Posterior tibial tendon tears: utility of secondary signs for MR imaging diagnosis.

To assess the range of appearance of both torn and normal posterior tibial tendons (PTTs) and to evaluate secondary signs related to abnormal biomechanics as aids in diagnosing PTT tears, 23 patients with complete PTT tears and 34 control patients were examined with magnetic resonance imaging at 1.5 T. Examiners were blinded to diagnosis. The diameter of the PTT was measured at the insertion and at the level of the ankle. The torn and control PTTs were bulbous distally (respective mean values, 6.2 mm vs 4.6 mm), with overlap in the range of tendon size. All PTTs also had overlap in the frequency of intra-tendon signal intensity (torn PTTs, 83%, vs control PTTs, 41%; T1-weighted, 61%, vs T2-weighted, 22%). The presence of a talonavicular abnormality was both a sensitive (82%) and specific (100%) sign of a PTT tear. The presence of medial tubercle hypertrophy (sensitivity, 89%; specificity, 75%) and an accessory navicular bone (sensitivity, 20%; specificity, 100%) were useful secondary signs of a complete PTT tear.