Tarsal Tunnel Syndrome: Can A Minimally Invasive Release Be Advantageous?
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.