I. Overview
Structure of the ankle tunnel
Tarsal tunnel syndrome, also known as metatarsal tunnel syndrome, is a condition in which the posterior tibial nerve is compressed within the ankle tunnel at the medial aspect of the calf joint, resulting in numbness, pain, and difficulty walking on the medial aspect of the foot, and was first reported by Keck in 1962.
The disease is most common in young adults who engage in strong physical labor or long-distance runners, and is mostly caused by aseptic inflammation and swelling degeneration of the tendons in the ankle canal or other causes of hyperplasia of the fibrous tissue around the posterior tibial nerve, resulting in increased pressure in the metatarsal canal. Metatarsal canal syndrome is one of the common clinical nerve entrapment syndromes.
In addition, women tend to wear tight boots in winter and are also prone to some of the symptoms of the syndrome.
II. Pathology
The ankle canal, also known as the metatarsal canal, is a bony fibrous canal located in the medial aspect of the ankle joint, a channel formed by the bone and fibrous tissue in the deep cellular tissue space at the back of the lower leg and the bottom of the foot. The posterior tibial nerve within this canal is compressed by the bony fibrous canal and produces a series of foot symptoms called the metatarsal canal syndrome.
The metatarsal canal travels from posterior to superior to anterior to inferior, forming an approximately 90° curvature, with the superficial surface covered by the split ligament and the deep part of the heel bone, talus and joint bundle. The metatarsal canal is arranged from anterior to posterior with the posterior tibial tendon, flexor digitorum longus tendon, posterior tibial artery and flexor digitorum longus tendon passing through it. When the foot activity is intense, the tendons in the metatarsal canal rub and swell when the ankle joint is sprained, the pressure increases due to the relative narrowing of the inner cavity of the metatarsal canal, which causes the posterior tibial nerve compression, or the split ligament degenerates and thickens, or the foot is congenitally deformed, which can also cause the posterior tibial nerve compression and toe canal syndrome.
The pathological changes after nerve entrapment, the changes in nerve function are proportional to the degree and duration of nerve entrapment. Early and repeated temporary ischemia may produce pain and sensory abnormalities. Prolonged nerve entrapment may result in demyelination and nerve degeneration, with numbness, muscle weakness and atrophy, and prolonged nerve conduction time in the foot.
Pathological changes include.
(i) the presence of nerve entrapment at the fibrous origin of the flexors, supporting bands and abductor muscles of the pedicle mother toe;
(ii) thickening of the tendon synovium, seen in patients with rheumatoid arthritis;
(iii) nerve entrapment due to post-traumatic fibrosis caused by fracture can be found in patients with fracture metatarsal tunnel syndrome.
III. Etiology
Metatarsal Tunnel Syndrome
1. Congenital factors Hypertrophy of the adductor muscles as well as deformity of the paraspinatus heel exostosis and flat feet can reduce the practical volume of the metatarsal canal, thus causing tibial nerve entrapment.
Fractures of the heel and ankle, such as poor repositioning and malunion, can also reduce the volume of the metatarsal canal. In addition, the base of the metatarsal canal is not smooth, which can cause compression and friction and injury to the tibial nerve.
Chronic injury Long-distance runners who are engaged in strong physical labor and frequent high-intensity plantarflexion and dorsiflexion of the ankle joint can cause tendinitis and tendon sheath congestion and edema due to increased tendon sliding and friction, and the corresponding thickening of the flexor support belt, which reduces the stretch of the metatarsal canal and increases the pressure in the canal, which can compress the tibial nerve and affect its blood supply, resulting in neurological dysfunction. In addition, patients with rheumatoid arthritis and osteoarthrosis can form hyperplastic bone redundancy, which can also compress the tibial nerve by protruding into the metatarsal canal.
4, internal factors of the metatarsal canal tendon sheath cysts, lipomas, varicose veins can also cause tibial nerve compression.
Other factors such as hypothyroidism, pregnancy, saphenous vein and small saphenous vein varices, etc.
