Morphological Evaluation of the Hip Joint and Pelvic Limb Bones of the Lowland Tapir (Tapirus terrestris Linnaeus, 1758) Using Radiography and Computed Tomography

Abstract

The study aimed to characterize, through imaging examinations—including radiographs and computed tomography—the hip joint and the bones of the thigh, leg and feet in Lowland tapirs (Tapirus terrestris). Ten pelvic limbs were collected, two from juveniles and the remaining from adults. The femoral head exhibited a rounded morphology with a well-defined fovea capitis and a short, thick neck. Three trochanters were identified, with the greater and third trochanters being particularly prominent. The femoral diaphysis was elongated and straight, and the distal end displayed a globular medial condyle and a flatter lateral condyle. The femoral trochlea consisted of medial and lateral trochlear crests of similar size, separated by a well-defined trochlear groove. The proximal tibia showed slightly concave tibial plateaus, with the lateral condyle being wider and a prominent intercondylar eminence. The fibula was positioned laterally along the entire tibia, with the interosseous space preserved. The talus presented a well-defined trochlea and a head articulating with the central tarsal bone. Tarsal bones I, III and IV were identified, with tarsal IV being elongated. Three metatarsals (II, III and IV) were observed, with metatarsal III relatively more developed. The third digit was larger than both the second and fourth digits. The Norberg angle, femoral head–neck inclination angle, mechanical lateral distal and proximal femoral angles, and anatomical medial proximal and lateral distal tibial angles were similar between the two imaging methods. In conclusion, the imaging examinations were complementary, enabling the characterization of morphological features reflecting the species' functional adaptations for cursorial and semi-aquatic locomotion.