The role of the saphenous nerve in experimental sciatic nerve mononeuropathy produced by loose ligatures: a behavioural study.

Four loose ligatures were tied round the sciatic nerve of rats to produce the model of altered pain sensation first described by Bennett and Xie (1988). Hyperalgesia and hyperaesthesia were detected from 4 days after tying ligatures, becoming maximal after 14 days; normal behaviour returned by 8 weeks post-operation. Using thermal tests involving immersion of the whole foot, it was found that section of the saphenous nerve at the time of, or within a week of, placing ligatures had the effect of abolishing the hyperaesthetic behaviour and instead caused hypoaesthesia from the 4th to 10-12th days. There was then a change to hyperaesthetic behaviour. The findings are interpreted as indicating that the early hyperaesthesia is possibly due to collateral sprouting, spreading nociceptor sensitivity of saphenous nerve fibres or both of these.