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COMPARATIVE STUDY ON THE STIFFNESS OF TRANSVERSE CARPAL LIGAMENT BETWEEN NORMAL SUBJECTS AND CARPAL TUNNEL SYNDROME PATIENTS‡ Hideaki Miyamoto,* Toshiki Miura,*,† Yutaka Morizaki,* Kosuke Uehara,* Takashi Ohe* and Sakae Tanaka* *Department
of Orthopaedic Surgery, Graduate School of Medicine The University of Tokyo, Tokyo, Japan †Department
of Orthopaedic Surgery JR Tokyo General Hospital, Tokyo, Japan Received 16 October 2012; Revised 24 November 2012; Accepted 26 November 2012 ABSTRACT The purpose of this study was to compare the stiffness of the transverse carpal ligament (TCL) between healthy volunteers and carpal tunnel syndrome (CTS) patients using sonoelastography. We studied 17 healthy volunteers (four men, 13 women; range 3784 years) and 18 hands of 13 patients with CTS (three men, ten women; range 4179 years). Thickness and elasticity of the TCL were evaluated by sonoelastography. Elasticity was estimated by strain ratio of an acoustic coupler, which has a standardized elasticity as a reference medium, to the TCL (AC / T strain ratio). The AC/T strain ratios of the healthy volunteers and the CTS patients were 6.0 and 8.1, respectively ( p ¼ 0:030). The AC/T strain ratio showed a positive correlation with the duration of symptoms in the CTS patients ( p ¼ 0:035; r ¼ 0:50). We concluded that increased stiffness of the TCL could be one of the causes for CTS. Keywords: Carpal Tunnel Syndrome; Elastography; Sonoelastography; Stiffness; Transverse Carpal Ligament.
INTRODUCTION
distorted contact on the median nerve with the neighboring structures such as transverse carpal ligament (TCL), finger , flexor tendons, and subsynovial connective tissue.2 3 Stiffness of soft tissues may be responsible for pathogenesis of various soft tissue problems of the hand including CTS and trigger finger. Recently, ultrasound has been utilised for the quantitative assessment of elasticity as well as thickness of the soft tissues using a new ultrasound-based technique, called
Carpal Tunnel Syndrome (CTS) is a common entrapment neuropathy of the median nerve at the wrist. The prevalence of CTS among females (4.5%) is higher than that among males (1.9%).1 The symptoms of CTS are numbness and tingling in area of the median nerve distribution, and weakness of the thumb opposition. The mechanism of CTS is believed to be an increased intracarpal tunnel pressure, which can be caused by
Correspondence to: Dr. Toshiki Miura, Department of Orthopaedic Surgery, JR Tokyo General Hospital, 2-1-3, Yoyogi, Shibuya-ku, Tokyo 151-8528, Japan. Tel: (þ81) 3-3320-2200, Fax: (þ81) 3-3370-8501, E-mail: [email protected] ‡ No benefits in any form have been received or will be received that are related directly or indirectly to the subject of this article. 209
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sonoelastography (SEG). For example, a study with SEG has shown that increased stiffness of the first annular pulley can cause snapping in a trigger finger.4 The purposes of this study were as follows: firstly, to define the elasticity and thickness of the TCL in healthy volunteers; and secondly, to compare the difference in elasticity and thickness of the TCL between healthy volunteers and CTS patients.
