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 IQ^TM 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.     

Finite element analysis for transverse carpal ligament tensile strain and carpal arch area

Mechanics of carpal tunnel soft tissue, such as fat, muscle and transverse carpal ligament (TCL), around the median nerve may render the median nerve vulnerable to compression neuropathy. The purpose of this study was to understand the roles of carpal tunnel soft tissue mechanical properties and intratunnel pressure on the TCL tensile strain and carpal arch area (CAA) using finite element analysis (FEA). Manual segmentation of the thenar muscles, skin, fat, TCL, hamate bone, and trapezium bone in the transverse plane at distal carpal tunnel were obtained from B-mode ultrasound images of one cadaveric hand. Sensitivity analyses were conducted to examine the dependence of TCL tensile strain and CAA on TCL elastic modulus (0.125–10 MPa volar-dorsally; 1.375–110 MPa transversely), skin-fat and thenar muscle initial shear modulus (1.6–160 kPa for skin-fat; 0.425–42.5 kPa for muscle), and intratunnel pressure (60–480 mmHg). Predictions of TCL tensile strain under different intratunnel pressures were validated with the experimental data obtained on the same cadaveric hand. Results showed that skin, fat and muscles had little effect on the TCL tensile strain and CAA changes. However, TCL tensile strain and CAA increased with decreased elastic modulus of TCL and increased intratunnel pressure. The TCL tensile strain and CAA increased linearly with increased pressure while increased exponentially with decreased elastic modulus of TCL. Softening the TCL by decreasing the elastic modulus may be an alternative clinical approach to carpal tunnel expansion to accommodate elevated intratunnel pressure and alleviate median nerve compression neuropathy.     

Apparent transverse compressive material properties of the digital flexor tendons and the median nerve in the carpal tunnel

Carpal tunnel syndrome is a frequently encountered peripheral nerve disorder caused by mechanical insult to the median nerve, which may in part be a result of impingement by the adjacent digital flexor tendons. Realistic finite element (FE) analysis to determine contact stresses between the flexor tendons and median nerve depends upon the use of physiologically accurate material properties. To assess the transverse compressive properties of the digital flexor tendons and median nerve, these tissues from ten cadaveric forearm specimens were compressed transversely while under axial load. The experimental compression data were used in conjunction with an FE-based optimization routine to determine apparent hyperelastic coefficients (μ and α) for a first-order Ogden material property definition. The mean coefficient pairs were μ=35.3 kPa, α=8.5 for the superficial tendons, μ=39.4 kPa, α=9.2 for the deep tendons, μ=24.9 kPa, α=10.9 for the flexor pollicis longus (FPL) tendon, and μ=12.9 kPa, α=6.5 for the median nerve. These mean Ogden coefficients indicate that the FPL tendon was more compliant at low strains than either the deep or superficial flexor tendons, and that there was no significant difference between superficial and deep flexor tendon compressive behavior. The median nerve was significantly more compliant than any of the flexor tendons. The material properties determined in this study can be used to better understand the functional mechanics of the carpal tunnel soft tissues and possible mechanisms of median nerve compressive insult, which may lead to the onset of carpal tunnel syndrome.     

A fluid-immersed multi-body contact finite element formulation for median nerve stress in the carpal tunnel

Carpal tunnel syndrome (CTS) is among the most important of the family of musculoskeletal disorders caused by chronic peripheral nerve compression. Despite the large body of research in many disciplinary areas aimed at reducing CTS incidence and/or severity, means for objective characterization of the biomechanical insult directly responsible for the disorder have received little attention. In this research, anatomical image-based human carpal tunnel finite element (FE) models were constructed to enable study of median nerve mechanical insult. The formulation included large-deformation multi-body contact between the nerve, the nine digital flexor tendons, and the carpal tunnel boundary. These contact engagements were addressed simultaneously with nerve and tendon fluid-structural interaction (FSI) with the synovial fluid within the carpal tunnel. The effects of pertinent physical parameters on median nerve stress were explored. The results suggest that median nerve stresses due to direct structural contact are typically far higher than those from fluid pressure.     

