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Board Review Neurology

Failed Nerve Decompression

Guido LaPorta, DPM, MS

Guido LaPorta, DPM, MS discusses tarsal tunnel syndrome and nerve decompression. Dr LaPorta begins by reviewing diagnosis and staging of nerve injury and discusses surgical correction and nerve decompression in detail. He focuses on what to do if the surgery fails including diagnosis and treatment of temporary, partial and no relief of symptoms.

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Goals and Objectives
  1. Define tarsal tunnel syndrome and discuss how it is diagnosed
  2. Review the staging of nerve injury and discuss the pathophysiology and nerve regeneration associated with each stage
  3. Identify common causes of failed nerve decompression including those that cause only temporary relief of symptoms, partial relief, and no relief of symptoms
  4. Discuss in detail how a neurostimulator is placed and what patient population it should be reserved for
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  • CPME (Credits: 0.75)

    PRESENT eLearning Systems, LLC is approved by the Council on Podiatric Medical Education as a provider of continuing education in podiatric medicine.

    PRESENT eLearning Systems, LLC has approved this activity for a maximum of 0.75 continuing education contact hours.

    Release Date: 03/16/2018 Expiration Date: 12/31/2018

  • Author
  • Guido LaPorta, DPM, MS

    Director Podiatric Medical Education
    Community Medical Center
    Scranton, PA

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  • Lecture Transcript
  • So you may think you're done with me but you are not because I have a few talks in a row here. The next one is failed nerve decompressions or injuries to nerves and I'm going to use the tarsal tunnel as the model for this because what happens to it, it can happen to any nerve. And what is tarsal tunnel, you know when you ask that diagnosis to somebody, they say, “Well it’s compression of the tubular nerve on the medial side of the ankle and it produces pain”. And that’s true. And you know the next thing I get is that it’s similar to carpal tunnel. And that’s true.

    But it’s interesting, isn’t it? In order to make the diagnosis of carpal tunnel the EMG and nerve conduction has to test six nerves in order to make it a tarsal tunnel it has to test 10 nerves. So they are not completely comparable, okay. They are not completely comparable.

    But when I asked my residents’ what’s tarsal tunnel, here is my answer. It’s a grade 3 nerve injury. It’s usually accompanied by a positive Tinel sign. And what is the Tinel’s sign tell you? What is the Tinel sign tell you, anyone.

    Does it tell you that the nerve is compressed? Does it tell you that the nerve has the ability to heal? Alright. The real answer is that when you get a positive Tinel sign you know the nerves A alive and is attempting to heal, you have no idea whether it can complete that process but it is attempting heal. The other thing I want my residents to know is that the first sign of a compressed nerve is a decrease or loss of static two-point discrimination. Difficult to measure in the foot but not impossible. You can measure it at the end of the hallux, the normal range there is about 5 mm two-point discrimination that they can appreciate, and in the heel it’s about 8 mm, okay.

    And if this compression syndrome is around long enough you begin to get wallerian degeneration of the nerve. And clinically this can be shown by sensory disturbances which you and I are very familiar with but what we forget about is atrophy. What we forget about is weakness at various muscle groups, okay. How does a radiologist help you make the diagnosis of tarsal tunnel? Any idea.

    If you order an MRI which I do on a number of these cases, not all. The radiologist can tell you whether or not there is atrophy of the abductor digiti minimi and that is pathognomonic of lateral plantar nerve compression. Every MRI reading radiologist knows that because it’s plastered all over their literature, alright. So when you get an MRI report back and says there's atrophy of the abductor digiti minimi that’s a significant finding. The only way that happens short of an over trauma is that you have compression of the lateral plantar nerve, okay.

    Alright so staging of injuries. We are all familiar with Seddon and Sunderland and Seddon’s classification divided it into three, alright Neuropraxia, Axonotmesis, Neurotmesis. Sunderland took it a little farther, alright. And he divided it into five different degrees. And when I talk to my residents I told them if you know this graph you can answer any nerve question on your board exams, forget about treating patients. You can pass any exam you have by knowing what's on this graph, alright.

