An unexpected shoulder competence: The measurement of the extra-corporeal space

Abstract

The shoulder competence in reaching movement has been known from the time. With this work we wanted to investigate the possible existence of an additional competence of the shoulder with respect to the ability to measure the extracorporeal space, using a new tool known as shoulder proprioceptive rehabilitation tool (SRPT) Observational case-control study on 50 subjects, 25 healthy subjects (HS) and 25 subjects with impingement syndrome (ISS) (2-3 for Neer classification). We proposed to both groups two different tasks using the SRPT: the first one to investigate the integration of visual information and proprioceptive afferents of the shoulder and the second one, inactive and passive modality, to investigate the discriminative proprioceptive capacity of the shoulder eyes closed. The tasks assessed the spatial error made by the shoulder joint in the movement of reaching on sagittal plane. The shoulder showed to have an accurate measurement capability during reaching movement (error of 1.22 cm to 1.55 cmin HS), even with eyes closed. In addition, this ability to measure the extra body space decreased in the impingement group, with a statistically significant difference compared to the healthy group ( P < 0.05 Mann-Whitney test). This difference was not correlated with age, gender, and the intensity of pain. The shoulder has a specific expertise in the measurement of the extracorporeal space during reaching movement that gradually decreased in the impingement syndrome.