Purpose
The strength of thumb abduction and index finger flexion was measured with a load
cell mounted on a custom-made device. The resulting ratio (thumb-index ratio, or TIR)
was used to diagnose carpal tunnel syndrome (CTS) and was compared with the gold standard
(electrodiagnostic studies). The ratio was used as an internal control in each subject.
Methods
Sixty-one patients (80 hands) with a clinically and electrodiagnostically confirmed
diagnosis of idiopathic CTS and a control group of 51 asymptomatic volunteers (102
hands) were evaluated. The strength of thumb abduction and index finger flexion was
measured in standardized fashion in each hand three times, and the mean was taken
to calculate TIR.
Results
Thumb-index ratio was statistically significant in differentiating between a CTS patient
and a normal control. A TIR of 0.51 had a 98% specificity and a 92% positive predictive
value for diagnosing CTS. Thumb-index ratio greater than 0.51 was neither sensitive
nor specific for diagnosis of CTS. Twenty-four (30%) hands in the investigational
group had a TIR ≤0.51 compared with 1 hand (1%) in the control group. There was a
significant difference in the TIR between hands with a motor amplitude of ≤4.0 mV
and those with an amplitude >4.0 mV.
Conclusions
Most patients with CTS do not appear to have notable weakness of thumb abduction strength.
A TIR ≤0.51 had high specificity for differentiating between CTS and controls. However,
the performance of this device needs to be evaluated in a general population of patients
who present with signs and symptoms of CTS before it would be clinically applicable.
Type of study/level of evidence
Diagnostic III.
Key words
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Article info
Publication history
Accepted:
April 18,
2007
Received:
July 30,
2006
Footnotes
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
Supported by the University of Cincinnati Orthopaedic Research and Education Foundation.
Identification
Copyright
© 2007 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.