    So what's a first-degree injury? It's a metabolic block or segmental demyelination, what's important to know about that? That's completely reversible. It will heal on its own completely usually in a few hours but it may take up to 3 to 6 weeks. So if you have a neuropraxia you know that that is going to completely heal. An EMG and nerve conduction can tell you the difference between first-degree and all the others. It can’t tell you whether you have second, third, fourth or fifth degree but it can tell you whether or not you have neuropraxia or a more serious injury.

    As you get down to grade 2 or degree 2 you have a loss of axonal continuity. This is important to know also. These are those injuries when we talked about ankle sprains yesterday and we talked about stretch injury this is basically a stretch injury, okay. You’ll lose some of the axons. Why is that important to know? It’s important to know because this will heal completely also but at a rate of about a millimeter a day financial month, okay third degree is what tarsal tunnel is.

    Tarsal tunnel is compression to the point where you lose a portion of the epineuriun. And unless that compression is released you get incomplete healing. It still will heal at a little rate of 1 mm a day until it reaches a plateau past which will not heal anymore, alright. So no tarsal tunnel that comes into the office is a surgical emergency, alight. What you need to ascertain from your history is how long have you had this, is it getting better? If it's getting better wait because it may be a second-degree injury but if the history says well you know it was getting better and then all of a sudden over the last two months it stayed exactly the same, maybe gotten a little worse, well then it’s a grade 3 injury or a 3rd degree injury. So you can make the diagnosis whether or not just by your history, alright.

    So what are the only reasons to operate on a tarsal tunnel immediately? One is atrophy of a muscle group, the second weakness and the third is persistent sensory pain unresponsive to any type of medication, alright. Those are the only three reasons why you need to schedule it soon otherwise you can wait. Now what’s a 4th degree injury? Well a 4th degree injury is what's referred to as a neuroma-in-continuity. And a neuroma-in-continuity is basically scar tissue within the nerve. So even though the nerve is trying to heal all these little axons that are going out can't get past the scar tissue, okay. Fourth degree and 5th degree behave the same way clinical. Fifth degree is an actual transection in the nerve, there's a gap between the two nerve endings.

    Fourth degree acts exactly the same way only it does so because there is scar within the nerve. And that scar maybe caused by any one of a number of conditions, for instance an Intraneural schwannoma can behave like a fourth degree nerve injury because it prevents the axons from getting by. The important thing to know, degree 4 and 5 do not heal at all, you need to do something about that or you needed to get it to somebody who can do something about that.

    So what about the tarsal tunnel? Well Dellon was the one who popularized the extensile incision or the curvilinear incision over the entire course of the medial malleolus and he emphasized the fact that you must release the distal tunnels, okay. And when you do this particular dissection the first thing you do is release the flexor retinaculum you usually see that it's a flimsy areolar cellular type tissue that you can quite easily put a hemostat under listed away from the nerve and in sizes. And when you do that you see the vena cava [indiscernible] [0:09:59] the artery and the nerve is the deepest structure in this tunnel, alright. It’s the deepest structure in this tunnel.

    Now the bottom arrow is pointing to a significant structure this is the top of the fascia covering the abductor muscle belly. Right behind this are the two distal tunnels for the medial and lateral plantar nerve. And if in fact then you cut that fascia over the muscle and then tease the muscle away so the fascia is cut, I’ve teased the muscle away from this fascia which is the separation between the abductor and the short flexor muscle belly and you can see I am putting an instrument right into one of the canals for the terminal branches so the medial terminal branch kind of goes this way. The lateral terminal branch kind of goes in line with the tibia.

    And you need to make these two tunnels one tunnel and therefore do that you need to excise this triangular band fascia. And unless you do that you haven't done a good tarsal tunnel release. Alright. And when you do that if you get really carried away you see a number of nerves some of which you didn’t realize were there. So one of the reasons [indiscernible] [0:11:36] incision is nerves, some of which you didn’t realize were there.

    So one of the reasons your incision if you make one this long needs to curve away from the medial malleolus is that there are two nerves very close to the medial malleolus, the terminal branch of the saphenous nerve and the recurrent articular branch to the ankle. You can bag those and not even know it if your incision is too close to the malleolus. What's the consequence of that?

