Assessment of the ratio of carpal contents to carpal tunnel volume in patients with carpal tunnel syndrome: a preliminary report

Time-varying changes in median nerve deformation and position in response to quantified pinch and grip forces

The ability of the median nerve (MN) to adapt in response to altered carpal tunnel conditions is important to mitigate compressive stress on the nerve. We assessed changes in MN deformation and position throughout the entire time course of hand force exertions. Fourteen right-handed participants ramped up force from 0% to 50% of maximal voluntary force (MVF) before ramping force back down in three different hand force exertion tasks (pulp pinch, chuck pinch, power grip). Pinch and grip forces were measured with a digital dynamometer, which were time synchronized with transverse carpal tunnel images obtained via ultrasound. Ultrasound images were extracted in 10% increments between 0% and 50% MVF while ramping force up (loading phase) and down (unloading phase). MN deformation and position relative to the flexor digitorum superficialis tendon of the long finger were assessed in concert. During loading, the nerve became more circular while displacing dorsally and ulnarly. These changes primarily occurred at the beginning of the hand force exertions while ramping force up from 0% to 20%, with very little change between 20% and 50% MVF. Interestingly, deformation and position changes during loading were not completely reversed during unloading while ramping force down. These findings indicate an initial reorganization of carpal tunnel structures. Mirrored changes in nerve deformation and position may also reflect strain-related characteristics of adjoining subsynovial connective tissue. Regardless, time-varying changes in nerve deformation and position appear to be an important accommodative mechanism in the healthy carpal tunnel in response to gripping and pinching tasks.

Carpal tunnel mechanics and its relevance to carpal tunnel syndrome

The carpal tunnel is an elaborate biomechanical structure whose pathomechanics plays an essential role in the development of carpal tunnel syndrome. The purpose of this article is to review the movement related biomechanics of the carpal tunnel together with its anatomical and morphological features, and to describe the pathomechanics and pathophysiology associated with carpal tunnel syndrome. Topics of discussion include biomechanics of the median nerve, flexor tendons, subsynovial tissue, transverse carpal ligament, carpal tunnel pressure, and morphological properties, as well as mechanisms for biomechanical improvement and physiological restoration. It is our hope that the biomechanical knowledge of the carpal tunnel will improve the understanding and management of carpal tunnel syndrome.

Effects of slight flexion-extension and radial-ulnar deviation postures on carpal tunnel volume

BACKGROUND

Non-neutral wrist postures are a commonly reported risk factor for carpal tunnel syndrome. It is unclear how slight flexion-extension and radial-ulnar deviation postures affect the carpal tunnel. The objective was to determine the effects of slight non-neutral postures by quantifying carpal tunnel volume.

METHODS

Computed tomography images were collected on ten cadaveric specimens in target postures of -20°, -10°, -5°, 0°, 5°, 10°, and 20° of flexion and - 10°, -5°, 0°, 5°, and 10° of radial-ulnar deviation. Surface meshes of the carpal tunnel, carpal bones, radius, and third metacarpal were generated with manual segmentation. Carpal tunnel volume was calculated as the volume between proximal and distal boundaries defined with anatomical landmarks and the orientation of the tunnel. The precise wrist posture of each scan was determined with inertial-based coordinate systems of the radius and third metacarpal.

FINDINGS

Through multiple linear regression it was determined that, over the observed range of postures, flexion-extension angle does not have a significant effect (p = 0.99) while radial-ulnar deviation angle has a significant effect of -5.9 mm³/degree (p = 0.003). The findings were consistent with previous studies of postural effects on carpal tunnel pressure.

INTERPRETATION

For the treatment and prevention of carpal tunnel syndrome, results suggest that attention should be given to slight radial-ulnar deviation postures (<10°), while slight flexion-extension postures (<20°) are of lesser consequence to carpal tunnel volume.

