The aim of this study was to provide reference measurements from the three tibiotarsal synovial recesses (plantarolateral, plantaromedial, and dorsomedial) from both right and left sound equine hock joints. For this study, proximodistal and plantarodorsal (PLD) diameters were ultrasonographically obtained from the synovial recesses of 24 sound Standardbred Trotter horses. A comparison between right and left limb measurements was also made. The dorsomedial recess has shown a variable PLD diameter (0.11–0.90 cm), although the plantarolateral recess has shown the most variable dimensions (0.3–1.5 cm). In many cases, great differences have been found between two tarsi within the same horse; in contrast, the plantaromedial recess of the tarsocrural joint has a more homogeneous PLD diameter (0.6–0.9 cm). Ultimately, the assessed echographic limits for the studied tarsal structures could serve to accurately evaluate the pathological variations for this breed.