UNLABELLED Evaluation of patient outcomes should include the use of validated scoring systems to determine disease-specific outcomes. Many scoring systems are being used for disorders of the ankle joint. However, not all instruments are capable of detecting changes associated with functional ankle instability (FAI), since their focus is toward pathological entities with greater impact on individual's physical and mental well-being. METHODS In this prospective study, 6 instruments were used to evaluate outcomes associated with an intervention aimed at improving FAI. Twenty ankles that had been unsuccessfully treated for FAI were treated with a single session of noninvasive monopolar capacitive-coupled radiofrequency (mcRF) and followed prospectively. RESULTS Five out of 6 instruments failed to show changes that could be correlated with patients' outcomes. Only one instrument, the Cumberland Ankle Instability Tool (CAIT) demonstrated enough sensitivity and correlated well with meaningful clinical differences. Based on study's success criteria (proper function, no pain, no adverse events, and patient satisfaction), 78% of the ankles treated had successful outcomes whereas 87.5% evidenced significant improvement based on CAIT (P < .001). No adverse events were present during the study. CONCLUSIONS The study of FAI is hampered by the lack of disease-specific questionnaires, which oftentimes introduce ceiling or flooring effects. The CAIT was capable of detecting changes in patients' condition and response to the noninvasive mcRF procedure without evidencing ceiling or flooring effects. In this study, the CAIT was found to be reliable, valid, sensitive to changes of clinical importance, in addition to being short and practical to use.