Performance of a high-repetition, high-force task induces carpal tunnel syndrome in rats

STUDY DESIGN: A randomized controlled prospective experimental study with some repeated measures. OBJECTIVES: To characterize behavioral, sensory, motor, and nerve conduction decrements, and histological changes in the median nerve in rats trained to perform a high-force repetitive task. BACKGROUND: Understanding of work-related carpal tunnel syndrome is hampered by the lack of experimental studies of the causes and mechanisms of nerve compression induced by repetitive motion. Most animal models of nerve compression have not employed voluntary repetitive motion as the stimulus for pathophysiological changes. METHODS AND MEASURES: Thirty Sprague-Dawley rats served as controls for 1 or more studies. Ten rats were trained to pull on a bar with 60% maximum force 4 times per minute, 2 h/d, 3 d/wk for 12 weeks. Motor behavior and limb withdrawal threshold force were characterized weekly. Grip strength and median nerve conduction velocity were measured after 12 weeks. Median nerves were examined immunohistochemically for ED1-positive macrophages, collagen, and connective tissue growth factor. RESULTS: Reach rate and duration of task performance declined over 12 weeks. Grip strength and nerve conduction velocity were significantly lower after 12 weeks than in controls. Limb withdrawal threshold increased between weeks 6 and 12. Median nerves at the level of the wrist showed increases in macrophages, collagen, and connective-tissue growth-factor-positive cells. These effects were seen in both the reach and nonreach limbs. CONCLUSIONS: This animal model exhibits all the features of human carpal tunnel syndrome, including impaired sensation, motor weakness, and decreased median nerve conduction velocity. It establishes a causal relationship between performance of a repetitive task and development of carpal tunnel syndrome.     

Median nerve trauma in a rat model of work-related musculoskeletal disorder

Anatomical and physiological changes were evaluated in the median nerves of rats trained to perform repetitive reaching. Motor degradation was evident after 4 weeks. ED1-immunoreactive macrophages were seen in the transcarpal region of the median nerve of both forelimbs by 5-6 weeks. Fibrosis, characterized by increased immunoexpression of collagen type I by 8 weeks and connective tissue growth factor by 12 weeks, was evident. The conduction velocity (NCV) within the carpal tunnel showed a modest but significant decline after 9-12 weeks. The lowest NCV values were found in animals that refused to participate in the task for the full time available. Thus, both anatomical and physiological signs of progressive tissue damage were present in this model. These results, together with other recent findings indicate that work-related carpal tunnel syndrome develops through mechanisms that include injury, inflammation, fibrosis and subsequent nerve compression.     

Carpal tunnel syndrome: morphologic changes after release of the transverse carpal ligament

We describe the morphologic changes that follow division of the transverse carpal ligament in patients with carpal tunnel syndrome. Fifteen hands in 12 patients with carpal tunnel syndrome were studied with magnetic resonance imaging before operation and for 6 weeks after operation. Eight hands were studied at 8 months after operation. Carpal arch width, anterior displacement of the carpal canal contents, and carpal canal volume were measured by use of multiplanar reformation and three-dimensional reconstruction of magnetic resonance images. There was a 24.2 +/- 11.6% increase in carpal canal volume 6 weeks after carpal tunnel release (p less than 0.001). This difference persisted at 8-month follow-up. There was an anterior displacement of carpal canal contents 3.5 +/- 1.9 mm from its original position 6 weeks after operation (p less than 0.001). This palmar displacement persisted at the 8-month follow-up. There was no statistically significant increase in carpal arch width 8 months after carpal tunnel release. We believe that division of the transverse carpal ligament restores median nerve function by increasing the volume of the carpal canal. This volumetric increase results from an anterior displacement of the newly formed transverse carpal ligament and not from a widening of the bony carpal arch.     

Anatomic investigations of nerves at the wrist: I. Orientation of the motor fascicle of the median nerve in the carpal tunnel

The orientation of the motor fascicle of the median nerve in the carpal tunnel was investigated in dissections of 50 hands. Topographically, the motor branch was located on the radial-volar aspect of the median nerve in 60% of the hands, the central-volar aspect in 22%, and between these two locations in the remaining 18%. In 56% of the hands, the motor branch passed through a separate distinct fascial tunnel before entering the thenar muscles. Awareness of these patterns will facilitate appropriate surgical management of thenar muscle weakness or wasting associated with the carpal tunnel syndrome.     

Endoscopic carpal tunnel release for recurrent carpal tunnel syndrome after previous open release.