Mutations in COMP cause familial carpal tunnel syndrome

Carpal tunnel syndrome (CTS) is the most common peripheral nerve entrapment syndrome, affecting a large proportion of the general population. Genetic susceptibility has been implicated in CTS, but the causative genes remain elusive. Here, we report the identification of two mutations in cartilage oligomeric matrix protein (COMP) that segregate with CTS in two large families with or without multiple epiphyseal dysplasia (MED). Both mutations impair the secretion of COMP by tenocytes, but the mutation associated with MED also perturbs its secretion in chondrocytes. Further functional characterization of the CTS-specific mutation reveals similar histological and molecular changes of tendons/ligaments in patients’ biopsies and the mouse models. The mutant COMP fails to oligomerize properly and is trapped in the ER, resulting in ER stress-induced unfolded protein response and cell death, leading to inflammation, progressive fibrosis and cell composition change in tendons/ligaments. The extracellular matrix (ECM) organization is also altered. Our studies uncover a previously unrecognized mechanism in CTS pathogenesis.

Familial carpal tunnel syndrome (CTS) is common, but causal genes are not characterized. Here the authors report two CTS-related mutations in two large families that impair secretion of COMP in tenocytes, leading to ER stress-induced unfolded protein response, inflammation and fibrosis in patients and mouse models.

Gender differences in carpal tunnel relative cross-sectional area: a possible causative factor in idiopathic carpal tunnel syndrome

Previous research has not established a consistent difference in hand size or carpal tunnel cross-sectional area between patients with and without carpal tunnel syndrome. We tested the hypothesis that there would be no difference in relative carpal tunnel sizes between men and women. We defined relative carpal tunnel size as the cross-sectional areas at the inlet (level of the pisiform) and outlet (level of the hook of the hamate) of the carpal tunnel divided by the length of the capitate (as a measure of hand size). We made the measurements on the magnetic resonance imaging scans of 50 men and 50 women taken for symptoms unrelated to carpal tunnel syndrome. The mean relative cross-sectional area was appreciably smaller in women than men (p < 0.05). This suggests that the carpal tunnel cross-sectional area relative to the size of the hand is constitutionally smaller in women than in men. This could in theory be a significant factor in patients developing carpal tunnel syndrome.

LEVEL OF EVIDENCE

V.

Median neuropathy in malunited fractures of the distal radius

PURPOSE

Irritation of the median nerve is a well-characterized complication after acute fractures of the distal radius, but there is limited literature on median neuropathy in malunited fractures. The aims of our prospective study were to estimate the prevalence of the median neuropathy, explore the relationship between radiographic findings and the condition, and investigate whether corrective osteotomy without carpal tunnel release was a sufficient treatment.

METHODS

Thirty consecutive patients, who were referred to us for treatment of symptomatic distal radial malunion, underwent nerve conduction studies of both wrists by one board-certified neurologist under standardized conditions. Test results were correlated with conventional radiographic parameters (radial tilt, radial inclination, palmar shift, ulnar variance, radiolunate and capitolunate angle) and computer tomography (CT) based measurements of the cross-sectional area of the carpal tunnel. After corrective osteotomy without carpal tunnel release, 10 of 13 patients with unilateral preoperative median neuropathy agreed to an electrodiagnostic re-examination by the same neurologist.

RESULTS

Nineteen patients demonstrated abnormal test results, but only seven patients complained about paresthesias of median-innervated fingers. There was no correlation between median neuropathy and conventional radiographic parameters. Surprisingly, the cross-sectional area of the carpal canal was significantly greater for patients with median neuropathy. Symptoms resolved in all patients after corrective osteotomy. Postoperatively, six of ten patients demonstrated improved nerve conduction studies, although only four patients demonstrated normal test results.

DISCUSSION

There is a high rate of subclinical median neuropathy in malunited distal radial fractures that cannot be predicted by conventional radiographic parameters. Corrective osteotomy without carpal tunnel release is a sufficient treatment for neuropathy in malunited distal radius fractures.

