The Effects of Joint Posture and Segment Lengths on the Thumb-Tip Force Produced by Flexor Pollicis Longus

The ability to hold an object between the thumb and the lateral aspect of the index finger (lateral pinch) is an important aspect of hand function. Previous studies suggest that current biomechanical models of the thumb do not accurately predict lateral pinch force [1, 2]. These studies modeled the thumb using simplified joint descriptions based on orthogonal and intersecting axes of rotation. A detailed anatomical study indicates that the axes of rotation of the thumb are actually both non-intersecting and non-orthogonal [3]. It has also been reported that the anatomical variability observed in the data support four different representations of thumb kinematics, all with non-intersecting and non-orthogonal axes [4].