Etiology Of Carpal Tunnel Syndrome Research Articles

In Vivo Study of Transverse Carpal Ligament Stiffness Using Acoustic Radiation Force Impulse (ARFI) Imaging

The transverse carpal ligament (TCL) forms the volar boundary of the carpal tunnel and may provide mechanical constraint to the median nerve, leading to carpal tunnel syndrome. Therefore, the mechanical properties of the TCL are essential to better understand the etiology of carpal tunnel syndrome. The purpose of this study was to investigate the in vivo TCL stiffness using acoustic radiation force impulse (ARFI) imaging. The shear wave velocity (SWV) of the TCL was measured using Virtual Touch IQTM software in 15 healthy, male subjects. The skin and the thenar muscles were also examined as reference tissues. In addition, the effects of measurement location and ultrasound transducer compression on the SWV were studied. The SWV of the TCL was dependent on the tissue location, with greater SWV values within the muscle-attached region than those outside of the muscle-attached region. The SWV of the TCL was significantly smaller without compression (5.21 ± 1.08 m/s) than with compression (6.62 ± 1.18 m/s). The SWV measurements of the skin and the thenar muscles were also affected by transducer compression, but to different extents than the SWV of the TCL. Therefore to standardize the ARFI imaging procedure, it is recommended that a layer of ultrasound gel be maintained to minimize the effects of tissue compression. This study demonstrated the feasibility of ARFI imaging for assessing the stiffness characteristics of the TCL in vivo, which has the potential to identify pathomechanical changes of the tissue.

Tendon Injury Produces Changes in SSCT and Nerve Physiology Similar to Carpal Tunnel Syndrome in an in Vivo Rabbit Model

The etiology of carpal tunnel syndrome (CTS) remains idiopathic in many cases. Noninflammatory fibrosis of the subsynovial connective tissue (SSCT) within the carpal tunnel is common in CTS, and some clinicians have hypothesized that this fibrosis might be a cause rather than an effect of CTS. An animal model in which to test this hypothesis would be useful. The principal objective of this study was to investigate the effect of a surgical injury on SSCT fibrosis and median nerve function within the carpal tunnel in an in vivo rabbit model. Rabbits were sacrificed 12weeks after surgery and were evaluated by mechanical testing, histology, transmission and scanning electron microscopy, and electrophysiology. SSCT fibroblast density (p < 0.0001) and collagen fiber size (p = 0.0004) were significantly higher, and the median nerve distal motor amplitude was significantly lower (p = 0.0018), in the tendon injury group SSCT than in either the sham or control groups. Our findings are similar to those seen in patients with carpal tunnel syndrome and suggest that the tendon injury procedure may be the basis of a new animal model of SSCT injury and, possibly, CTS.

The response of the rabbit subsynovial connective tissue to a stress-relaxation test

The subsynovial connective tissue (SSCT) in the carpal tunnel may play a role in the etiology of carpal tunnel syndrome (CTS), yet the material properties of the SSCT remain unclear. Thus, we investigated the mechanical response of the SSCT in a rabbit model. Twenty-four rabbit cadaver paws were used for mechanical testing; two paws were used for scanning electron microscopy (SEM) imaging. After testing normal tendon excursion, the divided third digit flexor digitorum superficialis (FDS) tendon was pulled to displacements of 2, 3.5, 5, or 8 mm, maintained at that position until force decay, and then the process was repeated. Normal excursion of the FDS averaged 4.8 mm. The ratio of the second peak force to the first peak force in the 2 mm group was 0.98 (SD = 0.16), which was significantly higher than the other groups (3.5 mm: 0.74, 5 mm, 0.63, and 8 mm: 0.59; p < 0.05). SEM showed ruptured fibrils in the displaced specimen. The declining force ratio with displacements >2 mm suggests damage to the SSCT within the physiological tendon excursion. These data may be useful in understanding SSCT mechanics in CTS, which is associated with SSCT fibrosis.

