Velocity-dependent changes in the relative motion of the subsynovial connective tissue in the human carpal tunnel

The impact of eccentric muscle contractions on peripheral nerve integrity

BACKGROUND AND AIMS

Besides muscle damage, eccentric contractions also impose significant mechanical loads on peripheral nerves. However, the impact of eccentric contractions on peripheral nerve properties remains unclear. We aimed to reveal the immediate (i.e., <2 h and short-term (i.e., <10 days) effects of eccentric contractions on functional, structural, morphological, physiological and biomechanical properties of peripheral nerves.

METHODS

Four electronic databases (PubMed, Science Direct, PEDro and Cochrane) were searched for animal and human studies which evaluated the immediate and/or short-term impact of eccentric contractions of upper or lower limb muscles on outcomes related functional, structural, morphological, physiological and biomechanical properties of peripheral nerves.

RESULTS

From a total of 2415 articles, two human and two animal studies met the selection criteria. Several signs of nerve damage following eccentric exercises were observed, such as reductions in myelin sheath thickness, nerve fibre diameter, sensory and motor nerve conduction velocity, and protein zero levels, alongside increased levels of macrophage-related protein and tropomyosin receptor kinase C. No significant changes were identified in growth-associated protein 43. It is worth noting that some variables exhibited differences in their time course between human and animal studies. Animal studies revealed that the effects were more pronounced when eccentric contractions were performed at higher velocities.

CONCLUSION

Current evidence is suggestive that eccentric contractions has the potential to alter the peripheral nerves structural, morphological, functional and physiological properties, which are indicative of nerve damage.

SYSTEMATIC REVIEW REGISTRATION

CRD42021285767.

Relative motion between the flexor digitorum superficialis tendon and subsynovial connective tissue is time dependent

The subsynovial connective tissue is an integral component of flexor tendon gliding in the carpal tunnel, which is strained during longitudinal tendon displacement. We tested the effects of repetition frequency and finger load on flexor tendon function throughout active finger movement. Eleven participants performed metacarpophalangeal joint flexion/extension of the long finger cyclically at three repetition frequencies (0.75, 1.00, 1.25 Hz) and two finger loads (3.5, 7 N). Relative displacement between the flexor digitorum superficialis tendon and subsynovial connective tissue was assessed as the shear-strain index with color ultrasound throughout the entire time history of finger flexion and extension. In addition, long finger joint angles were measured with electrogoniometry while flexor digitorum superficialis and extensor digitorum muscle activities were measured with fine-wire electromyography to characterize the finger movements. The shear-strain index increased with greater finger flexion (p = 0.001), representing higher relative displacement between tendon and subsynovial connective tissue; however, no changes were observed throughout finger extension. The shear-strain index also increased with higher repetition frequencies (p = 0.013) and finger loads (p = 0.029), further modulating time-dependent effects during finger flexion versus extension. Using ultrasound, we characterized the time-dependent response of the shear-strain index, in vivo, providing valuable data on flexor tendon function during active finger movement. Our results infer greater subsynovial connective tissue strain and shear during repetitive and forceful finger movements. Future research characterizing time-dependent effects in carpal tunnel syndrome patients may further elucidate the relations between subsynovial connective tissue function, damage, and carpal tunnel syndrome.

A non-invasive technique for evaluating carpal tunnel pressure with ultrasound vibro-elastography for patients with carpal tunnel syndrome: A pilot clinical study

Carpal tunnel syndrome (CTS) is a disorder that affects the median nerve at the wrist sufficient to cause impairment of nerve function. Elevated carpal tunnel pressure (CTP) leads to median nerve pathology, sensory, and motor changes in CTS patient. The techniques to quantify CTP used in clinic are invasive. This study aimed to investigate the feasibility of a noninvasive ultrasound vibro-elastography (UVE) to predict CTP in CTS patients and healthy individuals. The magnitudes of shear wave speed ratio (rSWS) of the 10 CTS patients (10 hands) and 6 healthy individuals (12 hands), and 10 cadaveric hands were compared using UVE. The ratios of intra to extra-carpal tunnel SWS in CTS patients was significantly higher than those in the healthy individuals (p = 0.0008) and cadaveric hands (p = 0.0015) with 500-g tendon tension. We estimated the CTP in the carpal tunnel using the mean rSWS of each group obtained from the present study and the linear approximation obtain from cadaveric hands data with 500-g tendon tension (y = 0.0036x + 1.1413). These results indicated that the elevated pressure applied to the 3rd flexor digitorum superficialis tendon in the carpal tunnel of CTS patients resulted in faster shear wave propagation. These results show that UVE was useful to indirectly estimate the CTP by measuring the rSWS; thus, they are potentially useful for the early diagnosis and assessment of CTS.

