Quantitative analysis of the intrinsic muscles of the hand

As part of a study involving three‐dimensional modeling of the hand, the intrinsic muscles of the hand were evaluated quantitatively to estimate the range of muscular forces crossing the fingers. The Brand method of dissection allowed determination of muscle volume, fiber length, and physiologic cross section to estimate the maximal force. The intrinsic muscles were grouped by components on the basis of their origins in the trilaminar scheme of Cunningham as (1) dorsal abductors from the central ray, exemplified by the bipennate dorsal interossei; (2) the intermediate layer consisting of inter‐phalangeal joint extensors, exemplified by the unipennate palmar interossei with insertions into the extensor expansion; and (3) a superficial layer of adductors arising from the third metacarpal ridge, referred to as contrahentes. The fiber lengths of either component of the dorsal interossei averaged 1.3 cm. The intermediate layer of muscle, numbered as flexores breves (FB), included the palmar interossei FB_4,7,9; the superficial components of the dorsal interossei FB_3,5,6,8; and the accessory adductor pollicis FB₂. Fiber lengths averaged 1.7 cm. The superficial heads of the flexor pollicis brevis and abductor digiti quinti are possibly the border representations of the intermediate layer as FB₁ and FB₁₀. The thenar muscles made up 37%, dorsal interossei 24%, palmar interossei (flexores breves) of the fingers 16%, lumbricals 7%, and hypothenar muscles 16% of the total intrinsic muscle mass. The ratio of muscle mass to fiber length, the physiologic cross‐sectional area, is useful in estimating available force. This quantitative analysis of the intrinsic musculature may find application in the understanding of hand function and biomechanics.