Ulnar shaft diameter as it relates to plate osteosynthesis: A cadaveric study

Ulnar shaft fractures are common and the standard of care treatment is with 3.5 ​mm plating. The purpose of this study was to measure diameters along the length of the ulna to provide information on screw length and appropriateness of 3.5 ​mm screws and plate location.

Ten embalmed cadaveric ulnas were dissected free of all soft tissues. The length of the ulna was measured and then divided by four. Transverse osteotomies were performed along the length of the ulna at ¼, ½ and ¾ its full length. The diameter of the ulna at these locations was then measured in a radio-ulnar direction as well as a volar-dorsal direction.

There were five female and five male specimens with an average age of 83.6 and 78.8 respectively. The smallest diameter in both the female and male specimens was in the distal ¾ shaft measured in a volar-dorsal direction with an average of 9.1 ​mm and 12 ​mm. The average volar-dorsal measurement was less than radio-ulnar measurement at all locations. The diameters increased along the ulna heading proximally.

This study provides information pertinent to screw width and length with respect to the ulnar shaft and calls in to question the use of 3.5 ​mm screws in the distal and midshaft ulnar diaphysis in females. Removal of 3.5 ​mm screws in the mid and distal ulnar shaft in females can leave a hole corresponding to 23% and 27% of the bone which can be concerning for a stress riser.