Subsynovial connective tissue development in the rabbit carpal tunnel

The carpal tunnel contains the digital flexor tendons and the median nerve, which are embedded in a unique network of fibrovascular interconnected subsynovial connective tissue (SSCT). Fibrous hypertrophy of the SSCT and subsequent adaptations in mechanical response are found in patients with carpal tunnel syndrome (CTS), but not much is known about the development of the SSCT. This observational study describes the morphological development of SSCT using histology and ultramicroscopy in an animal model at four time points between late-term fetuses through adulthood. A transition is seen between 3 days and 6 weeks post-partum from a dense solid SSCT matrix to a complex multilayered structure connected with collagenous fibrils. These preliminary data show a developmental pattern that matches an adaptive response of the SSCT to loading and motion. Understanding the anatomical development aids in recognizing the pathophysiology of CTS and supports research on new therapeutic approaches.

External Compression and Partial Ischemia Decrease Human Finger Flexor Tendon and Subsynovial Connective Tissue Relative Motion

Cumulative shear strain of the subsynovial connective tissue (SSCT) surrounding finger flexor tendons plays a significant role in the development and progression of carpal tunnel syndrome. Biomechanical risk factors can alter tendon-SSCT shear strain but the effects of external mechanical compression and localized ischemia have yet to be investigated. In a laboratory study with 19 healthy participants, color Doppler ultrasound imaging was used to quantify relative motion between the flexor digitorum superficialis tendon and SSCT during repetitive finger flexion-extension under various conditions of external mechanical compression (palmar and forearm compression), ischemia and different movement speeds (0.75 and 1.25 Hz). Forearm compression reduced tendon displacement (baseline = 28.5 ± 4.1 mm vs. forearm = 27.0 ± 4.6 mm; p = 0.043) and showed a trend for reduced SSCT displacement, while palmar compression had no significant effects on tendon-SSCT motion. Compared with baseline, partial ischemia decreased SSCT displacement (baseline = 22.9 ± 3.3 mm vs. ischemia = 22.0 ± 3.3 mm; p = 0.015), while tendon displacement remained unchanged. In all experimental conditions, faster movements elicited greater tendon-SSCT relative motion. Our findings suggest that palmar compression may not negatively impact tendon-SSCT relative motion, but forearm compression may require further investigation. Localized ischemia in the forearm may alter the gliding conditions within the carpal tunnel and affect tendon-SSCT relative motion, which bridges an important gap between blood flow in the carpal tunnel and shear injury risk. These findings contribute to the growing body of literature, supporting the role that cumulative tendon-SSCT shear injury may have on the pathomechanics of carpal tunnel syndrome. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:1038-1044, 2020.

Blood flow velocity but not tendon mechanics relates to nerve function in carpal tunnel syndrome patients

Carpal tunnel syndrome (CTS) develops from chronic compression of the median nerve. Chronic compression results in a number of vascular, structural and functional changes to the carpal tunnel tissues which ultimately manifest in the characteristic symptoms of CTS. The purpose of this study was to investigate the interplay of median nerve function, median nerve hemodynamics, and finger flexor tendon and subsynovial connective tissue (SSCT) mechanics in CTS patients. Thirty-five patients were recruited following nerve conduction study for this double-blinded imaging study. Ultrasound B-mode, pulse-wave Doppler, and colour Doppler images and videos were collected at the proximal carpal tunnel to quantify: (1) median nerve cross-sectional area, (2) intraneural blood flow velocity in 3 wrist postures (neutral (0°), flexion (15°), extension (30°)), and (3) flexor digitorum superficialis and SSCT displacement. Results demonstrate that intraneural blood flow velocity is dependent on median nerve function and wrist posture such that patients with mild CTS are more susceptible to the effects of non-neutral wrist postures. Tendon-SSCT mechanics do not appear to differ based on severity. This study stresses the importance of limiting exposure to non-neutral wrist postures in patients with early signs of the condition.