Recurrent carpal tunnel syndrome from various causes has been shown to occur in up to 19% of patients. Endoscopic carpal tunnel release has been used to decompress the median nerve in carpal tunnel syndrome for many years. However, endoscopic release for recurrent carpal tunnel syndrome after previous surgical release has not been reported. Nine hands in six patients had recurrent carpal tunnel syndrome five to 20 years after previous open carpal tunnel release. All the cases were successfully treated with endoscopic release.     

Clinical diagnosis of carpal tunnel syndrome: old tests-new concepts

BackgroundThe diagnosis of carpal tunnel syndrome (CTS) continues to be neurophysiologically and clinically controversial. Earlier data concluding that the higher prevalence of persons with symptoms suggestive of CTS but without evidence of median mononeuropathy highlights the need for a better understanding of the underlying pathophysiology and natural history of CTS to provide a less empirical foundation for diagnosis and clinical management.ObjectiveTo examine the relationship between the clinical manifestations of CTS with the outcome of the diagnostic tools (nerve conduction tests and ultrasonography), and its implication for clinical practice.MethodsTwo-hundred and thirty-two patients (69 male and 163 female, ages ranging between 20 and 91 years) with CTS manifestations and 182 controls were included in this study. Diagnosis of CTS was based on the American Academy of Neurology clinical diagnostic criteria. All patients and controls completed a patient oriented questionnaire, were subjected to clinical testing for provocative tests for carpal tunnel syndrome (Tinel's, Phalen's, Reverse Phalen's and carpal tunnel compression tests), blood check for secondary causes of carpal tunnel syndrome, nerve conduction testing as well ultrasonographic assessment of the carpal tunnel and median nerve.ResultsOne-hundred and seventy-seven out of 232 (76.3%) had abnormal nerve conduction studies. Forearm symptoms and tenosynovitis confirmed by US examination were found in 51.3% of cases. No significant difference was found on comparing anthropometric measures in the affected hands to the control group hands. A higher prevalence of positive Phalen's and CT compression were found in patients suffering from tenosynovitis regardless of their nerve conduction study results. Sensitivity of Tinel's, Phalen's, Reverse Phalen's and carpal tunnel compression tests was higher for the diagnosis of tenosynovitis than for the diagnosis of CTS (Tinel, 46% vs. 30%; Phalen's, 92% vs. 47%; Reverse Phalen's, 75% vs. 42%; carpal tunnel compression test, 95% vs. 46%). Similarly, higher specificity of these tests was found with tenosynovitis than CTS.ConclusionThe results of this study revealed that Tinel's, Phalen's, Reverse Phalen's and carpal tunnel compression tests are more sensitive, as well as being specific tests for the diagnosis of tenosynovitis of the flexor muscles of the hand, rather than being specific tests for carpal tunnel syndrome and can be used as an indicator for medical management of the condition.     

Results of treatment of severe carpal tunnel syndrome

A retrospective study was undertaken to determine the efficacy of carpal tunnel decompression in patients with advanced carpal tunnel syndrome. The criteria for inclusion in this study were unobtainable median sensory-evoked response and absent or prolonged median motor distal latency. Fifteen hands in 13 patients met these criteria. All patients had symptoms, including pain, weakness, or decreased sensation. Postoperative follow-up averaged 27 months. Symptomatic improvement was obtained in 14 of the 15 hands, and sensory-evoked response improved in 13 hands. Preoperative thenar atrophy was present in 10 of the 15 hands and was completely resolved in 2 of the 10 patients. These results indicate that carpal tunnel decompression is of benefit to patients with severe carpal tunnel syndrome. Long-standing symptoms, thenar atrophy, virtual anesthesia, and the absence of demonstrable sensory and motor-evoked responses are not contraindications to surgery.     

Single-portal endoscopic carpal tunnel release compared with open release : a prospective,randomized trial

