Radiological anatomy of the trochlear spine and associated bony structures around the superior oblique tendon: a CT-based study

The superior oblique muscle tendon is known to bend in the anterior orbit around a cartilaginous trochlea. The site where the tendon bends is frequently interested by the presence of a small depression, the trochlear fovea, and/or the trochlear spine. Exact topography, size and frequency of these items are still undetermined. For this purpose, we studied 120 orbits of individuals that underwent computed tomography for pathologies not involving the anterior orbit. We detected the presence of the trochlear spine in 10% of orbits and we determined its location and size. We also observed the presence of two tubercles (TT1 and TT2), with distinct positions relative to the tendon. TT1 was present in 5% of orbits and was located on the same spot of the spine differing from the latter only for its morphology. TT2 lied in a more advanced position and it was rarer (1,67% of orbits). The spine and the first type of tubercle were located above and behind the tendon reflection; the second tubercle lied below and ahead of the tendon reflection. A distinct trochlear fovea was detected in 25.83% of orbits and lied 3.42 ± 0.97 mm behind the orbital rim. Fovea diameters were 4.16 ± 1.08 mm × 3.84 ± 0.97 mm. In conclusion we demonstrate that in the anterior orbit a bony process is present in at least 15% or orbits. It is a note of interest for strabismus surgery when it is necessary to intervene on the superior oblique muscle or when it is needed access to the medial orbital wall.