MATERIALS AND METHODS This study was conducted with the approval of the Institutional Review Boards (IRBs) of our institution, and all participants provided written informed consent. Both hands of 17 healthy volunteers (four men, 13 women; mean age 60 years, range 3784 years) were included for the first experiment to define the elasticity and thickness of the normal TCL. Exclusion criteria for the first experiment were those undergoing hemodialysis, a scar on the wrist from prior trauma, joint disorder such as rheumatoid arthritis, or CTS symptoms. Sonographic examination of the TCL was performed with a 614 MHz linear-array transducer (HI VISION Avius, Hitachi Aloka Medical, Ltd, Tokyo). We attached an acoustic coupler which has a standardised elasticity as a reference medium (Acoustic coupler EZU-TECPL1, Hitachi Aloka Medical, Ltd, Tokyo) on the transducer (Fig. 1). All SEG examination was performed by an examiner. The subjects were asked to sit in front of an examination table with the elbow at 90 of flexion and the hand in supination. Fingers were kept in full extension during the measurement. The proximal palm at the level of the pisiform bone was scanned on an axial plane. SEG images were obtained by repeated compressions of the palm with the probe. For standardisation of the amount of pressure, we referred a visual feedback indicator on the SEG screen. Several compressiondecompression cycles were performed before the force and frequency of the probe compression became appropriate and the acoustic coupler was shown in a flat color. SEG equipment can display two real-time images simultaneously; conventional B-mode image and SEG image showing the region of interest (ROI) as a colored area (Fig. 2). The examination results are represented in a colour scale over the conventional ultrasound image and the resultant strain ratio between any two areas also can be calculated. The colour scale ranged from red for components with the greatest strain as the softest components, to blue for those with no strain as the hardest components. Green indicated average strain in the ROI. The elasticity of the TCL in
(A)
(B) Fig. 1 (A) The reference medium has a standardised elasticity. (B) The reference medium attaching with a probe.
this study was assessed as the strain ratio of the acoustic coupler to the TCL (AC/T strain ratio). Sonoelastography cannot well depict soft inclusions embedded in incompressible background material because inclusions would be unable to deform under load.5 There is no incompressible material surrounding the TCL: the overlying skin, fat, muscle is compressible soft tissue (Poisson’s ratio ¼ 0:4, 0.5, 0.4, respectively).6 Therefore, we evaluated the elasticity of the TCL by sonoelastography. In order to avoid any effect on the measurements of the AC/T strain ratio, we excluded the overlying skin, fat, muscle layer from the calculating area. Measurements were repeated three times and the resultant average strain ratio was calculated.
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Fig. 2 Axial ultrasound images of the carpal tunnel. (A) Schematic presentation of the axial image (AC: acoustic coupler, TCL: transverse carpal ligament, MN: median nerve, FT: flexor tendon). (B) On a conventional B-mode echo image, the TCL corresponds to the high-echo area between the arrowheads. (C) Elastography image at the same level as the B-mode image. The color represents the elasticity of the tissue within the region of interest, whose scale ranged from red for components with the greatest strain (softest components) to blue for those with no strain (hardest components). The elasticity of the TCL was assessed by the strain ratio of the acoustic coupler (b) to TCL (a).
We then evaluated 18 hands of 13 patients with symptomatic CTS (three men, ten women; mean age 62 years, ranging 4179 years) by SEG. The diagnosis of CTS was confirmed when both clinical provocation and electrodiagnostic testing were positive by a board-certified senior hand surgeon.7 Exclusion criteria were secondary CTS patients undergoing haemodialysis and joint disorder such as rheumatoid arthritis. Those who had a history of steroid injection into the carpal tunnel within three months were also excluded. All patients completed a visual analogue scale for pain (VAS, 0100 mm). The SEG examination was performed in a similar manner to the examination in the healthy volunteers mentioned earlier. The examiner was blinded to the diagnosis of CTS. Table 1
Table 1 Demographic Data for CTS Patients and Healthy Volunteers. Characteristics
CTS Patients
Healthy Volunteers
Age (years) Female Dominant hand VAS (0100 mm)
61.7 11.9 10/13 (77%) 10/18 (56%) 63.3 12.8
59.9 15.4 13/17 (76%) 17/34 (50%) —
Notes: Values are presented as the mean SD or number (%). CTS ¼ carpal tunnel syndrome, VAS ¼ visual analog scale for pain.
shows the baseline characteristics of the control subjects and CTS patients included in this study.
