Compression neuropathies of the posterior tibial nerve and its branches are a fairly common group of disorders, which are often misdiagnosed.1,2 In order to diagnose lesions of these nerves accurately, one must maintain a fairly high index of suspicion of their presentation. Relying on abnormal findings via electromyography and nerve conduction velocity testing is risky because the incidence of false negatives is quite high.2,3
In contrast, pressure specific sensory testing may produce false positive results. Although the classical presentation of tarsal tunnel syndrome involves compression of the posterior tibial nerve beneath the flexor retinaculum, more commonly, the compressed area is beneath the abductor hallucis muscle and primarily involves the medial calcaneal nerve. Since this nerve is a purely sensory nerve, nerve conduction testing is of little value.
Also bear in mind that tarsal tunnel syndrome is not a single entity. It encompasses compressive or traction injuries to the posterior tibial nerve and its terminal branches, the medial and lateral plantar nerves, as well as the medial and inferior calcaneal nerves.1,2,4,5
Since the site of injury can vary, symptoms will reflect this. For example, compression of the lateral plantar nerve will likely cause pain or numbness in the lateral forefoot while compression of the calcaneal nerves is associated with pain in the heel. Many patients who are diagnosed with plantar fasciitis and treated for that entity often have a poor response to treatment. There is a significant incidence of abnormal neurological findings in patients with chronic heel pain.1,3
Outcomes associated with the treatment of tarsal tunnel syndrome have not been universally favorable. Accordingly, there may be a collective reluctance among foot and ankle surgeons to engage in surgical decompression.3,6 Consider the traditional incision for this operation. The resultant scar follows closely after the incision, there is the course of the neurovascular bundle to contend with and the fact that the postoperative protocol immobilizes the foot and ankle. When one takes an objective view, it is easier to understand the high failure rate associated with this operation.
The development of a minimally invasive approach, which minimizes the risk of perioperative scarring and permits immediate movement with a rapid return to full activities, is something worthy of consideration.1
Salient Diagnostic Insights
When it comes to making the diagnosis of tarsal tunnel syndrome, I prefer to rely primarily on the history and physical examination. While the history may vary, the patient will usually relate a history of pain in the ankle, medial arch, heel or forefoot, which may be present upon first arising in the morning or following periods of rest. Sometimes the patient will describe waking up from sleep with complaints of pain or tingling when lying prone.
Patients may have difficulty describing their symptoms, particularly when it comes to localizing the area of pain or dysthesia. When the patient refers to pain in the forefoot or midfoot, and examination of the forefoot demonstrates a complete absence of confirmatory physical findings, the examiner should maintain a relatively high index of suspicion for the presence of an occult compression neuropathy.
There are four specific physical findings that may present when the posterior tibial nerve or any of its branches are irritated.1,2 One should test for numbness of any part or all of the sole of the foot by comparing the patient’s sensitivity to a light touch with the opposite foot. Physicians should regard the presence of a degree of numbness as a positive finding.
However, the absence of numbness while the foot is at rest does not preclude the presence of a compression neuropathy since compression of the posterior tibial nerve or any of its branches may only occur during weightbearing activities.
Like the flexor compartment of the wrist when the hand is flexed, the porta pedis of the foot is subject to an increase in pressure with certain positional changes.7 When the foot is plantarflexed and inverted (or in some individuals when one performs the opposite maneuver), the pressure in the porta pedis increases. For patients who have compression of the posterior tibial nerve or its branches, they may have numbness and sometimes pain when reproducing their complaint. Authors have referred to this as a positive Phalen’s test of the foot.1,2
Like carpal tunnel syndrome, the presence of nerve compression is a constant finding in patients with compressive neuropathies. However, the examiner must realize that the injury to the nerve may occur anywhere along the distribution of the nerves. The absence of pain under the flexor retinaculum should encourage the examiner to palpate both plantar nerves and the medial calcaneal nerve.
Use a moderate amount of pressure and hold the nerve for several seconds. If direct pressure over the site of entrapment reproduces the patient’s symptoms and/or causes radiation distally, the test is positive.1,2
The presence of a Tinel’s sign over any nerve suggests the presence of axonal damage and regeneration. Given the thickness of the muscular layer over the medial and lateral plantar nerves, one should percuss the nerves with a neurological hammer rather than a finger. Furthermore, the physician should ensure slight inversion of the hindfoot so the flexor retinaculum is relaxed and does not dampen the effect of the hammer.
How To Perform A Minimally Invasive Release Of The Posterior Tibial Nerve
Non-operative treatment of tarsal tunnel syndrome or compression of its terminal branches should include the use of therapeutic nerve blocks with a long-acting corticosteroid. One may also consider other modalities such as physical therapy, orthoses and compression stockings. Currently, there is no level 1 or level 2 evidence to support the non-operative treatment of tarsal tunnel syndrome.