Aberrant deep flexor muscles of the forearm associated with the accessory origin of first lumbrical muscle

Objective To find out variations in the deep forearm flexors that are associated with anomalous origin of the first lumbrical muscle. Introduction Muscular anomalies of the upper extremity could cause peripheral nerve disorders. Although variations in the attachments of lumbrical muscles have been commonly studied, muscle with an additional origin in the proximal aspect of the forearm from the deep flexors is not much discussed. Methods Fifty-three formalin-fixed upper limbs were dissected to assess the aberrant origin of the first lumbrical from the deep forearm flexors. The measurement, shape, origin, insertion and innervation of aberrant deep forearm flexors were noted and photographed. Results In two (3.77%) out of 53 upper limbs unilateral aberrant deep forearm flexors were found giving accessory anomalous origin to the first lumbrical muscle. In 11 cases (20.75%) the presence of accessory head of flexor pollicis longus was seen, and found co-existing with the aberrant deep forearm flexor in one (1.89%) limb. Discussion The clinical implication of these muscular anomalies, such as aberrant origins and hypertrophy of the first lumbrical, in nerve entrapments, especially in the aetiology of carpal tunnel syndrome, is considered. The awareness and identification of the muscular variations of the antebrachial and carpal regions will facilitate safe surgery of cases of median nerve entrapment syndromes.

Effect of finger position on the median nerve area within the carpal tunnel: an ultrasound imaging study

Introduction Finger flexion has been suggested to contribute to the aetiology of carpal tunnel syndrome (CTS). The purpose of this study was to measure the immediate effects of finger flexion on the cross-section area of the median nerve (MNA). Methods Thirty-one healthy volunteers participated in this experimental study. The MNA was measured at the level of hook of hamate using high-resolution ultrasonography during four different finger positions. Results A significant change in MNA during different finger positions was found ( F = 24.149, P &lt; 0.001). The biggest difference in MNA was recorded between full finger extension and forceful finger flexion (mean difference = 1.29 mm2, P &lt; 0.001). An inverse correlation between MNA and finger flexion was found (Pearson's r = −0.348, P = 0.002) where the MNA decreased as fingers moved toward flexion. Conclusion Finger flexion resulted in direct decrease in MNA, possibly contributing to median nerve compression. Clinical implications Hand therapists need to consider modifying their conservative treatment of CTS by limiting activities that require finger flexion and restricting the movement of the wrist and fingers to restrict finger flexion, thus limiting pressure increase on the median nerve.

The role of sexual intercourse in the etiology of carpal tunnel syndrome

The etiology of non-occupational carpal tunnel syndrome is not well understood. It is proposed that carpal tunnel syndrome can develop during sexual intercourse when the hands become repeatedly extended while under pressure from the weight of the upper body. Of the eight risk factors associated with non-occupational carpal tunnel syndrome, age, marital status, pregnancy and use of hormonal agents can be explained by changes in the frequency of sexual intercourse. On the other hand, obesity, macromastia and large chest circumference can be explained by the increased pressure imposed on the wrists by the heavier upper body associated with such conditions. The bilaterality of carpal tunnel syndrome can be explained by the fact that both hands are needed to support the upper body during sexual intercourse. A parallel decrease in the frequency of sexual intercourse and the incidence of carpal tunnel syndrome between the sixth and the seventh decades of life suggests a possible cause and effect relationship between sexual intercourse and carpal tunnel syndrome.

An additional muscle belly of the first lumbrical muscle

IntroductionLumbrical muscles play a vital role in the precision movements of the hand, along with the thenar, hypothenar and interossei muscles. The variation in the lumbrical muscle is clinically significant.Case presentationDuring routine dissection of an adult male cadaver, we observed an additional muscle belly of the first lumbrical muscle took origin from the tendon of the flexor digitorum superficialis (FDS) to the index finger, close to the proximal margin of the flexor retinaculum.ConclusionThe presence of such an additional muscle in the carpal tunnel should be considered in the aetiology of carpal tunnel syndrome (CTS).

