Proximal ulna morphometry: which are the "true" anatomical preshaped olecranon plates?

Abstract

Purpose: To define the optimum design of the anatomical preshaped olecranon plate.

Methods: The geometry of the proximal ulna was studied in 200 paired Caucasian ulnae, using a digital caliper and goniometer. Gender and side differences were analyzed. Results were compared with the corresponding geometrical parameters of three olecranon plates with different contour. All three plates were placed on the dorsal surface of a "model" ulna, i.e., a right dried ulna having osteometric parameters similar to the averages of our sample, and plate-to-bone fit was examined in two planes.

Results: The proximal ulna had an 8.48° (2.1°-15.7°) mean varus angulation and an 8.49° (1.70°-14.10°) mean anterior angulation, located on average 8.19 cm (5.68-11.66 cm) and 8.63 cm (5.28-11.92 cm) distal to the bone's most proximal point, respectively. The mean olecranon angle was 110.34° (98.70°-125.80°) and the olecranon length was 1.58 cm on average (1.20-2.12 cm). Only the plate having both varus and anterior angulation presented a good plate-to-bone fit in both planes.

Conclusions: A "true" anatomical preshaped olecranon plate should have both varus and anterior angulation close to the average angulations of the normal ulna and located in a certain distance from its proximal edge. The olecranon part of the plate should primarily not exceed the olecranon length and secondarily be close to the average olecranon angle. We believe that such a plate may facilitate intraoperative restoration of the proximal ulna complex anatomy, when dealing with comminuted or Monteggia fractures, thus leading to better postoperative results.