Narrowing carpal arch width to increase cross-sectional area of carpal tunnel--a cadaveric study

BACKGROUND

Carpal tunnel morphology plays an essential role in the etiology and treatment of carpal tunnel syndrome. The purpose of this study was to observe the morphological changes of the carpal tunnel as a result of carpal arch width narrowing. It was hypothesized that carpal arch width narrowing would result in increased height and area of the carpal arch.

METHODS

The carpal arch width of eight cadaveric hands was narrowed by a custom apparatus and cross-sectional ultrasound images were acquired. The carpal arch height and area were quantified as the carpal arch width was narrowed. Correlation and regression analyses were performed for the carpal arch height and area with respect to the carpal arch width.

FINDINGS

The carpal tunnel became more convex as the carpal arch width was narrowed. The initial carpal arch width, height, and area were 25.7 (SD1.9) mm, 4.1 (SD0.6) mm, and 68.5 (SD14.0) mm(2), respectively. The carpal arch height and area negatively correlated with the carpal arch width, with correlation coefficients of -0.974 (SD0.018) and -0.925 (SD0.034), respectively. Linear regression analyses showed a 1mm narrowing of the carpal arch width resulted in proportional increases of 0.40 (SD0.14) mm in the carpal arch height and 4.0 (SD2.2) mm(2) in the carpal arch area.

INTERPRETATION

This study demonstrates that carpal arch width narrowing leads to increased carpal arch height and area, a potential mechanism to reduce the mechanical insult to the median nerve and relieve symptoms associated with carpal tunnel syndrome.

Carpal Tunnel Cross-Sectional Area Affected by Soft Tissues Abutting the Carpal Bones

The carpal tunnel accommodates free movement of its contents, and the tunnel's cross-sectional area is a useful morphological parameter for the evaluation of the space available for the carpal tunnel contents and of potential nerve compression in the tunnel. The osseous boundary of the carpal bones as the dorsal border of the carpal tunnel is commonly used to determine the tunnel area, but this boundary contains soft tissues such as numerous intercarpal ligaments and the flexor carpi radialis tendon. The aims of this study were to quantify the thickness of the soft tissues abutting the carpal bones and to investigate how this soft tissue influences the calculation of the carpal tunnel area. Magnetic resonance images were analyzed for eight cadaveric specimens. A medical balloon with a physiological pressure was inserted into an evacuated tunnel to identify the carpal tunnel boundary. The balloon-based (i.e. true carpal tunnel) and osseous-based carpal tunnel boundaries were extracted and divided into regions corresponding to the hamate, capitate, trapezoid, trapezium, and transverse carpal ligament (TCL). From the two boundaries, the overall and regional soft tissue thicknesses and areas were calculated. The soft tissue thickness was significantly greater for the trapezoid (3.1±1.2mm) and trapezium (3.4±1.0mm) regions than for the hamate (0.7±0.3mm) and capitate (1.2±0.5mm) regions. The carpal tunnel area using the osseous boundary (243.0±40.4mm²) was significantly larger than the balloon-based area (183.9±29.7mm²) with a ratio of 1.32. In other words, the carpal tunnel area can be estimated as 76% (= 1/1.32) of the osseous-based area. The abundance of soft tissue in the trapezoid and trapezium regions can be attributed mainly to the capitate-trapezium ligament and the flexor carpi radialis tendon. Inclusion of such soft tissue leads to overestimations of the carpal tunnel area. Correct quantification of the carpal tunnel area aids in examining carpal tunnel stenosis as a potential risk factor for median nerve compression.

Compression and entrapment neuropathies

Peripheral nerve entrapments are frequent. They usually appear in anatomical tunnels such as the carpal tunnel. Nerve compressions may be due to external pressure such as the fibular nerve at the fibular head. Malignant or benign tumors may also damage the nerve. For each nerve from the upper and lower limbs, detailed clinical, electrophysiological, imaging, and therapeutic aspects are described. In the upper limbs, carpal tunnel syndrome and ulnar neuropathy at the elbow are the most frequent manifestations; the radial nerve is less frequently involved. Other nerves may occasionally be damaged and these are described also. In the lower limbs, the fibular nerve is most frequently involved, usually at the fibular head by external compression. Other nerves may also be involved and are therefore described. The clinical and electrophysiological examination are very important for the diagnosis, but imaging is also of great use. Treatments available for each nerve disease are discussed.