The biomechanics of subsynovial connective tissue in health and its role in carpal tunnel syndrome

Carpal Tunnel Syndrome (CTS) is the most common surgically treated problem in the hand. Aside from the neuropathy itself, the most common findings are fibrosis of the subsynovial connective tissue (SSCT) and increased intra carpal tunnel pressure. Normally, the SSCT is a multilayer tissue interspersed among the carpal tendons and nerve. As the tendons move, successive SSCT layers are recruited, forming a gliding unit and providing a limit to differential movement. Exceeding this limit, damages the SSCT as has been shown in both cadavers and animal models. This damage leads to a non-inflammatory response with progressive fibrosis and nerve ischemia leaving the SSCT more susceptible to injury. Although the direct consequences for patients are not fully understood, ultrasound research shows that this fibrosis restricts median nerve displacement during tendon loading. This article aims to provide insights into the mechanical properties of SSCT described so far and place it in the context of CTS pathophysiology. A theoretical damage model concerning the SSCT is proposed showing a chain of events and vicious cycles that could lead to the nerve compression as it is found in CTS. Although not complete, this model could explain the pathophysiological pathway of idiopathic CTS.

A Novel Adhesion Index for Verifying the Extent of Adhesion for the Extensor Digitorum Communis in Patients with Metacarpal Fractures

This study aims to determine if the relative displacement between the extensor digitorum communis (EDC) tendon and its surrounding tissues can be used as an adhesion index (AI) for assessing adhesion in metacarpal fractures by comparing two clinical measures, namely single-digit-force and extensor lag (i.e., the difference between passive extension and full active extension). The Fisher–Tippett block-matching method and a Kalman-filter algorithm were used to determine the relative displacements in 39 healthy subjects and 8 patients with metacarpal fractures. A goniometer was used to measure the extensor lag, and a force sensor was used to measure the single-digit-force. Measurements were obtained twice for each patient to evaluate the performance of the AI in assessing the progress of rehabilitation. The Pearson correlation coefficient was calculated to quantify the various correlations between the AI, extensor lag, and single-digit-force. The results showed strong correlations between the AI and the extensor lag, the AI and the single-digit-force, and the extensor lag and the single-digit-force (r = 0.718, −0.849, and −0.741; P = 0.002, P < 0.001, and P = 0.001, respectively). The AI in the patients gradually decreased after continuous rehabilitation, but remained higher than that of healthy participants.

Relative motion between the flexor digitorum superficialis tendon and paratenon in zone V increases with wrist flexion angle

Carpal tunnel syndrome is characterized by non-inflammatory fibrosis of the subsynovial connective tissue (SSCT), a paratenon-like structure inside the carpal tunnel. This pathology suggests repetitive and/or excessive shear forces are involved in injury development. We assessed relative motion between the flexor digitorum superficialis (FDS) tendon and adjacent paratenon in Zone V using colour Doppler imaging as 16 healthy participants completed three long finger movements (metacarpophalangeal joint flexion, proximal and distal interphalangeal joint flexion, full finger flexion) in three wrist postures (30° extension, 0°, 30° flexion). While the type of finger movement did not affect tendon-paratenon relative motion, we found a significant main effect of wrist posture (p < 0.001). Relative displacement between the FDS tendon and paratenon (as a percentage of tendon displacement) increased from 27.2% (95%CI = 24.8-29.5%) in 30° wrist extension to 39.9% (95%CI = 37.3-42.4%) in 30° wrist flexion. Optical motion capture confirmed that wrist posture did not affect metacarpophalangeal joint range of motion (p = 0.265) or proximal interphalangeal joint range of motion (p = 0.582). These results indicate that relative motion increased due to paratenon strain when the wrist was flexed. While our findings agree with previous cadaveric research in wrist flexion, we found that relative displacement decreased in 30° wrist extension (compared to 0°). These results differ from cadaveric research, possibly due to challenges maintaining anatomic fidelity of the viscoelastic paratenon tissue in vitro. Overall, our study suggests a greater susceptibility to shear injury during repetitive finger movements, particularly when the wrist is flexed. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1248-1255, 2016.