Adaptation of the Transverse Carpal Ligament Associated with Repetitive Hand Use in Pianists

The transverse carpal ligament (TCL) plays a critical role in carpal tunnel biomechanics through interactions with its surrounding tissues. The purpose of this study was to investigate the in vivo adaptations of the TCL’s mechanical properties in response to repetitive hand use in pianists using acoustic radiation force impulse (ARFI) imaging. It was hypothesized that pianists, in comparison to non-pianists, would have a stiffer TCL as indicated by an increased acoustic shear wave velocity (SWV). ARFI imagining was performed for 10 female pianists and 10 female non-pianists. The median SWV values of the TCL were determined for the entire TCL, as well as for its radial and ulnar portions, rTCL and uTCL, respectively. The TCL SWV was significantly increased in pianists relative to non-pianists (p < 0.05). Additionally, the increased SWV was location dependent for both pianist and non-pianist groups (p < 0.05), with the rTCL having a significantly greater SWV than the uTCL. Between groups, the rTCL SWV of pianists was 22.2% greater than that of the non-pianists (p < 0.001). This localized increase of TCL SWV, i.e. stiffening, may be primarily attributable to focal biomechanical interactions that occur at the radial TCL aspect where the thenar muscles are anchored. Progressive stiffening of the TCL may become constraining to the carpal tunnel, leading to median nerve compression in the tunnel. TCL maladaptation helps explain why populations who repeatedly use their hands are at an increased risk of developing musculoskeletal pathologies, e.g. carpal tunnel syndrome.     

Arteriovenous malformation of a persistent median artery with a bifurcated median nerve

A patient with arteriovenous malformations of the volar forearm and hand arising from a persistent median artery with an associated bifid median nerve is presented. Surgeons should be aware of high median nerve bifurcations, particularly when a persistent median artery is identified, and should remember that additional structures that can lead to nerve compression may be present in the carpal tunnel. Specifically, more than one median nerve may need to be identified and protected in such cases.     

Median nerve compression and trigger finger in the mucopolysaccharidoses and related diseases.

Patients with Hurler's syndrome (MPS-1H), I-cell disease (ML-II) and pseudo-Hurler's syndrome (ML-III) had median nerve compression and triggering of the fingers which limited finger extension. To our knowledge, this combination has not been reported previously in patients with mucopolysaccharidoses and related disorders. In all of our 3 cases the median nerve was compressed by thickened flexor tenosynovium. Synovectomy and resection of the volar carpal ligament improved the hand function in all, including the mentally retarded patient with Hurler's syndrome. Release of the fibroosseous tunnel in two patients was followed by an increased range of motion (but not full extension). A fourth patient, without a mucopolysaccharide storage disorder, also had the combination of trigger finger and carpal tunnel syndrome.     

Estrogen and progesterone receptors in carpal tunnel syndrome

Carpal tunnel syndrome (CTS) is a compression median nerve neuropathy common in women at menopausal age. The aim of this work was to study immunohistochemically the expression of estrogen (ER) and progesterone (PR) receptors in CTS and control specimens. Biopsies of transverse carpal ligament (TCL) and flexor tendon synovitis were collected from 23 women and from 7 men undergoing surgery for median nerve decompression at the wrist for CTS. In TCL and synovial tissue, cells expressed ER and PR with statistically significant differences related to the age and sex of patients. Immunoreactivity was observed in fibroblasts of TCL, and in lining cells and fibroblasts of synovial tissue. In women, the number of ER-positive cells in the TCL and synovial tissue increased with the age, peaking at 55-70 years, and then decreasing. PR-immunoreactivity was observed only in fibroblasts of TCL and its expression decreased with age, while no immunolabeling was found in the synovial tissue. In TCL samples, the number of ER- and PR-positive cells in non-CTS patients was significantly lower than in CTS patients. These results demonstrate that ER and PR are present in TCL and flexor tendon synovitis, suggesting a role for sex steroid hormones in the pathogenesis of CTS disease.     