A knowledge-based approach for carpal tunnel segmentation from magnetic resonance images

Carpal tunnel syndrome (CTS) has been reported as one of the most common peripheral neuropathies. Carpal tunnel segmentation from magnetic resonance (MR) images is important for the evaluation of CTS. To date, manual segmentation, which is time-consuming and operator dependent, remains the most common approach for the analysis of the carpal tunnel structure. Therefore, we propose a new knowledge-based method for automatic segmentation of the carpal tunnel from MR images. The proposed method first requires the segmentation of the carpal tunnel from the most proximally cross-sectional image. Three anatomical features of the carpal tunnel are detected by watershed and polygonal curve fitting algorithms to automatically initialize a deformable model as close to the carpal tunnel in the given image as possible. The model subsequently deforms toward the tunnel boundary based on image intensity information, shape bending degree, and the geometry constraints of the carpal tunnel. After the deformation process, the carpal tunnel in the most proximal image is segmented and subsequently applied to a contour propagation step to extract the tunnel contours sequentially from the remaining cross-sectional images. MR volumes from 15 subjects were included in the validation experiments. Compared with the ground truth of two experts, our method showed good agreement on tunnel segmentations by an average margin of error within 1 mm and dice similarity coefficient above 0.9.

Morphological analysis of the carpal tunnel

Although carpal tunnel release is one of the most commonly performed procedures in the USA, the morphology of the carpal tunnel as determined previously in the literature has been questioned. Previous methodology has been questioned for accuracy by recent studies. The purpose of this study was to perform a morphological analysis of the carpal tunnel and correlate carpal tunnel and hand dimensions. The carpal tunnels of ten cadaveric specimens were emptied of their contents and a silicone cast of the carpal tunnel was then created. This cast was then digitized, and the dimensions of the carpal tunnel were calculated. These dimensions were compared with the measured hand dimensions of the specimens. The width, depth, tilt angle, length, cross-sectional area, and volume of the carpal tunnel were 19.2 ± 1.7 mm, 8.3 ± 0.9 mm, 14.8 ± 7.8°, 12.7 ± 2.5 mm, 134.9 ± 23.6 mm(2), and 1,737 ± 542 mm(3), respectively. Width, depth, and cross-sectional area did not change significantly along the length of the carpal tunnel, but tilt angle did. The width of the palm strongly correlates with the width of the carpal tunnel. Other dimensional correlations did not reach statistical significance. The carpal tunnel is of uniform dimension along its length. The long axis of the carpal tunnel in cross-section rotates volarly from the radial side of the hand increasingly with distal progression along the carpal tunnel. Based on our analysis of ten cadaveric specimens, the width of the carpal tunnel may be estimated by the width of the palm using the equation: [Formula: see text].

Individual flexor tendon identification within the carpal tunnel: A semi-automated analysis method for serial cross-section MR images

Carpal tunnel syndrome is commonly viewed as resulting from chronic mechanical insult of the median nerve by adjacent anatomical structures. Both the median nerve and its surrounding soft tissue structures are well visualized on magnetic resonance (MR) images of the wrist and hand. Addressing nerve damage from impingement of flexor digitorum tendons co-occupying the tunnel is attractive, but to date has been restricted by lack of means for making individual identifications of the respective tendons. In this image analysis work, we have developed a region-growing method to positively identify each individual digital flexor tendon within the carpal tunnel by tracking it from a more distal MR section where the respective tendon identities are unambiguous. Illustratively, the new method was applied to MRI scans from four different subjects in a variety of hand poses. Conventional shape measures yielded less discriminatory information than did evaluations of individual tendon location and arrangement. This new method of rapid identification of individual tendons will facilitate analysis of tendon/nerve interactions within the tunnel, thereby providing better information about mechanical insult of the median nerve.