Position the patient on the operating table with a sandbag under the contralateral hip. This facilitates external rotation of the limb that you will be treating. Apply an extra wide arm board to the middle of the table, flex the hip and externally rotate it. Flex the knee so the leg is resting on the arm board. Then place a compressive wrap on the contralateral leg and lower the footrest.
Take care to prevent the contralateral hip and lumbosacral spine from being hyperextended by flexing the table and supporting the thigh with a pillow. This positioning affords the surgeon the ability to position him- or herself on three sides of the foot. Apply a pneumatic tourniquet either to the upper calf or the thigh.
Place the incision on the medial side of the heel and carry it from the tip of the malleolus to the point of the heel. Orient the incision so it lays one finger breadth above and behind the upper border of the abductor hallucis. This location gives the surgeon the ability to visualize proximally beneath the skin of the lower leg as well as plantarly into the sole of the foot.
Using a double-pronged skin hook, elevate the upper skin margin and dissect proximally along the plane of the crural fascia, carrying it approximately 7 cm above the line of the incision. Ensure the patient is in the Trendelenberg position to facilitate visualization of the crural fascia.
Insert a malleable retractor under the skin. The neurovascular bundle should be visible through the translucent fascia. Carefully make a small puncture at the level of the upper edge of the abductor fascia and immediately adjacent to the bundle. Insert a grooved director beneath the retinaculum and push it proximally. Release the distal crural fascia as far proximally as you can see. The surgeon should perform this part of the operation while sitting at the foot of the table.
Then reposition yourself so you are at the patient’s toes, looking across the foot toward the heel. Insert the grooved director under the fascia of the heel and cut the fascia, taking care to avoid inadvertent injury to the medial calcaneal nerve. Continue the release until the point of the director and the point of the scissors contact the medial surface of the calcaneus.
The medial calcaneal nerve should be visible beneath the cut fascia and is usually located within a bed of adipose. Trace the nerve distally to its bifurcation into posterior and descending branches. The posterior branch innervates the skin of the postero-inferior area of the heel while the descending branch pierces the superficial fascia of the abductor and gives off perforators that innervate the medial and plantar surfaces of the heel. The foramina where these branches perforate the fascia are points of compression and require release.
Then release the fascia over the anterior end of the incision all the way to the sheath of the flexor digitorum longus. The upper edge of the abductor should be free. Grasp the superior edge of the common fascia of the abductor with an Allis clamp and pull the muscle outward. Doing so exposes the anterior and posterior compartments, and the intervening septae. Cauterize the septae with a bipolar cautery. The septae serve as conduits for nerve and vascular pedicles to the muscle. Then cut the septae.
Then remove the deep fascia of the abductor hallucis along with the superficial end of the septum. At this point, the medial and lateral neurovascular bundles are surrounded by the muscle bellies of the abductor hallucis and the quadratus plantae. To ensure an adequate distal release, insert a finger into the porta pedis and lyse any remaining fibers of the septae in the sole of the foot.
Key Tips On Wound Closure And Post-Op Care
Release the pneumatic tourniquet and obtain hemostasis. Close the wound in a single layer with sutures or staples. Apply a non-adherent compression dressing from the toes to the knee. Patients may bear weight on the foot immediately but should have crutches for support.
Remove the compression dressing between the fifth and the seventh postoperative day, and apply a large Band-Aid. The patient should wear a short leg compression stocking for the next two weeks. The patient may wear clogs or any other shoe that does not irritate the incision. Have the patient begin physical therapy at this time as well. Encourage the patient to avoid limping and to go through a normal heel-toe gait progression without shifting his or her weight to the outer border of the foot. Remove sutures or staples between the 14th and 21st days post-op.
A minimally invasive approach to the tarsal tunnel has an advantage over traditional incisions in that it limits the contact of the resultant scar and the neurovascular bundle to one specific point. In addition, by limiting the soft tissue injury, it permits an earlier return to function. Finally, this technique places the incision within both Langer’s and the relaxed skin tension lines, reducing both the amount of scarring and injury to the lymphatic system.
Applying these principles to release of the posterior tibial nerve and its branches significantly improves patient outcomes, reduces the period of disability and reduces the risk of post-op complications.1,2
Dr. Jolly is a Clinical Professor of Surgery at the Temple University School of Podiatric Medicine. He is also a Clinical Professor of Surgery at the Des Moines University School of Podiatric Medicine. He is a Fellow and Past President of the American College of Foot and Ankle Surgeons.
Dr. Burks is a Fellow of the American College of Foot and Ankle Surgeons, and is board-certified in foot and ankle surgery. He is in private practice in Little Rock, Ark.
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