肌电图检查评估腕管综合征手术效果的临床分析

目的:探讨采用肌电图检查评估腕管综合征的手术治疗效果。方法:选取35例(患侧手共39侧)临床确诊为腕管综合征并接受腕管切开减压术治疗的患者,于手术前后分别行肌电图检查,应用正中神经传导检查和拇短展肌针极肌电图检查,分析患者手术前和手术后腕部正中神经功能的变化情况。结果:手术后,患者正中神经感觉传导潜伏期异常率(33%)、正中神经运动传导潜伏期异常率(36%)较手术前(72%、74%)明显下降(P0.05),正中神经感觉传导波幅(7.40±5.05)较手术前(4.86±3.60)显著降低(P0.001),拇短展肌静息状态下失神经电位的异常率(69%)、重收缩时募集电位异常率(13%)均较手术前(85%、26%)明显下降(P0.05)。患者手术前后正中神经感觉传导速度和运动传导速度对比差异无统计学意义(P0.05)。结论:腕管切开减压术可解除正中神经卡压状态,明显恢复正中神经功能,增强拇短展肌肌力,临床治疗效果好。肌电图检查可为腕管综合征患者手术治疗效果的评估提供客观的依据。     

Evaluation of the carpal tunnel based on 3-D reconstruction from MRI

While deviated wrist postures have been linked to the development of carpal tunnel syndrome, the relative contributions of posture-related changes in size, shape and volume of the carpal tunnel contribute to median nerve compression are unclear. The purpose of this study was two-fold: (1) to reconstruct the carpal tunnel from MRI data in neutral and non-neutral (30 degrees extension, 30 degrees flexion) wrist postures, and (2) to evaluate errors associated with off-axis imaging. Three-dimensional reconstruction of the carpal tunnels of 8 volunteers from the university community revealed that the orientation of the carpal tunnel was not directly explained by external wrist angle. The average orientation of the carpal tunnel was extended in all postures, ranging from 25 degrees +/-9 degrees in extension, 13 degrees +/-5 degrees in neutral and 4 degrees +/-4 degrees in the flexed wrist. Changing the orientation of the imaging plane to be perpendicular to the reconstructed carpal tunnel revealed that axial images overestimated cross-sectional area by an average of nearly 10% in extension, 4% in neutral and less than 1% in flexion. Similarly, adjusting the imaging plane to be perpendicular to external wrist angle overestimated cross-sectional area by an average of 2% in extension, 4% in neutral and 24% in flexion. Distortion of the carpal tunnel shape also became evident with rotation of the imaging plane. The data suggest that correction for the orientation of the carpal tunnel itself to be more appropriate than relying on external wrist angle. Computerized reconstruction provided detailed anatomic visualization of the carpal tunnel, and has created the framework to develop a biomechanical model of the carpal tunnel. Similar reconstruction of the tissue structures passing through (median nerve and flexor tendons) and entering the carpal tunnel (muscle tissue) will enable evaluation and partitioning of median nerve injury mechanisms.     

Anatomic observations of the carpal tunnel in cadavers with a report of unusual thickening of the perineurium of the median nerve

The carpal tunnel of 50 cadavers (100 hands) was dissected. Macroscopic finding included 14 median nerves with pressure signs (in 4 cadavers, unilaterally and 5 bilaterally). In three cadavers, marked synovitis was seen around the tendons and the nerve; in one, lipoma was evident; and in the rest, thickening of the volar carpal ligament was seen. Microscopic examination of the compressed nerves showed concentric thickening of the perineurium, thrombosis of veins, and intrafascicular fibrosis. In one nerve, the thickening of the perineurium was not concentric, but only at that part of the fascicle adjacent to the volar carpal ligament in an "onion peel" form.     

