To investigate the diagnostic validity of four radiological soft tissue signs Kager's sign (K), disruption to the tendon (D), loss of parallelism (P) and fusiform swelling of the tendon (F) on a lateral ankle x-ray to aid Achilles tendon rupture diagnosis.
We retrospectively identified two groups of patients; Group A consisted of patients with an Achilles tendon rupture and Group B included patients with a clinically intact Achilles tendon but with a lateral ankle ligament sprain. Three clinicians independently reviewed all patients' x-rays for each of the radiological features under investigation to determine whether a rupture was present or not. Inter-rater and Intra-rater reliability were calculated using the Kappa coefficient (Kc.) To determine the predicted value of the signs sensitivity, specificity, positive predicted values and negative predicted values were calculated.
85 patients x-rays were included in this study; Group A n = 47, Group B n = 38. The most valid radiological sign appeared to be loss of parallelism (sensitivity 70%, specificity 97%, kappa 0.55-0.58).
Clinicians reviewing a lateral ankle x-ray of a patient with an acute ankle injury should review the x-ray for loss of parallelism between the tendon and skin; identification of this radiological sign may alert the clinician to the possible diagnosis of a ruptured Achilles tendon. Reviewing this may reduce the number of missed Achilles ruptures.