Central versus eccentric internal fixation of acute scaphoid fractures.

ABSTRACT

PURPOSE: To accurately calculate the cross-sectional area of typical scaphoid fracture patterns and compare the amount of fracture surface area available for healing when a screw was positioned in the center of the scaphoid (central) versus perpendicular (eccentric) to the fracture plane. METHODS: We employed a laser scanning technique to create 3-dimensional models of the scaphoid and permit the precise calculation of area along any cross-sectional cut of the bone. We computed approximate bone apposition areas for typical acute Herbert and Fisher fractures for 10 dry bone specimens. Next, we modeled internal fixation for each of these fracture geometries with screws placed either along the central axis of the scaphoid or eccentrically, perpendicular to the fracture plane. We calculated the proportional areas occupied by the screw and remaining area available for fracture healing. RESULTS: The mean surface area of the simulated distal oblique, complete waist, and proximal pole fractures was 131, 86, and 58 mm(2), respectively. There was little difference in available area for complete waist and proximal pole fractures, but eccentric screw fixation perpendicular to the plane in distal oblique fractures consumed significantly less area than the centrally placed position. CONCLUSIONS: The area available for apposition is widely variable and depends on each bone's unique morphology, the orientation of the fracture plane, and the design of the screw. Of the 3 fracture patterns studied, the obliquity of the screw with respect to the long axis was greatest for distal oblique fractures where perpendicular (eccentric) placement is preferable to maximize surface area available for healing. CLINICAL RELEVANCE Given the poor vascular supply of the scaphoid and morbidity associated with scaphoid fracture nonunions, this study examined a key determinant of bone healing by characterizing the area of these fractures and amount of bone apposition available for blood flow and healing when internally fixed with a compression screw.