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Section: New Results

Shoulder biomechanics

Participant : Armel Crétual [contact] .

Shoulder hyperlaxity (SHL) is considered a main risk factor for shoulder instability and can be associated with different clinical shoulder instability presentations, such a multidirectional instability or unstable painful shoulder. Interestingly, quantification of shoulder laxity and hyperlaxity, particularly during physical examination, still remains an unsolved problem. Indeed, it is still frequently evaluated only through mono-axial amplitude, in particular using external rotation of the arm whilst at the side (ER1). We previously showed that this parameter is sensitive to inter-operator variability.

Therefore, we proposed a novel way to account for global shoulder mobility, the Shoulder Configuration Space Volume (SCSV) corresponding to the reachable volume in the configuration space of the shoulder joint [10] . In mechanics and robotics, the configuration space is the set of all reachable combination of coordinates. Considering the shoulder as the single joint between thorax and humerus instead of a combination of 4 actual joints (gleno-humeral, thoraco-humeral, scapulo-thoracic and sterno-clavicular), these coordinates are based upon the three joint angles defined by the International Society of Biomechanics (ISB) recommendations as plane of elevation orientation, elevation and axial rotation.

Then, this new index was examined through correlation to shoulder signs of hyperlaxity [19] for which we have shown a link with instability in patients who received a surgical procedure [18] .