Rounding of the inferior rectus muscle as a predictor of enophthalmos in orbital floor fractures.

In spite of established indications for early operative repair of orbital floor fractures 7-10% of patients treated nonoperatively develop enophthalmos. Clearly further indications for repair are required to prevent these post-injury complications. Rounding of the inferior rectus muscle on coronal computerized tomography (CT) scan results from a loss of soft tissue and bony support and may therefore be predictive of late enophthalmos.A four-year institutional review was conducted to identify patients with orbital floor fractures that had been treated nonoperatively. Patients were recruited for late clinical follow-up (mean 30 months) where clinically significant enophthalmos and diplopia were measured. Clinical results were correlated with measurements of the height-to-width ratio of the inferior rectus muscle on CT scans by a blinded examiner. Eighteen of 78 patients were available for late follow-up. Sixteen patients had no enophthalmos whereas 2 patients had enophthalmos. The inferior rectus height-to-width ratios measured in the unaffected orbits were statistically similar between the two groups. There was a significantly increased height-to-width ratio exceeding 1.00 in the affected orbit when the enophthalmos group was compared to the no enophthalmos group.A height-to-width ratio of the inferior rectus muscle on coronal CT scan of greater than or equal to 1.00 is predictive of late enophthalmos.