Purpose: To establish that the neurovascular bundle (NVB) of the inferior oblique muscle has ligamentous qualities that enable it to function as an ancillary origin to the muscle, particularly after anterior transposition of its insertion.
Methods: Fresh cadaveric eyes and eyes of surgical patients were studied. Eighteen orbits were dissected to demonstrate the linear course of the NVB and its adjacent fibrous bands. Intact orbits were analyzed histologically, as were autopsy and surgical specimens, to evaluate the capsule of the NVB and the adjacent fibrous bands. The elastic modulus was measured in NVB specimens and in superior oblique tendons. Six eyes in which recurrent inferior oblique muscle overaction developed after an anterior transposition procedure were surgically explored to determine the structure that was serving as its ancillary origin.
Results: Gross anatomic and microscopic studies showed a linear orientation of the NVB,with adjacent fibrous bands anteriorly joining the inferior oblique and inferior rectus muscle capsules. The NVB showed about 50% fibrocollagenous capsule, with the collagen fibers aligned parallel to the NVB. The elastic modulus was highest (stiffest) in the NVB and lowest in the superior oblique tendon. In patients who had undergone anterior transposition operations, the NVB served as the ancillary origin of the inferior oblique muscle.
Conclusion: The name of the NVB should be changed to neurofibrovascular bundle because it has a prominent fibrocollagenous capsule and is encased in fibrous tissue bands anteriorly. The neurofibrovascular bundle has a linear course and is relatively stiff. It binds the midposterior portion of the inferior oblique muscle posteriorly. Its ligamentous qualities enable it to function as an ancillary origin for the inferior oblique muscle.