Predicted effects of metacarpal shortening on interosseous muscle function

Matthew J. Meunier, Eric Hentzen, Michael Ryan, Alexander Y. Shin, Richard L. Lieber

Research output: Contribution to journalArticle

48 Scopus citations

Abstract

Purpose Metacarpal fractures are common in hand surgery. Metacarpal shortening ranging from 2 mm to as much as 10 mm has been deemed acceptable in the literature. We examined the effect of metacarpal shortening on interosseous muscle architecture and predicted force production capacity based on the standard muscle length-tension curve (commonly known as the Blix curve). Methods The dorsal interosseous muscles between the middle and ring finger metacarpals from 9 adult human cadaver hands were exposed and studied. The ring finger metacarpal was translated proximally in 2-mm increments in relation to a stationary middle finger metacarpal. Digital images were obtained and analyzed to define the length and orientation of individual muscle fibers with each incremental change in position. Results Interosseous muscle fiber length increased and pennation angle decreased uniformly with increasing proximal translation of the ring finger metacarpal. At 10 mm of shortening the fiber length had increased to 20.8 ± 1.8 mm, or to approximately 125% of optimum fiber length, and the pennation angle had decreased to 6.7°± 2.2°or by approximately 50%. Conclusions The interosseous muscles have been shown to have a high fiber-to-muscle length ratio. This ratio indicates that these muscles function optimally over a short range of lengths, leaving them vulnerable to derangement in function owing to alteration in the surrounding bony architecture. Based on the standard muscle length - -tension relationship we had predicted a steady linear decrease in interosseous power with proximal translation of the metacarpal. The results indicate an initial linear progression with a plateau at approximately 8 mm of shortening. At 2 mm of shortening there is an approximately 8% loss of power generation, at 10 mm of metacarpal shortening we predict the interosseous muscle to be capable of only approximately 55% of its optimum power compared with the resting position.

Original languageEnglish (US)
Pages (from-to)689-693
Number of pages5
JournalJournal of Hand Surgery
Volume29
Issue number4
DOIs
StatePublished - Jul 1 2004

Keywords

  • Biomechanics
  • fracture fixation
  • muscle architecture

ASJC Scopus subject areas

  • Surgery
  • Orthopedics and Sports Medicine

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