Wrist and carpal tunnel size and shape measurements: effects of posture

BACKGROUND

Wrist anthropometrics and posture have been implicated in the development of carpal tunnel syndrome, yet it remains unclear how external measurements relate to carpal tunnel parameters in neutral and non-neutral postures. The purposes of this study were (i) to evaluate the effect of slice orientation on several indices of carpal tunnel size and shape and (ii) to examine the relationship between carpal tunnel and external wrist dimensions.

METHODS

Three-dimensional static models were generated to measure carpal tunnel and wrist parameters for six wrists in three wrist postures (30 degrees flexion, neutral and 30 degrees extension). A simulated imaging plane enabled measurement of four carpal tunnel dimensions and two shape indices throughout the tunnel length, using "axial" and "tunnel" slice orientations (perpendicular to forearm and tunnel, respectively).

FINDINGS

Correction for tunnel orientation eliminated posture-related changes in tunnel size and shape noted at the distal end using "axial" alignment. "Tunnel" alignment reduced average carpal tunnel area and depth by nearly 15% in extension, but generally less than 5% in neutral and 2% in flexion. Subsequently, "tunnel" alignment also decreased carpal tunnel and non-circularity ratios to reveal a flatter, more elliptical shape throughout the tunnel in extension than neutral and flexion. Wrist dimensions correlated significantly with tunnel dimensions, but not tunnel shape, while wrist shape correlated significantly with tunnel shape, area and depth.

INTERPRETATIONS

Slice alignment with the carpal tunnel may improve the consistency of findings within and between patient and control populations, and enhance the diagnostic utility of imaging in clinical settings.

Carpal tunnel volume changes of the wrist under distraction

This study attempts to determine changes in carpal canal volume with distraction across the wrist. Uniform longitudinal distraction was maintained with two external fixators on the radial and ulnar aspects of the forearm axis of five cadaver specimens. After CT scanning, volume determinations were made at 5 mm increments beginning at the lunocapitate joint to a point 1.5 cm distal to the middle finger carpometacarpal joint. There was a statistically significant decrease of the mean total carpal canal volume from 0 to 4.54 kg of distraction, with no statistically significant decrease from 0 to 2.27 kg or 2.27 to 4.54 kg. The largest decrease occurred at 15 and 20 mm distal to the proximal edge of the transverse carpal ligament corresponding to the level of the hamate hook. Reduction in mean carpal canal volume was 10.2% and 7.5% at these distances, respectively, from 0 to 4.54 kg of distraction. Progressive distraction across the wrist causes a decrease in total carpal canal volume.

Carpal tunnel syndrome: a case-control study evaluating its relationship with body mass index and hand and wrist measurements

This case-control study investigated the associations between the body mass index (BMI), hand and wrist measurements and carpal tunnel syndrome (CTS). The hands and wrists of 50 patients with CTS and 50 age- and sex-matched controls were measured. The right and left wrist indices (wrist depth/wrist width) were significantly greater in CTS patients (mean = 0.71. SD = 0.04) than in the controls (mean = 0.69 SD = 0.04). The hand index (hand length/palm width) and BMI were not significantly different in the two groups. The hand, but not the wrist, index was found to correlate with the BMI. These results provide some support for a causative association between wrist morphometry, as measured by the wrist index, and CTS, but this difference is too small to be of diagnostic value in clinical or epidemiological practice. The results could also suggest that the previously reported association between CTS and the hand index may be secondary to differences in the BMI.

Carpal tunnel syndrome

Carpal tunnel syndrome is the most common compressive neuropathy of the upper extremity. As a result of median nerve compression, the patient reports pain, weakness, and paresthesias in the hand and digits. The etiology of this condition is multifactorial; anatomic, systemic, and occupational factors have all been implicated. The diagnosis is based on the patient history and physical examination and is confirmed by electrodiagnostic testing. Treatment methods range from observation and splinting, to cortisone injection and splinting, to surgical intervention. Both nonsurgical and surgical management provide symptom relief in most patients. The results of open and endoscopic surgery essentially are equivalent at 3 months; the superiority of one technique over the other has yet to be established.

