Orbital blow-out fractures: correlation of preoperative computed tomography and postoperative ocular motility

Abstract

Background/purpose: Although the management of orbital blow-out fractures was controversial for many years, refined imaging with computed tomography (CT) helped to narrow the poles of the debate. Many orbital surgeons currently recommend repair if fracture size portends late enophthalmos, or if diplopia has not substantially resolved within 2 weeks of the injury. While volumetric considerations have been generally well-served by this approach, ocular motility outcomes have been less than ideal. In one series, almost 50% of patients had residual diplopia 6 months after surgery. A fine network of fibrous septa that functionally unites the periosteum of the orbital floor, the inferior fibrofatty tissues, and the sheaths of the inferior rectus and oblique muscles was demonstrated by Koornneef. Entrapment between bone fragments of any of the components of this anatomic unit can limit ocular motility. Based on the pathogenesis of blow-out fractures, in which the fibrofatty-muscular complex is driven to varying degrees between bone fragments, some measure of soft tissue damage might be anticipated. Subsequent intrinsic fibrosis and contraction can tether globe movement, despite complete reduction of herniated orbital tissue from the fracture site. We postulated that the extent of this soft tissue damage might be estimated from preoperative imaging studies.

Methods: Study criteria included: retrievable coronal CT scans; fractures of the orbital floor without rim involvement, with or without extension into the medial wall; preoperative diplopia; surgical repair by a single surgeon; complete release of entrapped tissues; and postoperative ocular motility outcomes documented with binocular visual fields (BVFs). Thirty patients met all criteria. The CT scans and BVFs were assessed by different examiners among the authors. Fractures were classified into 3 general categories and 2 subtypes to reflect the severity of soft tissue damage within each category. "Trap-door" injuries, in which bone fragments appeared to have almost perfectly realigned, were classified as type I fractures. In the I-A subtype, no orbital tissue was visible on the sinus side of the fracture line. In the I-B subtype, soft tissue with the radiodensity of orbital fat was visible within the maxillary sinus. In type II fractures, bone fragments were distracted and soft tissue was displaced between them. In the II-A subtype, soft tissue displacement was less than, or proportional to, bone fragment distraction. In the II-B subtype, soft tissue displacement was greater than bone fragment distraction. In type III fractures, displaced bone fragments surrounded displaced soft tissue in all areas. In the III-A subtype, soft tissue and bone were moderately displaced. In the III-B subtype, both were markedly displaced. Motility outcomes were quantified by measuring the vertical excursion in BVFs. The interval between trauma and surgical repair was also determined.

Results: Among the 15 patients with a motility outcome in BVFs which was poorer than the median (86 degrees or less of single binocular vertical excursion), 4 patients (27%) had type A fractures; 11 patients (73%) had type B fractures. Among the 15 patients with a better outcome than the median (88 degrees or more), 10 patients (67%) had type A fractures; 5 patients (33%) had type B fractures. These differences became more defined as analysis moved away from the median. Among 5 patients with type B fractures and better than the median result in BVFs, 3 patients (60%) had surgical repair during the first week after injury. Among the 11 patients with type B fractures and less than the median result, 1 patient (9%) had repair during the first week.

Conclusions: When the CT-depicted relationship between bone fragments and soft tissues is considered, a wide spectrum of injuries is subsumed under the rubric of blow-out fractures. In general, greater degrees of soft tissue incarceration or displacement, with presumably greater intrinsic damage and subsequent fibrosis, appear to result in poorer motility outcomes. Although this retrospective study does not conclusively prove its benefit, an urgent surgical approach to selected injuries should be considered.