Volar Anatomy of the Proximal Phalanx: Implications for Screw Length Selection for Fixation of Shaft Fractures.

Abstract

To investigate the anatomy of the volar surface of the proximal phalanx of the hand, specifically the longitudinal groove running along the volar phalangeal shaft. We measured skeletonized proximal phalanges from 10 embalmed human cadaver hands at 5 equidistant points along the shaft. The difference between the maximum dorsal-palmar thickness of the shaft and thickness measured from the center of the volar groove to the most dorsal aspect of the phalanx indicated the depth of the groove at each point. These specimens underwent microtomography to characterize their osseous morphology further. Screws placed dorsal to palmar into the specimens and viewed fluoroscopically simulated the appearance of screw protrusion into the volar groove under intraoperative imaging. Similarly, screws placed into a fresh-frozen cadaveric hand illustrated possible screw impingement on soft tissue in vivo. The volar groove was most pronounced at the proximal and distal ends of the phalangeal shaft, becoming shallower along the midportion of the bone. The average difference between total bone thickness and thickness measured from the depth of the groove was significant at each of the 5 points of measurement along the phalangeal shaft for each of the 5 digits of the hand, including the thumb. Average groove depths ranged from 4% to 14% of total bone thickness, with a maximum individual measurement of 22%. Average depth of the groove at each of these positions ranged from 0.19 to 1.64 mm, reaching a maximum of 2.31 mm. We demonstrated that there is a longitudinal groove running the length of the phalangeal shaft. Viewed laterally, the cupped edges of the groove obscure its depth. Dorsally placed bicortical screws could protrude into the groove, remaining unnoticed on intraoperative imaging. The resulting impingement on the flexor tendon could lead to postsurgical stiffness or flexor tendon attritional rupture.