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Sonographic Findings in Severe Carpal Tunnel Syndrome and Normal Subjects. A Comparative Study

 Seyed abdolhossein Mehdinasab *, Nasser Sarrafan *, Bahram Aliakbarzadeh

* Assistant Professor of Orthopaedic Surgery,Department Of Othopaedic Surgery, Azadegan Street  , Imam khomeini Hospital , Jondishapur University of Medical Sciences. Ahwaz . Iran .

Address for Correspondence:

Dr. Mehdinasab, 
Azadegan Avenue,
Imam Khomeini Hospital,
Department of Orthopaedics,
Ahwaz. Iran.
E mail:
Tel no: 09161111052


Background:Sonography of the wrist has been suggested as a diagnostic tool in carpal tunnel syndrome (CTS), but there are controversies with regard to routine use of this tool in this disease. The aim of this study was to determine the sonographic findings of severe CTS with respect to carpal tunnel diameters, and to compare the results with normal wrists.

Material & Methods:39 wrists of 21 patients with clinical and electro diagnosis (NCV) evidence of CTS, who were candidate for surgery, and 42 normal wrists underwent sonography using a 7.5 MHz linear probe. The anteroposterior and transverse diameter of carpal tunnel, median nerve, and cross section area of the nerve were evaluated and compared.

Results:The average anteroposterior diameter of carpal tunnel in CTS (8mm) was less than normal wrists (10.05mm), which indicates a narrower canal in the severe form of this disease.

Average diameters of median nerve were more in CTS than normal wrists, with cross section area of 12.67mm2 and 10.29mm2 respectively.

Canclusion: sonography is a useful modality in diagnosis of severe CTS. We found out a decrease in anteroposterior diameter of carpal tunnel in severe cases of this disease, a finding which has not been considered previously. To evaluate the US results in mild to moderate CTS, more study will be needed

J.Orthopaedics 2007;4(4)e28

Carpal tunnel syndrome, Median nerve, wrist sonography, carpal tunnel diameter.

Carpal tunnel syndrome (CTS) is caused by compression on the median nerve at the wrist level and is the most common median nerve pathology. CTS is more prevalent in females between 30 to 60 years old and is commonly presented with numbness, tingling and pain in distal sensory distribution area of the median nerve. Long-term nerve compression can cause thenar muscular weakness and atrophy. CTS is caused by a number of entities which cause compression on the median nerve within the wrist. In its most severe form it is a chronic disabling condition.  

Generally any factor which decreases the carpal tunnel capacity or increases the tunnel constitutes can initiate CTS symptoms and signs (1, 2).

  Diagnosis is based on history, physical examination and also electro diagnosis evaluation of electromyography (EMG) and nerve conduction velocity (NCV)] of the median nerve. (3) These tests with sensitivity and specifity of 90% and 60% respectively are still standard for diagnosis of CTS.  Despite the reliability of these tests, there are some patients in whom the clinical findings and NCV, EMG results do not much with each other. and  a substantial number of symptomatic patients may have equivocal or negative results. When imaging studies are necessary, magnetic resonance has been the procedure of choice. However, this is a relatively expensive examination. (3, 4).

In recent years, sonographic examination of the median nerve has been suggested as a useful diagnostic alternative to EMG and NCV study. This has been primarily due to advances in digital imaging and new probes. Dynamic Sonography can be performed on the wrist with excellent delineation of both the normal median nerve and a compressed median nerve that defines carpal tunnel syndrome. Dynamic Sonography is a painless examination performed with the patient sitting. Sonography provides information as to why certain wrist motions predispose the patient to symptoms. Using Sonography, Carpal Tunnel Syndrome is diagnosed rapidly and at a significantly lower cost (less than half) than magnetic resonance imaging or electrodiagnostic studies.

Some authors believe the results of sonography are comparable with NCV and it can be used as a primary diagnostic tool (5).

  This study was performed to evaluate the sonographic findings in severe carpal tunnel syndrome and normal subject, and to compare the obtained results in two groups.  

Material and Methods :

We conducted a prospective controlled clinical study during a period of 19 months (between 2005 and 2006) in Imam Khomeini and Razi hospitals. All of the patients with documented CTS referred to our university orthopedic clinic were evaluated. The diagnosis was based on clinical and electro-diagnostic evaluations of EMG, NCV of median nerve.  Patients who were unresponsive to medical and supportive treatments and were candidates for surgery entered the study. Wrist sonography by an expert radiologist who was unaware from study was performed for all patients, using a Hitachi EUB525 machine with a linear 7.5 MHZ transducer. 21 patients enrolled the study, and treated by classic carpal tunnel release. 21 age and sex matched healthy volunteers were chosen as controls and sonography   of their carpal tunnel was performed for them too. Because dimensions of carpal tunnel might  be different according to the size and body mass, and also most of patients had bilateral CTS, so we tried to match the control subjects with regard to sex , age and body weight with CTS patients as could as possible. The measurements of diameters of carpal tunnel, median nerve, and cross section of the nerve were performed in two groups. Results were compared statistically using   Mann-whitney and T- test.

