Presence and anatomical characteristics of a common perineural sheath in the popliteal fossa

J. Vloka, A. Hadžić, J. Lesser, E. W. April, H. Gaetz, E. Kitain, D. M. Thys

Research output: Contribution to journalArticlepeer-review

Abstract

Introduction: An unusually quick onset of dense anesthesia is occasionally observed after popliteal nerve (PN) blockade. Frequently, the anesthesia is profound in the distribution of both divisions of the nerve, although the response to nerve stimulation or paresthesia is obtained only in the distribution of either tibial (TN) or common peroneal nerves (CPN). In this study, we examined a possible role of a common perineural sheath [1] in this phenomenon, by studying the popliteal fossa and lower leg for conductance and continuity of a tissue sheath surrounding the popliteal nerve and its two main divisions. Methods: Two groups consisting of five cadaver legs each, were randomly selected. In each leg, the posterior aspect of the calf was dissected, the TN exposed 10 cm below the popliteal crease and a 16G Teflon catheter was inserted into the perineurial fascial sheath surrounding the nerve. Fifteen ml of Blue Vinyl Acetate solution (Cabisco(r), Carolina Biological Supply Company) were injected into the TN sheath in group A and thirty ml were injected in group B. One hour later, the popliteal fossa was dissected and the spread of the solution within the TN and PN sheaths and their communication with the sheath of the CPN was observed. The representative tissue samples of the TN, PN and CPN were embeded in parafm, cross sectioned, stained with hematoxyllin and eosin or trichrome stains, and examined for placement of the catheter and distribution of the vinyl acetate. Results: The apparent division of the popliteal nerve occured at 49±24mm above the popliteal crease, with no significant difference between the two groups. In one leg in each group the solution leaked at the catheter insertion site, forming a pool of mjectate between the intermuscular fasciae. In the remaining 8 legs, the solution traveled 144±38mm (group A) and 171±50mm (group B) proximally within the sheath from the injection point. In all 8 legs, the solution readily filled the sheath, with minimal or no apparent leakage outside of the sheath. The injectate reached the PN nerve division in the popliteal fossa, bathing both the TN and CPN (Figure-1) in all legs except one in group A. Examination of the cross sections identified the catheter within the extraneural adipose connective tissue, which was permeated by the vinyl acetate. Discussion: Our results document the existence of a continuous perineural sheath enveloping the popliteal nerve that appears to communicate with the tibial and common peroneal nerves. Close approximation of the tip of the block needle to the nerve during the performance of the PN block occasionally could result in placement of the needle within the neural sheath. This could lead to substantial spread of local anesthetic solution within the sheath, exposing both divisions of the PN to the solution of local anesthetic, resulting in a fast and solid conduction blockade in the entire popliteal nerve distribution. These findings may have important clinical implications similar to those of perivascular techniques for other nerve blocks 12].

Original languageEnglish
Pages (from-to)13
Number of pages1
JournalRegional Anesthesia
Volume21
Issue number2 SUPPL.
StatePublished - 1996
Externally publishedYes

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