Abstract
Intraneural injection of a local anesthetic can damage the nerve, yet it occurs frequently during distal sciatic block with no neurological sequelae. This has led to a controversy about the optimal needle tip placement that results from the particular anatomy of the sciatic nerve with its paraneural sheath.The study population included patients undergoing lower extremity surgery under popliteal sciatic nerve block. Ultrasound-guidance was used to position the needle tip subparaneurally and to monitor the injection of the local anesthetic. Sonography and magnetic resonance imaging were used to assess the extent of the subparaneural injection.Twenty-two patients participated. The median sciatic cross-sectional area increased from 57.8 mm2 pre-block to 110.8 mm2 immediately post-block. An intraneural injection according to the current definition was seen in 21 patients. Two patients had sonographic evidence of an intrafascicular injection, which was confirmed by MRI in one patient (the other patient refused further examinations). No patient reported any neurological symptoms.A subparaneural injection in the popliteal segment of the distal sciatic nerve is actually rarely intraneural, i.e. intrafascicular. This may explain the discrepancy between the conventional sonographic evidence of an intraneural injection and the lack of neurological sequelae.
Highlights
An intraneural injection of local anesthetic during peripheral nerve block can cause serious and potentially permanent nerve damage [1]
There is a discrepancy between the reported incidence of intraneural injections in distal sciatic nerve block and the incidence of clinical signs of nerve damage associated with this procedure [2,3]
An intraneural injection during popliteal sciatic nerve (SN) block occurs in up to 94%, in two studies there was no evidence of nerve damage either in postoperative neurophysiological examination or in the clinical follow-up [2,3]
Summary
An intraneural injection of local anesthetic during peripheral nerve block can cause serious and potentially permanent nerve damage [1]. The currently recommended ultrasound criteria for the diagnosis of an intraneural injection into the sciatic nerve (SN) are the presence of a liquid pool “within outer epineurium”, an increase in the cross-sectional area of the nerve, and an increased tibial-peroneal spread [4]. Using these criteria, an intraneural injection during popliteal SN block occurs in up to 94%, in two studies there was no evidence of nerve damage either in postoperative neurophysiological examination or in the clinical follow-up [2,3].
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