Ultrasound Assessment of the Effectiveness of Carpal Tunnel Release on Median Nerve Deformation Yuichi Yoshii,1 Tomoo Ishii,1 Wen-lin Tung2 1 Department of Orthopaedic Surgery, Tokyo Medical University Ibaraki Medical Center, Ami 300-0395, Japan, 2Department of Rehabilitation, Ibaraki Prefectural University of Health Sciences, Ami, Japan
Received 3 October 2014; accepted 21 January 2015 Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jor.22843
ABSTRACT: To assess the biomechanical effect of carpal tunnel release (CTR), we evaluated the deformation and displacement patterns of the median nerve before and after CTR in carpal tunnel syndrome (CTS) patients. Sixteen wrists of 14 idiopathic CTS patients who had open CTR and 26 wrists of 13 asymptomatic volunteers were evaluated by ultrasound. Cross-sectional images of the carpal tunnel during motion from full finger extension to flexion were recorded. The area, perimeter, aspect ratio of a minimum enclosing rectangle, and circularity of the median nerve were measured in finger extension and flexion positions. Deformation indices, determined by the flexion–extension ratio for each parameter, were compared before and after CTR. After CTR, the deformation indices of perimeter and circularity became significantly larger and the aspect ratio became significantly smaller than those before CTR (p < 0.05). Those differences were more obvious when comparing the values between the patients before CTR and the controls. Since the deformation indices after CTR are similar to the patterns of normal subjects, the surrounding structures and environment of the median nerve may be normalized upon CTR. This may be a way to tell how the median nerves recover after CTR. ß 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res Keywords: median nerve; deformation; displacement; carpal tunnel release; ultrasound
Carpal tunnel syndrome (CTS), a pressure-induced neuropathy of the median nerve, is a common clinical problem. Clinical studies of patients with CTS typically show higher baseline pressures within the carpal tunnel than in normal control subjects.1–5 If conservative treatment is ineffective, surgical release of the flexor retinaculum is commonly selected to normalize the carpal tunnel pressure. Although carpal tunnel release (CTR) reliably reduces carpal tunnel pressure,6,7 surgery relieves symptoms in only 70–90% of patients.8–12 While in some cases patients’ lack of recovery may be due to the presence of more severe neuropathy, in many cases patients with similar degrees of neuropathy experience differing degrees of recovery,10,13,14 suggesting that other factors may be in play. However, other than reducing carpal tunnel pressure,6,7 the biomechanical effect of CTR has received little attention. In a previous study, we developed a technique to evaluate displacement and deformation patterns of the median nerve during finger motion using ultrasound imaging.15 It was found that there are differences in the deformation pattern of the median nerve during finger motion, upon comparing between CTS patients and normal controls. During the process of the study, we observed that there were some differences in the deformation patterns of the median nerve after CTR surgery. If it is possible to determine these differences, it may be useful to understand the effectiveness or the lack of effectiveness of CTR. Thus, we hypothesized that the deformation and displacement patterns of the median nerve during finger motion would differ between before and after CTR in CTS patients. In this Conflicts of interest: None. Grant sponsor: Japanese Society for Surgery of the Hand. Correspondence to: Yuichi Yoshii (T: þ81-29-887-1161; F: þ8129-888-8303; E-mail: [email protected]) # 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.
study, to assess the biomechanical effect of CTR, we evaluated the deformation and displacement patterns of the median nerve before and after releasing the carpal tunnel in idiopathic CTS patients. In addition, the same parameters were evaluated in normal subjects, and compared with CTS patients.
MATERIAL AND METHODS This study protocol was approved by our Institutional Review Board. Sixteen wrists of 14 idiopathic CTS patients who had open CTR (7 females, 7 males; age range 52–85, with a mean age of 63.9 years) and 26 wrists of 13 asymptomatic volunteers (8 females and 5 males; age range 42–64, with a mean age of 53.2 years) were evaluated by ultrasound. Patients were excluded if they reported a history of cervical radiculopathy, rheumatoid arthritis, osteoarthritis, gout, hemodialysis, sarcoidosis, amyloidosis, or traumatic injuries to the arm. Written consent was obtained from all study participants. CTS was diagnosed by both clinical findings and nerve conduction study. All of the patients received open CTR. According to the patients’ self-assessment for the recovery after the surgery, we divided the patients in four groups, that is, excellent: there were prominent improve of their symptoms, neither pain nor numbness in their hand (group 1), good: there were remarkable recovery of their symptoms but still there were slight pain or numbness (group 2), fair: there were no remarkable changes in their symptoms (group 3), poor: there were worsen or progress of the symptoms (group 4). Image Acquisition Procedure The image acquisition procedure followed that in a previous study.15 Each subject was imaged sitting with the elbow flexed and the forearm supinated. The forearm of the examinee was secured to a custom-made table with the wrist in the neutral position. An ultrasound scanner (Hi Vision Avius; Hitachi Aloka Medical, Ltd., Tokyo, Japan) equipped with a linear array transducer was set to a depth of 20 mm. Ultrasound evaluation was performed by an orthopedic surgeon trained in the image acquisition procedure. JOURNAL OF ORTHOPAEDIC RESEARCH MONTH 2015
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YOSHII ET AL.
