Evaluation of Function and Appearance of Adults With Untreated Triphalangeal Thumbs

Purpose: Triphalangeal thumb is a congenital malformation characterized by an additional phalanx of the thumb. Although surgical treatment of this condition is common practice, in the past this was not generally advised. Therefore, a population with an untreated triphalangeal thumb is still present. The purpose of this study is to compare function and appearance of adults with an untreated triphalangeal thumb to a normal population. Methods: Twelve adults with 23 hands with an untreated triphalangeal thumb, unilateral or bilateral, were examined using objective measurements (thumb movement, joint instability, pain, and strength) and subjective measurements (visual analog scale; Disabilities of the Arm, Shoulder, and Hand questionnaire; and Short Form 36 health survey). Results: Objective measurements showed no limitations in range of motion or in grip and pinch strength. No joint instability was found in the interphalangeal joints. Five thumbs had instability in the metacarpophalangeal joint. Strength of the thumb in anteposition was diminished to 64% compared to a normal population. Opposition was diminished to 62%, and metacarpophalangeal joint flexion strength was diminished to 61%. The patients scored lower compared to a normal population for the domain of social functioning in the Medical Outcome Study 36-item short form health survey; the Disabilities of the Arm, Shoulder, and Hand questionnaire showed no differences. Visual analog scale scores for appearance of the thumb were scored low (2.2 of 10) by the adults, in contrast to visual analog scale scores for function (7.7). Conclusions: The examined group of adults with an untreated triphalangeal thumb had adequate thumb movement. Thumb strength was diminished for all specific thumb functions (anteposition, opposition, and thumb flexion), as low as 55%, compared to normal controls. Self-rated scores indicate that patients perceived their functionality as good. The appearance, however, was rated much lower, implying a dislike of the thumb by the patients. This indicates that the main impact of an untreated triphalangeal thumb in daily functioning might not be the diminished function but rather the dissimilar appearance. Type of study/level of evidence: Therapeutic IV.

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