Search

The extensor apparatus, an aponeurosis that covers the dorsal side of each finger, transmits force from a number of musculotendons to the phalanges. Multiple tendons integrate directly into the structure at different sites and the extensor apparatus attaches to the phalanges at multiple points. Thus, prediction of the force distribution within the extensor apparatus, or hood, and the transmission to the phalanges is challenging, especially as knowledge of the underlying mechanical properties of the tissue is limited. We undertook quantification of some of these properties through material testing of cadaver specimens. We punched samples at specified locations from 19 extensor hood specimens. Material testing was performed to failure for each sample with a custom material testing device. Testing revealed significant differences in ultimate load, ultimate strain, thickness, and tangent modulus along the length of the extensor hood. Specifically, thickness, ultimate load, and ultimate strain were greater in the more proximal sections of the extensor hood, while the tangent modulus was greater in the more distal sections. The variations in mechanical properties within the hood may impact prediction of force transmission and, thus, should be considered when modeling the action of the extensor apparatus. Across the extensor hood, tangent modulus values were substantially smaller than values reported for other soft tissues, such as the Achilles tendon and knee ligaments, while ultimate strains were much greater. Thus, the tissue in the extensor apparatus seems to have greater elasticity, which should be modeled accordingly., Competing Interests: All authors of this manuscript have no conflicts of interest to declare., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Play fighting is a behavior exhibited by juveniles of many mammalian species, but the neurology of this behavior is poorly understood. In the present study lesions of the septal area or control operations were performed in rats at 23 days of age and social play was studied between the ages of 27-41 days of age. Septal lesions increased the frequency of play fighting and play initiation in both sexes; within the lesion and control groups males played more frequently and initiated more play bouts than females. Animals with septal lesions were somewhat lighter in body weight than controls, but since play frequency and body weight were not associated, it is unlikely that changes in body weight caused by the lesions are responsible for the effects of the lesions on play.