Effects of stretching the tibial nerve of the rabbit. A preliminary study of the intraneural circulation and the barrier function of the perineurium.

mobilisation, or bridging by a graft. The point at which attempts to achieve end-to-end union should be abandoned in favour of grafting must depend on the extent to which a nerve can be stretched without interfering with the process of repair. A research programme has been designed in order to provide an experimental basis for the treatment of such peripheral nerve lesions. As a first step the present study was initiated for the purpose of introducing an experimental model and of making some essential observations on the response of the intraneural vasculature to stretching. Qualitative and quantitative changes in microvascular flow as well as an increase in permeability are early indications of tissue injury. Accordingly, these parameters were chosen for analysis. Both clinical experience and experimental studies have made it clear that nerve trunks are highly resistant to stretching (Mitchell 1872, Denny-Brown and Doherty 1954, Leffert and Seddon 1965). The functional changes in a stretched nerve are highly dependent on the magnitude and character of the deforming force, as well as on the length of time during which it operates. The internal topography of the nerve trunk also plays an important role. The nerve fibres are distributed throughout the intrafascicular endoneurial space. The fascicles-. each surrounded by perineurium-are embedded in the epineurial tissue. The number, size and arrangement of the fascicles, together with the amount of epineurium present, influence both the severity and site of the stretch lesions (Sunderland 1968). The stress-strain properties of peripheral nerve trunks have been extensively investigated (Sunderland and Bradley 1961, 1968, Haftek 1970), and it is obvious that peripheral nerves possess a high degree of elasticity. However, with increasing traction force a point is reached when conduction is blocked though no significant morphological change can be detected (Sunderland 1968). A further increase leads to disruption of axons and fascicles. Under tension the cross-sectional area of the fascicles is reduced, causing an increase in