The Quality and Strength of Evidence for Etiology: Example of Carpal Tunnel Syndrome

The purpose of this investigation was to evaluate the quality and strength of scientific evidence supporting an etiologic relationship between a disease and a proposed risk factor using a scoring system based on the Bradford Hill criteria for causal association. A quantitative score based on the Bradford Hill criteria (qBHs) was used to evaluate 117 articles presenting original data regarding the etiology of carpal tunnel syndrome: 33 (28%) that evaluated biological (structural or genetic) risk factors, 51 (44%) that evaluated occupational (environment or activity-related) risk factors, and 33 (28%) that evaluated both types of risk factors. The quantitative Bradford Hill scores of 2 independent observers showed very good agreement, supporting the reliability of the instrument. The average qBHs was 12.2 points (moderate association) among biological risk factors compared with 5.2 points (poor association) for occupational risk factors. The highest average qBHs was observed for genetic factors (14.2), race (11.7), and anthropometric measures of the wrist (11.3 points) with all studies finding a moderate causal association. The highest average qBHs among occupational risk factors was observed for activities requiring repetitive hand use (6.5 points among the 30 of 45 articles that reported a causal association), substantial exposure to vibration (6.3 points; 14 of 20 articles), and type of occupation (5.6 points; 38 of 53 articles), with the findings being much less consistent. According to a quantitative analysis of published scientific evidence, the etiology of carpal tunnel syndrome is largely structural, genetic, and biological, with environmental and occupational factors such as repetitive hand use playing a minor and more debatable role. Speculative causal theories should be analyzed through a rigorous approach prior to wide adoption.

Carpal tunnel syndrome following arteriovenous forearm shunt in chronic dialysis patients--a review of 24 surgically treated patients

In a period from January 1981 to September 1985 271 patients underwent surgery because of a carpal tunnel syndrome (CTS). In 24 patients (30 operated hands) with permanent kidney failure the CTS followed an arterio-venous shunt procedure in the forearm. Although there is a considerable variability concerning the interval between dialysis and onset of symptoms of median nerve entrapment CTS in patients with chronic hemodialysis is considered to be a late complication. In contrast in patients with idiopathic CTS a considerable time-lag has been noted between onset of symptoms and operative treatment which may be due either to diagnostic difficulties and/or delayed referral. The clinical picture presents with typical signs of a median nerve compression, known as brachialgia paresthetica nocturna. Operative treatment which consists of surgical division of the transverse ligament in local anaesthesia without interfascicular neurolysis is followed by immediate and usually longlasting pain relief. The possible etiology of CTS in patients with chronic hemodialysis which seems to be due to multiple factors is discussed.

The mechanical properties of the rabbit carpal tunnel subsynovial connective tissue

The rabbit model is commonly used to study carpal tunnel syndrome (CTS). It has been proposed that the subsynovial connective tissue (SSCT) in the carpal tunnel may play a role in the etiology of CTS, but the material properties of the rabbit SSCT are unknown. The purpose of this study was to develop a method to measure the shear properties of the rabbit SSCT. In six rabbit cadaver forepaws, the excursion of the third digit flexor digitorum superficialis (FDS) and load to failure of the SSCT were measured in a custom device. The mean excursion to full flexion in this model was 7.08 mm (S.D. 0.77). The mean shearing force at full flexion was 317 mN (S.D. 166). At full flexion percentage of maximum shear force in the SSCT was 54.5% (S.D. 19.4). The mean energy absorbed at full flexion was 0.29 mJ (S.D. 0.31). The mean excursion needed to reach 5% of the maximum shear force was 3.04 mm (S.D. 0.99). The testing model presented in this study demonstrates structural parameters to evaluate the shear properties of the SSCT in a rabbit model. The data presented could be used for estimating sample sizes in a more comprehensive study of the effect of CTS on the SSCT properties.

