CT measurement of enophthalmos and enlargememt of orbital volume in blow-out fracture

Objective To investigate the relationship between enophthaltnos and enlargement of the orbital volume as well as the tendency of enophthalmos in blow-out fracture of the orbit by using CT scan. Methods (1) The fissures and foramina of the orbit were blocked in 6 orbits from 3 skull specimen. Fine sands were filled in the blocked orbit up to the line between the anterior surfaces of zygomaticofrontal processes as the standard plane, then the plastic eyeballs were put into the orbits. A simulate model of the expanded orbit was established by decreasing the sands filled in the orbit, and the quantity of the lost sands with the degree of the enophthalmos was correlated. (2)28 patients with single orbital blow-up fracture 1-350 days after injury were divided into 2 groups, one group≤24 days and the other24 days after the incident. The distance between the frontal edge of the eyeball to the line between the two zygomaticofrontal processes as well as the bony orbital volume on both sides were measured on axial scan images. The degree of expansion of the injured orbit and enophthalmos were demonstrated through the analyses on the differences between the bony orbital volume and enophthalmos on both sides. The correlation and linear relationship of the orbital volume and enophthalmos in both groups were studied, respectively. Results (1) The results from the simulate models showed that with a decrease of 1 ml of sand filled in the orbit, the degree of enophthalmos of the plastic eyeball was (1.11±0.37) mm in average and was significantly correlated to each other ( r = 0. 9866 ,P 0. 001). e ( enophthalmos in mm) and v ( degree of expansion of the simulate orbit in ml) were linear correlated, e = (1.18v-1.04) mm. (2) The results from the orbits in 15 cases (≤24 days) appeared that with 1 ml expansion of the orbit, the degree of enophthalmos was nonnormally distributed. The results showed that the expanded orbit would not result in an enophthalmos in this period of time, E and V (E:the degree of enophthalmos in the group of≤24 days in mm; V:the degree of expansion of the injured orbit in ml) had linear correlation, E=(0.85V-1.74) mm. While the analysis on the 13 cases of 24 days showed that every 1 ml orbital expansion would resulted in an enophthalmos of (0.71±0.45) mm in average, (r=0.6,P=0.001). E1 and V1 (E1: the degree of enophthalmos in the group of 24 days in mm, V1:the degree of expansion in ml) had linear correlation, E1=(0.86V1?0.60) mm. Conclusion The results of the study demonstrate that CT is an accurate and reliable imaging technique in the evaluation of the degree of expansion of the injured orbit and in the prediction of the possibility of the consequent enophthalmos and its degree. It is significantly helpful to the therapeutic planning for the quantity the retroglobal filling in the rectification of the enophthalmos.