At the wrist crease level (proximal carpal tunnel), the transducer was placed parallel to the wrist crease with the wrist in the neutral position. To minimize compression of the carpal tunnel contents, the transducer was applied to the skin without additional pressure. The transducer was maintained perpendicular to the skin surface of the wrist crease with reference to a protractor attached to the table. The median nerve was identified by cross-sectional ultrasonographic imaging. The participants were asked to flex and extend the four fingers (index, middle, ring, little). They were also asked to move from full finger extension (0˚ at each finger joint) to maximum flexion (i.e., until the fingertip touched the palm). Five cycles of motion were recorded. After imaging with an intact carpal tunnel, open CTR was performed. Then, the ultrasound images were taken again 3 months after surgery. Image Analysis Using Analyze 10.0 Software (Biomedical Imaging Resource, Mayo Clinic, Rochester, MN), the recorded images were reviewed and the initial and final frames of motion for the extension and flexion positions were chosen. On the basis of these images, the median nerve was outlined for both extension and flexion positions (Fig. 1). Displacement and deformation indices such as area, perimeter, aspect ratio of a minimum enclosing rectangle and circularity were measured. Displacement was defined as the distance of the centroid coordinates between the finger extension and flexion positions. To determine the minimum-enclosing rectangle, the algorithm was started by fitting the smallest possible tangential enclosing rectangle to the image and measuring its area. The image was then rotated in 1˚ steps over a range of 90˚, recalculating the rectangle area at each step. The characteristics of the smallest rectangle found over the search range were defined as the minimum-enclosing rectangle. The aspect ratio of the minimum-enclosing rectangle was defined as the ratio of the minor axis length divided by the major axis length. We also measured the circularity as a compactness measure. This was defined as (nerve perimeter)2/(nerve area 4p). The average of the five data sets was calculated for each parameter and used for further analysis. Finally, the deformation index, which was defined as the value of the flexion position divided by the value of the extension position, was measured for each parameter.
Statistical Analysis The results are expressed as mean SD. To compare the values before and after CTR, paired t-test was used. To compare the values between the patients and the controls, one factor analysis of variance (ANOVA) followed by Williams post hoc test was used. p values of
Received 3 October 2014; accepted 21 January 2015 Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jor.22843
ABSTRACT: To assess the biomechanical effect of carpal tunnel release (CTR), we evaluated the deformation and displacement patterns of the median nerve before and after CTR in carpal tunnel syndrome (CTS) patients. Sixteen wrists of 14 idiopathic CTS patients who had open CTR and 26 wrists of 13 asymptomatic volunteers were evaluated by ultrasound. Cross-sectional images of the carpal tunnel during motion from full finger extension to flexion were recorded. The area, perimeter, aspect ratio of a minimum enclosing rectangle, and circularity of the median nerve were measured in finger extension and flexion positions. Deformation indices, determined by the flexion–extension ratio for each parameter, were compared before and after CTR. After CTR, the deformation indices of perimeter and circularity became significantly larger and the aspect ratio became significantly smaller than those before CTR (p < 0.05). Those differences were more obvious when comparing the values between the patients before CTR and the controls. Since the deformation indices after CTR are similar to the patterns of normal subjects, the surrounding structures and environment of the median nerve may be normalized upon CTR. This may be a way to tell how the median nerves recover after CTR. ß 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res Keywords: median nerve; deformation; displacement; carpal tunnel release; ultrasound
Carpal tunnel syndrome (CTS), a pressure-induced neuropathy of the median nerve, is a common clinical problem. Clinical studies of patients with CTS typically show higher baseline pressures within the carpal tunnel than in normal control subjects.1–5 If conservative treatment is ineffective, surgical release of the flexor retinaculum is commonly selected to normalize the carpal tunnel pressure. Although carpal tunnel release (CTR) reliably reduces carpal tunnel pressure,6,7 surgery relieves symptoms in only 70–90% of patients.8–12 While in some cases patients’ lack of recovery may be due to the presence of more severe neuropathy, in many cases patients with similar degrees of neuropathy experience differing degrees of recovery,10,13,14 suggesting that other factors may be in play. However, other than reducing carpal tunnel pressure,6,7 the biomechanical effect of CTR has received little attention. In a previous study, we developed a technique to evaluate displacement and deformation patterns of the median nerve during finger motion using ultrasound imaging.15 It was found that there are differences in the deformation pattern of the median nerve during finger motion, upon comparing between CTS patients and normal controls. During the process of the study, we observed that there were some differences in the deformation patterns of the median nerve after CTR surgery. If it is possible to determine these differences, it may be useful to understand the effectiveness or the lack of effectiveness of CTR. Thus, we hypothesized that the deformation and displacement patterns of the median nerve during finger motion would differ between before and after CTR in CTS patients. In this Conflicts of interest: None. Grant sponsor: Japanese Society for Surgery of the Hand. Correspondence to: Yuichi Yoshii (T: þ81-29-887-1161; F: þ8129-888-8303; E-mail: [email protected]) # 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.