Aneurysm of the median artery causing recurrent carpal tunnel syndrome and anatomic review

A patient is presented who had recurrent carpal tunnel syndrome symptoms in his left hand 1 year after having undergone release of the transverse carpal ligament. On exploration, this was found to be due to an aneurysm of a median artery and possibly scarring due to this compression around the branches of the bifurcated median nerve. This represents the first case in the literature to comment on (1) the absence of bilaterality of the anatomic finding and (2) carpal tunnel syndrome relative to median artery aneurysm. With this in mind, a plea is made for careful exploration of the carpal tunnel, maintaining an incision as far to the ulnar side of the median nerve as technically possible with thorough visualization of the contents of the tunnel and any anatomic variance involved. The incidence of the combination of aberrant median artery with high bifurcation of the median nerve is unknown, as is the incidence of aneurysm of the median artery.     

The incidence of recurrence after endoscopic carpal tunnel release

Endoscopic carpal tunnel release has been used to decompress the median nerve in carpal tunnel syndrome for over the past decade, with an advantage (over the traditional "open" release) being decreased pain in the postoperative period. The goals of this study were to attempt to define the recurrence rate after endoscopic carpal tunnel release and to determine if it differs from that of open technique. The charts of 191 consecutive carpal tunnel syndrome patients treated operatively at the University of Missouri were reviewed. For this study, recurrent carpal tunnel syndrome was defined as documented cases in which the symptoms had resolved following surgical release but subsequently recurred, requiring surgical rerelease of the carpal tunnel. All endoscopic releases were performed using the Chow two-portal technique. Statistical analysis was performed using Fisher's exact test. A total of 103 patient hands had open carpal tunnel releases; 88 were endoscopically released. Total follow-up time (from the initial release) averaged 29 months for the open group and 22 months for the endoscopic group. There were no recurrences in the open group and six recurrences in the endoscopic group (7 percent, p = 0.008). All six recurrences were in worker's compensation patients. The median time between endoscopic release and rerelease was 8.5 months. There seems to be a statistically higher incidence of recurrence of carpal tunnel syndrome after endoscopic release compared with the traditional "open" release in our cases. Although the pathogenesis of this increased rate of recurrence is not clear, this should be considered when planning surgical release of the volar carpal ligament for carpal tunnel syndrome.     

Carpal tunnel syndrome caused by hand injuries.

Although carpal tunnel syndrome associated with injury to the wrist is common, it is possible to overlook symptoms of median nerve compression caused by an ascending tenosynovitis secondary to trauma distal to the wrist. One should look for these symptoms in such patients who complain of pain and weakness of the hand, and release the carpal tunnel if nerve compression is suspected.     

Clinical experience with the CO2 laser during carpal tunnel decompression

Scar tissue formation along the cut edges of the transverse carpal ligament has been found to be among the primary causes for persistent median nerve compression following carpal tunnel release with the steel scalpel. Since laser surgery has been shown to be effective in reducing incisional inflammatory reactions, hypertrophic scarring, and postoperative pain and edema, in achieving better hemostasis, the application of the carbon dioxide laser may be a more efficient surgical tool than the steel scalpel for carpal tunnel release. In 46 cases of carpal tunnel syndrome, the carbon dioxide laser was utilized to vaporize the transverse carpal ligament and seal its edges. The patients were then reevaluated at 1 week, 2 weeks, 6 months, 1 year, and 2 years. No intraoperative complications were encountered. Patients reported minimal postoperative pain, rapid return of sensibility, decreased paresthesia, and increased motor function. After 2 years, there have been no recurrent symptoms of median nerve compression in these patients.     

The Carpal Tunnel Syndrome—A Review of 100 Patients Treated Surgically

The carpal tunnel syndrome, or compression neuropathy of the median nerve at the wrist, is a common cause of burning pain, numbness and tingling in the hand. The diagnosis is suggested by nocturnal paresthesias in the thumb, index and long fingers associated with signs of irritability of the median nerve in the carpal tunnel at the wrist. Surgical treatment in the form of incision of the transverse carpal ligament should be performed before irreversible motor and sensory changes occur.     

Median nerve neuropathy in the forearm due to recurrence of anterior wrist ganglion that originates from the scaphotrapezial joint: Case Report

Background

Median nerve neuropathy caused by compression from a tumor in the forearm is rare. Cases with anterior wrist ganglion have high recurrence rates despite surgical treatment. Here, we report the recurrence of an anterior wrist ganglion that originated from the Scaphotrapezial joint due to incomplete resection and that caused median nerve neuropathy in the distal forearm.