An MRI evaluation of carpal tunnel dimensions in healthy wrists: Implications for carpal tunnel syndrome

BACKGROUND

Deviated wrist postures and pinch grip use have been linked to the development of carpal tunnel syndrome and are likely related to the size and shape of the carpal tunnel. The purpose of this study was to quantify carpal tunnel dimensions with changes in wrist posture and pinch grip.

METHODS

Eight healthy volunteers (4 male, 4 female) underwent magnetic resonance imaging of their dominant wrists under seven conditions which included: 30 degrees wrist extension, neutral and 30 degrees flexion (with and without a 10 N pinch force) and a fist with a neutral wrist. Cross-sectional area of the carpal tunnel and its contents were calculated at 3mm increments along the length of the tunnel and integrated to calculate volumes. Ratios were calculated between the contents of the tunnel to the tunnel itself for area and volume.

FINDINGS

The use of a correction factor significantly reduced volume and distal carpal tunnel area in flexed and extended wrists. Carpal tunnel areas were largest in neutral and smallest at the distal end with wrist flexion. An extended wrist resulted in the smallest carpal tunnel and content volumes as well as the smallest carpal tunnel content volume to carpal tunnel volume ratios. While men had significantly larger areas and volumes than women for both the carpal tunnel and it contents, there were no differences in ratios between the contents and tunnel size.

INTERPRETATION

A simple correction factor for non-perpendicular magnetic resonance images proved useful in relating volume changes to known pressure changes within the carpal tunnel. More inclusive and detailed evaluation of the carpal tunnel and its contents is required to fully understand mechanisms for median nerve compression in the carpal tunnel.

Pathomechanics of peripheral nerve loading. Evidence in carpal tunnel syndrome

Peripheral nerve injury is a common occurrence, with carpal tunnel syndrome (CTS) receiving the most attention. Nerve dysfunction associated with compression syndromes results from an interruption or localized interference of microvascular function due to structural changes in the nerves or surrounding tissues. This article reviews the physiologic, pathophysiologic, and histologic effects of compressing peripheral nerves in animal models, and then examines the evidence for similar processes in humans using CTS as a model.

Quantitative MRI of the wrist and nerve conduction studies in patients with idiopathic carpal tunnel syndrome

OBJECTIVE

To correlate morphological findings of idiopathic carpal tunnel syndrome (CTS) with the function of the median nerve.

METHODS

In this study, 105 wrists of 105 women patients with idiopathic CTS, and 36 wrists of 36 female volunteers were subjected to nerve conduction studies and MRI. Cross sectional area, signal intensity ratio, and the flattening ratio of the median nerve, carpal tunnel area, flexor tendon area, synovial area, and intersynovial space, and the palmar bowing of the transverse carpal ligament (TCL) were quantified by MRI and correlated with the severity of the disease determined by nerve conduction studies.

RESULTS

Cross sectional areas of the median nerve, flexor tendons, and carpal tunnel, and the palmar bowing of the TCL of the CTS groups were greater than in the control group, but differences were not detected among the CTS groups for the area of the flexor tendons and the carpal tunnel. Enlargement, flattening, and high signal intensity of the median nerve at the distal radioulnar joint level were more significant in the advanced than in the earlier stages of the disease. Increase in palmar bowing of the TCL was less prominent in the most advanced group. Linear correlation between the area of the carpal tunnel and palmar bowing of the TCL was noted.

CONCLUSION

Severity of the disease could be judged by evaluating not only longitudinal changes of signal intensity and configuration of the median nerve, but also palmar bowing of the TCL. Increased palmar bowing of the TCL was found to be associated with an increase in the area of the carpal tunnel.