Results :

21 patients (20 female and 1 male) with mean age of 48 years (ranging from 29 to 63), and 21 healthy controls with the mean age of 38 years (ranging from 24 to 58) entered the study...

  Thirty nine wrists from case group with CTS, (the operation was done on both hands in 18 female patients) and 42 wrists from control group were assessed by sonography

EMG, NCV of the median nerve in all of the patients was performed as a routine for diagnosis... Mean duration of symptoms were 28 months, (6 months to 62 months).

  The most common symptom was night paresthesia. Hand pain was observed in 90 percent of cases. 71 percent of patients reported pain accentuation at nights. (See table 2) Phalen test was positive in 89 percent of patients and in 65 percent of them, the test showed positive result in less than 30 seconds. Tinnel test was positive in 97 percent, thenar weakness and atrophy in 46 percent and nail dystrophic changes in 12 percent of patients. Electro-diagnostic studies showed different degrees of nerve impairment in all of patients. In 15 cases the symptoms and signs were more severe in right hand (the dominant hand).

 The results of wrist sonography in CTS group were as follow:

  The antero-posterior diameter of the median nerve in the tunnel was ranged from 2 to 4 millimeter (mean and median were 3.62 mm).

  The transverse diameter was between 3-4 mm (mean 3.52). The carpal tunnel antero-posterior diameter at the pysiform bone level ranged from 7 to 10 millimeter (mean were 8 mm) and its transverse diameter at the same level ranged from 17 to 21 millimeters (mean of 19.48 mm). Flexor retinaculum thickening and reduced echogenisity of the median nerve were observed in 8 cases this finding was not seen in normal wrists. In one case the median nerve bifurcation was seen. (Table 1, 2)   

Table 1: Results of clinical and electro diagnostic findings in CTS group

Table 2: Results of sonographic findings in CTS and control group

 Results of sonographic study in control group were as follow:

  The antero-posterior diameter of the median nerve at the tunnel was ranged from 3 to 4 millimeter (mean and median were 3.19 mm). Transverse diameter of the median nerve was 2-4 millimeter (mean of 3.24 mm). The antero-posterior diameter of carpal tunnel at the pysiform bone level ranged from 7 to 11 millimeter (mean and median were 10.05 mm) and its transverse diameter at the same level ranged from 19 to 22 millimeters (mean of 20.19 mm).(Table 3 and 4)

Discussion :

The few papers published on the use of sonography in carpal tunnel syndrome suggest it as   a useful diagnostic tool..

The main findings in favor of CTS has been increase .in cross-sectional area of median nerve with an area larger than 10.3 mm2 being highly predictive of carpal tunnel syndrome.(6) In symptomatic CTS with severe EMG and NCV abnormalities, the median nerve cross- sectional area is almost always more than 11 mm2.(7) In these conditions, the median nerve swelling is observed at its entry to the tunnel and seems wide in that area. (8). Fig: 1  

Fig 1:  Swelling of the median nerve at entry of carpal tunnel

    El Miedany et al compared the sonographic findings of CTS patients with normal subjects and found out  increase of the median nerve cross sectional area to more than 10 mm2 is highly compatible with clinical and NCV findings in CTS patients. They concluded that ultrasonography is a new and valuable tool in diagnosis and follow up of this disease. (9)

 Yesildag et al measured the median nerve cross sectional area at three points (before, through and after the transverse retinaculum). The mean value of three mentioned measurements had 88 percent sensitivity and 94 percent specificity in diagnosis of CTS. (10)

  Serria et al studied 40 hands of CTS patients and compared the results with 24 normal controls. The most reliable finding in sonography was increased flexor retinaculum thickness and cross sectional area of the median nerve with a specificity of 60 percent for CTS diagnosis. (7)

    Ultrasonography is a noninvasive cost effective diagnostic tool that takes much less time than NCV without unpleasant sense of electrode usage in NCV and EMG for patients. It is especially useful in diagnosis of some carpal tunnel causes such as abscess and space occupying lesions. Assessment of the flexor tendon movements and post operative follow up of patients are some of other advantages of wrist sonography. (8, 11)

    Sonography can also be used to estimate the wrist angle in which the least pressure is transferred to the median nerve, guiding the steroid injection to inflamed flexor digitorum tendon sheaths, guiding the release of carpal tunnel, assessing the existence of nerve swelling before canal and also the nerve widening through the canal, and thickening and palmar bowing of the carpal retinaculum. (8, 11, 12, 13)

Because all of patients in our study were of severe CTS, so the sonographic findings do not correlate in mild or moderate forms of disease.