Statistical Analysis We used the unpaired t test and Fisher’s exact test to compare demographic data between healthy volunteers and CTS patients. The Pearson correlation coefficients between age and the measurement values (thickness and strain ratio of the TCL) were calculated in the experiment with healthy volunteers. The unpaired t test was used for the comparison of the measurement values between healthy volunteers and CTS patients. We used multiple regression analysis to assess the relative contribution of the elasticity and thickness of TCL to VAS in CTS patients. The Pearson correlation coefficients between the duration of CTS symptoms and the measurement values were calculated in the experiment with CTS patients. Values of p < 0:05 were considered significant.
RESULTS Thicknesses of the normal TCL of dominant and non-dominant hands were 1:10:19 mm and 1:10:18 mm (mean SD), respectively. AC/T strain ratios of dominant and non-dominant hands were 6:02:8 and 6:03:2, respectively. There was
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(A)
(B)
Fig. 3 (A) Correlation between age and thickness of the TCL in healthy volunteers. There was no correlation ( p ¼ 0:20). (B) Correlation between age and elasticity of the TCL in healthy volunteers. The strain ratio of the acoustic coupler to the TCL had a positive correlation with age ( p < 0:0001; R ¼ 0:66).
no significant difference either in thickness ( p ¼ 0:78) or elasticity ( p ¼ 0:98) of the TCL between the dominant and non-dominant hands; therefore, measurement values of dominant and non-dominant hands were treated as equivalent thereafter. Although there was no correlation between age and thickness of the TCL ( p ¼ 0:20), there was a moderate positive correlation between age and elasticity ( p < 0:0001; R ¼ 0:66) in healthy volunteers (Fig. 3). Thickness of the TCL in the CTS patients was 1:3 0:21 mm, which was significantly thicker than that of the healthy volunteer (1:1 0:18 mm) ( p ¼ 0:011) (Fig. 4A). AC/ T strain ratio in the CTS patients was 8:1 3:7, which was
significantly higher than that of the healthy volunteers (6:0 2:9) ( p ¼ 0:030) (Fig. 4B). Multiple regression analysis demonstrated that both the elasticity and thickness contributed to VAS in CTS patients (Table 2). The predictive equation was: VAS ¼ 12:7 þ 1:79 AC=T strain ratio þ 28:8 TCL thickness (mm) ( p ¼ 0:019; R ¼ 0:64, adjusted R 2 ¼ 0:33). There is no correlation between the duration of CTS symptoms and thickness of the TCL ( p ¼ 0:61) (Fig. 5A). There was a moderate positive correlation between the duration of CTS symptoms and elasticity of the TCL ( p ¼ 0:035; R ¼ 0:50) (Fig. 5B).
DISCUSSION SEG has enabled in vivo quantitative evaluation of soft tissue stiffness. Our results showed that elasticity of the TCL tended to change with aging in normal subjects and that the TCL of CTS patients were significantly thicker and harder than that of normal subjects. We also showed that elasticity of the TCL was Table 2 Contribution of the Elasticity and Thickness of TCL to VAS by Multiple Regression Analysis. (A)
(B)
Fig. 4 Comparisons of thickness (A) and elasticity (B) of the TCL between healthy volunteers and CTS patients. The TCL of the CTS patients was significantly thicker ( p ¼ 0:011) and harder ( p ¼ 0:030) than that of the healthy volunteers (HV). Data is expressed as means (bars) SD (error bars). *p < 0:05.
Variable AC / T strain ratio Thickness (mm)
t Value
p Value
2.55 2.34
0.022 0.034
Note: TCL ¼ transverse carpal ligament, VAS ¼ visual analog scale for pain, AC / T strain ratio ¼ the strain ratio of the acoustic coupler to the TCL.
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In a histological study, 44 of 166 specimens of the TCL with idiopathic CTS showed mucoid change, amyloid deposits, inflammation, and chondrometaplasia.10 Electron microscopic analysis revealed the existence of varying diameters of collagen fibrils in dissected TCL of the CTS patients.11 These histological changes may explain the thickening and hardening of the TCL in CTS patients. This study has several limitations. Although it is reported that female carpal tunnels are less compliant than males in vivo,12 we did not evaluated gender difference because of small sample size. Volume of the intracarpal tunnel contents were not evaluated in this study because it is difficult to delineate the lateral sides of the carpal tunnel by ultrasound without sweep motion. We compared the stiffness of the TCL quantitatively between healthy volunteers and CTS patients, and concluded that increased stiffness of the TCL could be one of the causes for CTS.
