Thumb movements, motions, and moments.

An understanding of the movements of the thumb is essential for understanding thumb function and pathology and for planning therapeutic interventions. The thumb has three joints, which move about axes of rotation. The carpometacarpal and metacarpophalangeal joints have two offset axes of rotation and the interphalangeal joint has one. The thumb muscles act about these axes, and imbalances resulting from paralysis are explained by this model. The effects of tendon transfers and splints can be predicted by analyzing their effects at each joint and axis.