMG. Descriptive statistics and normalized movement and muscle activity plots were used to compare joint angles, sEMG patterns, and scapulohumeral rhythm between groups. Results: Data were collected for 14 participants (10M:4F), seven with FSHD and seven age- and sex- matched controls, with a mean (standard deviation) age of 41.6 (15.7). The FSHD (no surgery) group achieved lower mean (standard deviation) thoracohumeral elevation, most notably in flexion, 74.6° (29.2), and abduction 80.8° (31.2), compared to the CG, who achieved 126.9° (12.7) and 130.1° (10.8), respectively Despite these differences, range of movement for glenohumeral elevation was similar between groups. Considerable variability across the acromioclavicular and sternoclavicular joints was noted in all FSHD groups, with no clear between group differences. Scapulohumeral rhythm was reduced in the FSHD (no surgery) group. FSHD groups demonstrated prolonged and higher normalised activity levels of the trapezius, anterior deltoid, and infraspinatus muscles. This was most evident during the middle of the motion being carried out. Discussion: Evaluations that focus on arm position alone are insufficient for explaining why people with FSHD lose arm function. People with FSHD had lower thoracohumeral elevation angles compared to the CG, and the limited elevation was a result of altered scapula rather than glenohumeral joint kinematics. Timing and normalized sEMG levels for the FSHD group was variable, with no clear between-group differences. The scapular and muscle activity patterns observed in the FSHD group were heterogenous, which made identification of between groups difficult in our limited sample size. Conclusion: People with FSHD demonstrated limited arm movements primarily from altered scapular kinematics. The scapular and muscle activity patterns observed in the FSHD group were heterogenous which made identification of between groups difficult in our limited sample size.