Ultrasound gel-nerve contact: an experimental animal histologic study

Ultrasound (US) regional nerve block requires the use of gel applied over the skin. With subsequent needle insertion, some of the gel may adhere either on the shaft or within the needle lumen and may be carried to the perineural structures or intraneurally. We performed this experimental animal study to investigate the effects of US gel contact on the nerve histologic structure.

Nine male beagle dogs were studied. Dogs 1 to 3 were the control group and dogs 4 to 9 were the study group. Bilateral posterior tibial nerves were dissected and exposed for the control group. Nerve specimens were obtained for histologic examination immediately for the first dog, at 24 hours for the second dog, and at 48 hours for the third dog followed by wound closure. For the study group, bilateral posterior tibial nerves were exposed, and 2 mL US gel was applied locally directly on the nerve, followed by wound closure. Nerve specimens were excised at 24 hours from one side and at 48 hours from the other side. Nerve specimens were examined by a neuropathologist for evidence of nerve inflammation.

The control nerve specimens showed no significant pathology. Nerve specimens of the study group at the end of 24 hours of gel-nerve contact showed mild focal perineural inflammatory changes with clusters of polymorph leukocytes. At 48 hours, perineural moderate inflammatory changes with clusters of lymphocytes and macrophages were demonstrated in 2 animals. Long-term neurologic deficit in the form of limping was observed for all dogs.

Histologic features after perineural exposure to US gel are rather nonspecific and likely of no clinical significance. However, further studies are needed to determine the effect of US gel injection on intraneural tissues.