study, to assess the biomechanical effect of CTR, we evaluated the deformation and displacement patterns of the median nerve before and after releasing the carpal tunnel in idiopathic CTS patients. In addition, the same parameters were evaluated in normal subjects, and compared with CTS patients.
MATERIAL AND METHODS This study protocol was approved by our Institutional Review Board. Sixteen wrists of 14 idiopathic CTS patients who had open CTR (7 females, 7 males; age range 52–85, with a mean age of 63.9 years) and 26 wrists of 13 asymptomatic volunteers (8 females and 5 males; age range 42–64, with a mean age of 53.2 years) were evaluated by ultrasound. Patients were excluded if they reported a history of cervical radiculopathy, rheumatoid arthritis, osteoarthritis, gout, hemodialysis, sarcoidosis, amyloidosis, or traumatic injuries to the arm. Written consent was obtained from all study participants. CTS was diagnosed by both clinical findings and nerve conduction study. All of the patients received open CTR. According to the patients’ self-assessment for the recovery after the surgery, we divided the patients in four groups, that is, excellent: there were prominent improve of their symptoms, neither pain nor numbness in their hand (group 1), good: there were remarkable recovery of their symptoms but still there were slight pain or numbness (group 2), fair: there were no remarkable changes in their symptoms (group 3), poor: there were worsen or progress of the symptoms (group 4). Image Acquisition Procedure The image acquisition procedure followed that in a previous study.15 Each subject was imaged sitting with the elbow flexed and the forearm supinated. The forearm of the examinee was secured to a custom-made table with the wrist in the neutral position. An ultrasound scanner (Hi Vision Avius; Hitachi Aloka Medical, Ltd., Tokyo, Japan) equipped with a linear array transducer was set to a depth of 20 mm. Ultrasound evaluation was performed by an orthopedic surgeon trained in the image acquisition procedure. JOURNAL OF ORTHOPAEDIC RESEARCH MONTH 2015
1
2
YOSHII ET AL.
At the wrist crease level (proximal carpal tunnel), the transducer was placed parallel to the wrist crease with the wrist in the neutral position. To minimize compression of the carpal tunnel contents, the transducer was applied to the skin without additional pressure. The transducer was maintained perpendicular to the skin surface of the wrist crease with reference to a protractor attached to the table. The median nerve was identified by cross-sectional ultrasonographic imaging. The participants were asked to flex and extend the four fingers (index, middle, ring, little). They were also asked to move from full finger extension (0˚ at each finger joint) to maximum flexion (i.e., until the fingertip touched the palm). Five cycles of motion were recorded. After imaging with an intact carpal tunnel, open CTR was performed. Then, the ultrasound images were taken again 3 months after surgery. Image Analysis Using Analyze 10.0 Software (Biomedical Imaging Resource, Mayo Clinic, Rochester, MN), the recorded images were reviewed and the initial and final frames of motion for the extension and flexion positions were chosen. On the basis of these images, the median nerve was outlined for both extension and flexion positions (Fig. 1). Displacement and deformation indices such as area, perimeter, aspect ratio of a minimum enclosing rectangle and circularity were measured. Displacement was defined as the distance of the centroid coordinates between the finger extension and flexion positions. To determine the minimum-enclosing rectangle, the algorithm was started by fitting the smallest possible tangential enclosing rectangle to the image and measuring its area. The image was then rotated in 1˚ steps over a range of 90˚, recalculating the rectangle area at each step. The characteristics of the smallest rectangle found over the search range were defined as the minimum-enclosing rectangle. The aspect ratio of the minimum-enclosing rectangle was defined as the ratio of the minor axis length divided by the major axis length. We also measured the circularity as a compactness measure. This was defined as (nerve perimeter)2/(nerve area 4p). The average of the five data sets was calculated for each parameter and used for further analysis. Finally, the deformation index, which was defined as the value of the flexion position divided by the value of the extension position, was measured for each parameter.
Statistical Analysis The results are expressed as mean SD. To compare the values before and after CTR, paired t-test was used. To compare the values between the patients and the controls, one factor analysis of variance (ANOVA) followed by Williams post hoc test was used. p values of