References (B) Fig. 5 (A) Correlation between thickness of the TCL and the duration of CTS symptoms. There was no significant correlation ( p ¼ 0:61). (B) Correlation between elasticity of the TCL and the duration of CTS symptoms. The duration of CTS symptoms had a positive correlation with the strain ratio of the acoustic coupler to that of the TCL ( p ¼ 0:035; r ¼ 0:50).
related to pain score and duration of the symptoms in the CTS patients. Several authors suggested that the reduced compliance of the TCL increases intracarpal tunnel pressure in cadaver and animal models.7,8 We measured compliance of the TCL of the CTS patients in vivo. Our data of the CTS patients were comparable to the previous suggestions in cadaver and animal models. Previous study has shown that the duration and amount of pressure is associated with the neural dysfunction in a dosedependent manner.9 Our results suggested that elasticity of the TCL were associated with duration and severity of the symptoms of CTS. Increased elasticity of the TCL was suggested to cause chronic compression to the median nerve, which resulted in neural dysfunction.
1. Luckhaupt SE, Dahlhamer JM, Ward BW, Sweeney MH, Sestito JP, Calvert GM, Prevalence and work-relatedness of carpal tunnel syndrome in the working population, United States, 2010 national health interview survey, Am J Ind Med 2012. doi: 10.1002/ajim.22048. 2. Werner RA, Andary M, Carpal tunnel syndrome: pathophysiology and clinical neurophysiology, Clin Neurophysiol 113:13731381, 2002. 3. Ettema AM, Amadio PC, Zhao C, Wold LE, An KN, A histological and immunohistochemical study of the subsynovial connective tissue in idiopathic carpal tunnel syndrome, J Bone Joint Surg Am 86:1458 1466, 2004. 4. Miyamoto H, Miura T, Isayama H, Masuzaki R, Koike K, Ohe T, Stiffness of the first annular pulley in normal and trigger fingers, J Hand Surg [Am] 36:14861491, 2011. 5. Ophir J, Alam SK, Garra BS, Kallel F, Konofagou E, Krouskop TA, Merritt CRB, Righetti R, Souchon R, Srinivasan S, Varghese T, Elastography: imaging the elastic properties of soft tissues with ultrasound, J Med Ultrason 29:155171, 2002. 6. Vannah WM, Childress DS, Modelling the mechanics of narrowly contained soft tissues: the effects of specification of Poisson’s ratio, J Rehabil Res Dev 30:205209, 1993. 7. Li ZM, Masters TL, Mondello TA, Area and shape changes of the carpal tunnel in response to tunnel pressure, J Orthop Res 29:19511956, 2011. 8. Tung WL, Zhao C, Yoshii Y, Su FC, An KN, Amadio PC, Comparative study of carpal tunnel compliance in the human, dog, rabbit, and rat, J Orthop Res 28:652656, 2010.
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9. Diao E, Shao F, Liebenberg E, Rempel D, Lotz JC, Carpal tunnel pressure alters median nerve function in a dose-dependent manner: a rabbit model for carpal tunnel syndrome, J Orthop Res 23:218223, 2005. 10. Nakamichi K, Tachibana S, Histology of the transverse carpal ligament and flexor tenosynovium in idiopathic carpal tunnel syndrome, J Hand Surg [Am] 23:10151024, 1998.
11. Stransky G, Wenger E, Dimitrov L, Weis S, Collagen dysplasia in idiopathic carpal tunnel syndrome, Pathol Res Pract 185:795798, 1989. 12. Li ZM, Gender difference in carpal tunnel compliance, J Muscle Res 9:153159, 2005.
