Performing cadaveric experiments on the thumb to determine the potential contribution of thumb muscles to the endpoint force during grasping

Experimental measurements that broaden our understanding of human haptics will improve our ability to represent digit-object interactions in a virtual environment and to interpret grasp, manipulation and exploration phenomena as the use of haptic devices becomes common place to assess the function of the upper extremity. We performed cadaveric experiments to quantify the potential contributions of thumb muscles to the thumb-tip force produced during a static grasping task. Notably, we found that the flexor pollicis longus (FPL) and the ulnar head of the flexor pollicis brevis (FPBu) produced the largest force components perpendicular to the plane of the thumb nail and toward the object that would be grasped. The other muscles primarily produced forces either in the opposite direction or in the plane of the thumb nail. These findings suggest that FPL and FPBu are more suited to facilitate a stable grasp than the other muscles. These findings would help to explain the difficulty that a person, after neurologic injury to the thumb, would likely have grasping objects in a virtual environment.