Carpal Tunnel Syndrome: Under-recognition of Occupational Risk Factors by Clinicians

This study was performed in order to demonstrate that non-occupational physicians are often unaware of the possible role of occupational risk factors in the multifactorial etiology of carpal tunnel syndrome (CTS). Study participants consisted of 229 individuals, 127 cases of CTS matched with 102 controls. In only 41% of the cases did family or attending physicians in the hospital asked the concerned patients about their occupation or specific job tasks, and less than 10% of the cases were referred for further evaluation to an occupational physician. Occupational risk factors that were identified were: work with repeated movements of the wrist (OR=2.15, 95% CI=1.14-4.07) and work in a cold environment (OR=3.52, 95% CI=1.08-11.47). By improving the awareness of clinicians (and patients) to the possible role of work-related factors in the etiology of CTS, appropriate preventive measures can be introduced in order to reduce the burden of this syndrome.

Gliding characteristics between flexor tendons and surrounding tissues in the carpal tunnel: A biomechanical cadaver study

The purpose of this study was to investigate the gliding characteristics of flexor tendons within the carpal tunnel with varied wrist positions and tendon motion styles, which may help us to understand the relationship between carpal tunnel syndrome (CTS) and repetitive hand motion. Eight fresh human cadaveric wrists and hands were used. The peak (PGR) and mean (MGR) gliding resistance of the middle finger flexor digitorum superficialis tendon were measured with the wrist in 0, 30, and 60 degrees of flexion and extension. While moving all three fingers together, the PGR at 60 degrees flexion was significantly higher than that at 0, 30, or 60 degrees extension. While moving the middle finger alone, the PGR at 60 and 30 degrees flexion was significantly higher than the PGR at 60 degrees extension. The PGR moving the middle finger FDS alone was significantly greater than that for all three digits moving together in 0, 30, and 60 degrees flexion. Differential finger motion with wrist flexion elevated the tendon gliding resistance in the carpal tunnel, which may be relevant in considering the possible role of wrist position and activity in the etiology of CTS.

Gliding characteristics of flexor tendon and tenosynovium in carpal tunnel syndrome: A pilot study

The characteristic pathological finding in carpal tunnel syndrome (CTS) is noninflammatory fibrosis of the synovium. How this fibrosis might affect tendon function, if at all, is unknown. The subsynovial connective tissue (SSCT) lies between the flexor tendons and the visceral synovium (VS) of the ulnar tenosynovial bursa. Fibrosis of the SSCT may well affect its gliding characteristics. To investigate this possibility, the relative motion of the flexor tendon and VS was observed during finger flexion in patients undergoing carpal tunnel surgery, and for comparison in hands without CTS, in an in vitro cadaver model. We used a camera to document the gliding motion of the middle finger flexor digitorum superficialis (FDS III) tendon and SSCT in three patients with CTS during carpal tunnel release and compared this with simulated active flexion in three cadavers with no antemortem history of CTS. The data were digitized with the use of Analyze Software (Biomedical Imaging Resource, Mayo Clinic, Rochester, MN). In the CTS patients, the SSCT moved en bloc with the tendon, whereas, in the controls the SSCT moved smoothly and separately from the tendon. The ratio of VS to tendon motion was higher for the patients than in the cadaver controls. These findings suggest that in patients with CTS the synovial fibrosis has altered the gliding characteristics of the SSCT. The alterations in the gliding characteristics of the SSCT may affect the ability of the tendons in the carpal tunnel to glide independently from each other, or from the nearby median nerve. These abnormal tendon mechanics may play a role in the etiology of CTS.

Anomalous muscle belly to the index finger

An unusual variation of flexor digitorum superficialis was observed during the cadaver dissection. The flexor digitorum superficialis (FDS) had a normal origin and insertion, except to the index finger, where a muscle belly replaced the tendon of FDS. The unusual muscle belly originated as a continuation of FDS tendon in the carpal tunnel and inserted normally into the middle phalanx. A branch of the median nerve innervated the anomalous muscle belly. The anomalous muscle belly described here should be considered in the aetiology of carpal tunnel syndrome.

