A detailed study of metacarpophalangeal flexion and interphalangeal
extension movements of 141 fingers with complete intrinsic-muscle paralysis
due to leprosy showed that long flexors and long extensors produce movement
at the metacarpophalangeal and proximal interphalangeal joints
simultaneously, and not successively as is generally believed. The amounts
of flexion resulting from long flexor activity are almost equal at the two
joints and metacarpophalangeal flexion is achieved without excessive
flexion of the proximal interphalangeal joint, but this is masked by the
claw-finger deformity. The movement resulting from activity of the long
extensor is complex and there are three or more qualitatively different
patterns of extension. Although the long extensor produces simultaneous
extension at the metacarpophalangeal and proximal interphalangeal joints,
the latter consistently lags behind the former so that full extension is
not achieved at the proximal interphalangeal joint even when the
metacarpophalangeal joint is maximally extended. The diverse patterns of
extension are not related to duration of degree of clawing or to any
particular finger.