[A biomechanical study on internal fixation of proximal ulna combined with olecranon fracture]

To compare the biomechanical stability of Kirschner wire and tension band wiring, reconstruction plate combined with tension band wiring, and olecranon anatomical plate in fixing proximal ulna combined with olecranon fracture, so as to provide the theoretical evidence for clinical selection of internal fixation.

Eight specimens of elbow joints and ligaments were taken from eight fresh male adult cadaveric elbows (aged 26-43 years, mean 34.8 years) donated voluntarily. The model of proximal ulna combined with olecranon fracture was made by an osteotomy in each specimen. Fracture end was fixed successively by Kirschner wire and tension band wiring (group A), reconstruction plate combined with tension band wiring (group B), and olecranon anatomical plate (group C), respectively. The biomechanical test was performed for monopodium compression experiments, and load-displacement curves were obtained. The stability of the fixation was evaluated according to the load value when the compression displacement of fracture segment was 2 mm.

No Kirschner wire withdrawal, broken plate and screw, loosening and specimens destruction were observed. The load-displacement curves of 3 groups showed that the displacement increased gradually with increasing load, while the curve slope of groups B and C was significantly higher than that of group A. When the compression displacement was 2 mm, the load values of groups A, B, and C were (218.6 +/- 66.9), (560.3 +/- 116.1), and (577.2 +/- 137.6) N, respectively; the load values of groups B and C were significantly higher than that of group A (P < 0.05), but no significant difference was observed between groups B and C (t = 0.305, P = 0.763).

The proximal ulna combined with olecranon fracture is unstable. Reconstruction plate combined with tension band wiring and olecranon anatomical plate can meet the requirement of fracture fixation, so they are favorable options for proximal ulna combined with olecranon fracture. Kirschner wire and tension band wiring is not a stable fixation, therefore, it should not be only used for proximal ulna combined with olecranon fracture.