STANDARDIZED IMAGING OF THE POSTERIOR TIBIAL TENDON BY ULTRASOUND (13 MHZ)

Objectives: Tibialis posterior dysfunction is often diagnosed at a very late stage in its development. 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 according to the literature consists of degenerative changes and thickening of the posterior tibial tendon. 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 to be introduced.

Material and Methods: Investigating 140 feet of 35 female and 35 male (the left and right sides were equally represented) without any foot deformities, standardized planes were defined by use of a 13 MHz linear array transducer in order to display the posterior tibial tendon. In exactly defined loci of the tendon a diameter was measured using two longitudinal sections proximal and distal to the medial malleolus. Likewise, two diameters and the resulting cross section of the tendon were determined, using two transverse sections at the level of the subtalar joint facet and the medial malleolus.

Results: A healthy tendon appears homogenous and echo-rich in orthogonal ultrasounds and displays average areas of 18.6 sq.mm. (SD 5,2 sq.mm.) for females and 20,9 sq.mm. (SD 5,8 sq.mm.) for males at subtalar joint facet level and 17.2 sq.mm. (SD 3.6 sq.mm.) for females and 21.6 sq.mm (SD 4.3 sq. mm.) for males at medial malleolus level in transverse sections. In 89% of all feet examined at the height of the medial malleolus, the tendon is surrounded by a hypoechoic halo which has a size smaller then two times the cross section of the flexor digitorum longus tendon.

Conclusion and clinical relevance: Reference values of tendon thickness and of intratendinal echostructure at reproducible loci facilitate delimitations from pathological tendon alterations. The exact delineation of intratendineal echos by high frequency array transducers and standardized examination techniques that measure tendons size is the prerequisit to enable an early assessment and registration of degenerative alterations concerning the posterior tibial tendon.