Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis

Of the anatomical reduction and fixation methods used to treat distal radius fracture, non-bridging external fixation has the advantage of enabling early wrist motion. The surgical technique relies on successful placement of the pin in individual fracture fragments. The present study aimed to identify the safe zone of pin insertion for a non-bridging external fixator into the distal radius that avoids metal impingement of extensor tendons.

The width and length of the septal attachments of the extensor retinaculum were measured on axial MR images of 62 wrists.

The 2-3 septum was the widest and longest, with a width of 2-7 mm and a location 0-36 mm proximal to the wrist joint. The width of the 1-2 septum was 2-6 mm, and was widest at 10 mm proximal to the joint. The 1-2 septum was triangular-shaped, while the 2-3 septum was oval-shaped. The 3-4 and 4-5 septa had narrow attachments and were adequate for pin insertion (with a pin 1-2 mm in width) at a position less than 8 mm proximal to the wrist. The width of the 1 R septum (radial to the 1st septum) was 2-6 mm at the radiovolar aspect of the wrist.

There were two safe pin insertion sites; the first was safe at the distal aspect only (8-10 mm proximal to the wrist) and included the 1-2, 3-4, and 4-5 septa, while the second was safe from 0 mm to 32-38 mm proximal to the wrist and included the 1 R and the 2-3 septa. The 1 R septum had adequate size for use as a new pin insertion site that aligns in the internervous plane and has minimal risk of superficial radial nerve injury.