[Dynamic analysis of olecranon osteosyntheses--an in vitro comparison of two osteosynthesis systems].

Introduction: The aim of the present study was to develop a test setup with continuous angle alteration to imitate elbow joint motion for the mechanical evaluation of tension band wiring and a newly designed intramedullary nail.

Materials And Methods: The servo-pneumatical test stand worked with a rotational angle-adjusted and a linear force-adjusted engine. The fracture model was dynamically tested under cyclic loading imitating elbow joint motion. In total, 14 fresh cadaver upper extremities underwent olecranon fracture by means of transverse osteotomy and were assigned to two groups: tension band wiring and intramedullary nailing. There was a continuous angle alteration between 0 and 1000 of flexion, with continuous changing pull force between 25 N and 150 N. Two steel pins were placed in the proximal, two in the distal olecranon fragment for video analysis of the motion between the two pairs of pins. Displacement in the fracture gap was determined after 4 and 300 cycles.

Results: After 300 cycles, the displacement in the fracture fixation model was significantly higher in the tension band wiring group than in the intramedullary nailing group.

Discussion: Other studies evaluating biomechanical properties of olecranon osteosyntheses with joint involvement did not change the force direction dynamically. We introduced a test setup with continuous angle alteration to imitate joint motion. This is an important step for accurate biomechanical evaluation of the treatment of different fixation methods in olecranon fractures. The tested nailing system showed significant advantages in loosening under cyclic loading compared to tension band wiring.