    You will get a neuroma of those nerves which may hurt more than the original tarsal tunnel. So be careful of that. Frequently when you're in there you are trying to determine whether there's any intraneural or subepineural scarring, well how do you find that? Well one easy way to do it is to get a tuberculin syringe filled with saline and inject it under the epineurium and what you're expecting to see is the epineurium baloon out circumferentially around the nerve. If it doesn't if part of the epineurium is adhered to the underlying nerve that part of the epineurium needs to be removed. So you have to do an epineurotomy or an intraneural dissection. Okay. Enough of that.

    So you do your tibial nerve decompression, what are the results that you normally see? Well I kind of dump them into four categories. You either get complete relief, everybody is happy or you get no improvement at all right from the start. Patient tells you first postoperative visit feels terrible. I still have my symptoms I don't feel any better at all. That rarely happens. What usually happens is you either get partial improvement or you get somewhere down the road recurrent entrapment, alright.

    And that recurrent entrapment usually occurs 6 to 7 months after the initial decompression, alright. So why do tarsal tunnels fail? You may have had an incorrect initial diagnosis, you may have done an incomplete release; only you know that if you did the original surgery because I can tell you. I mean what are you going to do call up the previous surgeon and say did you do an incomplete release? The chances are you are not going to get a very accurate answer from that person, right. So the only way you know if one was done is if you did the original surgery.

    You can have adhesive neuritis. An adhesive neuritis is probably the most common recurrent problem. You can have a postsurgical neuroma because you cut a nerve or a branch of the nerve that you weren’t even aware was there and that can happen, I mean these nerves are very small in this particular area. You can do intraneural damage. Don't inject steroid in a nerve, it causes scar tissue much to your surprise that’s the opposite of what you would expect but intraneural Cortizone causes scarring.

    You may have a double crush syndrome, we’ll talk about that in a minute or maybe a combination of problems, alright. So when I look at tarsal tunnel decompression and I only got partial improvement, there can be any one of a number of reasons for that. There may be a systemic disease which is producing nerve symptoms and if that's the case you need to work that up and refer for appropriate treatment of that systemic disease or you can have a double crush syndrome or you can have an incomplete release. So what do you do about that?

    Well if you are sure that there was an incomplete release you can do a revision neurolysis, but I would suggest that if you do that that you hedge your bet and put some kind of barrier in there. You don't have to use a vein, you don't have to use anything, you can use a collagen wrap that almost every company makes now to protect the nerve from the healing skin and subcutaneous tissue.

    Your results from that is either going to be relief or no relief. And if you get no relief from your revision neurolysis I would never do a third one, ever do a third one. I’ve had patients in the office who’ve had seven tarsal tunnel releases, okay. And I kind of wonder, you know why, I mean were you actually getting relief from some of these that made the surgeon want to try it again? And you know the answer is invariably no, I got no relief from any of them. So I can't imagine why you would expect the sixth one to work better than the third one. You get one shot at it and you may be lucky and get a second shot, the revision neurolysis after that forget about it.

    And if somebody comes in and they have life altering pain from this problem I do a peripheral nerve stimulator which I’ll show you in a minute. So revision tarsal tunnels the literature is scant on this, they are not well populated studies but here is one in 1994 that notes that scarring that requires you to remove the epineurium has a less favorable results than those with minimal scarring and there's a number of ways of doing a revision neurolysis, you can do a barrier procedure which means you wrap nerve in a vein or you can do muscle flap or you can do a neuro wrap off-the-shelf collagen wrap. Or you can do a containment procedure which means this nerves causing pain I’ll sacrifice it and bury it in either enervated skeletal muscle or medullary bone. How do you make that decision.

    Well usually you want to take a noncritical nerve, like if somebody came in and had a sural nerve issue where you are going to be numb on the outside of your foot here and in the fifth toe. Most patients who have significant pain think trading numbness for pain is a good deal, okay. So I do containment procedures on noncritical nerves and I do barrier procedures on critical nerves.

    Here is the way I used to do it, you get a greater saphenous vein I would be devalve it and I would wrap the inner endothelial surface around the nerve so here was one of those nerves, I can tell you right now today I would never do this on a nerve that looks this bad although we did get some relief with this it was nowhere near what I would expect. In there you see the nerve wrapped with the vein which keeps the scar tissue away from that nerve. Vein wrapping has mixed results.

