Alonso-V'azquez, Ana, Lauge-Pedersen, Henrik, Lidgren, Lars and Taylor, M.
The effect of bone quality on the initial stability of ankle arthrodesis with internal fixation. A finite element simulation
Foot and Ankle International, 25, (11), .
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Background: Despite uniform operating techniques, lack of fusion still
occurs after ankle arthrodesis. Differences in the biological healing
potential may be a factor but the mechanical performance of the
arthrodesis construct because of varying bone quality also may be
important. Internal compression techniques are preferred because of
higher union rates, shorter fusion times, and fewer complications. A
three-screw configuration has been shown to be more stable than a
two-screw configuration, but it is not obvious when it should be used.
Methods: Three-dimensional finite element models of intact and flat-cut
ankle arthrodeses were built, using two and three screws in different
configurations. Poor bone quality was simulated by decreasing Young’s
modulus of the bone. The constructs were loaded in torsion and
dorsiflexion, and micromotions at the fusion site were measured.
Results: Bone quality had a marked effect on the stability at the
arthrodesis site. Inserting two screws at 30 degrees relative to the
longitudinal axis of the tibia in an intact arthrodesis seemed the best
option, especially as bone quality worsened. The addition of a third
screw increased the stability at the arthrodesis site. Conclusions:
Overall, intact joint surfaces and three-screw fixation, with the
lateral and medial screws inserted produced the most stable arthrodesis
constructs when bone quality was poor. Clinical Relevance. Ankle
arthrodeses are technically demanding because of the shape and small
size of the talus. Preoperative planning is an absolute necessity to
determine placement and number of screws. This study shows that poor
bone quality decreases the stability of the arthrodesis constructs,
suggesting that an attempt should be made to create the most stable
three-screw configuration. Finite element models can be used as an
effective preoperative tool for planning screw number and placement
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