A Novel Method for the Objective Assessment of Thenar Atrophy

摘要

Purpose: Although thenar atrophy is caused by a variety of clinical conditions, it is commonly associated with carpal tunnel syndrome. Thenar atrophy has been mostly assessed subjectively. The purposes of the study are to test a simple, novel, objective and quantitative test for the assessment of thenar atrophy; and to correlate this test with subjective evaluation of thenar atrophy.Methods: The apparatus consisted of a box with a clear glass sheet on the top uncovered surface, with a digital camera placed in the base of the box. Group 1 included 106 healthy volunteers with a total of 212 hands. Group 2 was formed from 36 patients with a total of 72 hands with carpal tunnel syndrome. Thenar atrophy was classified subjectively as none, mild, moderate and severe. Patients and subjects were asked to press their hands facing down on the glass sheet and digital photos were taken. The technique relies on the fact that the area where pressure is exerted on the palm blanches. Photos were transferred to photo processing software. After enhancement the photos were transferred to an image analysis software. The thenar area (A) and the rest of the palm area (B) were measured. The thenar ratio was calculated as A divided by A plus B multiplied by hundred.Results: Hands with thenar atrophy had a statistically significant lower thenar ratio than healthy hands (19.9±6.7 vs 35.6±8.0; P value <0.0001). Subjective assessment of atrophy correlated with the thenar ratio.Conclusions: This method can be used as a simple objective test for the assessment and follow-up of thenar atrophy. Introduction The thenar eminence constitutes the intrinsic muscles of the hand that are responsible for complex movements of the thumb. Atrophy of thenar muscles can be caused by a variety of clinical conditions. Although thenar atrophy is commonly associated with carpal tunnel syndrome (CTS)1; it is also associated with liver cirrhosis2, thoracic outlet syndrome3 and Weill-Marchesani syndrome4. In CTS, thenar atrophy is usually associated with longstanding or severe cases5,6,7. However, the finding of thenar atrophy has been found to have limited or no value in distinguishing patients with CTS from those without it8. The main reason for this is the low sensitivity of clinical thenar atrophy as a diagnostic test (0.04 to 0.28)9,10,11. On the other hand, thenar atrophy has been reported to have a high specificity for CTS (0.82 to 0.99)9,10,11. Subjective evaluation of thenar atrophy has been reported widely in the literature in order to evaluate the outcome of carpal tunnel release 12,13,14,15,16. Some authors have graded the subjective evaluation of thenar atrophy as none, mild to moderate or severe based on the bulk and contour of the thenar eminence13. There have been a few attempts to standardize and assess thenar atrophy objectively. Magnetic resonance imaging showed moderate correlation with thenar atrophy17. Tuncali D et al18 developed the thenar index for the objective assessment of thenar atrophy using static hand imprints with high specificity and acceptable sensitivity for thenar atrophy.The aims of this study are to test a simple, novel, objective and quantitative test for the assessment of thenar atrophy, and correlate this test with subjective evaluation of thenar atrophy. Patients and methods Patients and subjectsDigital photos of both hands pressed on a glass sheet using the apparatus described below were taken from volunteers (Group 1) and patients with CTS (Group 2). Group 1 included healthy adult subjects who did not suffer from any medical problems, peripheral or central nervous system disorders and did not have a past history of trauma to the upper extremity. Group 2 included patients with bilateral CTS awaiting carpal tunnel release surgery. However, not all patients had clinical evidence of atrophy. Thenar atrophy was assessed by one of the authors (LAG) as none, mild, moderate and severe. The age, gender, hand dominance and occupation of each su