Background: Internal fixation of osteoporotic ankle fractures is associated with failure of fixation. This study compared different augmentation methods biomechanically.
Materials and methods: In nine paired fresh-frozen cadaver legs, an identical supination-external rotation type II ankle fracture was created. Fractures were stabilized using an eight-hole locking plate. In four pairs, two screws were inserted across the syndesmosis for purchase in the tibial metaphysis. One leg from each pair was randomly selected for injection of calcium sulphate-calcium phosphate graft into the screw holes. Each leg was mounted to an MTS machine in a custom loading frame. Axial cyclic loading to body weight was performed to measure displacement at the fracture site, followed by rotational loading to failure simulating a supination external rotation injury. Data were analyzed using a two-way paired t-test and ANOVA.
Results: The specimens used had a mean bone mineral density of 0.49 +/- 0.15 (SD) g/cm(2), and a mean age of 83 +/- 12 years. In the biomechanical tests, there were no significant differences between augmented and non-augmented locking plates without the tibia-pro-fibula screws in axial stiffness (p = 0.10), external rotation angle at failure (p = 0.42), failure torque (p = 0.57), energy absorbed before failure (p = 0.47), and motion at the fracture site with cyclic axial loading (p = 0.15). There were no significant differences between augmented and non-augmented locking plates with the tibia-pro-fibula screws in the external rotation angle at failure (p = 0.83), failure torque (p = 0.58), and failure energy (p = 0.4). However, the overall strength of the fixation tended to increase with tibia-pro-fibula screws and augmentation.
Conclusion: Internal fixation of an osteoporotic lateral malleolar fracture using a locking plate and screws provided a construct comparable in strength to that augmented with calcium sulfate-calcium phosphate graft and/or tibia-pro-fibula screws.
Clinical relevance: Strategies to augment internal fixation of osteoporotic ankle fractures may minimize risk for failure of fixation and may enable early weight bearing mobilization and return to function in elderly patients.