MEASURING SCAPULAR MOVEMENT USING THREE-DIMENSIONAL ACROMIAL PROJECTION.

Abstract

Background The current jig standard for measuring scapulohumeral movement of the shoulder complex only allows for static measurements of scapular positioning. Methods We compared scapular positioning as determined by a scapular jig with that projected from a marker triad placed on the acromion process of the scapula using an infrared motion capture system. Nine individuals performed abduction and scaption shoulder movements while arm and shoulder positioning were recorded during static and dynamic trials. Virtual scapulae were projected from surface marker triads on participants' acromia and compared with the position of three scapular landmarks identified by placement of a customized plastic jig. Static and dynamic positioning at a series of angles was compared to the jig standard to determine validity of the technique. Results There were no statistically significant differences between the virtual projections and jig standard for scapular external rotation, upward rotation, and anterior-posterior tilt planar measurements. Dynamic positioning correlated well with static projections, but virtual scapular projections generally overestimated upward rotation of the scapulae, as compared to the jig. This could potentially be corrected through the development of a linear correction factor. Conclusion Acromial projection allows for reproducible, non-invasive dynamic video motion capture of the scapula.