The Scaphoid Safe Zone: A Radiographic Simulation Study to Prevent Cortical Perforation Arising from Different Views

Abstract

Purpose: The purpose of this study was to simulate and calculate the probability of iatrogenic perforation of the scaphoid cortical bone when internal fixation appeared to be safe on radiographs. The results will assist surgeons in determining proper screw placement.

Methods: Thirty scaphoids were reconstructed using computed tomography data and image-processing software. Different central axes were determined by the software to simulate the surgical views. The safe zone (SZ) and risk zone (RZ) were identified on the axial projection radiographs by comparing the scaphoid bone stenosis measured by the fluoroscopic radiographs with a three-dimensional reconstruction of the scaphoid stenosis. Each original axial projection radiograph was zoomed and compiled to match a calculated average image. The RZ, SZ, and probability of perforations in various quadrants were calculated.

Results: Using a volar view (approach), the mean risks of cortical perforation were 25% with screws and 36% with k-wires. Using a dorsal view (approach), the mean risks of cortical perforation were 18% with screws and 30% with k-wires. A high risk of perforation was detected at the ulnar-dorsal zone.

Conclusion: Surgeons should be wary of screws that appear to lie close to the scaphoid cortex on both anteroposterior (AP) and lateral radiographs, particularly in the ulnar-dorsal and radial-dorsal quadrants, because such screws are likely to perforate the cortex. The position of the internal fixator should be assessed using a diagram outlining the various SZs. Therapeutic, Level III.

Fig 1. Simulated radiographs views and three-dimensional simulation of the reconstruction.

(a), (b): Simulated radiographs anteroposterior (AP) and lateral views, Boundary radial–volar (Brv) line was parallel to the screw axis within the scaphoid was maximized (MSL)/cylinder (MSL/CYL) and lateral view, tangential to the mid- scaphoid curve. The radial–dorsal boundary (Brd), the ulnar–volar boundary (Buv), and the ulnar–dorsal boundary (Bud) were constructed and simulated using the same method. (c): Three-dimensional simulation of the reconstruction.

Fig 2. Projection views.

(a) Axillary view. Original radial boundary (dotted line) was translated toward the ulnar side (yellow arrow). Red dot shows the axis point. (b) Axis projection view. Figure shows the risk zone (RZ), including the RD, UD, RV, and UV quadrants. The safe zone (SZ) is denoted by the green area. Blue lines mark the boundaries. (c) Screw cross-section view. Circles represent the cross-section of the screw, and purple areas represent the trajectory of the screw. We could not accurately identify the screw’s position when it was perpendicular on AP radiographs.

Fig 3. Wrist coordinate system.

Horizontal plane(red), sagittal plane(green) and coronal plane(blue).

Fig 4. Mean ratio of different risk zones (RZs).

(a): Mean ratio of different risk zones (RZs) with screw arising from the screw axis within the scaphoid was maximized (MSL)/cylinder (MSL/CYL) axis. (b): Mean ratio of different RZs with K-wire arising from the MSL/CYL axis.

Fig 5. Axial view was obtained by tilting the C-arm of the fluoroscope.

(a): Volar axial view of the X-ray projection (MSL axis). (b): Dorsal axial view of the X-ray projection (CYL axis).