Assessment of Median Nerve Mobility by Ultrasound Dynamic Imaging for Diagnosing Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) is the most common peripheral neuropathy and is characterized by median nerve entrapment at the wrist and the resulting median nerve dysfunction. CTS is diagnosed clinically as the gold standard and confirmed with nerve conduction studies (NCS). Complementing NCS, ultrasound imaging could provide additional anatomical information on pathological and motion changes of the median nerve. The purpose of this study was to estimate the transverse sliding patterns of the median nerve during finger movements by analyzing ultrasound dynamic images to distinguish between normal subjects and CTS patients. Transverse ultrasound images were acquired, and a speckle-tracking algorithm was used to determine the lateral displacements of the median nerve in radial-ulnar plane in B-mode images utilizing the multilevel block-sum pyramid algorithm and averaging. All of the averaged lateral displacements at separate acquisition times within a single flexion–extension cycle were accumulated to obtain the cumulative lateral displacements, which were curve-fitted with a second-order polynomial function. The fitted curve was regarded as the transverse sliding pattern of the median nerve. The R² value, curvature, and amplitude of the fitted curves were computed to evaluate the goodness, variation and maximum value of the fit, respectively. Box plots, the receiver operating characteristic (ROC) curve, and a fuzzy c-means clustering algorithm were utilized for statistical analysis. The transverse sliding of the median nerve during finger movements was greater and had a steeper fitted curve in the normal subjects than in the patients with mild or severe CTS. The temporal changes in transverse sliding of the median nerve within the carpal tunnel were found to be correlated with the presence of CTS and its severity. The representative transverse sliding patterns of the median nerve during finger movements were demonstrated to be useful for quantitatively estimating median nerve dysfunction in CTS patients.

The effect of tendon excursion velocity on longitudinal median nerve displacement: differences between carpal tunnel syndrome patients and controls

The subsynovial connective tissue (SSCT) is a viscoelastic structure connecting the median nerve (MN) and the flexor tendons in the carpal tunnel. Increased strain rates increases stiffness in viscoelastic tissues, and thereby its capacity to transfer shear load. Therefore, tendon excursion velocity may impact the MN displacement. In carpal tunnel syndrome (CTS) the SSCT is fibrotic and may be ruptured, and this may affect MN motion. In this study, ultrasonography was performed on 14 wrists of healthy controls and 25 wrists of CTS patients during controlled finger motions performed at three different velocities. Longitudinal MN and tendon excursion were assessed using a custom speckle tracking algorithm and compared across the three different velocities. CTS patients exhibited significantly less MN motion than controls (p ≤ 0.002). While in general, MN displacement increased with increasing tendon excursion velocity (p ≤ 0.031). These findings are consistent with current knowledge of SSCT mechanics in CTS, in which in some patients the fibrotic SSCT appears to have ruptured from the tendon surface.

Validation of color Doppler sonography for evaluating relative displacement between the flexor tendon and subsynovial connective tissue

OBJECTIVES

A common pathologic finding in carpal tunnel syndrome is fibrosis and thickening of the subsynovial connective tissue. This finding suggests an etiology of excessive shear forces, with relative longitudinal displacement between the flexor tendon and adjacent subsynovial connective tissue. The purpose of this study was to validate color Doppler sonography for measurement of tendon displacement over time.

METHODS

Eight unmatched fresh frozen cadaver arms were used to evaluate color Doppler sonography for measurement of tendon displacement. The middle flexor digitorum superficialis tendon was moved through a physiologic excursion of 20 mm at 3 different tendon velocities (50, 100, and 150 mm/s).

RESULTS

We found that color Doppler sonography provided accurate measurement of tendon displacement, with absolute errors of -0.05 mm (50 mm/s), -1.24 mm (100 mm/s), and -2.36 mm (150 mm/s) on average throughout the tendon excursion range. Evaluating relative displacement between the tendon and subsynovial connective tissue during finger flexion-extension movements also offered insight into the gliding mechanism of the subsynovial connective tissue. During flexion, we observed a curvilinear increase in relative displacement, with greater differential motion at the end range of displacement, likely due to the sequential stretch of the fibrils between successive layers of the subsynovial connective tissue. In extension, there was a linear return in relative displacement, suggesting a different unloading mechanism characterized by uniform relaxation of fibrils.

