Anatomy and function of lumbrical muscles.

The lumbrical muscles are unique in having their origin and insertion on tendons. The lumbricals assist in metacarpophalangeal joint flexion; they contribute to interphalangeal joint extension by acting as deflexors of the proximal interphalangeal joint. Anatomically, they are highly specialized in terms of their architectural properties, with a small physiologic cross-sectional area but long fiber length. Their unique properties indicate that they are probably important in fast, alternating movements and fine-tuning digit motion.