Ultrasonography in Tarsal Tunnel Syndrome

Article Ultrasonography in Tarsal Tunnel Syndrome Masahiro Nagaoka, MD, Hiromi Matsuzaki, MD Objective. The purpose of this study was to clarify the diagnostic value of ultrasonography in tarsal tunnel syndrome. Methods. Seventeen patients (17 feet) with tarsal tunnel syndrome were treated between 1988 and 2003. Preoperative ultrasonography was performed, and the cause of the syndrome was confirmed intraoperatively in all cases. Long and short axes of the tarsal tunnel were scanned to ascertain the presence of any space-occupying lesion. Results. The causes of tarsal tunnel syndrome, as confirmed by surgery, were ganglia (n = 10), talocalcaneal coalition (n = 1), talocalcaneal coalition associated with ganglia (n = 3), and varicose veins (n = 3). Among the cases involving ganglia, hypoechoic or anechoic regions were observed. The mean sizes ± SD of these regions were 19.4 ± 8.8 mm in the long axis, 15.2 ± 6.3 mm in the short axis, and 10.4 ± 3.8 mm in depth. Of these, 3 ganglia were not clearly palpable before surgery and were small: 10 10 7, 13 11 9, and 9 8 7 mm. Among the cases involving talocalcaneal coalition, ultrasonography indicated a beak-shaped bony process on the short axis images. Although these 3 cases were associated with ganglia, this could not be determined by preoperative palpation. Conclusions. As a diagnostic imaging technique for tarsal tunnel syndrome, ultrasonography is extremely useful for identifying space-occupying lesions. Ultrasonography should be performed routinely in patients with suspected tarsal tunnel syndrome. Key words: entrapment neuropathy; ganglion; talocalcaneal coalition; tarsal tunnel syndrome; ultrasonography. Abbreviations MRI, magnetic resonance imaging Received January 24, 2005, from the Orthopaedic Department, Surugadai Nihon University Hospital, Tokyo, Japan. Revision requested February 14, 2005. Revised manuscript accepted for publication March 14, 2005. Address correspondence to Masahiro Nagaoka, MD, Orthopaedic Department, Surugadai Nihon University Hospital, 1-8-13 Kanda Surugadai, Chiyoda-ku, Tokyo 101-8309, Japan. Tarsal tunnel syndrome is a neuropathic entrapment of the tibial nerve and its branches on the medial side of the ankle and is characterized by numbness and pain in the toes and sole of the foot. Although this syndrome is a common form of entrapment syndrome of the lower extremity, it is not as common as carpal tunnel syndrome. Studies have documented that tarsal tunnel syndrome can be caused by trauma, foot deformation, varicose veins, ganglia, or talocalcaneal coalition. 1 4 Tarsal tunnel syndrome is diagnosed by clinical examination and based on findings such as area of sensory disturbance and positive Tinel sign over the tarsal tunnel that are then confirmed by electrodiagnosis. Diagnostic imaging is also useful for ascertaining the cause of tarsal tunnel syndrome. Although radiography is essential in the diagnosis of talocalcaneal coalition, ultrasonography and magnetic resonance imaging (MRI) can be useful for diagnosing soft-tissue lesions. 5 8 Our study reports the utility of ultrasonography for preoperative diagnosis in 2005 by the American Institute of Ultrasound in Medicine J Ultrasound Med 2005; 24:1035 1040 0278-4297/05/$3.50

