An analysis of talar surface area occupied by screw fixation in ankle fusions

BACKGROUND: Ankle arthrodesis remains the benchmark of treatment for end-stage arthrosis of the ankle joint. Despite that, the incidence of nonunion can be as high as 15%. Various strategies have been used to reduce the incidence of nonunion, including multiple compression screws and larger diameter screws to improve mechanical stability and compression. The space occupied by an increasing amount of hardware across a finite surface area available for fusion has prompted concern that this strategy may be counterproductive and may reduce the biological potential of the construct. The purpose of this study was to look at 40 anatomic sawbone specimens of the ankle to determine the amount of talar surface contact area used by the screw fixation during arthrodesis. METHODS: Four groups were created to examine different techniques for arthrodesis. Simulated ankle arthrodeses were done using two- or three-screw fixation with 6.5-mm and 7.3-mm screws. Hardware was subsequently removed and the surface area used by the passing screws was measured. Total surface areas were calculated for each of the 40 specimens. RESULTS: The maximal surface area of the talus occupied by screws occurred when using three 7.3-mm screws. This configuration used 16% of the possible talar surface area available for arthrodesis. CONCLUSION: The use of additional screw fixation when performing an ankle arthrodesis does not sacrifice a major amount of the tibiotalar contact area and will most likely not affect the biologic environment needed to obtain fusion.