Tarsal tunnel syndrome (TTS) is an entrapment neuropathy of the posterior tibial nerve or of its branches (medial plantar, lateral plantar, or calcaneal

Introduction

Tarsal tunnel syndrome (TTS) is an entrapment neuropathy of the posterior tibial nerve or of its branches (medial plantar, lateral plantar, or calcaneal

발목터널증후군의 영상 및 신경전도검사 특징과 수술적 치료 효과 분석

양지원

¹

¹

²

¹

가천대학교 길병원 ¹신경과, ²정형외과

Tarsal Tunnel Syndrome: Analysis for Characteristics of MRI and Nerve Conduction Study, and the Outcome of Decompression Surgery

Jiwon Yang

, Hyeon-Mi Park

, Hong-Ki Park

, Yeong-Bae Lee

Departments of

Neurology and

Orthopedic Surgery, Gachon University Gil Medical Center, Incheon, Korea

Received September 15, 2015

Revised (1st) October 29, 2015, (2nd) November 4, 2015 Accepted November 4, 2015

Corresponding Author: Yeong-Bae Lee

Department of Neurology, Gachon University Gil Medical Center, 21 Namdong-daero 774beon-gil, Namdong-gu, Incheon 21565, Korea Tel: 82-32-460-3346, Fax: 82-32-460-3344, E-mail: [email protected]

Objective: In this retrospective study, the authors aimed to reveal radiological, electrophysiological characteristics of

Method: Thirty-three patients underwent unilateral tarsal tunnel decompression. Ankle MRI and nerve conduction study

Results: Twenty-eight of 33 (84.8%) patients showed symptomatic recovery and 23 (69.7%) showed improvement

Improvements in nerve conduction study parameters were observed mainly in conduction velocity of lateral plantar nerves. There was no significant clinical factor to predict postoperative outcome.

Conclusion: In the present study, postoperative outcomes from the clinical and electrophysiological perspectives

Key Words: magnetic resonance imaging, nerve conduction study, tarsal tunnel syndrome, treatment outcome, surgical

Copyright © by Korean Association of EMG Electrodiagnostic Medicine

This is an Open Ac cess article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

ORIGI NAL ART ICLE

ISSN 1229-6066 http://dx.doi.org/10.18214/jkaem.2015.17.2.69 J Korean Assoc EMG Electrodiagn Med 17(2):69-75, 2015

J Korean Assoc

Electrodiagn Med EMG

nerve) under the flexor retinaculum at the medial side of the ankle.

Those with TTS usually complain of a dull aching pain on the plantar aspect of the foot. The condition is distressing, but its accurate diagnosis is difficult because its symptoms are similar to those associated with other lower limb conditions, such as, radiculopathy, polyneuropathy, or local orthopedic problem. Electrophysiological and radiological investigations are currently used to diagnose TTS, determine its etiology, and predict treatment outcomes.

However, some controversy remains regarding false negative electrophysiological studies and undefined etiologies based on radiological studies, and these make it difficult to institute surgical decompression at the proper time. Furthermore, the outcome of decompression varies widely according to published reports.

This retrospective study was undertaken; 1) to reveal radiological, electrophysiological characteristics of tarsal tunnel syndrome (TTS), and 2) to present the results of our TTS patients with respect to electro- physiological and symptomatic changes after decom- pression.

Materials and Methods

1) Subjects

Thirty-three patients (16 men and 17 women, mean age 49 years; range 20~72) that underwent tarsal tunnel release between January 2011 and December 2012 were reviewed in their medical records. This study was approved by our institutional review board.

Diagnosis was based on the clinical ground. All subjects complained of a disabling burning or tingling sensation or dysesthesia on the sole of foot. They were decided to undergo surgery when they did not feel better at all despite of taking medicine and life style change (rest, using soft footwear, etc) for more than 1 month. To exclude TTS-mimicking disease, patients underwent nerve conduction study (NCS) and electromyography (EMG) in bilateral lower limbs before

and after operation. None of 33 had radiculopathy, plexopathy or had systemic disease which would be capable of causing polyneuropathy. All subjects underwent ankle MRI at the symptomatic foot.