Ultrasonography in Tarsal Tunnel Syndrome Figure 1. Malleolar-calcaneal axis. 17 patients (17 feet) with tarsal tunnel syndrome and investigates the diagnostic value of the technique. Materials and Methods Between 1988 and 2003, ultrasonography was performed preoperatively and then surgery was performed on 17 patients (11 men and 6 women; 17 feet) with tarsal tunnel syndrome. The mean age was 42.4 years (range, 12 72 years). Tarsal tunnel syndrome affected the right foot in 8 patients and the left foot in 9 patients. All patients showed a positive Tinel sign with percussion of the tibial nerve over the tarsal tunnel on the affected side. In all cases, electrophysiologic examination confirmed abnormality in sensory nerve conduction velocity between the big toe and the tarsal tunnel or distal latency of the abductor hallucis muscle. Ultrasonographic examinations were performed with an SSD-1200 scanner (Aloka Co, Ltd, Tokyo, Japan) equipped with a probe (10-MHz mechanical sector transducer), and images were evaluated by an orthopedic surgeon (M.N.) with several years of experience in musculoskeletal ultrasonography. Ultrasonographic examinations were performed within 1 week before surgery. The probe was positioned parallel (short axis) and perpendicular (long axis) to the malleolar calcaneal axis (Figure 1). 9 Preoperative ultrasonographic findings were compared with intraoperative findings. If a ganglion was suspected, the size, location, morphologic characteristics, and relationship between the posterior tibial artery and the ganglion were ascertained. The maximum diameters of each mass were measured along the long axis and short axis and from a perspective of depth. Results The causes of tarsal tunnel syndrome, as determined on the basis of intraoperative findings, were ganglia in 10 cases, talocalcaneal coalition in 1 case, talocalcaneal coalition associated with ganglia in 3 cases, and varicose veins in 3 cases. The findings based on preoperative ultrasonography were consistent with the intraoperative findings. There were no false-negative results in our study. Ultrasonographic examinations in the 13 cases involving ganglia showed hypoechoic or anechoic regions. The mean sizes ± SD of these regions were 19.4 ± 8.8 mm (range, 8 31 mm) in the long axis, 15.2 ± 6.3 mm (range, 8 25 mm) in the short axis, and 10.4 ± 3.8 mm (range, 4 16 mm) in depth. The size and morphologic characteristics of the ganglia as determined intraoperatively were consistent with data from the preoperative ultrasonographic examination. Regarding the relationship between the posterior tibial artery and the ganglion in these cases, the artery was positioned under the ganglion in 7 cases, on top of the ganglion in 4 cases, and adjacent to the ganglion in 2 cases. A mass was clearly preoperatively palpable in the tarsal tunnel in 11 of the 17 cases. These cases involved a ganglion (n = 8) or talocalcaneal coalition associated with a ganglion (n = 3). Of the 6 impalpable cases, a diffuse swelling was seen in 3 patients but was not palpable, and the 3 ganglia were small: 10 10 7, 13 11 9, and 9 8 7 mm. The other 3 cases were due to varicose veins. The varicose veins appeared as bulbous intermittent hypoechoic shadows in ultrasonographic examination. The 4 cases of tarsal tunnel syndrome caused by talocalcaneal coalition were confirmed by radiography. Ultrasonography revealed a beakshaped bony process on short axis images. Although ganglia accompanied 3 cases, these were not detected by palpation preoperatively. 1036 J Ultrasound Med 2005; 24:1035 1040

Nagaoka and Matsuzaki Case Presentation Case 1 A 64-year-old man had a 2-month history of numbness in the left foot. Numbness persisted and was marked in the big toe. The area inferior to the medial malleolus was diffusely swollen, and the Tinel sign was positive. Although radiography showed no abnormality, ultrasonography revealed a hypoechoic region inferior to the medial malleolus (Figure 2). Surgery was performed, and a ganglion was observed under the flexor retinaculum; the tibial nerve was compressed under the ganglion (Figure 3). The ganglion arising from the flexor pollicis longus muscle tendon sheath was resected with the tendon sheath. Numbness disappeared 4 months after surgery. Case 2 A 16-year-old girl had a 2-month history of numbness of the right foot. The medial side of the right foot and big toe exhibited numbness. A bony prominence was seen inferior to the medial malleolus of the tibia, and the Tinel sign was positive. Radiography showed shadowing indicative of talocalcaneal coalition (Figure 4). Ultrasonography depicted the coalition as a beak-shaped lesion shadowing in the long axis scan. In addition, imaging in the short axis scan showed an elliptical 8-mm hypoechoic region, suggesting that the talocalcaneal coalition was complicated by a ganglion (Figure 5). Surgery was performed. A ganglion was on the coalition (Figure 6), and the medial plantar nerve was over the ganglion and subject to friction during dorsal flexion of the ankle. The coalition and ganglion were excised. Numbness disappeared 2 months after surgery. Although conditions similar to tarsal tunnel syndrome had been reported previously, Keck (1962) 10 and Lam (1962) 11 were the first to use that particular terminology. The tibial nerve passes through the medial side of the ankle and branches into the medial plantar nerve, lateral plantar nerve, and medial calcaneal branch. 9 This area is called the tarsal tunnel and is made of a neurovascular bundle, a posterior tibial tendon, a flexor digitorum longus tendon, and a flexor hallucis longus tendon. These components are covered by the flexor retinaculum from the medial malleolus of the tibia to the calcaneus. Unlike the carpal tunnel, however, components are separated within the tarsal tunnel by a septum 3,12 ; therefore, slight changes in this space can easily result in neuropathy. The causes of tarsal tunnel syndrome include idiopathic conditions, traumatic conditions (eg, calcaneal or ankle fracture), foot deformities (varus or valgus heel), space-occupying lesions, and varicose veins. 1,4,13,14 In the Japanese literature, tarsal tunnel syndrome caused by spaceoccupying lesions is well documented, with cases involving ganglia and talocalcaneal coalition being prominent. 15,16 In 1991, Takakura et al 17 found that a ganglion or talocalcaneal coalition was the cause of tarsal tunnel syndrome in 31 of 50 feet. Ultrasonography can be a valuable means of diagnosing cases such as these. Talocalcaneal coalition is a congenital fibrous, cartilaginous, or osseous union that often leads to tarsal tunnel syndrome. Ultrasonography is capable of showing the beak-shaped bony prominence in the tarsal tunnel that indicates talocalcaneal coalition, without the need for radiography or computed tomography. Furthermore, although radiography can identify this beak-shaped bony prominence, it is not capable of showing ganglia that often accompany this condition. 16,18 In 1998, Takakura et al 19 performed preoperative MRI in 5 of 7 patients with talocalcaneal coalition involving ganglia, and although the ganglia were detected preoperatively in 3 cases, they were found only during Figure 2. Case 1. Long axis sonogram showing an elliptical hypoechoic shadow. Discussion J Ultrasound Med 2005; 24:1035 1040 1037

