Summary

Manual examination underperforms the instrumented evaluation with the MRI-PATD protocol to estimate ankle joint laxity and ligament tears, with the PATD displaying higher diagnostic accuracy to identify ankles with previous anterolateral ligament tears, but with suboptimal performance to exclude those with previous ankle sprains but with intact ligaments.

Abstract

Background

Lateral ankle sprain is the most frequently reported musculoskeletal injury in physically active individuals. A tear to the anterolateral ankle ligaments can result in ankle joint laxity and lead to mechanical ankle instability. Assessment of ankle joint laxity has been a cornerstone step in the diagnosis of patients with instability, with important implications for treatment indications.

Purpose

The purpose of this study was to evaluate joint laxity of ankles with and without a previous anterolateral ligament tears using an arthrometer compatible with magnetic resonance imaging (MRI) – the Porto Ankle Testing Device (PATD) - and compare its diagnostic performance against manual examination.

Methods

This study enrolled 90 ankles with previous ankle sprains, of which 50 had a previous anterolateral ligament tear (confirmed by MRI). All ankles underwent manual physical examination (anterolateral drawer and talar tilt tests) by an experienced Foot and Ankle Orthopaedic surgeon and evaluated with MRI by a musculoskeletal radiologist. All ankles also underwent instrumented stress testing with the PATD within MRI setting. The PATD applies external stress to the ankle joint aiming to mimic the anterolateral drawer (posteroanterior translation with internal rotation) and the talar tilt manual tests within the MRI. Ankle laxity was calculated as the difference of joint position before and after stress testing for anterior talus translation (ATT), talar tilt (TT) and subtalar tilt (STT). Laxity measurements were computed by the difference of talar and calcaneus bony position between the ankle resting position and after stress tests during the MRI exam. Manual exam was compared against the PATD results thought the Spearman's correlation. Diagnostic accuracy was calculated for manual exam and PATD evaluations with cut-off points were computed by maximizing specificity and sensitivity coordinates in the receiver operating curve (ROC) and selected according to the highest Youden index.

Results

Manual exam showed very weak Spearman's rho values when compared to the PATD evaluation for the anterolateral drawer (ρ=-0.030, p=0.797) and for talar tilt test (ρ=-0.057, p=0.627). Manual exam showed poor validity in correctly estimating ankle laxity in more extreme cases, underestimating in cases of large laxity and overestimating in cases with lower laxity. Diagnostic accuracy was always superior in the PATD evaluation for either anterior talofibular ligament (ATFL) or calcaneofibular ligament (CFL) previous tears. The PATD ATT as the most sensible (82%) and the anterolateral drawer the most specific (80%) for ATFL tears, while the STT was the most accurate metric (sensibility, 67%; specificity, 58%) for CFL tears.

Conclusion

Manual examination underperforms the instrumented evaluation with the MRI-PATD protocol to estimate ankle joint laxity. The PATD showed higher diagnostic accuracy to identify ankles with previous anterolateral ligament tears, but with suboptimal performance to exclude those with previous ankle sprains but with intact ligaments. Both diagnostic approaches should be used in combination when diagnosing ankles with previous sprain to better ascertain the severity of ankle laxity and achieve a more accurate diagnosis.