Relating applied strain to the type and severity of structural damage in the rat median nerve using second harmonic generation microscopy.

INTRODUCTION: Stretch injuries in peripheral nerves can cause pain, paralysis, and loss of sensation. Although optimal treatment depends on the degree of injury, it is difficult to determine the severity of induced nerve damage.
METHODS: The load-deformation curves of rat median nerves were generated from monotonic load-to-failure experiments to determine low, medium, and high strain levels. Additional excised median nerves were then elongated to induce damage at low (4%), medium (10% and 12%), and high (14% and 20%) tensile strains and the resulting structural damage was evaluated using second harmonic generation (SHG) imaging and light microscopy.
RESULTS: No substantial structural changes occurred at 4% strain, but higher strain values resulted in disruption of the normal collagen architecture.
CONCLUSIONS: The results demonstrate a spectrum of structural damage that can be monitored using SHG, a non-destructive imaging modality, and that the pattern of damage may correspond to functional deficit.