Dimensional analysis of the distal phalanx with consideration of distal interphalangeal joint arthrodesis using a headless compression screw

Background: Headless compression screws have been used for arthrodesis of the distal interphalangeal joint with good clinical results. However, some distal phalanges are too small, thus precluding their use, or increasing complication rates.

Methods: In order to validate our digital measurements, radiographs of five cadaveric hands were obtained. The distal phalanges of these fingers were measured using our institution's digital radiograph software. The cadavers were then dissected, and the actual phalanges were measured to confirm the accuracy of the digital measurements; 200 consecutive hand radiographs were then measured to obtain average width and heights of the narrowest measurements of the distal phalanx of each finger. Subgroup analysis of each finger for age and gender was completed.

Results and conclusions: Females were routinely smaller than their male counterparts. No age-related differences were seen. A substantial number of fingers were found to be too small to allow for use of headless compression screws; 42 % of small finger distal phalanges are too small to accommodate 2.8-mm threads, and that number increases to 81 % with 3.2-mm threads and 97 % with 3.5-mm threads. Few distal phalanges, regardless of which finger, are large enough to accommodate 3.5-mm-diameter threads; 22% of female ring finger distal phalanges are smaller than 2.8 mm, and 66 % of ring fingers are smaller than 3.2 mm. Based on our measurements, a surprising number of distal phalanges are smaller than the trailing thread diameter of commonly commercially available headless screws. Care must be taken in selecting implants for distal interphalangeal (DIP) fusion.