Superiorly and transversely orienting the bicortical suspension device provides optimal anterolateral stability to the proximal tibiofibular joint: a finite-element study.

Purpose: Instability of the proximal tibiofibular joint (PTFJ) can be treated with bicortical suspension (BCS) fixation. However, the ideal location, orientation, and configuration to apply one or two BCS devices are not clear.

Methods: A finite-element model of the PTFJ was created from a female adult's CT dataset. Anterior and posterior ligaments at the PTFJ were modeled and suppressed to simulate stable and unstable joints. Fifty-six models simulated 56 device placements along guiding tunnel lines that connect eight entry locations on the fibular head to seven exit points on the anteromedial tibia. Doubling device stiffness created 56 more models. Combing any two placements created 1176 double-device configurations which were categorized to be crossed, divergent or parallel. Displacement of the fibular head relative to the fixed tibia under 100 N anterolateral and posteromedial forces was assessed.

Results: Different placements had 2.1-27.9 mm translation with 0.7-8.9° internal rotation under anterolateral loading, and 1.8-5.2 mm translation with 6.1-7.9° external rotation under posteromedial loading. More transverse and superior orientations were associated with smaller anterolateral translation; more posterior and superior entry locations were associated with smaller internal rotation. The median (IQR) reductions in anterolateral translation by doubling device stiffness and by adding a second device were 0.8 (IQR 0.5-1.0) and 0.8 (IQR 0-6.1) mm, respectively. The type of double-device configurations had no significant effect on fibular motion.

Conclusion: Surgeons should drill the guiding tunnel superiorly and transversely to ensure the optimal restoration of the PTFJ anterolateral stability.