Dynamic assist splinting for attenuated sagittal bands in the rheumatoid hand.

The extensor mechanism of the hand is complex, requiring effective functioning of all involved structures, including the sagittal bands. The sagittal bands function to maintain the extensor tendons in midline and to limit their distal excursion. Injury to the sagittal bands or sagittal band attenuation can cause instability and ulnar displacement/subluxation of the extensor tendons into the valleys between the digits and lead to a subsequent loss of active finger extension at the metacarpophalangeal joints. Secondary conditions may also develop, such as swan-neck deformity, as is frequently observed in the rheumatoid arthritis population. To prevent or reduce an extension lag and secondary changes and to maintain the functional use of the hand, a dynamic metacarpophalangeal extension assist splint is necessary. This splint enables extension at the metacarpophalangeal joints, thus enabling the functional use of the hand. This article reviews the biomechanics of the sagittal bands and the corrections that enable finger extension at the metacarpophalangeal joints, thus preventing secondary conditions.