Electromyographic Evaluation of Extraocular Muscle Contractibility after Artificial Muscle Incarceration in the Rabbit

Kim, Soon Hyun; Rah, Sang Hoon; Choi, Yong Joon; Rohr, Weon Seuk

Abstract

The orbital blowout fracture has been increasingly noticed due to trauma and traffic accidents. The diagnostic confirmation is early established by CT scan, but indication for surgical treatment, the technique for repair, and timing of repair are still controversial. The main symptoms of orbital fracture include diplopia, enophthalmos and hypesthesia in distributions of the infraorbital nerve. These are usually accompained by other symptoms such as emphysema of the eyelids, ptosis, epistaxis and ocular injury. Among these diplopia and enophthalmos are considered as main surgical indications. Especially operation is performed when the contractibility of extraocular muscle(EOM) is changed due to incarceration of EOM and persistent diplopia at straight forward gaze or downward gaze. Many theories for sugical repiar timing are insisted but at present the accepted timing for operation is posttraumatic 1-2 weeks. To prevent the fibrosis and atrophy of extraocular muscle from the incarceration of EoM due to orbital fracture is the indication of surgery. To estimate the optimal time to perform the operation, we checked the EOM contractivilty by electromyography before and after artificial muscle incareceration in the rabbit. The results were as follows. The differences in RMS(root mean square) and MRV(mean rectified voltage) were not shown before or after the artivicial incarceration of extraocular muscle until the 5th day of the surgery. But the RMS and MRV measurements performed on the 7th day decreased significantly and these decreases were sustained. According to the results of this experiment. if the incarceration of the extraocular muscle due to the orbital fracture is diagnosed, relieving the incarceration by surgery before the 7th day can prevent the change of EOM contractibility. It will provide significant benefit, in maintaining the normal functioin of the extraocualr muscle.