Sciatic functional index following induction of injury in the sciatic nerve of rats

Sciatic functional index (SFI) as a behavioral method was used to assess the functional recovery following experimentally-induced various injuries in the sciatic nerve, spinal cord, and brain. In the present study, the functional recovery after induction of injury in the sciatic nerve was investigated in rats using SFI. Twenty-four rats were divided into three groups including sham-operated (SS), Loose ligation (LL), and crushing with fine forceps (CF). For induction of sciatic nerve injury, rats were anaesthetized with a mixture of ketamine (180 mg/kg) and xylazine (3 mg/kg). Then, skin and muscles were incised and the sciatic nerve trunk was exposed. In SS group the same manipulation was performed. In LL group four ligatures (5.0 catgut) were loosely tied around the sciatic nerve about 1-mm spacing. In CF group four points of sciatic nerve were crushed using a fine forceps. The muscles and skin were then closed with catgut sutures. In the SFI test, rats walked along a 60 cm long runway lined with plain paper after first pressing their hindpaws onto an inkpad. The tracks left by the rats were then measured and four parametyers were taken: the length of each footprint, the distance to the next opposite footprint, the toe spread distance between 1st and 5th digits, and the distance between 2nd and 4th digits. The value for both injured and uninjured sides were entered into an empirical equation determined by de Medinaceli (1982). This test was conducted on rats in the 5th, 3 rd and 1st days before surgery and 1st, 2nd, 4th, 5th, 10th, 14th, 19th, and 25th days after the surgery. Data were analyzed by factorial ANOVA and Duncan test. The results showed that in the intact rats the average score of SFI was –5.4 ± 1.7. In SS group the SFI scores did not change during the course of study (-9.4 ± 4.6). In LL group SFI scores were more negative (-91.8 ± 11.2). In CF group the SFI scores were more negative till 14th day after the surgery, but in the 19th and 25th days after the surgery, SFI scores become less negative (-31.5 ± 5.5). From the results of this study it is concluded that in the various models of sciatic nerve injures, SFI method, especially using stamp and paper, might serve as a good tool in the investigation of functional recovery. Sciatic nerve injury induced by ligation produces more degenerative and regenerative changes than that of crushing.