Normal Ultrasonographic Parameters of the Posterior Tibial, Peroneal, and Achilles Tendons.

Tendinopathy of the foot and ankle is common and can lead to pain or functional limitations. The most frequently affected tendons in the foot and ankle are the posterior tibial, peroneal, and Achilles. We used ultrasound to determine normal values for these tendons. From 2015 to 2016, a prospective, standardized bilateral lower extremity ultrasound examination protocol was performed by a musculoskeletal ultrasonographer of the 4 tendons and above and below the malleoli as appropriate. A total of 199 patients with 398 extremities were identified, consented, and participated in the study. Most tendons were normally distributed. The average size of the tendons was as follows: Achilles 5.0 mm (range 2.8-11.2 mm); peroneus long above the malleolus 2.1 mm (range 0.7-3.6 mm), below the malleolus 2.9 mm (range 0.8-6.3 mm); peroneus brevis above the malleolus 1.2 cm (range 0.3-4.0 mm), below the malleolus 1.3 mm (range 0.5-4.8 mm); posterior tibial tendon above the malleoli 3.7 mm (range 1.9-8.1 mm), below the malleolus 4.6 cm (range 1.8-11.8 mm). Standard deviations and distribution curves were similarly calculated for each tendon. This baseline data can assist clinicians in their diagnostic ability with ultrasound. Given its low cost, lack of ionizing radiation and dynamic ability along with an improved understanding of normative data it may become an increasingly used diagnostic modality. Levels of Evidence: Level II: Diagnostic.