IV. Clinical manifestations
The clinical manifestations of this disease can have various variations. Usually, patients complain of diffuse radiating pain, burning pain, tingling or numbness on the bottom of the foot. 1/3 of patients have pain radiating proximally, a phenomenon known as Valleix phenomenon. Usually, the symptoms of ankle tunnel syndrome are very diffuse and are not limited to a specific tendon around the ankle. Some patients may complain of symptoms located on the posterior medial aspect of the ankle, or abnormal sensation throughout the foot. Symptoms may worsen with activity and exercise and improve with rest. Some patients may complain of nocturnal symptoms, caused by direct compression in a particular position or in the ankle canal area during sleep. Prolonged symptomatic nerve entrapment may result in weakness and atrophy of the intrinsic muscles of the foot, most often resulting in a high arched foot and/or claw toe.
The proximal type of entrapment results from compression of the tibial nerve before it migrates into the plantar nerve branches. Thus, the entire tibial nerve distribution below the ankle is involved.
The distal form results from compression of the end of a nerve branch, usually the medial or lateral plantar nerve.
Medial plantar nerve entrapment occurs within the fibromuscular canal formed by the bunion and navicular tuberosity. Patients may have clubfoot or may be long-distance runners who are most susceptible to this condition, often referred to as “jogger’s foot”. The symptoms are burning pain along the medial arch of the foot that radiates to the first, second, third and part of the fourth toe.
Lateral plantar nerve entrapment is more common than medial plantar nerve entrapment and occurs where the nerve travels through the plantar aspect of the foot. Entrapment of the first branch of the lateral plantar nerve can cause severe heel pain. Distal to this branch of the nerve, the lateral plantar nerve travels obliquely through the plantar within an isolated channel. Compared to the medial plantar nerve, this segment of the lateral plantar nerve undergoes acute bending within the canal and has a reduced relative blood supply, making it more susceptible to morbidity.
V. Diagnosis
1. Medical history
There is diffuse radiating pain, burning pain, tingling pain or numbness in the innervated area of the plantar tibial nerve. The symptoms of pressure are aggravated by activity and improve at rest. Exclude lumbar spine lesions, nerve damage caused by systemic diseases, etc.
2. Physical examination
Percussion of the tibial nerve or its branches in the ankle canal may induce sensory abnormalities. Direct pressure on the segment of the tibial nerve in the ankle canal can induce plantar symptoms. Pressure should usually be applied continuously for 30 seconds or more to induce symptoms in patients. Standing and walking postures may reveal a flatfoot or forefoot abduction, both of which can increase pressure on the tibial nerve within the ankle canal. Palpate along the entire ankle canal for any occupying lesions, such as tendon sheath cysts.
3.Imaging
X-ray plain radiographs of the ankle foot can reveal major skeletal lesions, such as bony bulge or tarsal coalition; CT examination can help further evaluate suspected skeletal lesions; MRI can detect impingement of the ankle canal contents caused by an occupying lesion or varus.
4.Electrophysiological examination
There is up to 90% accuracy in the diagnosis of ankle tube syndrome. A complete electrophysiological examination includes motor and sensory nerve conduction examinations as well as electromyography. Positive signs are slowed conduction within or distal to the ankle canal and intrinsic myofibrillatory potentials. The sensitivity of abnormal sensory conduction rates was higher (90%) compared to the sensitivity of abnormal terminal motor delays (54%). Thus, when abnormal motor conduction delays are not present it is not sufficient to exclude the diagnosis of ankle tube syndrome. Although electrophysiological findings are accurate, they do not correspond well to intraoperative findings and to postoperative clinical findings. Therefore, electrophysiologic examination can be used to confirm a suspicious clinical diagnosis or is more useful to rule out a concomitant proximal nerve injury rather than to make a specific diagnosis.