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Hand Surgery, Vol. 18, No. 2 (2013) 209214 © World Scientific Publishing Company DOI: 10.1142/S0218810413500251
COMPARATIVE STUDY ON THE STIFFNESS OF TRANSVERSE CARPAL LIGAMENT BETWEEN NORMAL SUBJECTS AND CARPAL TUNNEL SYNDROME PATIENTS‡ Hideaki Miyamoto,* Toshiki Miura,*,† Yutaka Morizaki,* Kosuke Uehara,* Takashi Ohe* and Sakae Tanaka* *Department
of Orthopaedic Surgery, Graduate School of Medicine The University of Tokyo, Tokyo, Japan †Department
of Orthopaedic Surgery JR Tokyo General Hospital, Tokyo, Japan Received 16 October 2012; Revised 24 November 2012; Accepted 26 November 2012 ABSTRACT The purpose of this study was to compare the stiffness of the transverse carpal ligament (TCL) between healthy volunteers and carpal tunnel syndrome (CTS) patients using sonoelastography. We studied 17 healthy volunteers (four men, 13 women; range 3784 years) and 18 hands of 13 patients with CTS (three men, ten women; range 4179 years). Thickness and elasticity of the TCL were evaluated by sonoelastography. Elasticity was estimated by strain ratio of an acoustic coupler, which has a standardized elasticity as a reference medium, to the TCL (AC / T strain ratio). The AC/T strain ratios of the healthy volunteers and the CTS patients were 6.0 and 8.1, respectively ( p ¼ 0:030). The AC/T strain ratio showed a positive correlation with the duration of symptoms in the CTS patients ( p ¼ 0:035; r ¼ 0:50). We concluded that increased stiffness of the TCL could be one of the causes for CTS. Keywords: Carpal Tunnel Syndrome; Elastography; Sonoelastography; Stiffness; Transverse Carpal Ligament.
INTRODUCTION
distorted contact on the median nerve with the neighboring structures such as transverse carpal ligament (TCL), finger , flexor tendons, and subsynovial connective tissue.2 3 Stiffness of soft tissues may be responsible for pathogenesis of various soft tissue problems of the hand including CTS and trigger finger. Recently, ultrasound has been utilised for the quantitative assessment of elasticity as well as thickness of the soft tissues using a new ultrasound-based technique, called
Carpal Tunnel Syndrome (CTS) is a common entrapment neuropathy of the median nerve at the wrist. The prevalence of CTS among females (4.5%) is higher than that among males (1.9%).1 The symptoms of CTS are numbness and tingling in area of the median nerve distribution, and weakness of the thumb opposition. The mechanism of CTS is believed to be an increased intracarpal tunnel pressure, which can be caused by
Correspondence to: Dr. Toshiki Miura, Department of Orthopaedic Surgery, JR Tokyo General Hospital, 2-1-3, Yoyogi, Shibuya-ku, Tokyo 151-8528, Japan. Tel: (þ81) 3-3320-2200, Fax: (þ81) 3-3370-8501, E-mail: [email protected] ‡ No benefits in any form have been received or will be received that are related directly or indirectly to the subject of this article. 209
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sonoelastography (SEG). For example, a study with SEG has shown that increased stiffness of the first annular pulley can cause snapping in a trigger finger.4 The purposes of this study were as follows: firstly, to define the elasticity and thickness of the TCL in healthy volunteers; and secondly, to compare the difference in elasticity and thickness of the TCL between healthy volunteers and CTS patients.
