Use of intrinsic thumb muscles may help to improve lateral pinch function restored by tendon transfer

Joseph D. Towles*, Vincent R. Hentz, Wendy M Murray

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Background: For surgical reconstruction of lateral pinch following tetraplegia, the function of the paralyzed flexor pollicis longus is commonly restored. The purpose of this study was to investigate if one of the intrinsic muscles could generate a more suitably directed thumb-tip force during lateral pinch than that of flexor pollicis longus. Methods: Endpoint force resulting from 10 N applied to each thumb muscle was measured in eleven upper extremity cadaveric specimens. We utilized the Kruskal-Wallis test (α = 0.05) to determine whether thumb-tip forces of intrinsic muscles were less directed toward the base of the thumb, i.e., proximally directed, than the thumb-tip force produced by flexor pollicis longus. Additionally, a biomechanical model was used to assess the effect of an increase in tendon force on intrinsic muscle endpoint forces. Findings: All of the intrinsic muscles produced thumb-tip force vectors, ranging from 127° to 156°, that were significantly (P < 0.009) less proximally directed than that of flexor pollicis longus (66° (46°)). A biomechanical model predicted that intrinsic muscle thumb-tip forces would vary non-linearly with tendon force. A 2-fold increase in tendon force produced, on average, a 2.3-fold increase in force magnitude and an 8° shift in force direction across all intrinsic muscles. Interpretation: This study suggests the possibility of using an intrinsic muscle, e.g., the flexor pollicis brevis (ulnar head), instead of flexor pollicis longus, to produce a more advantageously directed thumb-tip force during lateral pinch in the surgically-reconstructed tetraplegic thumb and thus potentially enhance function.

Original languageEnglish (US)
Pages (from-to)387-394
Number of pages8
JournalClinical Biomechanics
Issue number4
StatePublished - May 1 2008


  • Intrinsic thumb muscles
  • Lateral or key pinch
  • Tetraplegic hand
  • Thumb muscles
  • Thumb-tip force
  • Upper extremity tendon transfer

ASJC Scopus subject areas

  • Biophysics
  • Orthopedics and Sports Medicine


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