Variable Bone Density of Scaphoid: Importance of Subchondral Screw Placement

Abstract

Ideal internal fixation of the scaphoid relies on adequate bone stock for screw purchase; so, knowledge of regional bone density of the scaphoid is crucial. The purpose of this study was to evaluate regional variations in scaphoid bone density. Three-dimensional CT models of fractured scaphoids were created and sectioned into proximal/distal segments and then into quadrants (volar/dorsal/radial/ulnar). Concentric shells in the proximal and distal pole were constructed in 2-mm increments moving from exterior to interior. Bone density was measured in Hounsfield units (HU). Bone density of the distal scaphoid (453.2 ± 70.8 HU) was less than the proximal scaphoid (619.8 ± 124.2 HU). There was no difference in bone density between the four quadrants in either pole. In both the poles, the first subchondral shell was the densest. In both the proximal and distal poles, bone density decreased significantly in all three deeper shells. The proximal scaphoid had a greater density than the distal scaphoid. Within the poles, there was no difference in bone density between the quadrants. The subchondral 2-mm shell had the greatest density. Bone density dropped off significantly between the first and second shell in both the proximal and distal scaphoids. In scaphoid fracture ORIF, optimal screw placement engages the subchondral 2-mm shell, especially in the distal pole, which has an overall lower bone density, and the second shell has only two-third the density of the first shell.

Factors Associated with Scaphoid Nonunion following Early Open Reduction and Internal Fixation

“…Missed diagnosis frequently results in delay in initial treatment and may contribute to increased risk of both nonunion and malunion. 10,12,[15][16][17] Additional factors that have been investigated to affect the rate of union following open reduction internal fixation (ORIF) include screw trajectory [18][19][20][21] and implant type. [22][23][24] There are conflicting data regarding optimal screw orientation, with some studies show greater compression with central placement along the longitudinal axis of the scaphoid 25 while others demonstrate the biomechanical advantage of screws placed more perpendicular to the fracture plane.…”

“…19,20,26 Still other biomechanical studies suggest screw purchase into the dense 2-mm subchondral shell as a key factor in stability of scaphoid fractures. 21,27 While these studies provide biomechanical data, they are limited in that they do not provide clinical correlates in patient series.…”

Bone Morphology and Vascular Supply of Pedicled Distal Radius Bone Using Nano-Computed Tomography

“…In a recent analysis of the bone density of the scaphoid, Swanstrom et al 18 determined the proximal and distal poles of the scaphoid bone have differing density and that subchondral bone density drops significantly as the distance from the cortex increases. This has been demonstrated to be important for internal fixation.…”

Dual‐energy contrast‐enhanced CT to evaluate scaphoid osteonecrosis with surgical correlation

“…The patient's dual energy CT scan data were loaded into Syngo via. The chest – pooled blood volume algorithm was selected with the default settings and then the maximum Hounsfield unit (HU) was changed from −600 to +500 in order to increase the threshold of displayed densities such as contrast‐enhancing material in dense bone, including the scaphoid which has a Hounsfield unit of approximately 500 . This also enabled generation of visible and assessable colour maps which were stored for reference on PACS.…”