Our pediatric patients often present with painful injuries to the extremities which warrant treatment with potentially painful procedures. In our effort to minimize pain, these patients may receive local anesthetic injection, which can be painful in itself (especially to the sole of the foot!) or even receive sedation using agents like Nitric Oxide, ketamine or propofol- all of which require significant departmental resources, not to mention a non-insignificant risk to the patient. Many of these injuries can potentially be treated with targeted regional anesthesia instead, which is requires minimal resources, generally tolerated very well by the patient, offers true anesthesia to the region of interest all while being safe to the patient if performed correctly. The use of ultrasound guidance adds not only a layer of safety to the procedure but also improves efficacy, and should be considered for all nerve blocks performed in the ED.
Below, we outline a few cases in which regional anesthesia to the foot was utilized and some guidance on how to perform this extremely useful procedure.
Patient 1:
15y healthy female presenting with an abscess overlying her L plantar MTP joint surrounding a 'wart.' Seen at Urgent care and started on cefalexin without improvement, and now developing streaking redness to foot. She was otherwise well. After an ultrasound-guided posterior tibial block, she underwent successful I&D without addition of local anesthetic.
Figure 1: Plantar Abscess
Patient 2:
7 year old healthy male presenting with L foot pain after stepping on a needle 2d prior. Seen at Urgent Care with X-ray demonstrating a foreign body in the plantar foot. After an ultrasound-guided posterior tibial nerve block he underwent successful foreign body removal under real-time C-arm guidance.
Mid way through the procedure (with a hemostat buried in his foot) he asked us to let him know when we were going to start.
Figure 2: Xray with metallic plantar foreign body
Ultrasound-guided Posterior Tibial Block:
The posterior tibial nerve provides sensory innervation to the bulk of the plantar foot. It is easiest identified just posterior to the medial malleolus in close proximity to the posterior tibial artery.
Figure 3: transducer and needle location for in-plane approach to ultrasound guided posterior tibial block
It has the appearance of a honeycomb, with clusters of hypoechoic circles with a hyperechoic outer ring.
Figure 4: Illustration of nerve bundle vs ultrasound appearance of peripheral nerve (yellow circle)
It can be tracked proximally (video 1) ideally to just above the level of the origin of the Achilles tendon where it is amenable to block approach from the posterior calf. This is beneficial as the needle trajectory at this location is close to perpendicular to the ultrasound beam, which assists with needle visualization.
Figure 5: Needle trajectory and impact on ultrasound reflection.
Needle perpendicular to beam (left) will appear brighter due to increased reflections, while steeper angles (right) will cause image degradation due to information reflected away from transducer
Given the favorable needle angle, it is possible to use a small gauge needle to perform the procedure, and thus minimize discomfort with initial needle insertion. We prefer to use a 27G 1.5" needle, directed using a real-time in-plane approach After aspirating to confirm lack of blood vessel injection, incremental amounts of anesthetic (in these cases 1% lidocaine w/ epi) can be injected, for a total of ~5 cc. Anesthetic should be seen dissecting next to and around the nerve (video 2) The needle can be repositioned as needed to improve spread around the nerve, but completely surrounding the nerve is not necessary. Depending on the anesthetic used, there will be a slight delay in onset of anesthesia to the affected region. In this case, with 1% lidocaine with epinephrine, the block usually takes 10-15 minutes to 'set-up'
Figure 6: Position of tibial nerve to artery (red/yellow lines) in location of potential blockade and nerve distribution of posterior tibal block (blue), with saphenous nerve distribution (pink) and sural nerve distribution (red)
Figure 7: Ultrasound appearance at location of block. (FHL=Flexor Hallucis Longus mm., N=Posterior tibial nerve, Red circle= posterior tibial artery FDL=Flexor digitorum longus tendon, TP=tibialis posterior tendon)
Video 1: Using dynamic scanning to locate posterior tibial nerve
Video 2: Needle insertion and deposition of local anesthetic
Remember: the next time you have a painful procedure to the plantar foot, maybe there's a better way...
References:
1. Colgrove RC. Posterior tibial nerve block.Foot Ankle Int.2001;22:839–840.
2. Soares LG, Brull R, Chan VW. Teaching an old block a new trick:ultrasound-guided posterior tibial nerve block. Acta Anaesthesiol Scand. 2008;52:446–447.
3. Redborg KE, Antonakakis JG, Beach ML, et al. Ultrasound improves the success rate of a tibial nerve block at the ankle.Reg Anesth Pain Med.2009;34:256–260.
4. Chin KJ, Wong NW, Macfarlane AJ, et al. Ultrasound-guided versusanatomic landmark-guided ankle blocks: a 6-year retrospective review.Reg Anesth Pain Med.2011;36:611–618.
5. Wathen JE, Neubrand T, Do H. Regional anesthesia in the pediatricemergency department. Clin Pediatr Emerg Med. 2017;18:268–285
6. Shah A, Morris S, Alexander B, et al. Landmark Technique vs Ultrasound-Guided Approach for Posterior Tibial Nerve Block in Cadaver Models. Indian J Orthop. 2020 Jan 13;54(1):38-42. doi: 10.1007/s43465-019-00012-6. PMID: 32211127; PMCID: PMC7065735.
Written By: Matthew Moake, MD, PhD
Edited by: Aalap Shah, MD
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