2) Nerve conduction study

Routine NCS was performed on the peroneal nerve (motor), posterior tibial nerve (motor), sural nerve (sensory), medial plantar nerve (MPN, [motor and sensory]), and lateral plantar nerve (LPN, [motor and sensory]). Distal motor latency (DML), motor and sensory nerve conduction velocity (NCV) and compound muscle action potential (CMAP) was measured.

Electromyography was performed in muscles subserved by the tibial and peroneal nerves, and the dorsal rami of the spinal nerve distribution. All tests were performed using a Nicolet Viking IV EMG machine (Viasys Health Care, Madison, Wisconsin) by a single electromyographer. The foot skin temperature was measured at the start of the assessment, and kept at 32~34

C.

We considered the values abnormal as below: 1) normal DML and NCV of posterior tibial nerve + delayed distal latency or reduced NCV of both plantar (MPN and LPN) nerves, 2) absence of significant plantar nerve action potential despite of repetitive stimulation.

And it was considered abnormal if it was 8 m/s slower than the asymptomatic MPN and/or the distal NCV of the sural nerve of the same side or a CMAP amplitude decrement of more than 30% across the tarsal tunnel.

Furthermore, we sorted the objective severity of TTS

by electrophysiological parameters. Feet with abnormal

plantar NCS results were classified as: 0, normal

CV and DML; 1, normal absolute CV with abnormal

comparative tests;

2, slowing of plantar (sensory

or motor nerve) CV with normal DML; 3, slowing of

CV and prolonged DML; 4, absence of plantar SAP

and abnormal DML; 5, absence of sensory and motor

responses.

3) Clinical outcome measurement

Clinical outcome was measured by physician- patient interview at the time of the operating surgeon’s preoperative and postoperative follow-up visits. The postoperative status was obtained by inquring into the change of numeric rating scale for pain, disappearance of spontaneous pain, recovery from pain aggravation with walking. Clinical improvement was considered when a patient got more than 60% of pain relief and well-being sense in daily life after operation.

4) Statistics

Statistical analysis was conducted using Wilcoxon’s signed rank test, Mann-Whitney U test, or Fisher’s exact test as appropriate. The basic package of SPSS (version 18, Chicago, IL) was used for analysis. p-values of < 0.05 were considered significant.

Results

1) Demographic data

Thirty-three patients (16 men and 17 women) under- went surgical intervention when there is no clinical improvement after conservative treatment for at least one month. Mean patient age was 49 ± 14 years and mean symptom duration was 22 ± 29 months. Mean follow-up duration after operation was 9 ± 10 months.

Average time to repeat nerve conduction study after decompression was 67 ± 35 days. Bilateral symp- toms were present in 11 of 33 (33.3%) patients. In patients with unilateral symptom, the left foot was affected in 14 (42.4%) and the right foot in 8 (24.2%).

Operation was performed on the worse symptomatic foot when bilateral symptoms appeared, and thus, it was conducted on the left foot in 16 (48.5%) and on the right foot in 17 (51.5%). Clinical improvement rated by the extent of pain relief and returns to usual life, was observed in 28 (84.8%) patients, but little or no improvement was evident in the other 5 (15.2%) (Table 1). Operational complication was seen in 4 patients, usually with painful swelling at the ankle and

resolved in a week. There were no wound infections, deep venous thrombosis or overnight anesthetic administrations.

2) Electrophysiological results

Twenty-five patients had NCS results consistent with tarsal tunnel syndrome and eight had normal NCS results. Of the 8 patients with normal NCS, five had bilateral symptoms. Of the 25 patients with an abnormal NCS, 9 had involvements of both motor and sensory plantar nerves, 12 had sensory nerve involvement only, and 4 had motor nerve involvement only. Most patients (n = 22, 66.7%) had grade 2 of electrophysiological severity. After decompressive operations, all parameters of NCS were improved than before the surgery. With the right tarsal tunnel decompression, medial plantar sensory CV was improved from 37.0 ± 11.6 m/s to 40.1 ± 12.2 (p = 0.008), lateral plantar motor and sensory CV was also significantly improved (motor CV: 41.2 ± 4.8 m/s to 44.6 ± 4.2 m/s, p = 0.030; sensory CV: 39.2 ± 6.0 m/s

Table 1. Demographic Characteristics

Total 33

Sex (male:female) 16:17

Age (years, mean ± SD) 49 ± 14

Duration of symptom (months, mean ± SD) 22 ± 29 Duration of follow-up (months, mean ± SD) 9 ± 10 Time between the surgery and repeated study

