Incomplete Tears of the Medial Calcaneal Insertion of the Superficial Digital Flexor Tendon of a Hind Limb in Three Horses

Twelve tarsi from six horses humanely destroyed for reasons unrelated to the study were dissected and measurements of the calcaneal insertions of the superficial digital flexor tendon (SDFT) were acquired. The medial calcaneal insertions of the SDFT ranged in length and thickness from 4.0 to 5.4 cm and 0.3 to 0.5 cm, respectively, and the lateral calcaneal insertions ranged in length and width from 4.0 to 6.3 cm and 0.3 to 0.5 cm, respectively. The calcaneal insertions of the SDFT of both hind limbs of six horses with no history or clinical signs of hind limb lameness and no palpable abnormality of the tarsi were examined ultrasonographically. The medial calcaneal insertion of the SDFT was of uniform echogenicity, thickest at the attachment to the SDFT, and smoothly tapering to its insertion on the plantaromedial aspects of the calcaneus. The lateral calcaneal insertion was less echogenic adjacent to the SDFT than the tendon itself but was of similar echogenicity toward the insertion on the plantarolateral aspect of the calcaneus. Three horses with full-thickness incomplete tears of the medial calcaneal insertion of the SDFT had variable enlargement of the calcaneal bursa, an unstable (n = 2) or stable (n = 1) SDFT and lameness. The presence of an extensive but incomplete full-thickness tear of the medial calcaneal insertion of the SDFT was determined ultrasonographically in all horses.