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.     

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 morphological study of the peri- and epineurium in the compression zone of the median nerve in carpal tunnel syndrome

The structure of the peri- and epineurium of the median nerve in the carpal tunnel syndrome was studied by light and transmission electron microscopy. Electron microscopy confirms the flattened lamellar arrangement of the perineurial cells, but in contrast to the normal architecture the perineurial component of the median nerve in carpal tunnel syndrome consists of 20-25 layers of ramified squamous-type cells, each layer being separated from the adjacent one by a wide space containing thick bundles of collagen fibrils. The perineurial cells are bounded on both sides by a basement membrane which is of substantial thickness. A prominent feature is the occurrence of multiple pinocytotic vesicles and caveolae opening on both the internal and external aspects of the flattened cells. They also contain bundles of closely aggregated filaments. In the spaces between the perineurial cells we find, in some places, extremely disoriented and individually abnormal fibrils and fine filaments arranged in form of a spider web. Matrix vesicles can also be seen. The epineurium of the median nerve in the carpal tunnel syndrome is also considerably thickened, and the attachment is solid, so that the median nerve is relatively immobile constricted like an hourglass. The thick collagen fibers are orientated predominantly parallel to the axis of the nerve, but circular fibers can also be seen. Apart from fibroblasts, the outer layer of the epineurium contains mast cells and vasa nervorum as well as myelinated nervi nervorum. Variable quantities of fat are also present, particularly in the surrounding loose connective tissue.     

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.     

Myoepithelioma within the carpal tunnel: a case report and review of the literature

Myoepitheliomas of the extremity are rare and usually benign, while a minority display malignant features. This case demonstrates the diagnosis and management of myoepithelioma within the carpal tunnel. Clinical and radiological tumour features were evaluated. Hematoxylin and eosin stained tumour sections were examined, and immunohistochemistry was performed. Histology revealed a nodular mass of epithelioid cells in clusters within a myxoid/chondroid stroma. No mitoses were noted. Cytokeratins, neuron-specific enolase, synaptophysin, glial fibrillary acidic protein, and S100 were positive on immunohistochemistry. A literature review revealed very few prior reports of myoepithelioma in the wrist, and limited data concerning any relationship between recurrence and quality of surgical margins. In this case, wide local excision would have significantly compromised dominant hand function, and therefore a marginal excision was deemed appropriate in the context of bland histological features. Surgical margins noted in future case reports will aid clinical decision making.     

A comparison of flexor tenosynovectomy, open carpal tunnel release, and open carpal tunnel release with flexor tenosynovectomy in the treatment of carpal tunnel syndrome

The purpose of this study was to identify the advantages and disadvantages of performing a flexor tenosynovectomy without dividing the transverse carpal ligament, an open carpal tunnel release, and an open carpal tunnel release with flexor tenosynovectomy in the treatment of carpal tunnel syndrome. From 1990 to 1998, a retrospective study was done in which a flexor tenosynovectomy was performed in 133 patients without division of the transverse carpal ligament and compared with 68 patients who had an open carpal tunnel release and 75 patients who had an open carpal tunnel release and flexor tenosynovectomy. Patients were followed up for an average period of 30 weeks with history and physical findings and nerve conduction velocities and for an average period of 2.6 years with telephone interviews. There was a 2.3 percent incidence of pillar pain in the flexor tenosynovectomy group, which may explain the earlier return to their regular jobs at an average time of 9.9 weeks, compared with 10.7 weeks for the carpal tunnel release group and 12.0 weeks for the carpal tunnel release/flexor tenosynovectomy group. The latter two groups had an incidence of pillar pain of 12.1 percent and 25.3 percent, respectively. Postoperative grip strength was statistically significantly improved in the flexor tenosynovectomy group compared with the other two groups, where adjustments were made for sex and preoperative grip strengths with standard error of adjusted means. In the flexor tenosynovectomy group, 20.6 percent of patients had a previous open or endoscopic carpal tunnel release with recurrent carpal tunnel syndrome, compared with 5.2 percent in the open carpal tunnel release group and 21.6 percent in the open carpal tunnel release with flexor tenosynovectomy group. Excisional biopsies of flexor tenosynovium in the flexor tenosynovectomy, open carpal tunnel release, and open carpal tunnel release with flexor tenosynovectomy groups revealed an incidence of fibrosis in 89.2 percent, 88.9 percent, and 87.7 percent of specimens, respectively. Edema was a frequent finding, but an active inflammatory response was seldom seen. The findings in this study indicate that because of a significant decrease in pillar pain, a flexor tenosynovectomy in the treatment of carpal tunnel syndrome would likely benefit workers who use the palm of the hand in heavy manual or highly repetitive work by allowing them to return to regular duty sooner.     