BACKGROUND: Carpal tunnel syndrome is a common condition causing hand pain and numbness. Endoscopic carpal tunnel release has been demonstrated to reduce recovery time, although previous studies have raised concerns about an increased rate of complications. The purpose of this prospective, randomized study was to compare open carpal tunnel release with single-portal endoscopic carpal tunnel release. METHODS: A prospective, randomized, multicenter center study was performed on 192 hands in 147 patients. The open method was performed in ninety-five hands in seventy-two patients, and the endoscopic method was performed in ninety-seven hands in seventy-five patients. All of the patients had clinical signs or symptoms and electrodiagnostic findings consistent with carpal tunnel syndrome and had not responded to, or had refused, nonoperative management. Follow-up evaluations with use of validated outcome instruments and quantitative measurements of grip strength, pinch strength, and hand dexterity were performed at two, four, eight, twelve, twenty-six, and fifty-two weeks after the surgery. Complications were identified. The cost of the procedures and the time until return to work were recorded and compared between the groups. RESULTS: During the first three months after surgery, the patients treated with the endoscopic method had better Carpal Tunnel Syndrome Symptom Severity Scores, better Carpal Tunnel Syndrome Functional Status Scores, and better subjective satisfaction scores. During the first three months after surgery, they also had significantly (p < 0.05) greater grip strength, pinch strength, and hand dexterity. The open technique resulted in greater scar tenderness during the first three months after surgery as well as a longer time until the patients could return to work (median, thirty-eight days compared with eighteen days after the endoscopic release). No technical problems with respect to nerve, tendon, or artery injuries were noted in either group. There was no significant difference in the rate of complications or the cost of surgery between the two groups. CONCLUSION: Good clinical outcomes and patient satisfaction are achieved more quickly when the endoscopic method of carpal tunnel release is used. Single-portal endoscopic surgery is a safe and effective method of treating carpal tunnel syndrome.     

Carpal tunnel pressure alters median nerve function in a dose-dependent manner: a rabbit model for carpal tunnel syndrome.

BACKGROUND: An in vivo animal model for carpal tunnel syndrome (CTS) is presented which allows for graded application of pressure to the median nerve within the carpal canal. We hypothesized that such pressure would cause electrophysiologic changes in the median nerve in a dose-related manner, with NCS/EMG changes consistent with CTS in humans. METHODS: In 40 New Zealand white rabbits, ranging from 2 to 2.5 kg, angioplasty catheters were placed in the carpal tunnel in the forepaws and pressures ranging from 50 to 80 mmHg applied to one side while the contralateral side served as the control and remained uninflated. Pressure was applied until a 15% increase in distal motor latency was obtained for 2 consecutive weeks by nerve conduction studies. RESULTS: All the experimental limbs exhibited a 15% increase in distal motor latency. None of the control limbs showed a significant increase in distal motor latency. In the experimental animals the 15% delay was achieved in approximately 4-5 weeks in the 50-70 mmHg groups and in approximately 1 week in the 80 mmHg group. CONCLUSION: This new animal model for CTS demonstrates a direct cause and effect relationship between carpal tunnel pressure and median nerve dysfunction. We anticipate that this in vivo model with clinically relevant outcomes will facilitate identification of injury mechanisms, and will serve as a basis for future development of novel interventions and treatments.     

Internal neurolysis fails to improve the results of primary carpal tunnel decompression

This prospective, randomized study compares two treatment methods in patients with primary carpal tunnel syndrome. Decompression of the transverse carpal ligament was done in thirty-two hands (thirty patients) and decompression of the transverse carpal ligament with the addition of an internal neurolysis of the median nerve was done in thirty-one hands (twenty-nine patients). Relief of symptoms was described in eighty-eight percent of the patients with carpal ligament release and eighty-one percent of patients with carpal ligament release plus internal neurolysis. Improvement in hand sensibility testing, in thenar muscle strength, and atrophy was noted in both treatment groups with no statistical difference between groups. The addition of an internal neurolysis to division of the transverse carpal ligament does not add significant improvement in the sensory or motor outcome of patients with primary carpal tunnel syndrome.     

Accuracy of a portable electroneurometer for measuring distal motor latency

Background A facile electromyographic test in the outpatient clinic is needed to evaluate the outcome of screening for carpal tunnel syndrome. The purpose of the current prospective study was to compare the accuracy of Nervepace digital electroneurometer (Nervepace) and Dantec Neuromatic 2000M (Dantec) measurements of a wide range of distal motor latency (DML) of the median nerve. Methods The DML values for 112 of 126 median nerves examined with Nervepace and conventional electromyography, Dantec were statistically analyzed in this prospective study. The 30 hands of 15 clinically healthy adults 20–24 years old served as the reference group. Sixty consecutive patients (96 hands) with idiopathic carpal tunnel syndrome provided a wider range of DML values. All of the patients had standard clinical tests and standard motor (Dantec and Nervepace) and sensory (Dantec) electrodiagostic tests before endoscopic carpal tunnel release. Results The DML was measurable in all 30 hands of the reference group, in all 96 hands of the patients by Dantec, but in only 82 hands (52 patients) by Nervepace. Nervepace and Dantec DML values of 6.0 ms or less had high correlation and agreement. Conclusions Correlation and agreement decreased significantly among values greater than 6.0 ms.     