(days, mean ± SD)

67 ± 35

Symptom side

Both 11 (33.3%)

Left 14 (42.4%)

Right 8 (24.2%)

Decompression side

Left 16 (48.5%)

Right 17 (51.5%)

Symptom improvement

Improved 28 (84.8%)

No change 5 (15.2%)

Worse 0 (0.0%)

Electrophysiological improvement

Improved 23 (69.7%)

No change* 9 (25.2%)

Worse 1 (3.0%)

History of ankle or foot trauma 6 (18.2%) SD: standard deviation

*including numbers of normal nerve conduction study before operation (n = 8)

to 41.8 ± 5.7 m/s, p < 0.001). With the left tarsal tunnel decompression, lateral plantar motor CV was improved from 38.6 ± 11.6 m/s to 41.8 ± 5.4 m/s (p = 0.033).

In terms of severity, patients of 13 in 22 with grade 2 recovered as normal NCS (Table 2 and Fig. 1).

3) Relations between clinical and electrophy- siological results

Of 25 patients with abnormal NCS before operation, 23 showed improvements in both clinical and electrophysiological results. On the other hand, 1 patient showed symptom recovery without NCS improvement, and the other showed unimproved symptom and NCS. Of 8 patients with normal NCS before and after operation, 4 showed symptomatic improvement and the others did not. No significance could be attached to trauma history (p = 0.652), the presence of an anatomical causative lesion (p = 1.000), symptom duration (p = 0.365), age (p = 0.975), or sex (p = 0.688) with respect to clinical outcomes. Of 5 patients that did not experience symptom recovery, patients with preoperative normal NCS (n = 4, p =

0.008) and bilateral symptom (n = 3, p = 0.304) showed no clinical improvement.

4) Radiological and operative evaluation findings All 33 patients underwent ankle MRI at the sympto- matic foot before decompression. Eighteen patients (54.5%) had abnormal radiological finding involving the tarsal tunnel, that is, ganglion cyst (n = 5), vein engorgement (n = 4), bony coalition (n = 3), accessory muscle belly (n = 3), or tenosynovitis (n = 3). Operative finding revealed more causative lesions involving the tarsal tunnel that were not observed by preoperative radiology, and some of them were overlapped. These were hypertrophied muscle or thickened fascia (n = 8), vein engorgement (n = 13), ganglion cyst (n = 5), bony coalition or mass (n = 4), nerve branch entrapment (n

= 1), and accessory muscle belly (n = 3). Six patients (18.2%) had no specific lesion in MRI or surgical field, and underwent simple adhesiolysis (Supplementary Table and Fig. 2).

Discussion

Tarsal tunnel syndrome (TTS) is caused by nerve compression in the tarsal tunnel, and can arise from ankle trauma, space-occupying lesions, bony defor-

Table 2. Comparison NCS Results before and after Operation

Preoperation Postoperation p-value

Tarsal tunnel decompression at the right ankle (n=17)

Right medial plantar nerve

DML (ms) 4.9 ± 1.0 4.7 ± 0.6 0.202

MCV (m/s) 41.0 ± 6.5 42.5 ± 4.6 0.323 SCV (m/s) 37.0 ± 11.6 40.1 ± 12.2 0.008

Right lateral plantar nerve

DML (ms) 5.1 ± 1.1 4.9 ± 0.6 0.290

MCV (m/s) 41.2 ± 4.8 44.6 ± 4.2 0.030

SCV (m/s) 39.2 ± 6.0 41.8 ± 5.7 < 0.001

Tarsal tunnel decompression at the left ankle (n=16)

Left medial plantar nerve

DML (ms) 5.1 ± 0.7 4.8 ± 0.7 0.297

MCV (m/s) 40.2 ± 6.2 41.0 ± 4.0 0.334 SCV (m/s) 40.9 ± 6.6 43.6 ± 5.1 0.135 Left lateral plantar nerve

DML (ms) 5.2 ± 0.7 5.0 ± 0.7 0.140

MCV (m/s) 38.6 ± 11.6 41.8 ± 5.4 0.033

SCV (m/s) 41.0 ± 7.7 43.8 ± 5.5 0.093 NCS: nerve conduction study, DML: distal motor latency, MCV: motor nerve conduction velocity, SCV: sensory nerve conduction velocity, SAP: sensory action potential