CONCLUSIONS

We demonstrated the validity of color Doppler displacement for use in the evaluation of relative motion. Color Doppler sonography is useful in our understanding of the behavior of the subsynovial connective tissue during tendon excursion, which may elucidate the role of finger motion in the etiology of shear injury.

Development of a kinematic model to predict finger flexor tendon and subsynovial connective tissue displacement in the carpal tunnel

Finger flexor tendinopathies and carpal tunnel syndrome are histologically characterised by non-inflammatory fibrosis of the subsynovial connective tissue (SSCT) in the carpal tunnel, which is indicative of excessive and repetitive shear forces between the finger flexor tendons and SSCT. We assessed flexor digitorum superficialis (FDS) tendon and adjacent SSCT displacements with colour Doppler ultrasound as 16 healthy participants completed long finger flexion/extension movements captured by a motion capture system. FDS tendon displacements fit a second-order regression model based on metacarpophalangeal and proximal interphalangeal joint flexion angles (R(2) = 0.92 ± 0.01). SSCT displacements were 33.6 ± 1.7% smaller than FDS tendon displacements and also fit a second-order regression model (R(2) = 0.89 ± 0.01). FDS tendon and SSCT displacement both correlated with finger joint thickness, enabling participant-specific anthropometric scaling. We propose the current regression models as an ergonomic method to determine relative displacements between the finger flexor tendons and SSCT.

PRACTITIONER SUMMARY

Relative displacements between the finger flexor tendons and SSCT provide insight into gliding and friction in the carpal tunnel. Our regression models represent a move towards mechanistic-based ergonomic risk assessment of the wrist/hand. This is a natural evolution of ergonomic methods based on tendon-joint interaction.

Altered Ulnar Nerve Kinematic Behavior in a Cadaver Model of Entrapment

BACKGROUND:

Ulnar nerve entrapment at the elbow is more than a compressive lesion of the nerve. The tensile biomechanical consequences of entrapment are currently marginally understood.

OBJECTIVE:

To evaluate the effects of tethering on the kinematics of the ulnar nerve as a model of entrapment neuropathy.

METHODS:

The ulnar nerve was exposed in 7 fresh cadaver arms, and markers were placed at 1-cm increments along the nerve, centered on the retrocondylar region. Baseline translation (pure sliding) and strain (stretch) were measured in response to progressively increasing tension produced by varying configurations of elbow flexion and wrist extension. Then the nerves were tethered by suturing to the cubital tunnel retinaculum and again exposed to progressively increasing tension from joint positioning.

RESULTS:

In the native condition, for all joint configurations, the articular segment of the ulnar nerve exhibited greater strain than segments proximal and distal to the elbow, with a maximum strain of 28 ± 1% and translation of 11.6 ± 1.8 mm distally. Tethering the ulnar nerve suppressed translation, and the distal segment experienced strains that were more than 50% greater than its maximum strain in an untethered state.

CONCLUSION:

This work provides a framework for evaluating regional nerve kinematics. Suppressed translation due to tethering shifted the location of high strain from articular to more distal regions of the ulnar nerve. The authors hypothesize that deformation is thus shifted to a region of the nerve less accustomed to high strains, thereby contributing to the development of ulnar neuropathy.

A handy review of carpal tunnel syndrome: From anatomy to diagnosis and treatment

Carpal tunnel syndrome (CTS) is the most commonly diagnosed disabling condition of the upper extremities. It is the most commonly known and prevalent type of peripheral entrapment neuropathy that accounts for about 90% of all entrapment neuropathies. This review aims to provide an outline of CTS by considering anatomy, pathophysiology, clinical manifestation, diagnostic modalities and management of this common condition, with an emphasis on the diagnostic imaging evaluation.

