Dispersion of helical axes during shoulder movements in young and elderly subjects

Temporiti, Federico and Cescon, Corrado and Furone, Roberta and Barbero, Marco and Gatti, Roberto (2019) Dispersion of helical axes during shoulder movements in young and elderly subjects. UNSPECIFIED. In: WCPT2019 Proceedings World Confederation for Physical Therapy Congress, 2019, May 10th-13th, Geneva, Switzerland.

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Background: Shoulder complex is characterized by little congruence among its articular surfaces. This condition assigns an important role to neuromuscular control, in order to minimize the displacement of the joint rotation centre during upper limbs movements. This displacement can be due not only by neuromuscular control but also by surface morphology and can be estimated through the analysis of Helical Axes (HAs) dispersion. The different surfaces morphology between young and elderly subjects or the different neuromuscular control that affect the dominant respect non-dominant arm could result in different HAs dispersion. Purpose: The aim of this study was to collect the shoulder HAs dispersion during upper limbs movements performed with dominant and non dominant arms by young and elderly subjects in order to have normative data to use for successive studies addressed to subjects undergone to shoulder rehabilitation or surgery. Methods: Forty volunteers were enrolled in the study (20 young: age 24.8±2.8 years and 20 elderly: age 71.7±6.3 years). Subjects were asked to perform cycles of 15 repetitions of rotation, flexion, elevation and abduction movements performed at constant speed with the dominant and non dominant arm. A cluster of five retro-reflective markers was fixed on each arm, while four markers were placed on the trunk in order to represent them as rigid bodies. The movements were detected with an optoelectronic system, using a sample rate of 100 Hz. Mean Distance (MD) from HAs barycenter and Mean Angle (MA) were used as HAs dispersion indexes. In addition, movements was also divided in portions of RoM in order to evaluate MD and MA for each of them. Results: Young subjects showed lower MD for shoulder rotation, flexion, and elevation movements (p< 0.001) and smaller MA for shoulder rotation movement (p< 0.001) compared to the elderly. Moreover, dominant arm showed lower MD for shoulder rotation (p=0.049) and flexion (p=0.019) and smaller MA for shoulder rotation (p< 0.001) compared to non dominant arm. Finally, MD and MA did not differ among the RoM portions in each of the four tasks. Conclusion(s): Young subjects showed significant lower HAs dispersion in all movements, independently by the portions of RoM. Moreover, HAs dispersion resulted lower in dominant respect to the non dominant arm. This results could be explained by mean of a different neuromuscular control of shoulder complex stability and the joints degeneration described in elderly subjects. Implications: HAs parameters showed to be a promising non-invasive technique to analyze shoulder rotation centre kinematics. The ability to reflect different structural and functional conditions could promote their introduction in clinical field. Our results could be used as reference in further studies addressed to investigate the joint rotation centre displacement at the level of the shoulder complex after rehabilitation or surgery for shoulder instability

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