Rupture of the Deep Layer of the Deltoid Ligament: Is the External Rotation Stress Test Diagnostic?

Background The integrity of the deep layer of the deltoid ligament is a critical determinant of ankle joint stability. The external rotation stress test, a common physical examination for assessing medial structural integrity, has suboptimal diagnostic sensitivity, potentially leading to false negative findings. Methods According to the Lauge-Hansen classification,seventeen patients were diagnosed with supination-external rotation type IV, nine patients were diagnosed with pronation-external rotation type IV,four patients were diagnosed with pronation-abduction type III, and two patients were diagnosed with supination-adduction type II. Eleven patients were preoperatively diagnosed with deep deltoid ligament rupture (with a medial malleolar gap≥5mm compared to the contralateral side or with lateral subluxation/dislocation of the talus).Twenty-one patients were intraoperatively diagnosed with deep deltoid ligament rupture (with a medial malleolar gap≥5mm or lateral subluxation of the talus after reduction of the ankle fracture, as demonstrated by a positive external rotation stress test or Cotton test). All patients underwent external rotation stress and Cotton testing.A comparative analysis of the diagnostic performance for deep deltoid ligament rupture was conducted between the individual and combined application of the two tests. Statistical analyses were performed via SPSS software (version 26.0), with a P value < 0.05 considered statistically significant. Results The results of the external rotation stress test, the Cotton test, and the combined application of both testing methods were as follows: the accuracies were 68.75%, 78.13%, and 96.88%, respectively, and the missed diagnosis rates were 31.25%, 21.88%, and 3.12%, respectively. These tests can lead to missed diagnoses, and the Cotton test appears to be more sensitive than the external rotation stress test. Moreover, the combined application of the two methods significantly improved the diagnostic rate of deep deltoid ligament rupture compared with the external rotation stress test (P = 0.004 < 0.05) and the Cotton test (P = 0.031 < 0.05). Conclusions The external rotation stress test, a commonly used method for physical examination of the ankle joint, demonstrated limitations in diagnosing deep deltoid ligament ruptures in this cohort. Therefore, the Cotton test and external rotation stress test should be performed together to improve the positive rate.