Prediction of suspicious ankle instability using the calcaneofibular ligament cross-sectional area

Background An injured calcaneofibular ligament (CFL) is a major cause of ankle instability (AI). Previous research has demonstrated that the thickness of the calcaneofibular ligament (CFLT) is correlated with higher-grade sprains and ankle instability. However, inflammatory hypertrophy is distinct from ligament thickness; accordingly, we considered that the calcaneofibular ligament cross-sectional area (CFLCSA) as a potential morphological parameter to analyze inflammatory CFL. We hypothesized that the CFLCSA was a key morphologic parameter in AI diagnosis. Methods We gathered the CFL data of 26 AI patients and 25 control subjects who had undergone ankle magnetic resonance imaging (A-MRI), and it had revealed no evidence of AI. Ankle level T1-weighted coronal A-MRI images were acquired. Using our image analysis program (INFINITT PACS), we analyzed the CFLT and CFLCSA at the CFL on the A-MRI. The CFLCSA was measured as the whole ligament cross-sectional area of the CFL that was most hypertrophied in the transverse A-MR images. The CFLT was measured at the thickest level of CFL. Results The mean CFLT was 3.49±0.82 mm in the control group, and 4.82±0.76 mm in the AI group. The mean CFLCSA was 33.31±7.02 mm2 in the control group, and 65.33±20.91 mm2 in the AI group. The AI patients had significantly greater CFLT (P<0.001) and CFLCSA (P<0.001) than the control group participants. A receiver operating characteristic (ROC) curve analysis in the evaluation of the diagnostic tests showed that the optimal cut-off score of the CFLT was 4.06 mm, with 76.9% sensitivity, 76.0% specificity, and an area under the curve (AUC) of 0.89 (95% CI, 0.79-0.99). The optimal cut-off threshold of the CFLCSA was 43.85 mm2, with 92.3% sensitivity, 92.0% specificity, and AUC of 0.94 (95% CI, 0.86-1.00). Conclusions Even though the CFLT and CFLCSA were both significantly associated with AI, the CFLCSA was a more sensitive diagnostic test.