Wilmer Eye Institute, Johns Hopkins Hospital, Baltimore, MD, USA.
PURPOSE:A trap-door fracture, in which an extraocular muscle is incarcerated in a small orbital wall defect, is typically seen in the pediatric population and most commonly involves the orbital floor and inferior rectus. It is often cited as an indication for acute fracture repair, and previous studies have indicated that rapid identification and early repair of this type of fracture are associated with a better outcome. We have noted that a subset of patients with medial rectus entrapment, exhibit signs and symptoms that differ from patients with inferior rectus entrapment. In order to learn more about the prevalence and outcomes associated with medial rectus entrapment, we have reviewed our experience with pediatric trapdoor fractures and compared inferior rectus with medial rectus entrapment. In addition, we report cadaveric anatomic studies, and a modification of the transconjuctival approach to the medial orbit.
METHODS: Clinical studies: A retrospective chart review of all patients pediatric orbital fractures treated at our institution from 1991-2004 was performed with IRB approval. Twenty-seven of the 68 patients treated during this period had a trapdoor fracture with incarceration of a rectus muscle utilizing the following inclusion criteria: 1) Attending note stating the patient had a history and exam consistent with a trapdoor fracture 2) a CT scan demonstrating a trapdoor fracture 3) an operative note stating forced ductions were positive and there was incarceration of the muscle was present.
Anatomic studies: The anatomy of the surgical approach to the medial orbit approach was delineated in 8 cadaver orbits, 4 left orbits and 4 right orbits. Intraoperative digital video recordings were then made illustrating the relevant anatomic landmarks.
RESULTS:Of the 27 patients with rectus muscle entrapment, 4 were found to have entrapment of the medial rectus muscle (3 male and 1 female). The most common presenting symptom with medial rectus entrapment was double vision (100%), and nausea/vomiting and pain with eye movement were less common (25%); whereas, with inferior rectus entrapment double vision was also most common (92%), but nausea/vomiting (63%) and pain with eye movement (50%) was also significant. The strabismus associated with medial rectus entrapment was characterized by a mixed restrictive and paretic pattern implying not only incarceration of the muscle, but muscle dysfunction, as opposed to inferior rectus entrapment, in which restrictive strabismus was typical. The 4 patients were repaired through approach that was defined in cadaveric studies consisting of a 12-14 mm transconjunctival incision between the plica, and the caruncle. Dissection through this incision was performed in the avascular plane posteriorly and medially to the posterior lacrimal crest, then medially to the medial orbital wall. All four patients underwent operative repair within 24 hours of their presentation, with resolution of their diplopia within 6 weeks.
CONCLUSION:Medial rectus entrapment represents an uncommon form of pediatric trapdoor fractures, with a different pattern of strabismus then we have previously described in inferior rectus muscle entrapment. The surgical approach defined in cadaveric studies and untilized here represents a simple, safe, effective, and direct exposure of the medial orbit.