The effect of low- and high-velocity tendon excursion on the mechanical properties of human cadaver subsynovial connective tissue

Fibrosis of the subsynovial connective tissue (SSCT) in the carpal tunnel is the most common histological finding in carpal tunnel syndrome (CTS). Fibrosis may result from damaged SSCT. Previous studies found that with low-velocity (2 mm/s), tendon excursions can irreversibly damage the SSCT. We investigated the effect of tendon excursion velocity in the generation of SSCT damage. Nine human cadaver wrists were used. Three repeated cycles of ramp-stretch testing were performed simulating 40%, 60%, 90%, and 120% of the middle finger flexor tendon superficialis physiological excursion with an excursion velocity of 60 mm/s. Energy and force were calculated and normalized by values obtained in the first cycle for each excursion level. Data were compared with low-velocity excursion data. For high-velocity excursions, a significant drop in the excursion energy ratio was first observed at an excursion level of 60% physiological excursion (p < 0.024) and that for low-velocity excursions was first observed at 90% physiological excursion (p < 0.038). Furthermore, the energy ratio was lower at 60% for high velocities (p ≤ 0.039). Increasing velocity lowers the SSCT damage threshold. This finding may be relevant for understanding the pathogenesis of SSCT fibrosis, such as that accompanying CTS, and a relationship with occupational factors.

Repetitive differential finger motion increases shear strain between the flexor tendon and subsynovial connective tissue

Non-inflammatory fibrosis and thickening of the subsynovial connective tissue (SSCT) are characteristic in carpal tunnel syndrome (CTS) patients. These pathological changes have been linked to repetitive hand tasks that create shear forces between the flexor tendons and SSCT. We measured the relative motion of the flexor digitorum superficialis tendon and SSCT during two repetitive finger tasks using color Doppler ultrasound. Twelve participants performed flexion-extension cycles for 30 min with the long finger alone (differential movement) and with all four fingers together (concurrent movement). Shear strain index (SSI, a relative measure of excursion in flexion and extension) and maximum velocity ratio (MVR, the ratio of SSCT versus tendon during flexion and extension) were used to represent shear. A linear effect of exertion time was significant and corresponded with larger tendon shear in differential motion. The flexion SSI increased 20.4% from the first to the 30th minute, while MVR decreased 8.9% in flexion and 8.7% in extension. No significant changes were found during concurrent motion. These results suggest that exposure to repetitive differential finger tasks may increase the risk of shear injury in the carpal tunnel.

A non-invasive technique for estimating carpal tunnel pressure by measuring shear wave speed in tendon: a feasibility study

Although a close relationship between carpal tunnel pressure and median nerve dysfunction has been found, the current methods for pressure measurements are invasive, using a catheter in the carpal canal to monitor the pressure. A noninvasive method for quantifying carpal tunnel pressure would be useful as an alternative to the catheter method. In this study, a simplified experimental model was developed to measure the shear wave speed in a canine Achilles tendon under different tunnel pressures. The results showed that the speed of waves through the inside-tunnel tendon had a linear relationship with the pressure in the tunnel (first measurement: r=0.966, P<0.001; second measurement: r=0.970, P<0.001). This indicates that the tendon could serve as a strain gauge to evaluate the tunnel pressure by detecting the changes of wave propagation speed. However, further validations in human cadavers and clinical subjects are necessary.

Peripheral nerve: from the microscopic functional unit of the axon to the biomechanically loaded macroscopic structure

Peripheral nerves are composed of motor and sensory axons, associated ensheathing Schwann cells, and organized layers of connective tissues that are in continuity with the tissues of the central nervous system. Nerve fiber anatomy facilitates conduction of electrical impulses to convey information over a distance, and the length of these polarized cells necessitates regulated axonal transport of organelles and structural proteins for normal cell function. Nerve connective tissues serve a protective function as the limb is subjected to the stresses of myriad limb positions and postures. Thus, the tissues are uniquely arranged to control the local nerve fiber environment and modulate physical stresses. In this brief review, we describe the microscopic anatomy and physiology of peripheral nerve and the biomechanical properties that enable nerve to withstand the physical stresses of everyday life.

Speckle-tracking sonographic assessment of longitudinal motion of the flexor tendon and subsynovial tissue in carpal tunnel syndrome

OBJECTIVES

The aim of this study was to image both tendon and subsynovial connective tissue movement in patients with carpal tunnel syndrome and healthy control volunteers, using sonography with speckle tracking. To estimate accuracy of this tracking method, we used in vivo measurements during surgery to validate the motion estimated with sonography.

