Assessing Rotational Ankle Instability Through Postural Control Testing: Coronal Instability Outperforms Conventional Imaging.

BACKGROUND: Deltoid ligament (DL) injuries are increasingly recognized in chronic ankle instability (CAI), drawing clinical attention to rotational ankle instability (RAI). Cadaveric studies have shown that RAI can increase ankle rotation; however, current examination methods for RAI remain limited. As they neither provide adequate insight into ligamentous structural damage nor clearly characterize the rotational instability. This study aimed to evaluate the characteristic rotational instability of RAI and, based on this indicator, investigate which postural control parameters best represent rotational instability and how these parameters can be quantified to assess diagnostic utility using postural control parameters and establish quantitative diagnostic thresholds. METHODS: We included 32 patients with CAI who underwent a postural control assessment, combining center of pressure (COP) analysis with the sensory organization test (SOT). Talar tilt angle and medial clear space were also measured via anteroposterior radiographs and magnetic resonance imaging (MRI) to assess DL injuries. Final diagnoses of RAI or CAI were made in the DL based on arthroscopic findings. Receiver operating characteristic (ROC) curves were constructed to determine the diagnostic performance of each indicator. RESULTS: In RAI, the ratio of coronal-plane sway to sagittal-plane sway amplitude during motion was significantly elevated, a phenomenon we term "coronal instability." Coronal instability emerged as a strong predictor of RAI, with an area under the ROC curve (AUC) of 0.95 (95% CI, 0.810-0.996; p < 0.0001). Its optimal cutoff value of 0.81 yielded a sensitivity of 83.33% and a specificity of 100%, surpassing imaging-based measures such as radiography and MRI (AUC = 0.567-0.844). CONCLUSION: Coronal instability, measured through a noninvasive postural control assessment, demonstrates high sensitivity and specificity for diagnosing RAI. This method offers a valuable clinical tool for accurately identifying RAI and may complement or outperform traditional imaging techniques in certain cases.