MATERIALS AND METHODS This study was conducted with the approval of the Institutional Review Boards (IRBs) of our institution, and all participants provided written informed consent. Both hands of 17 healthy volunteers (four men, 13 women; mean age 60 years, range 3784 years) were included for the first experiment to define the elasticity and thickness of the normal TCL. Exclusion criteria for the first experiment were those undergoing hemodialysis, a scar on the wrist from prior trauma, joint disorder such as rheumatoid arthritis, or CTS symptoms. Sonographic examination of the TCL was performed with a 614 MHz linear-array transducer (HI VISION Avius, Hitachi Aloka Medical, Ltd, Tokyo). We attached an acoustic coupler which has a standardised elasticity as a reference medium (Acoustic coupler EZU-TECPL1, Hitachi Aloka Medical, Ltd, Tokyo) on the transducer (Fig. 1). All SEG examination was performed by an examiner. The subjects were asked to sit in front of an examination table with the elbow at 90 of flexion and the hand in supination. Fingers were kept in full extension during the measurement. The proximal palm at the level of the pisiform bone was scanned on an axial plane. SEG images were obtained by repeated compressions of the palm with the probe. For standardisation of the amount of pressure, we referred a visual feedback indicator on the SEG screen. Several compressiondecompression cycles were performed before the force and frequency of the probe compression became appropriate and the acoustic coupler was shown in a flat color. SEG equipment can display two real-time images simultaneously; conventional B-mode image and SEG image showing the region of interest (ROI) as a colored area (Fig. 2). The examination results are represented in a colour scale over the conventional ultrasound image and the resultant strain ratio between any two areas also can be calculated. The colour scale ranged from red for components with the greatest strain as the softest components, to blue for those with no strain as the hardest components. Green indicated average strain in the ROI. The elasticity of the TCL in
(A)
(B) Fig. 1 (A) The reference medium has a standardised elasticity. (B) The reference medium attaching with a probe.
this study was assessed as the strain ratio of the acoustic coupler to the TCL (AC/T strain ratio). Sonoelastography cannot well depict soft inclusions embedded in incompressible background material because inclusions would be unable to deform under load.5 There is no incompressible material surrounding the TCL: the overlying skin, fat, muscle is compressible soft tissue (Poisson’s ratio ¼ 0:4, 0.5, 0.4, respectively).6 Therefore, we evaluated the elasticity of the TCL by sonoelastography. In order to avoid any effect on the measurements of the AC/T strain ratio, we excluded the overlying skin, fat, muscle layer from the calculating area. Measurements were repeated three times and the resultant average strain ratio was calculated.
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(B)
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Fig. 2 Axial ultrasound images of the carpal tunnel. (A) Schematic presentation of the axial image (AC: acoustic coupler, TCL: transverse carpal ligament, MN: median nerve, FT: flexor tendon). (B) On a conventional B-mode echo image, the TCL corresponds to the high-echo area between the arrowheads. (C) Elastography image at the same level as the B-mode image. The color represents the elasticity of the tissue within the region of interest, whose scale ranged from red for components with the greatest strain (softest components) to blue for those with no strain (hardest components). The elasticity of the TCL was assessed by the strain ratio of the acoustic coupler (b) to TCL (a).
We then evaluated 18 hands of 13 patients with symptomatic CTS (three men, ten women; mean age 62 years, ranging 4179 years) by SEG. The diagnosis of CTS was confirmed when both clinical provocation and electrodiagnostic testing were positive by a board-certified senior hand surgeon.7 Exclusion criteria were secondary CTS patients undergoing haemodialysis and joint disorder such as rheumatoid arthritis. Those who had a history of steroid injection into the carpal tunnel within three months were also excluded. All patients completed a visual analogue scale for pain (VAS, 0100 mm). The SEG examination was performed in a similar manner to the examination in the healthy volunteers mentioned earlier. The examiner was blinded to the diagnosis of CTS. Table 1
Table 1 Demographic Data for CTS Patients and Healthy Volunteers. Characteristics
CTS Patients
Healthy Volunteers
Age (years) Female Dominant hand VAS (0100 mm)
61.7 11.9 10/13 (77%) 10/18 (56%) 63.3 12.8
59.9 15.4 13/17 (76%) 17/34 (50%) —
Notes: Values are presented as the mean SD or number (%). CTS ¼ carpal tunnel syndrome, VAS ¼ visual analog scale for pain.
shows the baseline characteristics of the control subjects and CTS patients included in this study.