Anatomic investigation of the role of the lumbrical muscles in carpal tunnel syndrome

This study investigates whether the proximal origins of the lumbrical muscles contribute significantly to the etiology of carpal tunnel syndrome. We explored the carpal canals of 128 hands in patients undergoing carpal tunnel release for carpal tunnel syndrome. The origins of the lumbrical muscles were examined at the time of surgery and their relation to the transverse carpal ligament was recorded in all cases. Also, 40 cadaveric hands were dissected to determine the lumbrical muscle origins. In the hands of patients with idiopathic carpal tunnel syndrome, the lumbrical muscle origins were located significantly more proximal in the canal than were the muscles in the cadaveric hands. Younger patients whose jobs required repetitive hand motions had large lumbrical muscles and origins that were more proximal than the lumbricals found in the hands of fresh cadavers.

Location of impaired sensory conduction of the median nerve in carpal tunnel syndrome

Sensory conduction of the median nerve at the carpal tunnel for eight consecutive 1 cm segments of the nerve was evaluated in 217 hands of 153 of our patients with carpal tunnel syndrome. Impairment was found to be highly focal and often confined to a single 1 cm segment of the nerve. The section of the nerve at or just distal to the distal margin of the carpal tunnel was affected most frequently, the section within the tunnel was affected less often, and the section proximal to the tunnel at the level of the mid-carpal and radio-carpal joints was affected least. The greatest contrast between frequencies of slowing at adjacent segments occurred at the proximal and distal margins of the carpal tunnel. The distribution of the nerve impairment was similar between the sexes; however, among the men the segment affected most frequently was located 1 cm distal to the segment affected most frequently among the women. The general pattern of slowing which we found does not substantiate some commonly-held opinions about the aetiology of carpal tunnel syndrome.

Location of Impaired Sensory Conduction of the Median Nerve in Carpal Tunnel Syndrome

Sensory conduction of the median nerve at the carpal tunnel for eight consecutive 1 cm segments of the nerve was evaluated in 217 hands of 153 of our patients with carpal tunnel syndrome. Impairment was found to be highly focal and often confined to a single 1 cm segment of the nerve. The section of the nerve at or just distal to the distal margin of the carpal tunnel was affected most frequently, the section within the tunnel was affected less often, and the section proximal to the tunnel at the level of the mid-carpal and radio-carpal joints was affected least. The greatest contrast between frequencies of slowing at adjacent segments occurred at the proximal and distal margins of the carpal tunnel. The distribution of the nerve impairment was similar between the sexes; however, among the men the segment affected most frequently was located 1 cm distal to the segment affected most frequently among the women. The general pattern of slowing which we found does not substantiate some commonly-held opinions about the aetiology of carpal tunnel syndrome.

A Checklist for Carpal Tunnel Syndrome

Efforts to control the incidence of Carpal Tunnel Syndrome (CTS) in industry should focus on introducing the shop supervisor to those basic biomechanical principles underlying the etiology of CTS; i.e., it is the supervisor who best monitors an employee's reactions to prescribed work methods, tools, and concomitant postures. A three-part, pictorially illustrated checklist was developed: Part I assists in the identification of upper-extremity working postures; Part II facilitates the judgement of force/torque levels by identifying the implemented tool and the material which it acts on; and Part III examines the mechanical stresses resulting from hand-tool and/or limb-worksurface interfaces. Copies of the checklist were distributed to several AT&amp;T manufacturing, installation, service, data, and material management centers to determine its readability, relevance, time for completion, and utility in terms of orienting the supervisor to the said principles. In general, supervisory input indicated that the checklist catered mainly to the manufacturing sector: most manufacturing supervisors found the form to be readable, pertinent, and edifying.

Primary carpal tunnel stenosis as a cause of entrapment of the median nerve.

The aetiology of carpal tunnel syndrome in about 50% of patients is not clear. These patients are frequently older woman. Measurements of the carpal tunnel cross-sectional area in eleven female patients revealed a narrow carpal tunnel as compared with female or male controls. Primary carpal tunnel stenosis as a cause of entrapment of the median nerve is postulated.