The study of peripheral nerve compression began in earnest in the late 1980's with a number of researchers; among which was A. Lee Dellon, M.D. who is a professor of Plastic Surgery and Neurosurgery at Johns Hopkins University Medical School. As a result of his research, Dr. Dellon has published over 100 papers and a number of books on the subject of peripheral nerve entrapment.
As the nerves leave the spinal chord to innervate the remainder of the body, they are required to pass around and through the bones, muscles, lingaments and tendons of the extremities in order to reach their ultimate destination. In doing so, there are areas of the body where these nerves must pass through very small canals or tunnels. Two of these important tunnels are: in the wrist, the carpal tunnel; and in the ankle, the tarsal tunnel. It is in these two areas that the nerves leading to the hands and feet become trapped and compressed, causing symptoms of numbness, weakness, tingling and burning pain. Our area of expertise is the tarsal tunnel on the inside of the ankle and in some cases the anterior tarsal tunnel in the front of the ankle.
HOW DO THESE NERVES BECOME COMPRESSED?
As nerves pass through these very small tunnels, there are a number of reasons why they can become compressed. Sometimes injuries and surgery to repair ankle injuries can cause scar tissue in the areas of the tunnels. Even repeated ankle sprains over a life time can cause Tarsal Tunnel Syndrome which we will talk about in a minute. More recently, studies have shown that some of the agents used in chemotherapy treatment (Cisplatin and Taxol) are also causative agents in peripheral neuropathy. The vast majority of peripheral neuropathy patients that we treat; however, are diabetics. We will address this first.
In diabetes, there are three causative principles that lead to the compression of the nerves as they pass through these restricted tunnels:
- In a diabetic with elevated sugar levels; even though they are in good control, the sugar is attracted to the nerve. In the nerve, the sugar is metabolically changed into a substance called Sorbitol. Sorbitol is a substance that attracts water and therefore the nerve becomes larger in volume (swollen).
- As the nerve becomes swollen within the small tunnel, the increased external pressure causes a decreased blood flow to the nerve causing what is called nerve ischemia. As the nerve does not have it's normal blood supply, the consequence is the perception of parathesias. This is the feeling of tingling, burning and then numbness over a period of time. If this is prolonged, some death of the nerve will occur.
- Lastly, there is within the nerve a "flowing" of protein that is used to repair and rebuild damage done to nerves with injuries and daily living. This has been given the name of axoplasmic flow. When there is compression of the nerve as we have described, there is a decrease or slowing of this transport of proteins and thus the nerve is unable to repair itself. When this happens, the nerve becomes hardened and is unable to slide back and forth within the tunnel as we walk. This causes further damage. This was first demonstrated in studies in rats and then later in humans. This is largely the work of Dr. Dellon.
With these studies and conclusions; Dr. Dellon postulated that if he could somehow make the tunnel larger, then the nerve could expand and the symptoms and the nerve damage would be resolved.
WHAT IF I AM NOT A DIABETIC AND HAVE THESE SYMPTOMS?
If you are not a diabetic and have the symptoms, the first thing that must be determined is that indeed you are not a diabetic or a pre-diabetic. There are millions of people who have what is called Metabolic Syndrome or pre-diabetes. A blood test is needed to determine this.
If indeed you are not a diabetic, nerve compression can still occur in these same canals in the ankle. This is called Tarsal Tunnel Syndrome. It is a well known fact that Carpal Tunnel Syndrome is caused by repetative motion in the wrist. This causes a thickening of the fascia that covers the canal. Basically all that needs to be said about this is that walking and running are the most repetative thing that we do. Thus the ligament covering the Tarsal Tunnel becomes thickened, compressing the nerve and causing the same symptoms that the diabetics feel. The only difference between diabetic neuropathy and tarsal tunnel syndrome is that tarsal tunnel can sometimes only affect one side.
As Dr. Dellon was researching these conditions he discovered several additional tunnels in the ankle that had not previously been identified. He found that when these tunnels were decompressed (surgically opened) that the results (relief of pain and return of sensation) skyrocketed from about 70% to 85%.
Also as a result of this rsearch, Dr. Dellon developed a method of testing the nerves that has proven to be more reliable that the traditional EMG. We discuss this under Nerve and Vascular Testing.
WHO IS A CANDIDATE FOR SURGERY?
Certainly the most ideal candidate for surgery is one who is in the very early stages of neuropathy. Because there is little damage done to the nerves at this point, relief of pain and restoration of sensation occurs very quickly. For those who have had it for years, generally the pain diminishes very quickly and then the restoration of sensation occurs over a period of months. For a diabetic, there must be adequate circulation (which we test) and the last Hemoglobin A1c must have been at 7 or below.
HOW ARE THE NERVES DECOMPRESSED?
This procedure is done on an outpatient basis at the Ford Center for Foot Surgery. The procedure is done under Intravenous Sedation (not a general anesthetic) and a regional block anesthetic.
Because we are working with very small nerves, this is considered microsurgery as it is done under magnification.
Once you are comfortably sedated and all of the preparations are made, an incision is made on the inside of the ankle down to the sole of the foot. The incision is then deepened with all of the "bleeders" being cauterized. The band of tissue that is covering the tarsal tunnel is identified and the "roof" of the tunnel covering the nerve, vein and artery is removed. The nerve is then located and is freed from any other bands of tissue. Often the nerve is attached to the artery with scar tissue and they have to be separated. The nerve is inspected and if the sheath covering the nerve is tight or damaged it is opened (internal neurolysis). Once this is done, a second deep incision is made and the nerve passing to the heel (calcaneal nerve) is identified and that canal is opened in a similar fashion. A third deep incision is then made toward the sole of the foot and the last canal is identified. This is actually two side by side canals. This is the most difficult part of the decompression because this canal lies under a muscle. The roof of this canal is identified and removed as well as the septum (division) between the two canals. The nerves now freed are covered with fatty tissue and the skin closed.
If you have an entrappment on the top of the foot, a similar procedure is done in the front of the ankle.
WHAT CAN I EXPECT AFTER SURGERY?
The two most significant complications from this surgery are infection and formation of scar tissue. We do everything that we can to prevent infection. At the time of surgery you will be given an I.V. antibiotic and then oral antibiotics for 5 days following the surgery. To prevent scar tissue formation in the wound we have you do ankle exercises hourly for the first week. This keeps the nerve mobile.
As far as pain is concerned; it is our experience that patients have very little pain following the procedure. Most require little if any medication for pain. As the healing of the nerve progresses, there may be some tingling and shooting pains that we call "zingers". This is normal and inidicates to us that the nerve is healing. Generally, there will be significant relief of the neuropathy pain immediately and then as the days and weeks go by, sensation will return to your feet. With that, you will feel an improvement in balance. Studies have shown that it can take up to a year for complete healing of the nerve; thus, we don't consider you "finished" for about a year. We will do testing during that time to measure improvement.
If you have any questions concerning this, please feel free to contact us.