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.     

AC impedance of the perineurium of the frog sciatic nerve

The AC impedance of the isolated perineurium of the frog sciatic nerve was examined at frequencies from 2 Hz to 100 kHz. A Nyquist plot of the imaginary and real components of the impedance demonstrated more than 1 capacitative element, and a DC resistance of 478 +/- 34 (SEM, n = 27) omega cm2. Transperineurial potential in the absence of externally applied current was 0.0 +/- 0.5 mV. The impedance data were fitted by nonlinear least squares to an equation representing the generalized impedance of four equivalent circuits each with two resistive and two capacitative elements. Only two of these circuits were consistent with perineurial morphology, however. In both, the perineurial cells were represented by a resistive and capacitative element in parallel, where capacitance was less than 0.1 microF/cm2. The extracellular matrix and intercellular junctions of the perineurium were represented as single resistive and capacitative elements in parallel or in series, where capacitance exceeded 2 microF/cm2. Immersion of the perineurium in low conductance Ringer's solution increased DC resistive elements as compared with their values in isotonic Ringer's solution, whereas treatment for 10 min with a hypertonic Ringer's solution (containing an additional 1.0 or 2.0 mol NaCl/liter of solution) reduced DC resistive elements, consistent with changes in perineurial permeability. The results indicate that (a) perineurial impedance contains two time constants and can be analyzed in terms of contributions from cellular and extracellular elements, and (b) transperineurial DC resistance, which is intermediate between DC resistance for leaky and nonleaky epithelia, represents intercellular resistance and can be experimentally modified by hypertonicity.     

Comparison of partial excision with simple section of the transverse carpal ligament in the treatment of carpal tunnel syndrome

In the surgical treatment of carpal tunnel syndrome, debate has commonly focused on whether decompression should be performed by open or blind techniques. Contrarily, the goal of the present study was to determine whether instead of simple section, partial excision of the transverse carpal ligament has contributed to better results. Because complete healing of the transverse carpal ligament observed during reoperations has been reported elsewhere, the charts of 75 carpal tunnel syndrome patients who had been treated with open technique at Dokuz Eylül University were reviewed. Statistical analysis was performed using the Fisher's exact test and Student's t test when appropriate. Thirty-five patients had been treated with simple section of the transverse carpal ligament, whereas 40 had been treated with partial excision. Internal neurolysis was also performed in 19 of the patients, 11 of whom were treated with partial excision. The average follow-up time was 3.8 years. The comparisons regarding the overall operative outcomes did not show any significant difference between the two different techniques of releasing the transverse carpal ligament. In patients treated without neurolysis, results of partial excision of the transverse carpal ligament improved when compared with those of simple section, but this superiority was not statistically significant. There seemed to be statistically higher reoperation rates and worse outcomes after neurolysis (p < 0.05). Reoperation was required in eight patients (11 percent). Five of the patients who underwent reoperation had initially been treated with partial excision and neurolysis, whereas two had been treated with simple section and neurolysis. Another patient who had undergone reoperation had initially undergone only simple section. The mean time to return to work or daily activities did not differ between the types of applied technique for releasing the transverse carpal ligament. However, neurolysis lengthened these periods significantly when performed (p < 0.05). In the present study, partial excision of the transverse carpal ligament without adding neurolysis offered relatively better results than simple section. Verification of this finding endoscopically, if applicable, may improve the success rate of surgical therapy in patients with carpal tunnel syndrome.     

Genetic linkage analysis of the carpal tunnel syndrome

Two generations of a family with autosomal dominant carpal tunnel syndrome were studied for genetic linkage to 20 informative polymorphic blood markers. No linkage was demonstrated between the syndrome and the markers tested; exclusion of close linkage (lod score less than -2.0) was found for MNSs, ACP, GALT, GPT, GLO, Hp, Gc, and Pi.