Statistical Analysis We used the unpaired t test and Fisher’s exact test to compare demographic data between healthy volunteers and CTS patients. The Pearson correlation coefficients between age and the measurement values (thickness and strain ratio of the TCL) were calculated in the experiment with healthy volunteers. The unpaired t test was used for the comparison of the measurement values between healthy volunteers and CTS patients. We used multiple regression analysis to assess the relative contribution of the elasticity and thickness of TCL to VAS in CTS patients. The Pearson correlation coefficients between the duration of CTS symptoms and the measurement values were calculated in the experiment with CTS patients. Values of p < 0:05 were considered significant.
RESULTS Thicknesses of the normal TCL of dominant and non-dominant hands were 1:10:19 mm and 1:10:18 mm (mean SD), respectively. AC/T strain ratios of dominant and non-dominant hands were 6:02:8 and 6:03:2, respectively. There was
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(A)
(B)
Fig. 3 (A) Correlation between age and thickness of the TCL in healthy volunteers. There was no correlation ( p ¼ 0:20). (B) Correlation between age and elasticity of the TCL in healthy volunteers. The strain ratio of the acoustic coupler to the TCL had a positive correlation with age ( p < 0:0001; R ¼ 0:66).
no significant difference either in thickness ( p ¼ 0:78) or elasticity ( p ¼ 0:98) of the TCL between the dominant and non-dominant hands; therefore, measurement values of dominant and non-dominant hands were treated as equivalent thereafter. Although there was no correlation between age and thickness of the TCL ( p ¼ 0:20), there was a moderate positive correlation between age and elasticity ( p < 0:0001; R ¼ 0:66) in healthy volunteers (Fig. 3). Thickness of the TCL in the CTS patients was 1:3 0:21 mm, which was significantly thicker than that of the healthy volunteer (1:1 0:18 mm) ( p ¼ 0:011) (Fig. 4A). AC/ T strain ratio in the CTS patients was 8:1 3:7, which was
significantly higher than that of the healthy volunteers (6:0 2:9) ( p ¼ 0:030) (Fig. 4B). Multiple regression analysis demonstrated that both the elasticity and thickness contributed to VAS in CTS patients (Table 2). The predictive equation was: VAS ¼ 12:7 þ 1:79 AC=T strain ratio þ 28:8 TCL thickness (mm) ( p ¼ 0:019; R ¼ 0:64, adjusted R 2 ¼ 0:33). There is no correlation between the duration of CTS symptoms and thickness of the TCL ( p ¼ 0:61) (Fig. 5A). There was a moderate positive correlation between the duration of CTS symptoms and elasticity of the TCL ( p ¼ 0:035; R ¼ 0:50) (Fig. 5B).
DISCUSSION SEG has enabled in vivo quantitative evaluation of soft tissue stiffness. Our results showed that elasticity of the TCL tended to change with aging in normal subjects and that the TCL of CTS patients were significantly thicker and harder than that of normal subjects. We also showed that elasticity of the TCL was Table 2 Contribution of the Elasticity and Thickness of TCL to VAS by Multiple Regression Analysis. (A)
(B)
Fig. 4 Comparisons of thickness (A) and elasticity (B) of the TCL between healthy volunteers and CTS patients. The TCL of the CTS patients was significantly thicker ( p ¼ 0:011) and harder ( p ¼ 0:030) than that of the healthy volunteers (HV). Data is expressed as means (bars) SD (error bars). *p < 0:05.
Variable AC / T strain ratio Thickness (mm)
t Value
p Value
2.55 2.34
0.022 0.034
Note: TCL ¼ transverse carpal ligament, VAS ¼ visual analog scale for pain, AC / T strain ratio ¼ the strain ratio of the acoustic coupler to the TCL.
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In a histological study, 44 of 166 specimens of the TCL with idiopathic CTS showed mucoid change, amyloid deposits, inflammation, and chondrometaplasia.10 Electron microscopic analysis revealed the existence of varying diameters of collagen fibrils in dissected TCL of the CTS patients.11 These histological changes may explain the thickening and hardening of the TCL in CTS patients. This study has several limitations. Although it is reported that female carpal tunnels are less compliant than males in vivo,12 we did not evaluated gender difference because of small sample size. Volume of the intracarpal tunnel contents were not evaluated in this study because it is difficult to delineate the lateral sides of the carpal tunnel by ultrasound without sweep motion. We compared the stiffness of the TCL quantitatively between healthy volunteers and CTS patients, and concluded that increased stiffness of the TCL could be one of the causes for CTS.
