Safety of posterior ankle arthroscopy portals in different ankle positions: a cadaveric study

Purpose To investigate anatomic relation of standard and coaxial ankle arthroscopy portals with neurovascular structures during different degrees of ankle motion. Methods Twenty posterior ankles of ten fresh cadavers were assessed. Posteromedial, posterolateral and coaxial (transmalleolar) portals were created using 4-mm Steinmann pins in accordance with the defined technique in neutral position. The ankles were then dissected, and the distance from the portals to the peroneal tendons, short saphenous vein and sural nerve was measured laterally and that from the tibial nerve, flexor hallucis longus tendon and posterior tibial artery was measured medially. Changes in the distance between these structures were noted in neutral positions, 15° of dorsiflexion and 30° plantar flexion. Results In the neutral position, the mean distance of the conventional posterolateral portal to the sural nerve was 6 mm (SD 2.9, range 2.7–14.5). The mean distance of the posterolateral coaxial portal to the peroneal tendon was 1.6 mm (SD 0.55, range 1.1–2.9). The mean distance of the posteromedial portal to the FHL was 2.11 mm (SD 1.1, range 0–4.7). The mean distance of the posteromedial coaxial portal to the posterior tibial artery was 6 mm (SD 1.4, range 3.9–9.5). Although not statistically significant, the distance between the portal and neurovascular structures increased in dorsiflexion for the portals placed posteriorly to the neurovascular structures and increased in plantar flexion for the portals placed anterior to the neurovascular structures. Conclusions In comparison with the portals made in the neutral position, the distance between neurovascular structures and portals changes with portal placement in plantar flexion and dorsiflexion. In clinical practice, therefore, it might be safer to place the posteromedial–posterolateral portals in dorsiflexion and posterolateral–posteromedial coaxial portals in plantar flexion. The tibial nerve is closer to the posteromedial coaxial in dorsiflexion and could be in danger if making this portal with the foot in this position.