[The experimental study on acute and chronic expansion of the facial nerve]

To investigate and compare the feasibility of acute and chronic expansion of the facial nerve so as to provide referable parameters for clinical practice.

Buccal branches of rabbits' facial nerve were expanded with the expander designed and manufactured by us. The nerve was elongated 10 mm per 10 min in the acute group, and 1.5-2.0 mm per day in the chronic group. The nerve injury due to expansion, the nerve retraction after expansion and the limit of elongation were investigated. When the expansion was completed, 1.0 cm segments of the nerve in both acute and chronic groups were removed and epineurium neurorrhaphy was performed. The same length of the nerve in the control group was resected and replanted. Electromyogram(EMG) and nerve conductive velocity (NCV) were measured at the 15th week of expansion to assess the function of the repaired nerve. The pathological changes were also observed.

1. The nerve retracted obviously during the first hour after expansion. The difference were significant between the acute group (37.6 +/- 4.5)% and the chronic group (8.2 +/- 2.1)%. 2. Excluding the retraction portion, the limit elongation was (18.7 +/- 2.4)% and (31.8 +/- 2.4)% in acute and chronic group respectively. 3. To get the same elongation within the limit, nerve injury was more severe pathologically in the acute group than in the chronic one at the end of the expansion while EMG and NCV were not different considerably. 4. Within the limit elongation, the same result of neurorrhaphy was gained in the acute, chronic and the control groups.

Acute expansion of the facial nerve is feasible. When the defect is less than 20% of the nerve, acute expansion is indicated. When it is over 20% but less than 30%, a chronic method should be taken into consideration. The same outcome of repair should be gained if the expansion is within the limit elongation.