References (B) Fig. 5 (A) Correlation between thickness of the TCL and the duration of CTS symptoms. There was no significant correlation ( p ¼ 0:61). (B) Correlation between elasticity of the TCL and the duration of CTS symptoms. The duration of CTS symptoms had a positive correlation with the strain ratio of the acoustic coupler to that of the TCL ( p ¼ 0:035; r ¼ 0:50).
related to pain score and duration of the symptoms in the CTS patients. Several authors suggested that the reduced compliance of the TCL increases intracarpal tunnel pressure in cadaver and animal models.7,8 We measured compliance of the TCL of the CTS patients in vivo. Our data of the CTS patients were comparable to the previous suggestions in cadaver and animal models. Previous study has shown that the duration and amount of pressure is associated with the neural dysfunction in a dosedependent manner.9 Our results suggested that elasticity of the TCL were associated with duration and severity of the symptoms of CTS. Increased elasticity of the TCL was suggested to cause chronic compression to the median nerve, which resulted in neural dysfunction.
1. Luckhaupt SE, Dahlhamer JM, Ward BW, Sweeney MH, Sestito JP, Calvert GM, Prevalence and work-relatedness of carpal tunnel syndrome in the working population, United States, 2010 national health interview survey, Am J Ind Med 2012. doi: 10.1002/ajim.22048. 2. Werner RA, Andary M, Carpal tunnel syndrome: pathophysiology and clinical neurophysiology, Clin Neurophysiol 113:13731381, 2002. 3. Ettema AM, Amadio PC, Zhao C, Wold LE, An KN, A histological and immunohistochemical study of the subsynovial connective tissue in idiopathic carpal tunnel syndrome, J Bone Joint Surg Am 86:1458 1466, 2004. 4. Miyamoto H, Miura T, Isayama H, Masuzaki R, Koike K, Ohe T, Stiffness of the first annular pulley in normal and trigger fingers, J Hand Surg [Am] 36:14861491, 2011. 5. Ophir J, Alam SK, Garra BS, Kallel F, Konofagou E, Krouskop TA, Merritt CRB, Righetti R, Souchon R, Srinivasan S, Varghese T, Elastography: imaging the elastic properties of soft tissues with ultrasound, J Med Ultrason 29:155171, 2002. 6. Vannah WM, Childress DS, Modelling the mechanics of narrowly contained soft tissues: the effects of specification of Poisson’s ratio, J Rehabil Res Dev 30:205209, 1993. 7. Li ZM, Masters TL, Mondello TA, Area and shape changes of the carpal tunnel in response to tunnel pressure, J Orthop Res 29:19511956, 2011. 8. Tung WL, Zhao C, Yoshii Y, Su FC, An KN, Amadio PC, Comparative study of carpal tunnel compliance in the human, dog, rabbit, and rat, J Orthop Res 28:652656, 2010.
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H. Miyamoto et al.
9. Diao E, Shao F, Liebenberg E, Rempel D, Lotz JC, Carpal tunnel pressure alters median nerve function in a dose-dependent manner: a rabbit model for carpal tunnel syndrome, J Orthop Res 23:218223, 2005. 10. Nakamichi K, Tachibana S, Histology of the transverse carpal ligament and flexor tenosynovium in idiopathic carpal tunnel syndrome, J Hand Surg [Am] 23:10151024, 1998.
11. Stransky G, Wenger E, Dimitrov L, Weis S, Collagen dysplasia in idiopathic carpal tunnel syndrome, Pathol Res Pract 185:795798, 1989. 12. Li ZM, Gender difference in carpal tunnel compliance, J Muscle Res 9:153159, 2005.