    Typically you can get six or seven patients out of 10 to have good results but a quarter of the patients may actually work do worse so they need to know that, right. Here's using a muscle flap, this is the abductor hallucis which is liberated from its attachment on the calcaneus, it's then pivoted in a dorsal direction to cover the nerve to prevent scarring from on top.

    You can use a nerve protector and these are usually highly purified collagen structures which are porous to the point where they will prevent scar tissue from getting in but allow metabolites to exit, come in various sizes in lengths and typically they’ll prevent scar, minimize entrapment concentrate growth factors because they won't let them come out and they can also guide regenerating fiber, so here you can see these collagen wraps placed in various areas on the nerve. And here's a nerve that's delivered and then it wrapped with a collagen wrap.

    Now here was an interesting case. This is the lady who had seven tarsal tunnel syndrome surgeries. So I couldn’t get a peripheral nerve stimulator approved for her so I said, you know I'm not sure what to do, you have this terrible nerve I know it's a mess, your only answer in my mind is the nerve stimulator, I don't want to sacrifice the nerve. And she asked me, why, she was a PhD who taught chemistry at SUNY Binghamton.

    And I said, well you are going to get all kinds of problems in the foot, you are going to hammer toes. She said I already have hammer toes. So I stepped away a little bit known and tried to see the forest and she was right, she had every complication you can possibly have from this tarsal tunnel so sacrificing the nerve wasn’t going to do anything. So here we went in, you know when we talked about everything [indiscernible] [0:21:48] is the nerve you can see it start to thicken. Up top is normal nerve, down here is that the thickened nerve and when it was separated from the distal area, you can see the thickness bulbousness and loss of fascicles, it just doesn’t look like a nerve, it looks like scar tissue, alright.

    So all of that is cut back to normal nerve tissue and that’s the scar that was removed and then you can see the fascicles now so this is fairly normal nerve and we buried into the soleus muscle belly and mysteriously symptoms her improve from like an 8 to 3 1/2 which is life altering, alright. So in this case this is the only case that I can remember that I sacrificed a critical nerve and it was for the reasons I mentioned.

    If you have a systemic disease you need to address the underlying etiology and you could have a double crush syndrome, what does that mean? Well double crush syndrome means that there is a nerve problem somewhere else that is contributing to the symptoms, that could be compression higher up or it could be peripheral neuropathy so I know the tarsal tunnel is a clinical diagnosis but I get an EMG and nerve conduction on everyone I’m going to operate on.

    And the only reason I do that is because the EMG and nerve conduction I know will miss the diagnosis 20% of the time, but it will tell me if there's a peripheral neuropathy, it will tell me if there's a plexopathy, a radiculopathy, a myopathy it'll tell me if there is anything anywhere else that will affect the results of my decompression so I can then alert the patient as to what they might possibly expect.

    Temporary relief with recurrence, I mentioned adhesive neuritis usually occurs 6 to 7 months after the initial procedure, rule out infection and hematoma, you can do a revision neurolysis with the techniques that I have just mentioned, if that fails, stop. These people need either a spinal cord or peripheral nerve stimulator. I like peripheral nerve stimulators for mononeuritis problems. So if I can isolate the symptoms to one nerve then I like the peripheral nerve stimulator. And I’ll show you what that looks like, here's a couple of examples, here is we open up to do a tarsal tunnel syndrome and lo and behold there is a neuroma in continuity of the tibial nerve.

    I've also seen neuroma in continuities of the common peroneal nerve. So that brings me to neurostimulation. And neurostimulation, here I'm asking the patient to plot where they have pain and to rate it on a scale of 10 visual analog scale and here I am going down to the tibial nerve above the injury, that's a little electrode that I sutured to the fascia and then circumvented so that I have a fascial graph covering the electrode. I then deliver the posterior tibial nerve and I suture the electrode to that nerve.

    Now in the beginning this was done under general anesthetic and I numb the edges of the wound. The anesthesiologist would wake the patient up and would stimulate the nerve to find out if it was covering the areas of pain. I no longer do that. We found that if you do a posteromedial placement of the electrode that you get the majority of the fascicles to go to the foot. In addition the initial electrodes even though they were large only had four electrodes. The new ones that I now use have 16 electrodes in them. And you get a far better coverage of the nerve, alright. So then the fascia and electrode is sutured to the nerve. I then run the electrode up to the battery which is buried in the lower thigh which in our institution is called the upper leg. And there you see the placement of that.

