Functional recovery after transection of the sciatic nerve at an early age: a pilot study in rats

It is often clinically noted that peripheral nerve transections in infants and very young children seem to show better functional recovery after nerve repair compared with adult patients. There can be several reasons for this (e.g. outgrowing axons might have maintained their potential to locate their genuine target muscle, the distance from the lesion site to the target organ is shorter, or there is enhanced compensational capacity of central brain areas at early stages of development). We decided to study the effects on walking performance of sciatic nerve transection and repair in nine rats at the youngest age at which appreciable numbers of motoneurons survive transaction (10th day of life). The follow-up period was 52 weeks. Walking movements were recorded on video and performance was qualitatively assessed. The stance factor and the sciatic function index were calculated and abnormalities such as automutilation of the toes or flexion contractures were noted. Postmortem inspection aimed to examine the continuity of the regenerated nerve and the presence of neuromas. Nine days after the transection and nerve repair, walking performance in all rats was close to the level in rats that had not undergone the procedure. Exorotation of the hind leg on the operated side was observed in only two rats. However, 20 days after lesioning the walking performance started to deteriorate, and walking patterns in all but one rat showed severe disability until the end of the observations. Only one out of the nine animals walked relatively undisturbed, with a sciatic function index approaching normal values but with an abnormal stance factor. We conclude that a sciatic nerve transection in rats aged 10 days leads to long-term impairments in walking patterns.