Assessing the safe direction of instruments during posterior ankle arthroscopy using an MRI model.

Abstract

The safety of posterior ankle arthroscopy is still the subject of debate. The purpose of this study was to evaluate the anatomical relationship between the posterior portals and the neurovascular structures using magnetic resonance imaging (MRI) to determine the safety of posterior portals in posterior ankle arthroscopy. Forty ankles from 38 patients who had undergone MRI scanning for ankle disorders were assessed (18 males, 20 females). For each ankle, the angles of the presumed position of the portals to the posterior neurovascular structures and the malleoli were measured on 4-mm proximal slices from the anterior tip of the fibula. The shortest distance from the sural nerve and the tibialis posterior neurovascular bundle to the position of the posterior portals was measured. The average distance between the posteromedial portal and the tibialis posterior neurovascular bundle was 18 ± 3 mm, whereas the average distance between the posterolateral portal and the sural nerve was 15 ± 3 mm. In 100% of ankles, there were no neurovascular structures lying within the region between the anterior tip of fibula and the posteromedial portal or between the posterior tip of fibula and the posteromedial portal. In 32 ankles (80%), the medial neurovascular structures were present on the medial side of the line running between the anterior tip of medial malleolus and the posteromedial portal. The posterior neurovascular structures were not in immediate proximity to where we estimated the posteromedial and posterolateral portals to be located. The findings of the present MRI-based study suggest that arthroscopic instruments oriented toward the fibula may be safely introduced into the posterior ankle without injuring the neurovascular structures.