Chapter 25 Imaging nerve and muscle with ultrasound

Over the last two decades significant advances in ultrasound have made it possible for investigators to image and interpret pathologic changes in muscle and nerve. In addition to being able to assess the pathologic changes in these structures themselves, ultrasound also provides the unique ability to identify anatomic lesions responsible for nerve or muscle injury. They can be correlated with changes in neural structures or affected muscles. Like electrodiagnostic studies, ultrasound is portable and inexpensive, but it is even less invasive, and surprisingly sensitive in detecting a variety of unusual and common causes of neuromuscular dysfunction. Given recent developments in the field, ultrasound shows promise as the technique most suitable for clinical neurophysiologists and neuromuscular clinicians in the growing field of imaging. Such involvement is required to best adopt and exploit the potential of imaging for the research and clinical evaluation of neuromuscular disorders.

Biochemical evaluation of serum and flexor tenosynovium in carpal tunnel syndrome

In total, 41 consecutive patients with "idiopathic carpal tunnel syndrome" and abnormal electrophysiologic findings who underwent carpal tunnel release were studied prospectively. The focus of this investigation was the evaluation of the levels of specific chemical mediators within the serum and flexor tenosynovium of these patients. Blood was collected from these patients within 1 week prior to carpal tunnel release, and flexor tenosynovium was obtained at time of surgery. Specimens were then analyzed to determine the levels of interleukins 1 and 6, prostaglandin E(2) (PGE(2)), and malondialdehyde bis diethyl acetal. These values were compared to those of controls who had no evidence of carpal tunnel syndrome. A significant increase was noted in the serum malondialdehyde and tenosynovial levels of malondialdehyde, interleukin 6, and prostaglandin PGE(2) compared to controls. The elevated levels of these biologic factors and the absence of interleukin 1 elevation support a noninflammatory ischemia-reperfusion etiology for so-called "idiopathic carpal tunnel syndrome" that causes progressive edema and fibrosis of the tissues within the carpal canal. These findings correlate with previous histopathology reports. We believe that "idiopathic carpal tunnel syndrome" is an "-osis" not an "-itis."

The relationship between basal joint arthritis and carpal tunnel syndrome: an MRI pilot study

PURPOSE

This investigation explored 2 questions. First, does basal joint arthritis lead to morphologic alterations that significantly narrow the carpal tunnel? Second, does trapezial excision alter the morphology of the carpal tunnel and decompress the median nerve?

METHOD

Four patients with basal joint arthritis alone were treated with ligament reconstruction and tendon interposition (LRTI) arthroplasty. Three patients with basal joint arthritis and carpal tunnel syndrome were treated with LRTI and carpal tunnel release. Preoperative and postoperative magnetic resonance imaging (MRI) scans were obtained to assess differences in carpal tunnel volume and morphology between the groups before and after surgery.

RESULTS

The difference in preoperative carpal tunnel volume between groups was not significantly different. Carpal tunnel volume increased by 7% with LRTI and by 24% after LRTI and carpal tunnel release. The anteroposterior diameter of the carpal canal increased in both groups to allow a volar migration of the median nerve.

CONCLUSION

LRTI increases the anteroposterior diameter and volume of the carpal tunnel. A larger comparative study would be necessary to determine whether LRTI is sufficient to decompress the carpal tunnel.

Magnetic resonance neurography studies of the median nerve before and after carpal tunnel decompression

OBJECT

Recently developed novel MR protocols called MR neurography, which feature conspicuity for nerve, have been shown to demonstrate signal change and altered median nerve configuration in patients with median nerve compression. The postoperative course following median nerve decompression can be problematic, with persistent symptoms and abnormal results on electrophysiological studies for some months, despite successful surgical decompression. The authors undertook a prospective study in patients with carpal tunnel syndrome, correlating the clinical, electrophysiological, and MR neurography findings before and 3 months after surgery.

