We examined the effects of carpal tunnel syndrome on thumb strength in multiple directions to test the hypothesis that a force deficit would be most severe in directions associated with abduction. Twelve right-handed women with carpal tunnel syndrome in the right hand, and 12 age-matched, gender-matched, right-handed control subjects were included. Thumb strength was measured in all directions in the transverse plane perpendicular to the longitudinal axis of the thumb. Force envelopes, the boundary of maximal force magnitude, were constructed using the directional forces. The force envelope or envelope area did not differ between the control subjects and the patients with carpal tunnel syndrome. The percentage contributions of force quadrant to the envelope area did not differ between the patients and the control subjects. Our results support the concept that thumb strength is relatively preserved with carpal tunnel syndrome, and failed to support the traditional belief that carpal tunnel syndrome preferentially impairs thumb abduction strength. The data suggest the commonly used testing of thumb abduction strength may not be an effective means to evaluate the existence or severity of carpal tunnel syndrome.
Level of evidence: Diagnostic study, Level III (study of nonconsecutive patients; without consistently applied "gold" standard). See the Guidelines for Authors for a complete description of levels of evidence.