Meeting Abstract
Bats move their wings in dynamic, three-dimensional patterns. These motions originate partly from complex interactions between the bones that make up the shoulder and arm. Some research has proposed transient, cyclic contact between the scapula and humerus beyond the glenohumeral joint. This might serve to transmit force, allowing muscles inserting on the scapula only to add to flight power by remotely actuating the humerus. Since these proximal elements of the wing skeleton are deeply embedded in muscle, radiographic techniques are necessary to directly explore their kinematics. We used XROMM (X-Ray Reconstruction of Moving Morphology) to reconstruct in vivo scapular and humeral motion in Carollia perspicillata at high spatial and temporal resolution. Following validation, we were able to model the glenohumeral joint as a ball and socket articulation. We found that movements of the humerus with respect to the scapula did not account for the full extent of the wing’s motion in the transverse plane, indicating substantial contributions from a highly mobile scapula. While we observed periodic association between the features on the humerus and scapula, the elevation of the humerus relative to the scapula did not remain constant during these periods. This is inconsistent with a primarily force-transmitting role for the interaction. Instead, contact appeared to coincide with periods of limited long-axis rotation of the humerus. This result suggests a mechanism for constraining the humeral head, preventing translation and intermittently constraining its rotation with respect to the glenoid. Such traits may provide added stability to this crucial articulation during the downstroke. Funded by AFOSR.