    We just submitted the paper for publication. We’ve done over 70 of these over the last eight years and it's one of the most gratifying procedures I do for patients who have pain. They get life altering changes in their pain reduction. This is one on a common peroneal nerve and you can see the tunneling and then attached to the battery. You can do common peroneal and tibial nerve if you wish, in fact there are lot of people doing studies now on patients with diabetic neuropathy to see if these peripheral stimulators on both of those nerves will in fact improve symptoms.

    The literature which I have to update in this talk is far better result wise as the equipment improve, in fact there was just a letter or an article by Giancarlo Barolat who practices in Denver. He used to run the neuromodulation service at Jefferson Medical School and Hospital moved to Denver to set up a huge pain service and the results are fantastic with these. I think it's because you are attaching it right to the nerve that’s causing the problem. So the injured nerve I would suggest that if you have somebody come into the office that has a recurrent tarsal tunnel that you need at the very least to get an EMG and nerve conduction and an MRI.

    And the reason for that is that you need to determine if there's any etiology that may have affected the result of the previous decompression and you also need to look for scar tissue. You need to look for space occupying masses which may have been missed. And I think before you embark on a treatment program, especially if that treatment program requires reintervention that you owe it to that patient to make as accurate a diagnosis as possible so that you leave no stone unturned. I would also recommend that revisional procedure is the maximum because I've done a lot of tarsal tunnel surgery and nerve decompression. You get one good chance at a good result. Your second timing gives you a best, a 50% result, after that it's all downhill so I would get these people to a pain clinic and get them evaluated for neuromodulation if they’ve had two failed tarsal tunnel procedures.

    Okay, so we have a minute, are there any questions, if not I am going to—

    Q: What is [indiscernible] [0:30:25] battery replacement?

    Speaker: Okay, very good question. There are two types of batteries that you can use, one of which is rechargeable. The non-rechargeable batteries will last anywhere from 5 to 8 years depending on usage because your patients will use these differently. Some people will only use them when they are sleeping. They can put up with it during the day it’s when they are sleeping that it bothers them terribly. Others will run it 24 hours a day so that one obviously is going to wear out lot quicker.

    The newer ones are smaller and rechargeable. These are reserved for desperate patients. A rechargeable battery and one lead cost $24,000. And the insurance company goes nuts until I tell them, why don’t you look at your physical therapy bills for this patient because you spent $24,000 in two months on physical therapy which has done nothing for this patient. And when they do that I always ask for a peer-to-peer review, in other words I want to talk to a doc.

    And when I explained to the doc, the patient doesn't want a spinal cord or a spinal cord is only affective half the time because you have no guarantee you are going to get the right nerve stimulated. The only way to guarantee that is to attach it to the nerve that's causing the problem and the cost of this device is going to save you hundreds of thousands of dollars over the course of this patient's life between medications, physical therapy et cetera, et cetera. I've never had one turned down because it just makes sense, it just make sense. So $24,000 is a drop in the bucket. Anything else, yes.

    Q: [indiscernible] [0:32:45]

    Speaker: Another good question, thank you. We did that for a period of time and I think the issue is that to cover the amount of nerve you would have to with a neural wrap, actually takes more deception. So you can’t cover the entire breadth of the tibial nerve and then each of the terminal branches with a neural wrap because you are basically talking about using about $10,000 worth of material for something where there's no evidence that it actually makes a difference and as it turned out it didn’t make a difference. We thought the same thing that made sense but it didn’t.

    Q: [indiscernible] [0:33:56]

    Speaker: There are basically three companies who make this device Medtronic is one St. Jude's and ANS. I've used them all. They are equal. They are all the same technology so you know it's a matter of who your hospital has a contract with. Okay break time. So please while you're here or in the near future jot down your thoughts about the program we take them very seriously, we are always looking to improve what we present. We certainly are interested in what you want to hear and we would be very appreciative if you take the time to evaluate the whole process. Okay thanks for your attention.