Ultrasonography in Tarsal Tunnel Syndrome A B Figure 3. Case 1. A, After the flexor retinaculum was cut, the medial plantar nerve was found to be compressed by a ganglion. B, The ganglion was separated from the medial plantar nerve. surgery in 2 cases. In our 3 cases of talocalcaneal coalition involving ganglia, the ganglia were detected preoperatively by ultrasonography in all cases. Because ganglia are sometimes involved in the onset of symptoms of tarsal tunnel syndrome, ultrasonography should be conducted preoperatively even when the condition has already been identified by radiography. Figure 4. Case 2. Radiograph showing talocalcaneal coalition. Asterisk indicates a portion of the beak. Several MRI studies on tarsal tunnel syndrome have been reported 6,20 23 ; however, relatively few studies involving ultrasonography have been conducted. Because ultrasonography is highly capable of showing small lesions, identification of small masses that cannot be shown by MRI may be possible. Kerr and Frey 24 noted that MRI showed no abnormalities in 17 of 19 surgical cases, including 1 case of a ganglion and 8 cases of varicose veins or varicosities; however, in 1 of the 2 patients in whom MRI showed no abnormality, a small ganglion was seen during surgery. 24 In our study, MRI was performed in only a small number of patients, and, subsequently, the results cannot be easily compared; however, small ganglia that were not palpable in the tarsal tunnel were shown on preoperative ultrasonography in 4 cases. Because dynamic analysis is possible with ultrasonography, arterial pulsation is easily assessed. This type of information is useful for ascertaining positional relationships of the tarsal tunnel to a space-occupying lesion and nerves. In addition, during surgery, preoperative knowledge of the location of any spaceoccupying lesion is very useful. Moreover, if a large ganglion is seen, aspiration can be performed if a nerve is located on the bone side of the ganglion. 1038 J Ultrasound Med 2005; 24:1035 1040

Nagaoka and Matsuzaki A Figure 5. Case 2. A, Short axis sonogram showing the beak-shaped region. Asterisk indicates a portion of the beak. B, Long axis sonogram showing a small hypoechoic region (arrow) on top of the beak. B Varicose veins have been closely examined as a causative factor in tarsal tunnel syndrome. 10,12,13,23,25,26 Lau and Daniels 14 reviewed 25 articles that studied 186 cases of tarsal tunnel syndrome in 164 patients and found that varicosities were the primary cause in 13% of all operated cases; however, this figure reflects only operated cases. Our study also deals only with varicosity as a clear abnormal intraoperative finding. Future studies will need to analyze the role of varicose veins in idiopathic cases. As a diagnostic imaging technique for tarsal tunnel syndrome, ultrasonography is extremely useful for diagnosing space-occupying lesions. When tarsal tunnel syndrome is suspected, ultrasonography should be performed routinely. Figure 6. Case 2. A, The medial plantar nerve (arrow) was positioned above the talocalcaneal coalition. B, A small ganglion (arrow) was found under the medial plantar nerve. A B J Ultrasound Med 2005; 24:1035 1040 1039

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