METHODS

Thirty patients and eight control volunteers were recruited to the study. The MR neurography consisted of axial and sagittal images (TR = 2000 msec, TE = 60 msec) obtained using a temporomandibular surface coil, fat saturation, and flow suppression. Maximum intensity projection images were used to follow the median nerve through the carpal tunnel in the sagittal plane. Magnetic resonance neurography in patients with carpal tunnel syndrome demonstrated proximal swelling (p < 0.001) and high signal change in the nerve, together with increased flattening ratios (p < 0.001) and loss of nerve signal in the distal carpal tunnel (p < 0.05). Sagittal images were very effective in precisely demonstrating the site and severity of nerve compression. After surgery, division of the flexor retinaculum could be demonstrated in all cases. Changes in nerve configuration, including increased cross-sectional area, and reduced flattening ratios (p < 0.001) were seen in all patients. In many cases restoration of the T. signal intensity toward that of controls was seen in the median nerve in the distal carpal tunnel. Sagittal images were excellent in demonstrating expansion of the nerve at the site of surgical decompression.

CONCLUSIONS

In this study the authors suggest that MR neurography is an effective means of both confirming compression of the median nerve and its successful surgical decompression in patients with carpal tunnel syndrome. This modality may prove useful in the assessment of unconfirmed or complex cases of carpal tunnel syndrome both before and after surgery.

Practical anatomy of the carpal tunnel

The carpal tunnel is most narrow at the level of the hook of the hamate. The median nerve is the most superficial structure. It has specific relationships to surrounding structures within the carpal tunnel to the ulnar bursa, flexor tendons, and endoscopic devices placed inside the canal. The importance of the ring finger axis is stressed. Knowledge of topographical landmarks that mark the borders of the carpal tunnel, the hook of the hamate, superficial arch, and thenar branch of the median nerve ensure appropriate incision placement for endoscopic as well as open carpal tunnel release surgery. Anatomy of the transverse carpal ligament, its layers and relationships to adjacent structures including the fad pad, Guyon's canal, palmar fascia, and thenar muscles has been discussed. Fibers derived primarily from thenar muscle fascia with connections to the hypothenar muscle fascia and dorsal fascia of the palmaris brevis form a separate fascial layer directly palmar to the TCL and can be retained. This helps to preserve postoperative pinch strength. The fat pad in line with the ring finger axis overlaps the deep surface of the distal edge of the TCL and must be retracted in order to visualize the distal end of the ligament. Whereas the ulnar artery within Guyon's canal is frequently located radial to the hook of the hamate, injury to this structure has not been a problem during ECTR surgery. Variations of the median nerve and its branches, as well as the palmar cutaneous nerve distribution, have been reviewed. A rare ulnar-sided thenar branch from the median nerve, interconnecting branches between the ulnar and median nerves located just distal to the end of the TCL, and transverse ulnar-based cutaneous nerves can be injured during open or ECTR surgery. Anomalous muscles, tendons or interconnections, and the lumbricals during finger flexion may be seen within the carpal tunnel. These structures can be the cause of compression of the median nerve. The anatomy of the carpal tunnel and surrounding structures have been reviewed with emphasis on clinical applications to endoscopic and open carpal tunnel surgery. A thorough knowledge of the anatomy of the carpal tunnel is essential in order to avoid complications and to ensure optimal patient outcome. An understanding of the contents and their positions and relationships to each other allows the surgeon to perform a correct approach and accurately identify structures during procedures at or near the carpal tunnel.

Pathophysiological tissue changes associated with repetitive movement: a review of the evidence

Work-related musculoskeletal disorders (WMSDs) represent approximately one third of workers' compensation costs in US private industry, yet estimates of acceptable exposure levels for forceful and repetitive tasks are imprecise, in part, due to lack of measures of tissue injury in humans. In this review, the authors discuss the scope of upper-extremity WMSDs, the relationship between repetition rate and forcefulness of reaching tasks and WMSDs, cellular responses to injury in vivo and in vitro, and animal injury models of repetitive, forceful tasks. The authors describe a model using albino rats and present evidence related to tissue injury and inflammation due to a highly repetitive reaching task. A conceptual schematic for WMSD development and suggestions for further research are presented. Animal models can enhance our ability to predict risk and to manage WMSDs in humans because such models permit the direct observation of exposed tissues as well as motor behavior.