Validation of Double Posteromedial Arthroscopic Portals in Ankle Arthroscopy: Anatomic Study (SS-53)

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The authors present an anatomic study to validate the double posteromedial ankle arthroscopic approach. These portals permit posterior access to the joint and hindfoot compartment for arthroscopy and instrumentation.. The aim of the study was to assess the safety of approach, despite considering this area at high risk. The advantage is to be able to treat posterior compartment pathology without changing supine positioning during those procedures for anterior disorders which require also a posterior surgical step. Six specimens underwent posteromedial arthroscopy keeping the ankle supine in frontal view to the surgeon. Based on van Dijk's and Ljoi's anatomic studies on posterior approaches in prone assessment, authors have reproduced the same portals rotating 90° medially the peroneal one and placing both on the same medial side, positioning the first 1cm. above the line from tip of tibial malleolus to Achilles' tendon, the second one 5 cm superiorly to former. The arthroscope is inserted inferiorly, the shaver superiorly and is pushed antero-inferiorly until touching the scope sheath, triangulating in vertical plane. FHL tendon represents the medial landmark to prevent neurovascular injury. All ankles were then dissected along portals exposing the deep structures to measure their distance to the posteromedial neurovascular structures and to the calcaneal branch of the posterior tibial nerve. In all the specimens the results showed a mean distance of 11 mm from tibial artery and nerve and 13 mm from same tibial nerve's calcaneal branch, at the level of the skin portal. The distance to neurovascular bundle increased with the depth of approach as it reached the lateral malleolus. Thus any movement of surgical instruments is safe related to their tips staying lateral to the FHL tendon. This structure represents the medial border to the progression of instruments because it lies very close to the posterior tibial bundle and must be respected as insurmountable. The dissection has shown the presence of a safe triangular area, deployed of any risky anatomic structure, delimited by Achilles' tendon posteriorly, calcaneal tuberosity inferiorly, FHL tendon anteriorly, which are all well palpable under the skin. The posterior tibio-talar and the posterior subtalar joint space are under direct view, such as the posterior peroneal edge and the superior site of the calcaneal tuberosity: with the foot in dorsiflexion the posterior talar dome shows about one fourth of its surface. By anterior approaches is not possible to explore posterior compartment and to check any posterior hindfoot problem. Patients who present both anterior and posterior ankle disorders must presently be assessed in a prone position second step or postpone further treatment during a second surgery. These portals and positioning have not been described in the literature. In addition, posteromedial portals have been discouraged for years because of the proximity to medial structures. This study demonstrates the advantages and the safety of the two posteromedial portals within the triangular safe zone.