METHODS

We recruited 22 healthy volunteers and 18 patients with carpal tunnel syndrome. Longitudinal sonograms of the middle finger flexor digitorum superficialis tendon and subsynovial connective tissue were obtained during finger flexion and extension. The images were analyzed with a speckle-tracking algorithm. The ratio of the subsynovial connective tissue velocity to tendon velocity was calculated as the maximum velocity ratio, and the shear index, the ratio of tendon to subsynovial connective tissue motion, was calculated. For validation, we recorded flexor digitorum superficialis tendon motion during open carpal tunnel release.

RESULTS

The shear index was higher in patients than controls (P < .05), whereas the maximum velocity ratio in extension was lower in patients than controls (P < .05). We found good intraclass correlation coefficients (>0.08) for shear index and maximum velocity ratio measurements between speckle-tracking and in vivo measurements. Bland-Altman analyses showed that all measurements remained within the limits of agreement.

CONCLUSIONS

Speckle tracking is a potentially useful method to assess the biomechanics within the carpal tunnel and to distinguish between healthy individuals and patients with carpal tunnel syndrome. This method, however, needs to be further developed for clinical use, with the shear index and maximum velocity ratio as possible differentiating parameters between patients with carpal tunnel syndrome and healthy individuals.

Ultrasonographic assessment of longitudinal median nerve and hand flexor tendon dynamics in carpal tunnel syndrome

INTRODUCTION

Changes in subsynovial connective tissue (SSCT) in carpal tunnel syndrome (CTS) patients may result in altered dynamics; consequently, quantification of these dynamics might support objective diagnosis of CTS.

METHODS

We measured and compared longitudinal excursion of the flexor digitorum superficialis and profundus tendons, the median nerve, and the SSCT between the most and least affected hands of 51 CTS patients during extension-to-fist motion.

RESULTS

Median nerve and flexor digitorum superficialis tendon excursions in the most affected hands were smaller than in the least affected hands of the same patients, whereas the excursions of the flexor digitorum profundus were larger. Based on these excursions, logistic regression models classified between 67% and 86% of the hands correctly as having CTS.

CONCLUSIONS

The altered hand dynamics in CTS patients may have implications for the pathophysiology and clinical evaluation of CTS, and ultrasound-based classification models may further support the diagnosis of CTS.

Ultrasonographic assessment of flexor tendon mobilization: effect of different protocols on tendon excursion

BACKGROUND

Different mobilization protocols have been proposed for rehabilitation after hand flexor tendon repair to provide tendon excursion sufficient to prevent adhesions. Several cadaver studies have shown that the position of the neighboring fingers influences tendon excursions of the injured finger. We hypothesized that the positions of adjacent fingers influence the long finger flexor digitorum profundus tendon excursion, measured both absolutely and relative to the surrounding tissue of the tendon.

METHODS

Long finger flexor digitorum profundus tendon excursions and surrounding tissue movement were measured in zone V in eleven healthy subjects during three different rehabilitation protocols and two experimental models: (1) an active four-finger mobilization protocol, (2) a passive four-finger mobilization protocol, (3) a modified Kleinert mobilization protocol, (4) an experimental modified Kleinert flexion mobilization model, and (5) an experimental modified Kleinert extension mobilization model. Tendon excursions were measured with use of a frame-to-frame analysis of high-resolution ultrasound images.

RESULTS

The median absolute long finger flexor digitorum profundus tendon excursions were 23.4, 17.8, 10.0, 13.9, and 7.6 mm for the active four-finger mobilization protocol, the passive four-finger mobilization protocol, the modified Kleinert mobilization protocol, the experimental modified Kleinert flexion mobilization model, and the experimental modified Kleinert extension mobilization model, respectively, and these differences were all significant (p ≤ 0.041). The corresponding relative flexor digitorum profundus tendon excursions were 11.2, 8.5, 7.2, 10.4, and 5.6 mm. Active four-finger mobilization protocol excursions were significantly (p = 0.013) greater than passive four-finger mobilization protocol excursions but were not significantly greater than experimental modified Kleinert flexion mobilization model excursions (p =0.213).

CONCLUSIONS

The present study demonstrated large and significant differences among the different rehabilitation protocols and experimental models in terms of absolute and relative tendon displacement. More importantly, the present study clearly demonstrated the influence of the position of the adjacent fingers on the flexor tendon displacement of the finger that is mobilized.