应用环指感觉神经传导速度测定诊断腕管综合征

目的探讨应用环指感觉神经传导速度(sensory nerve conduction velocity, SCV)诊断腕管综合征的方法。方法对18例(26手)腕部感觉动作电位潜伏期正常的患者，行顺向感觉神经传导速度测定，测定环指正中神经和尺神经SCV，中指正中神经SCV，对其结果进行比较，并与15例正常人(30手)作对照。结果中指正中神经SCV的异常率为50％，环指正中神经与尺神经SCV差值的异常率为84．6％。刺激6例(9手)患者环指后在正中神经腕部可记录到双峰波，对照组则未见。结论在腕管综合征肌电图的诊断中，比较正中神经和尺神经SCV的差值是早期诊断腕管综合征的敏感指标之一。     

Recovery from symptoms after carpal tunnel syndrome surgery in males in relation to vibration exposure

A follow-up study was conducted in forty-one men (fifty-five hands) treated surgically for carpal tunnel syndrome. The number of hours of vibration exposure and exactly which hand tool was used were recorded and each tool was categorized according to vibration level. The patients were divided into a low exposure and a high exposure group. Age at surgery, mean distal latency in the median nerve, and the duration between onset of symptoms and surgery were similar for the two groups. Only one patient experienced nocturnal paresthesia at follow-up in the low exposure group in contrast to twelve in the high exposure group. This corresponded to an age-standardized odds ratio (relative risk) of eighteen for nocturnal paresthesia after surgery in the high exposure group, with the low exposure group as referents. Previous vibration exposure may influence the recovery after carpal tunnel surgery.     

轻中度腕管综合征药物治疗长短期疗效

目的探讨轻中度腕管综合征药物治疗的长短期疗效。方法门诊随访24例(35腕)口服四联药(弥可保、地巴唑、维生素B1、维生素B6)的轻中度腕管综合征病人。病人在入组时、治疗4个月、6个月后及停药1年后来我院门诊随访,向医生汇报其近期临床症状表现,自评其患手功能并填写Boston腕管问卷调查表(BCTQ)。病人在入组时及治疗6个月后,需接受患肢桡侧3指感觉神经传导速度(SNCV)检测。结果药物治疗后病人临床症状明显好转,短期(4个月、6个月)临床有效率可高达94.3%,长期(停药后1年)临床有效率可高达91.4%。BCTQ功能总评分及桡侧3指SNCV也较治疗前有明显恢复。结论弥可保联合地巴唑、维生素B1及维生素B6治疗轻中度腕管综合征有很好的长短期疗效。     

Dose-responsiveness of electrophysiologic change in a new model of acute carpal tunnel syndrome

This study was done to determine the dose-responsiveness during the development of acute pressure-induced median neuropathy in rabbits and to develop a new animal model of acute carpal tunnel syndrome. Twenty-three rabbits were used. Carpal tunnel syndrome was induced by infusing a controlled saline solution into the carpal tunnel of rabbits using a 21-gauge needle under general anesthesia to elevate the carpal tunnel pressure. The changes in the amplitude and latency of the compound muscle action potential obtained by abductor pollicis recording were observed after a complete conduction block, and after the release of pressure at various pressure levels. Pressures greater than 30 mm Hg applied to the carpal tunnel caused a remarkable electrophysiologic change. A higher pressure level resulted in a shorter time required for a complete conduction block and also for recovery after the release of pressure. Complete conduction block occurred between 40 and 50 minutes at a pressure of 100 mm Hg. The degree of recovery after a conduction block was related inversely to the pressure-time integrals. Our animal model reflects the pathophysiology of acute carpal tunnel syndrome and shows a regular dose-responsiveness during the development of acute pressure-induced neuropathy.     

A new diagnostic test for carpal tunnel syndrome.

A new test, called the carpal compression test, consists of application of direct pressure on the carpal tunnel and the underlying median nerve. The results of the Tinel percussion test, the Phalen wrist-flexion test, and the new test were evaluated in thirty-one patients (forty-six hands) in whom the presence of carpal tunnel syndrome had been proved electrodiagnostically, as well as in a control group of fifty subjects. For the diagnosis of carpal tunnel syndrome, the carpal compression test was found to be more sensitive and specific than the Tinel and Phalen tests.     

