Screw length in volar locking plate fixation for distal radial fractures

Purpose: To develop a reference for the distal screw length in volar locking plate fixation for distal radial fractures in an East Asian population.

Methods: 12 pairs of forearm specimens from 11 male and one female East Asian cadavers were scanned using computed tomography. On sagittal images of the distal radius, the mean cortex-to-cortex distance of 8 quadrants was measured as a reference for the distal screw length. In addition, intra-operative 3-dimensional fluoroscopy of 10 male and 10 female patients who underwent volar locking plate fixation for distal radial fractures was used to validate the distal screw length in the cadaveric reference. 76 distal locking screws were applied in the 8 quadrants; their cortex-to-cortex distances were measured.

Results: The mean cortex-to-cortex distances at quadrants A, B, C, D, E, F, G, and H were 15.4 mm, 19.6 mm, 20.8 mm, 20.0 mm, 13.3 mm, 18.0 mm, 18.8 mm, and 17.4 mm, respectively. In 45% of the specimens, the 2 screws inserted at quadrants C and D were longest. Distal screws (quadrants A to D) were significantly longer than proximal screws (quadrants E to H) [p=0.02]. In intra-operative 3-dimensional fluoroscopic images, 2 of the 76 distal locking screws penetrated the dorsal cortex (one in quadrant A and one in quadrant F). The mean screw length was 88.0% of the cortex-to-cortex distance. Referenced to the cadaveric data, 88.2% of the screws could be safely inserted without penetrating the dorsal cortex, and the remaining 11.8% of screws (5 at quadrant D, one at quadrant B, and 3 at quadrant C; all in female patients) could potentially cause dorsal cortex penetration of 2 to 4 mm. In male patients, the mean screw length was 76.1% of the cortex-to-cortex distance based on the cadaveric reference. In female patients, when the screw length was 4 mm less than the cadaveric reference, the mean screw length would be 72.0% of the referenced cortex-to-cortex distance, with no dorsal cortex penetration.

Conclusion: In female patients, the screw length should be 4 mm less than the cadaveric reference to avoid dorsal cortex penetration.