*All values were expressed as mean ± standard deviation.

p < 0.05

Pre-operation 4

3

2

Severity grade 1

0

Post-operation 24

Fig. 1. Changes of electrophysiological severity before and after opera-

tion. According to the result of plantar nerve conduction velocity (CV)

and distal motor latency (DML), electrophysiological severity was

scored and compared before and after operation. After operation,

median grade of electrophysiological severity was improved from 2

to 0 (normal) using Wilcoxon signed rank test (p < 0.001).

mities, hypertrophied muscle or tendinopathy, hind foot varus or valgus, a systemic condition, such as, diabetes, hypothyroidism, rheumatoid arthritis, gout, pregnancy, or others.

Many cases of TTS remain idiopathic, but recent advances in diagnostic radiology increasingly enable the identification of structural abnormalities.

In particular, MR imaging with its excellent soft tissue contrast and ability to demonstrate musculotendinous and neurovascular structures, clearly demonstrates the anatomy of the tarsal tunnel and its contents and the presence and extent of causative lesions.

In one MRI study, abnormal findings were observed in 85% of patients with TTS.

Furthermore, this information aids when deciding on surgical treatment and determining the extent of decompression required. In the present study, anatomical lesions were evident in 18 patients by ankle MRI, and 15 of these concurred with operative findings; in the other 3 findings differed (case No. 8,

11, and 23). Nine causative lesions, which were not remarkable by MRI, were newly identified during operation. Operative findings confirmed the presence of two or more causative lesions in 7 patients. The most commonly reported anatomical etiology of TTS by small operational case series varies. One research reported that etiology frequencies of ganglion cyst (36%), talocalcaneal coalition (30%), idiopathic (18%), and traumatic (10%).

In our series, hypertrophied muscle or thickened fascia and vessel engorgement was the most prevalent, and no relation was found between type of etiology and postoperative outcome. MRI results showed good accuracy for determining the presence of a ganglion cyst, an accessory muscle, or bony coalition, whereas demonstrated relatively low detection rate of a vessel engorgement or a thickened fascia. In view of the limitations of electrophysiological studies, which cannot suggest candidates for operative treatment, MRI

Fig. 2. MRI and operative findings of

one patient (case No. 20). Her ankle

MRI revealed complicated ganglion

cyst within flexor retinaculum and

consisted with operative result. It was

excised and the pathologic result was

compatible with ganglion cyst.

is still necessary for the proper evaluation of TTS.

A complete electrophysiological study involves a nerve conduction study (NCS) and electromyography (EMG), and may provide further information about the degree of individual nerve functional deficits, exclude other associated peripheral neuropathies, and allow assessments of temporal changes after treatment, and thus, they are essential diagnostic tools. Although no international guidelines have been issued regarding clinical and electrophysiological diagnostic criteria,

slow sensory nerve conduction and the absence of sensory action potentials of plantar nerves are the most consistent diagnostic findings for TTS, and are present in 90.5% of patients.

Measurements of motor NCVs and prolonged distal motor latencies are easily obtained and aid the diagnosis,

but are less sensitive and are only present in 52.4%.

The clinical and electrophysiological outcomes of tarsal tunnel decompression have been reported on a few occasions. Proportions of clinical successes have been reported to be 44% (14 of 32 cases), 43% (9 of 21 cases), or 51%, whereas electrophysiological improvement were higher.

In this study, symptomatic improve- ment was achieved in 28 feet (84.8%), and 23 feet (69.7%) had good electrophysiological outcomes after decompression. These surgical outcomes are more satisfactory than those reported in previous studies.

The present study concurs with other studies that abnormalities in sensory nerve conduction (21 of 33, 63.6%) are more frequently detected than abnormalities in motor nerve conduction (13 of 33, 39.4%). However, unlike previous studies, in which abnormalities were more frequently associated with the lateral plantar nerve than the medial plantar nerve,

in the present study, abnormalities were associated equally with these both plantar nerves before decompression.

Historically, the success rate of tarsal tunnel decom pression has been reported to vary from 44% to 96%.

The factors that contribute to a poor prognosis are old age, chronic symptoms, accompanying muscle weakness and atrophy, a female gender, and an idiopathic or

posttraumatic etiology.

