Clinical indicators of normal thumb length in adults

This study was undertaken to obtain clinical indicators of normal relative thumb length in adults.

Fifty two normal hands in 26 volunteers were analyzed. There were 10 women and 16 men. The average age was 34 years (range, 23-47 years). Eighteen of the volunteers (36 hands) were Chinese and 8 were Caucasian (16 hands). All the subjects were healthy with no history of trauma or disease affecting the hand. The relative distal extent of the tip of the thumb was measured against 2 parameters: the length of the proximal phalanx of the index finger and the distance between the proximal digital crease and proximal interphalangeal crease of the index finger. The obtained values were designated as the thumb-proximal phalanx (TPP) index and the thumb-digital crease (TDC) index, respectively.

The TPP index was 0.69 (standard deviation = 0.09) and the TDC index was 0.41 (standard deviation = 0.15). There were no statistically significant differences between the right and left hands nor were there any between male and female hands. It was also noticed that when the thumb was adducted the thenar crease and thumb interphalangeal crease came into contact with one another in 90% of the hands. Consequently, an arc traced along the thenar crease could be extended smoothly into the interphalangeal crease of the thumb. This was termed the thenar arc. Positive or negative variances of the thenar arc correlated statistically with variations of the TPP and TDC indexes.

This study provides 3 simple clinical indicators of normal thumb length: the TPP index, the TDC index, and the thenar arc. Statistical analysis of the TPP and TDC indexes showed that the values are independent of gender, race, or laterality of the hands examined. These 3 indicators may help the clinician determine normal relative thumb length when reconstructing the thumb in adults.