Evaluation of functional nerve recovery with Visual-SSI--a novel computerized approach for the assessment of the static sciatic index (SSI).

Complete nerve transection (neurotmesis) of the rat sciatic nerve is a well-established animal model. The most frequently used behavioural for evaluation of neurotmesis-induced deficits is the walking track analysis with calculation of the sciatic functional index (SFI). More recently, the static sciatic index (SSI) has been developed, which shows a good correlation with the SFI. However, despite all advantages (high accessibility, easy handling, high accuracy, cost-effectiveness), the SSI is still not widely used. We, therefore, developed a novel programme ("Visual-SSI"), which will be made freely available for the assessment of the SSI. As gold-standard for the treatment of neurotmesis-induced nerve gaps, autologous nerve transplantation studies in the rat sciatic nerve model (n=16 [6 weeks], n=8 [12 weeks]) were carried out to test the effectiveness and feasibility of the Visual-SSI software. We observed a significant recovery starting from the pre-operative condition over the 3rd, 6th, 9th weeks until the 12th week after surgery (p<0.05). Theoretically, the SSI can be calculated from both rearing and normal standing position of the rats and we investigated whether the SSI is affected differentially by these positions. We observed no significant differences between animals in a rearing and normal standing stance (p>0.05). The present method combines efficiency (simplicity of use, rapid and economical setup) with accurate and precise quantification of the functional regeneration in the sciatic nerve lesion model of the rat.