Case presentation

A 47-year-old right-handed housewife noted the appearance of soft swelling on the volar aspect of her left distal forearm, and local resection surgery was performed twice at another hospital. One year after the last surgery, the swelling reappeared and was associated with numbness and pain in the radial volar aspect of the hand. Magnetic resonance imaging revealed that the multicystic lesion originated from the Scaphotrapezial joint and had expanded beyond the wrist. Exploration of the left median nerve showed that it was compressed by a large ovoid cystic lesion at the distal forearm near the proximal end of the carpal tunnel. We resected the cystic lesion to the Scaphotrapezial joint. Her symptoms disappeared 1 week after surgery, and complications or recurrent symptoms were absent 13 months after surgery.

Conclusions

A typical median nerve compression was caused by incomplete resection of an anterior wrist ganglion, which may have induced widening of the cyst. Cases with anterior wrist ganglion have high recurrence rates and require extra attention in their treatment.     

Test of a new technique for the diagnosis of carpal tunnel syndrome.

Several new techniques for carpal tunnel syndrome diagnosis have been developed in the last few years. This work tests a technique that compares the distal motor latency of the median nerve to the second lumbrical muscle (2L) with the distal motor latency of the ulnar nerve to the interossei muscle (INT). Results from 40 normal hands give the superior limit of the normal difference (2L-INT) as 0. 26 ms (&xmacr;+3 SD). In 55 hands with different levels of carpal tunnel syndrome, this new technique was more sensitive and accurate than the conventional test which uses the distal motor latency of the median nerve to the abductor pollicis brevis muscle (APB), especially in the less severe cases. With the absence of the compound muscle action potentials of the APB muscle caused by severe thenar atrophy, it is much easier to obtain the potential from the 2L muscle. We concluded that this is a sensitive, simple, rapid, and non-invasive new technique, and therefore, it should be incorporated as part of the routine ENMG procedures for carpal tunnel syndrome diagnosis.     

Comparison of the Effects of Flexion and Extension of the Thumb and Fingers on the Position and Cross-Sectional Area of the Median Nerve

Objective

To assess the separate effects of thumb and finger extension/flexion on median nerve position and cross-sectional area.

Methods

Ultrasonography was used to assess median nerve transverse position and cross-sectional area within the carpal tunnel at rest and its movement during volitional flexion of the individual digits of the hand. Both wrists of 165 normal subjects (11 men, 4 women, mean age, 28.6, range, 22 to 38) were studied.

Results

Thumb flexion resulted in transverse movement of the median nerve in radial direction (1.2±0.6 mm), whereas flexion of the fingers produced transverse movement in ulnar direction, which was most pronounced during flexion of the index and middle fingers (3.2±0.9 and 3.1±1.0 mm, respectively). Lesser but still statistically significant movements were noted with flexion of the ring finger (2.0±0.8 mm) and little finger (1.2±0.5 mm). Flexion of the thumb or individual fingers did not change median nerve cross-sectional area (8.5±1.1 mm²).

Conclusions

Volitional flexion of the thumb and individual fingers, particularly the index and middle fingers, produced significant transverse movement of the median nerve within the carpal tunnel but did not alter the cross-sectional area of the nerve. The importance of these findings on the understanding of the pathogenesis of the carpal tunnel syndrome and its treatment remains to be investigated.     

Finite element simulation of the mechanical impact of computer work on the carpal tunnel syndrome

Carpal tunnel syndrome (CTS) is a clinical disorder resulting from the compression of the median nerve. The available evidence regarding the association between computer use and CTS is controversial. There is some evidence that computer mouse or keyboard work, or both are associated with the development of CTS. Despite the availability of pressure measurements in the carpal tunnel during computer work (exposure to keyboard or mouse) there are no available data to support a direct effect of the increased intracarpal canal pressure on the median nerve.