Introduction: When approaching the infratemporal fossa through the middle fossa, the mandibular condyle is an important lateral structure that must be avoided to avoid injury to the temporomandibular joint. The mandibular fossa lies within a triangle with its apex at the foramen spinosum, its anterior arm extending to the root of the zygoma, and its posterior arm extending to the external auditory canal. We describe this imaginary triangle on the floor of the middle fossa, to denote the underlying mandibular fossa where drilling should be avoided.
Methods: Six cadaveric heads with 8 dissected middle fossa approaches underwent computed tomography with navigation protocols. The heads were registered using a neuronavigation system and the foramen spinosum was identified. Measurements of the anterior and posterior borders of the mandibular condyle were made to define the boundaries of the triangle.
Results: The foramen spinosum was 7.7 mm (SD: 0.87 mm) medial to the medial border of the mandibular fossa. The anterior border of mandibular condyle was 38.8° anterior and 54° posterior to the foramen spinosum and the estimated medial border of the mandibular condyle. The anterior border was less than or equal to the angle between the foramen spinosum and the posterior root of the zygoma in all specimens. However, the posterior border of this triangle was larger than the angle between the foramen spinosum and the external ear canal in 4 of 8 sides.
Conclusions: When drilling laterally within the middle fossa, this triangle extending from the foramen spinosum can be useful for avoiding inadvertent exposure of the mandibular condyle and subsequent injury to the temporomandibular joint.
Patient Care: By helping surgeons avoid a potential complication of drilling within the middle fossa.
Learning Objectives: By the conclusion of this session, participants should be able to understand a technique for avoiding the mandibular condyle when drilling laterally within the middle fossa.