VI. Differential diagnosis
1, metatarsalgia This is a symptomatic diagnosis, mostly seen in women around 30 years old, with a prevalence in those who wear pointed high heels. The earliest symptom is pain, burning pain or tightness in the forefoot, and in severe cases the pain can involve the toes or calf, usually relieved after changing shoes, with pressure pain outside the metatarsal head on examination, which can be accompanied by callus, and the toes can be flexed and deformed.
2, the foot performance of diabetes Patients have a history of diabetes. As the patient’s small blood vessels are mostly involved, there is small vessel sclerosis and degeneration, so that the blood supply to the involved organ tissues is insufficient causing nerve ischemia and hypoxia and metabolic degeneration. In addition, because the white blood cells of diabetic patients have a reduced ability to resist infection, it is easy to cause infection. In the foot manifested as toe ischemic pain, the little toe is common, the foot vibration, pain and temperature sensation disappeared, the foot intrinsic muscle atrophy, near the dorsal side of the interphalangeal joint (earthworm muscle) in the metatarsophalangeal joint plantar toe flexion (interosseous muscle) disorder, which can form claw toe deformity, serious cases can have a small toe necrosis infection. x-ray can be seen in the metatarsal vascular calcification shadow, foot bone dissolution osteoporosis, Charcot arthritis.
3, foot rheumatoid arthritis for the local manifestations of systemic lesions, female patients are more common, the local manifestations of the bottom of the foot pain when walking pain heavy metatarsal phalangeal joint is most susceptible to involvement. Thereafter can invade any part of the foot, can be accompanied by tenosynovitis around the joint along the tendon sheath with swelling pain. Late stage can appear forefoot deformity, such as pointed foot foot inversion, foot valgus, valgus and other episodes of ESR increase, X-ray film can be seen joint space narrowing, osteoporosis, joint destruction and dislocation, etc.
4, foot gouty arthritis Most commonly seen in men when the initial onset of more in the first metatarsal phalangeal joint rapid onset of pain, severe pain, pressure pain is obvious, the local skin has redness and swelling, the pain can last a few days to a few weeks during the attack often recurrent, intermittent period without any symptoms, the blood uric acid can increase during the attack, joint puncture fluid such as calcium uric acid crystals can be found in a clear diagnosis, chronic patients X-ray film can be seen near the joint surface worm-like shadow.
VII. Treatment
1.Non-surgical treatment
The surgical treatment of ankle tunnel syndrome caused by occupational lesions is usually the most effective. For patients without typical lesions, conservative treatment should be attempted before surgical treatment.
Non-steroidal anti-inflammatory drugs can be used to reduce inflammation and local irritation around the nerve. To reduce the tension on the tibial nerve, especially in patients with clubfoot, a brace can be used to limit anterior rotation. These braces are particularly suitable for jogging feet. The brace should be designed with a medial wedge heel pad and forefoot support, and must have an adaptive overstep at the arch (rather than direct arch support) to eliminate the increased stress on the bunion muscles. Correction of deformities by supporting the medial longitudinal arch can lead to increased pain and discomfort. In patients where dorsiflexion of the ankle joint can induce painful symptoms, the use of a one-inch high heel can successfully improve symptoms. The elevated heel reduces the tension exerted on the nerve. If a patient with flat feet requires a custom brace, then an elevated heel design can be incorporated as well. Short-term braking may be considered for those with severe symptoms. The use of compression compression stockings can reduce slow venous return.
2.Surgical treatment
If the compression comes from a flexor support band, an occupying lesion or surrounding soft tissue, and conservative treatment fails, surgical release of the tibial nerve should be considered. Postoperative compression bandaging is recommended, such as splinting or plastering of the ankle, or the use of a compression cold therapy device to limit swelling in the incision area and aid in postoperative hemostasis. The foot is elevated for 7 to 10 days and weight-bearing is avoided to reduce inflammation and wound tension. Most patients complained of significant symptomatic improvement within 6 weeks after surgery, with maximum symptomatic improvement achieved after 6 months.