I am seeing too many drug injection injuries of the tibial nerve at the level of the tarsal tunnel, especially in very young patients. If you do inject steroids into the tarsal tunnel for tarsal tunnel syndrome, I have to ask a simple question: Why?
I know the answers are going to be: “because that’s what I learned in residency,” “that is the way I was taught,” “I want to treat it conservatively,” or something like “it’s a neuritis and I want to treat the inflammation.” Another common reason that I frequently hear is “because that’s the way they do it for carpal tunnel syndrome.”
I would respond to these answers with some follow-up questions: “Is the tarsal tunnel the same as the carpal tunnel?” “Is it really a neuritis?” “If that’s the way you were taught, have you done any follow-up study or research since that time?”
When you really ponder this question and look at peripheral nerve physiology and the pathophysiology of tarsal tunnel syndrome specifically, you will be much more reluctant to jam a signature “cocktail” of triamcinolone, Marcaine, B12, dexamethasone and any other ingredients or combinations in your special elixir.
What is really happening when we put our special elixir in or around the nerve? There are two important things we need to differentiate here: extraneural and intraneural. There is a huge difference folks, even if you are just injecting bacteriostatic saline. Yes, even saline injected in the intrafascicular region can cause nerve injection injury.
I always think back to some of those decerebrate professors who taught me how to give a “PT” injection. “You always need to elicit a paresthesia,” they would espouse (remember, that’s the way they were taught). “That way you can find the nerve.”
Really great stuff, huh? How many of you are good enough to maintain that precise needle placement when the patient and his leg are flying off the table in opposite directions? Occasionally, you will not only get an expletive hurled at you but the needle will end up in the provider.
I have seen posterior tibial nerve injury from simple lidocaine injections (fortunately the patient almost always gets better after about eight weeks of discomfort) because the provider had to elicit a paresthesia.
In fact, I teach students and residents specifically not to elicit a paresthesia. Sometimes it will happen but that is vastly different than trying to elicit a paresthesia every time you attempt to block a tibial nerve. There is a simple concept here. Know your anatomy, infiltrate slowly, place the agent near and around the nerve and, at the first sign of a paresthesia, back up a millimeter or two. Small gauge needles like 30 g are excellent and much more comfortable. Every time you stick something into a nerve, something gets damaged. Bigger needle, bigger damage. Blow more in, blow more out—fascicles that is.
So if saline can damage a nerve, what about other agents? Whitlock demonstrated that even extraneural infiltration of ropivacaine can cause nerve damage with epineural fibrosis in the rodent model.1 MacKinnon studied the effects of steroid injections and she reported that only intrafascicular injections caused damage but that damage varied by the agent used.2
Hydrocortisone and triamcinolone caused axonal and myelin degeneration. These agents simply are neurotoxic. When one injects these types of agents into the nerve, they cause intraneural fibrosis, which is a type XI peripheral nerve injury (neuroma in continuity).
Okay, now I hear the gears churning. “If I can’t even put saline in there without potential of hurting the nerve, what can I inject in there?” A really good thing would be nothing. “Nothing” cannot hurt the nerve. If you think it is neuritis, then give the patient a whopping systemic dose of a steroid. He or she will probably love you even more because you have temporarily treated the patient’s degenerative hips as well.
If you want to be conservative, try orthoses. They work sometimes and when the orthotic exacerbates the patient’s condition, it is almost pathognomonic that the patient has a tarsal tunnel syndrome. Budak showed that pronation caused distal latencies in the medial and lateral plantar nerves.3
Here is one to get you going. Maybe you should stick a subtalar implant into the sinus tarsi? Graham showed improvement with intra-tunnel pressures recently by decreasing pronation with subtalar arthroereisis.4 I know some of you are asking how that can be conservative. Well, folks, arthroereisis causes no permanent nerve injury and one can easily remove the implant if there is a complication. If the patient is really pronating badly, isn’t it better to treat the real etiology than just a symptom out at the “tip of the iceberg”?
What about the difference in anatomy between the tarsal tunnel and the carpal tunnel? Even though steroid injections can treat carpal tunnel syndrome, this method of conservative care is waning in use, especially by hand surgeons. At least there are some synovial sheaths in the carpal tunnel that can react to an anti-inflammatory if it is present in the sheaths. This is not analogous in the tarsal tunnel.
However, when it comes to carpal tunnel syndrome, research has found that corticosteroid injections decrease the success rate of neurolysis.5 So why give the patient something which will only be temporary at best, could potentially cause a permanent nerve injection injury and decrease the potential surgical outcome if it comes to neurolysis?
1. Whitlock EL, Brenner MJ, Fox IK, Moradzadeh A, Hunter DA, Mackinnon SE. Ropivacaine-induced peripheral nerve injection injury in the rodent model. Anesth Analg. 2010; 111(1):214-220.
2. Mackinnon SE, Hudson AR, Gentili F, Kline DG, Hunter D. Peripheral nerve injection injury with steroid agents. Plast Reconstr Surg. 1982; 69(3):482-490.
3. Budak F, Bamac B, Ozbek A, Kutluay P, Komsuoglu S. Nerve conduction studies of lower extremities in pes planus subjects. Electromyogr Clin Neurophysiol. 2001; 41(7):443-446.
4. Graham ME, Jawrani NT, Goel VK. The effect of HyProCure® sinus tarsi stent on tarsal tunnel compartment pressures in hyperpronating feet. J Foot Ankle Surg. 2011; 50(1):44-49.
5. Gelberman RH, Aronson D, Weisman MH. Carpal-tunnel syndrome. Results of a prospective trial of steroid injection and splinting. J Bone Joint Surg Am. 1980; 62(7):1181-1184.