Dear Editor,
The superficial peroneal nerve (SPN, L4-S1) is one of the terminal branches of the common peroneal nerve (CPN). SPN block (SPNB) is performed using either landmark-guided or ultrasound-guided technique as a component of the ankle block. Isolated SPNB is used to provide incision congruent regional anesthesia/analgesia (RA) in surgeries involving the dorsum of the foot. We write this letter to discuss some anatomical facts about SPN and describe a novel peripheral nerve stimulation (PNS)-guided block technique.
The SPN is a mixed nerve.[1] After arising from the CPN, the SPN travels deep to the peroneus longus (PL) muscle in the lateral compartment of the leg. Then, it runs between the PL and the extensor digitorum longus (EDL) muscles proximally and peroneus brevis (PB) and EDL muscles distally [Figure 1a and b]. SPN pierces the crural fascia and becomes superficial through the peroneal tunnel at the junction of the upper two-thirds and lower one-third of the leg.[2] Proximal to the ankle, SPN divides into the medial and intermediate dorsal cutaneous branches, which innervate the anterolateral aspect of the leg and the greater part of the dorsum of the foot, excluding the first web space. SPN gives motor innervation to the PL and PB muscles. Thus, it is responsible for the eversion of the foot, which is the desired evoked motor response during neurostimulation [Figure 1c].
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Figure 1: Superficial peroneal nerve (SPN) block: (a) Position of the leg and anatomical landmark; (b) Transverse section of the leg at the junction of the proximal two-thirds and distal one-third of the line joining lateral condyle of the tibial (LC) and lateral malleolus (LM); (c) Needle entry point; (d) Placement of the linear transducer over the needle entry point; (e) Ultrasound image of SPN. EDL-extensor digitorum longus, EHL-extensor hallucis longus, TA-tibialis anterior, DPN-deep peroneal nerve, ATV-anterior tibial vessels, PL-peroneus longus, PB-peroneus brevis, TP-tibialis posterior, FHL-flexor hallucis longus, FDL-flexor digitorum longus, PV-peroneal vessels, TN-tibial nerve, PTV-posterior tibial vessels, LSV-long saphenous vein, SL-soleus muscle, AT-Achilles tendon, SN-sural nerve, F-fibula, T-tibia
PNS-guided SPNB can be performed by stimulating the motor component. The SPN is targeted at the level where it becomes superficial after penetrating the crural fascia. This level was found at about 12 cm proximal to the ankle joint, corresponding to the junction of the upper two-thirds and lower one-third of the leg.[3]
Based on the cadaveric studies, we developed a novel PNS-guided approach, which we describe as the “SANTU” (Santosh-Tuhin) technique of SPNB. The patient lies supine or lateral, and the side to be blocked is kept over a pillow or padded support [Figure 1a]. The lateral condyle of the tibia and the lateral malleolus are identified. A line joining these two points is divided into three parts, and the junction of the proximal two-thirds and distal one-third is marked. At this point, the needle is inserted perpendicular to the skin in the groove between the EDL muscle anteriorly and the PB muscle posteriorly [Figure 1c]. The initial settings are set at the current of 1–1.5 mA, frequency of 1 Hz, and pulse duration of 1 millisecond. The current is gradually decreased to 0.4 mA once the desired response, that is, foot eversion, is achieved. After negative aspiration, 3–5 mL of local anesthetic is injected.
A small artery and vein usually accompany the SPN.[4] An ultrasound image can visualize and confirm the presence of a small pulsatile artery near SPN [Figure 1d and e]. Hence, regional anesthesiologists must be careful during SPNB to avoid inadvertent vessel injury and systemic injection of LA.
In conclusion, SPN can be blocked using a neurostimulation technique. However, further anatomical and clinical studies are warranted.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References
1. Ribak S, Fonseca JR, Tietzmann A, Gama SA, Hirata HH. The Anatomy and morphology of the superficial peroneal nerve J ReconstrMicrosurg. 2016;32:271–5
2. Agthong S, Huanmanop T, Sasivongsbhakdi T, Ruenkhwan K, Piyawacharapun A, Chentanez V. Anatomy of the superficial peroneal nerve related to the harvesting for nerve graft Surg RadiolAnat. 2008;30:145–8
3. Valisena S, Gamulin A, Hannouche D. the intraseptal course of the superficial peroneal nerve: An anatomic study Foot Ankle Int. 2021;42:1171–8
4. Nagabhooshana S, Vollala VR, Rodrigues V, Rao M. Anomalous superficial peroneal nerve and variant cutaneous innervation of the sural nerve on the dorsum of the foot: A case report Cases J. 2009;2:197
