trochlear

Trochlear is an anatomical term derived from the Latin trochlea, meaning a small pulley. In anatomy, the word is used both as a noun and an adjective to describe structures that resemble or function as pulleys, as well as specific named structures such as the trochlear nerve.

The most well-known use is the trochlear nerve, or cranial nerve IV. This motor nerve supplies the superior oblique muscle of the eye, which contributes to intorsion, depression, and abduction of the eyeball. The nerve originates in the midbrain, its fibers cross to the contralateral side, and the nerve exits the brainstem on the dorsal surface. It travels through the cavernous sinus and enters the orbit via the superior orbital fissure, continuing to the superior oblique. Trochlear nerve palsy can cause vertical diplopia that worsens with looking downward, often improving when the head is tilted toward the unaffected side.

In skeletal anatomy, trochlear surfaces describe pulley-like features that guide articulation. The distal humerus has a trochlea that articulates with the trochlear notch of the ulna, forming a hinge-like elbow joint. The femur has a trochlear groove that interfaces with the patella, guiding kneecap movement. The term also appears in relation to the trochlea of the superior oblique tendon, a fibrocartilaginous pulley in the orbit that redirects the tendon’s path.

Thus, trochlear denotes pulley-shaped structures or functions across neuroanatomy and musculoskeletal anatomy.