Objectives: Tibialis posterior dysfunction is often diagnosed at a very late stage. However, the early diagnosis of tibialis posterior dysfunction is crucial for therapeutic aspects and especially for the operative prognosis. The morphological correlate of the tibialis posterior dysfunction consists of degenerative changes and thickening of the posterior tibial tendon [2, 9, 11]. By means of a high frequency linear array transducer, a standardized technique of examination as well as reference values of cross-sections of posterior tibial tendon are introduced.
Material and methods: Investigating 51 healthy subjects (102 feet) without any foot deformities, standardized planes were defined by use of a 13 MHz linear array transducer in order to delineate the posterior tibial tendon. At exact anatomic landmarks, tendon diameters were measured using two longitudinal sections proximal and distal to the medial malleolus. Likewise, two diameters and the resulting roughly calculated cross-section of the tendon were determined, using two transverse sections at the level of the subtalar joint facet and the medial malleolus. The findings obtained by ultrasound in four female patients with the diagnosis of a tibialis posterior dysfunction confirmed during surgery are compared to the aforementioned 51 healthy subjects.
Results: A healthy tendon appears homogeneous and echo-rich in orthogonal ultrasound and displays average areas of 18.4 sq.mm. (SD 5.9 sq.mm.) at the subtalar joint facet level and 19.2 sq.mm (SD 4.8 sq.mm.) at medial malleolus level in transverse sections. The corresponding areas obtained in patients with tibialis posterior dysfunction were clearly enlarged than in healthy subjects. In 85% of all feet examined at the level of the medial malleolus, the tendon is surrounded by a hypoechoic halo which has a size smaller than two times the cross-section of the flexor digitorum longus tendon.
Conclusion and clinical relevance: Reference values of tendon thickness and of intratendinous echo-structures at reproducible landmarks facilitate delimitations from pathological tendon alterations. The exact delineation of intratendineal echoes by high frequency array transducers and standardized examination techniques that measure tendons size is a prerequisite to enable an early assessment and registration of degenerative alterations and thickening of the posterior tibial tendon.