The results of our study shows a meaningful statistical difference between two groups with regard to AP diameter of median nerve, cross sectional area of it, and AP diameter of carpal tunnel, with P.value < 0.005. However the difference between transverse diameters of tunnel was not significant in two groups. The average cross sectional area of median nerve in CTS and control group were 12.67 mm2 and 10.29 mm2 respectively. The range of these values in CTS and normal wrists shows some overlapping, so the sensitivity and specifity of US can not accurately be assessed with this study.

Almost all previous studies of sonography in diagnosis of CTS indicate an increase in cross section area of median nerve, with a cut- off point of 10mm2 as the upper limit for normal values. In our study, the dimension of tunnel itself was measured. We found out the narrow anteroposterior carpal tunnel in severe CTS, a finding which t has not been reported previously.  It seems people with a narrower anteroposterior diameter of carpal tunnel are potentially more prone to develops CTS.


 Sonography is a useful modality in diagnosis of severe CTS. We found out a decrease in anteroposterior diameter of carpal tunnel in severe cases of this disease. A finding which has not been considered previously. This finding of narrow carpal tunnel may be considered as a predisposing factor in severe CTS. To evaluate the US results in mild to moderate disease, more study will be needed.

Reference :

1- Phillip E. wright II. Carpal tunnel syndrome. In: Terry Canal S. Campbell's Operative orthopaedics 10 the ed. Mosby. 2003; 3761-62.

2- Brown feard tanzer: Entrapment neuropathies of the upper extremity. In fly JE, el: Hand surgery...Ed 3 Baltimore , 1982.william, s and wikins.

3- Shirde AJ, Dreizint, and fisher MA: the carpal tunnel syndrome. A clinical electrodiagnostic analysis, Electromyography. Clin Neurophysio1981; l 21: 143.

4- Gellman H,Gelberman RH tan AM, and Botte MJ:carpal tunnel syndrome, an evaluation of the provocative diagnostic test.J.Bone Joint sury.1986 ;63-A: 735

5- Wong SM, Griffith JE, Hui AC. Discriminatory sonographic criteria for the diagnosis of carpal tunnel syndrome. Arthritis rheuma.jul 2002; 46-(7):1914-21.

6- Duncan I, Sullivan P, loams F: sonography in the diagnosis of carpal tunnel syndrome. AJR AMJ roentgenol. Sep 1999; 137(3):681-4.

7- Sarria L, cabada T, Cozcolluela R, et al.Carpal tunnel syndrome: usefulness of sonography.Eur Radiol.2000; 10(12):1920-5

8- Buchberger W, Judmaier W, Birbamer G, et al: Carpal tunnel syndrome: Diagnosis with high-Resolution sonography.AJR AM J Roentgenol, Oct 1992; 159(4): 793-8

9- EL.Miedany YM, Aty SA, Ashours: ultrasonography versus nerve conduction study in patients with carpal tunnel syndrome: rheumatology. ( Oxford ),Epub

Apr 2004; 887-95.

10- Yesildag A, Kutiuhan N, Koyuncuogiu HP, el: the role of ultrasonogruphy in the diagnosis of carpal tunnel syndrome. Clini-racliol, Oct 2004; 59(10): 910-5

11- Teefey SA, Middleton WD, Boyer Ml.sonography of the hand and wrist. Semin Ultrasound CT MR, Jun 2002; 21(3):192-204.

12- Kuo MH, Leong CP, Cheng YF, Chang HW. Static wrist position associated with least median nerve compression: sonographic evaluation evaluation. Am J Phys Med Rehabil. 2001 Apr; 80(4):256-60.

13- Wilinand AA, Swen A, Johannres W G. Carpal tunnel sonography by the rheumatolgist versus NCV by the neurologist, Journal rheumatol 2001;28:62-9.


This is a peer reviewed paper 

Please cite as : Seyed abdolhossein Mehdinasab : Sonographic Findings in Severe Carpal Tunnel Syndrome and Normal Subjects. A Comparative Study

J.Orthopaedics 2007;4(4)e28





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