Carpal tunnel syndrome surgery: identification of a neurophysiological high-risk category

Surgical decompression of the median nerve is a standardized treatment for carpal tunnel syndrome. After surgery a clinical and neurophysiological improvement is observed also on severe cases. We report 4 cases of carpal tunnel syndrome (CTS) in the hands of 3 patients with prolonged median wrist-thenar distal motor latency (longer than 10 ms, normal values < 4.0 ms) and absence of digit-wrist sensory responses. In these patients surgery caused complete loss of median nerve function. Such a marked increase of median distal motor latency (DML) is rare (0.6% in 500 CTS hands consecutively examined in our laboratory) and suggests the presence of a chronic condition with severe disruption of the myelin. On the basis of these anecdotal observations, we suggest that patients with median DML of 10 ms or more be considered at high risk for CTS surgery failure. Received: 5 July 2000; Accepted: 6 October 2000     

Investigation of segmental carpal tunnel pressure in patients with idiopathic carpal tunnel syndrome--is it necessary to release the distal aponeurotic portion of the flexor retinaculum in endoscopic carpal tunnel release surgery?

Segmental carpal tunnel pressure was measured in 12 hands of 11 idiopathic carpal tunnel syndrome patients before and after two-portal endoscopic carpal tunnel release. We aimed to determine at which part of the carpal tunnel the median nerve could be compressed, and to evaluate whether carpal tunnel pressure could be reduced sufficiently at all segments of the carpal tunnel after the surgery. Pressure measurements were performed using a pressure guide wire. The site with the highest pressure corresponded to the area around the hamate hook; the pressure in the area distal to the flexor retinaculum could be pathogenically high (more than 30 mmHg) before the surgery. The two-portal endoscopic carpal tunnel release achieved sufficient pressure reduction in all segments of the carpal tunnel when the flexor retinaculum and the fibrous structure between the flexor retinaculum and the palmar aponeurosis were completely released.     

Age delays the recovery of distal motor latency after carpal tunnel syndrome surgery

Background

Studies have shown slow healing of peripheral nerve injury in elderly patients. Carpal tunnel syndrome (CTS) is the most frequent compressive mononeuropathy, affecting mostly older people and females. Few studies have assessed electrophysiological differences between younger and older patients. We aimed to evaluate age-dependent differences in electrophysiological parameters preoperatively and postoperatively over a 100-day postoperative period.

Method

This retrospective study included 258 hands of patients who underwent conventional open-technique carpal tunnel syndrome surgery. Patients with paresthesia in the median nerve distribution or with impaired sensation or abnormal findings in sensory and motor median nerve conduction studies were enrolled. The age dependence of the preoperative values of distal motor latency, amplitude of the compound motor action potential and sensory conduction velocity was estimated using regression analysis.

Results

Statistically significant age dependence was found for the preoperative distal motor latency, compound motor action potential, amplitude and sensory conduction velocity. The repair of segmental demyelination was nearly twice as slow in the older group, at a 5 % significance level, even when comparing groups with the same preoperative distal motor latency.

Conclusions

Analysis of preoperative nerve conduction parameters indicates that surgery for carpal tunnel syndrome is performed later in older patients.     

Carpal tunnel syndrome: associated abnormalities in ulnar nerve function and the effect of carpal tunnel release on these abnormalities

Twenty of 59 hands (34%) of patients with carpal tunnel syndrome had abnormalities in sensibility testing of both median and ulnar nerves by either two-point discrimination, Semmes-Weinstein monofilament testing, or both. Before surgery, 53% of patients complained of paresthesias and/or numbness in ulnar nerve distribution. Eighty percent of the hands had abnormal Semmes-Weinstein monofilament testing of the ulnar nerve. Thirty-five percent had abnormal two-point discrimination. Forty-one percent had abnormal electromyographic testing of the ulnar nerve. All hands had median nerve decompression alone. Guyon's canal was not released. After surgery, 89% of patients had improvement in paresthesias and/or numbness of the ulnar nerve. Ninety-four percent had improvement in Semmes-Weinstein monofilament testing. Eighty-six percent had improvement in two-point discrimination. Patients with a residual abnormality in ulnar nerve sensibility also had continued abnormality in median nerve sensibility. A significant percentage of patients with carpal tunnel syndrome also have signs and symptoms of ulnar nerve compression. Most improved with carpal tunnel release alone.