Identification of normal and pathological posterior inter-malleolar ligament with dedicated high-field vs low-field MRI. A pilot study

Aim: the aim of the study was to determine an objective measure of detection of posterior inter-malleolar ligament (PIML) through a magnetic resonance (MRI) of the ankle with two dedicated scanners: high-field (1-Tesla: HMF) and low-field (0.2-Tesla: LMF). Methods: two-hundred subjects were randomly recruited for the study and then divided in two groups (HMF and LMF). We retrospectively evaluated the MRI of the ankle in the two groups of patients. PIML evaluation was performed globally and separately using different scan planes. Results: in HMF and LMF, the PIML was identified respectively in 55 and 11% of cases. PIML was classified as "indeterminate" in 28 and 57% of patients, and "absent" in 17 and 32% of patients. In HMF and LMF the isolated evaluation on the coronal, axial and sagittal planes allowed PIML identification respectively in 100 and 100%, 67.27 and 45.45%, 45.45 and 12.4% of cases. In 5 cases (4/5 of HMF) we also observed a posterior ankle impingement syndrome (PAIS) determined by the PIML, with ligament changes (5/5) and associated synovial reactions (1/5), and an arthroscopic confirmation was obtained in 3/5 cases. Conclusion: the presence of the PIML seems to be a possible cause of PAIS and the use of a high-field MR scanner seems optimal for its identification.