Nonselective nerve fibre damage in peripheral nerves after experimental thermocoagulation

In this study the morphological effects of local heat application by controlled thermocoagulation to the sciatic nerve of rabbits are investigated. It concentrates on the question of a possible selective elimination of nerve fibres depending on their calibers. Temperatures of 50 degrees C, 55 degrees C, 60 degrees C, 70 degrees C and 90 degrees C were applied for 45 seconds. The nerves were examined histolgically after 2-3 minutes, 7 and 12 days and 5 weeks. The light and electronmicrographs show no differential vulnerability of small myelinated or unmyelinated fibres as proposed by Sweet and Wepsic [20]. At a temperature of 50 degrees C no fibre is damaged whereas at 60 degrees C the fibre damage extends over nearly the total cut surface of the nerve. Even at the critical temperature of 55 degrees C affecting only part of the cross-section no predilection of any fibre caliber was observed. In summary thermocoagulation seems not to be able to cause selective fibre damage.