Alternatively, the presence of a space-occupying lesion and a positive Tinel’s sign are strongest predictors of a favorable outcome.

In the present study, decompression showed favorable outcome in clinical symptoms and electrophysiological results. Somewhat surprisingly, no factor was found to be significantly related with outcome. Nevertheless, we speculate that preoperative normal NCS results and bilateral symptoms predict a poor surgical response by looking into our case series.

This study has some limitations that should be considered, that is, a small number of patients were recruited, and the subjects were not evenly distributed in terms of their preoperative functional or electro- physiological severity. Despite this, we believe that tarsal tunnel decompression can be considered favorable treatment option and warranted when the effect of conservative treatment is not obtained.

Conclusion

Summarizing, 28 of the 33 TTS patients (84.8%) that underwent decompressive operation achieved enough pain relief and 23 of the 33 (69.7%) had improved electrophysiological results after operation.

Preoperative MR results were found to be positive in 18 of the 33 patients (54.5%). It appears that tarsal tunnel decompression is warranted in patients that remain symptomatic after prolonged conservative treatment.

Supplementary Materials

Supplementary materials can be found via http://dx.

doi.org/10.18214/jkaem.2015.17.2.69

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Case No.

Sex/

Age

MRI finding Operative finding Clinical outcome NCS outcome

1 F/55 No remarkable finding

Flexor retinaculum hypertrophy

Improved Worse

2 F/45

Accessory muscle belly in flexor retinaculum

Same Improved Improved

3 F/23 Ganglion cysts Same Improved Improved

4 M/32 No remarkable finding Adhesion No change No change

5 F/48 Ganglion cyst

1. Ganglion cyst 2. Tortuous vein

Improved Improved

6 M/58 No remarkable finding

1. Varicose vein 2. Thickened FHL & AH

fascia

Improved No change

7 F/52 Ganglion cyst Same Improved Improved

8 M/65

Tenosynovitis (tibialis posterior)

1. Flexor retinaculum hypertrophy 2. Thickened AH fascia 3. Vein engorgement and

adhesion

Improved Improved

9 F/62 No remarkable finding

1. Varicose vein 2. Thickened abductor

hallucis fascia 3. Peroneous brevis

muscle tendon tear

No change Improved

10 F/59 No remarkable finding Adhesion Improved Improved

11 F/58

Tenosynovitis (tibialis posterior)

1. Varicose vein 2. Adhesion

Improved Improved

14 M/20 No remarkable finding Adhesion Improved Improved

15 F/56 Talocalcaneal coalition Same Improved Improved

16 M/50 No remarkable finding

Flexor retinaculum hypetrophy

Improved Improved

17 M/58 Vein engorgement

1. Thickened AH fascia 2. Enlarged posterior

tibial artery

Improved Improved

18 M/59 Vein engorgement

Tortuous posterior tibial artery and vein

Improved No change

19 M/48 No remarkable finding Adhesion Improved Improved

20 M/62 Ganglion cyst Same Improved Improved

21 M/38 No remarkable finding

Hypertrophied AH muscle

Improved Improved

22 F/72 No remarkable finding

Lateral plantar nerve entrapment and severe

degeneration

Improved No change

23 F/59

Tenosynovitis (tibialis posterior)

Varicose vein No change No change

24 M/25

FDL accessory muscle belly in the tarsal tunnel

Same No change No change

25 M/46

FDL accessory muscle belly in the tarsal tunnel

1. Same 2. Round bony mass at

the medial malleolus

Improved Improved

26 F/63 No remarkable finding Adhesion Improved No change

27 M/53

Varicose vein Tenosynovitis (tibialis

posterior)

1. Varicose vein 2. Adhesion

Improved Improved

28 F/27 No remarkable finding

3. Lateral plantar nerve hypertrophy

Improved Improved

29 F/53 No remarkable finding Adhesion Improved No change

30 F/57 No remarkable finding Varicose vein Improved Improved

31 F/63 No remarkable finding Varicose vein Improved No change

32 M/24 Talocalcaneal coalition Same Improved Improved

33 F/46 Ganglion cyst Same Improved Improved

NCS: nerve conduction study, AH: abductor hallucis, FDL: flexor digitorum longus, FHL: flexor hallucis longus

*

abnormal NCS before operation;

normal NCS before operation