Biomechanical properties of the transverse carpal ligament under biaxial strain

The transverse carpal ligament (TCL) influences carpal stability and carpal tunnel mechanics, yet little is known about its mechanical properties. We investigated the tissue properties of TCLs extracted from eight cadaver arms and divided into six tissue samples from the distal radial, distal middle, distal ulnar, proximal radial, proximal middle, and proximal ulnar regions. The 5% and 15% strains were applied biaxially to each sample at rates of 0.1, 0.25, 0.5, and 1%/s. Ligament thickness ranged from 1.22 to 2.90 mm. Samples from the middle of the TCL were thicker proximally than distally (p < 0.013). Tissue location significantly affected elastic modulus (p < 0.001). Modulus was greatest in the proximal radial samples (mean 2.8 MPa), which were 64% and 44% greater than the distal radial and proximal ulnar samples, respectively. Samples from the middle had a modulus that was 20–39% greater in the proximal versus more distal samples. The TCL exhibited different properties within different locations and in particular greater moduli were found near the carpal bone attachments. These properties contribute to the understanding of carpal tunnel mechanics that is critical to understanding disorders of the wrist. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:757–763, 2012     

Pressure–morphology relationship of a released carpal tunnel

We investigated morphological changes of a released carpal tunnel in response to variations of carpal tunnel pressure. Pressure within the carpal tunnel is known to be elevated in patients with carpal tunnel syndrome and dependent on wrist posture. Previously, increased carpal tunnel pressure was shown to affect the morphology of the carpal tunnel with an intact transverse carpal ligament (TCL). However, the pressure–morphology relationship of the carpal tunnel after release of the TCL has not been investigated. Carpal tunnel release (CTR) was performed endoscopically on cadaveric hands and the carpal tunnel pressure was dynamically increased from 10 to 120 mmHg. Simultaneously, carpal tunnel cross‐sectional images were captured by an ultrasound system, and pressure measurements were recorded by a pressure transducer. Carpal tunnel pressure significantly affected carpal arch area (p < 0.001), with an increase of >62 mm² at 120 mmHg. Carpal arch height, length, and width also significantly changed with carpal tunnel pressure (p < 0.05). As carpal tunnel pressure increased, carpal arch height and length increased, but the carpal arch width decreased. Analyses of the pressure–morphology relationship for a released carpal tunnel revealed a nine times greater compliance than that previously reported for a carpal tunnel with an intact TCL. This change of structural properties as a result of transecting the TCL helps explain the reduction of carpal tunnel pressure and relief of symptoms for patients after CTR surgery. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 616–620, 2013     

Effect of wrist posture on carpal tunnel pressure while typing

Long weekly hours of keyboard use may lead to or aggravate carpal tunnel syndrome. The effects of typing on fluid pressure in the carpal tunnel, a possible mediator of carpal tunnel syndrome, are unknown. Twenty healthy subjects participated in a laboratory study to investigate the effects of typing at different wrist postures on carpal tunnel pressure of the right hand. Changes in wrist flexion/extension angle (p = 0.01) and radial/ulnar deviation angle (p = 0.03) independently altered carpal tunnel pressure; wrist deviations in extension or radial deviation were associated with an increase in pressure. The activity of typing independently elevated carpal tunnel pressure (p = 0.001) relative to the static hand held in the same posture. This information can guide the design and use of keyboards and workstations in order to minimize carpal tunnel pressure while typing. The findings may also be useful to clinicians and ergonomists in the management of patients with carpal tunnel syndrome who use a keyboard. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1269–1273, 2008     

Carpal arch and median nerve changes during radioulnar wrist compression in carpal tunnel syndrome patients

The purpose of this study was to investigate the morphological changes of the carpal arch and median nerve during the application of radiounlarly directed compressive force across the wrist in patients with carpal tunnel syndrome. Radioulnar compressive forces of 10 N and 20 N were applied at the distal level of the carpal tunnel in 10 female patients diagnosed with carpal tunnel syndrome. Immediately prior to force application and after 3 min of application, ultrasound images of the distal carpal tunnel were obtained. It was found that applying force across the wrist decreased the carpal arch width (p < 0.001) and resulted in increased carpal arch height (p < 0.01), increased carpal arch curvature (p < 0.001), and increased radial distribution of the carpal arch area (p < 0.05). It was also shown that wrist compression reduced the flattening of the median nerve, as indicated by changes in the nerve's circularity and flattening ratio (p < 0.001). This study demonstrated that the carpal arch can be non‐invasively augmented by applying compressive force across the wrist, and that this strategy may decompress the median nerve providing symptom relief to patients with carpal tunnel syndrome. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1234–1240, 2016.     

Effects of static fingertip loading on carpal tunnel pressure

The purpose of this study was to explore the relationship between carpal tunnel pressure and fingertip force during a simple pressing task. Carpal tunnel pressure was measured in 15 healthy volunteers by means of a saline-filled catheter inserted percutaneously into the carpal tunnel of the nondominant hand. The subjects pressed on a load cell with the tip of the index finger and with 0, 6, 9, and 12 N of force. The task was repeated in 10 wrist postures: neutral; 10 and 20° of ulnar deviation; 10° of radial deviation; and 15, 30, and 45° of both flexion and extension. Fingertip loading significantly increased carpal tunnel pressure for all wrist angles (p = 0.0001). Post hoc analyses identified significant increases (p <0.05) in carpal tunnel pressure between unloaded (0 N) and all loaded conditions, as well as between the 6 and 12 N load conditions. This study demonstrates that the process whereby fingertip loading elevates carpal tunnel pressure is independent of wrist posture and that relatively small fingertip loads have a large effect on carpal tunnel pressure. It also reveals the response characteristics of carpal tunnel pressure to fingertip loading, which is one step in understanding the relationship between sustained grip and pinch activities and the aggravation or development of median neuropathy at the wrist.     

Release of the transverse carpal ligament alone is associated with elevated pressure beneath the distal volar forearm fascia in a cadaver model of carpal tunnel syndrome

PURPOSE: The purpose of this study is to determine whether release of the distal volar forearm fascia (DVFF) is necessary at the time of median nerve decompression for carpal tunnel syndrome. METHODS: Five fresh-frozen cadaver specimens were mounted vertically with the hand dependent and a 2.27-kg weight suspended from the fingers. A pressure sensor wire was used to measure pressures starting just distal to the transverse carpal ligament (TCL). The wire was withdrawn proximally in 5-mm increments and into the forearm until pressure was below 10 mm Hg. An incision in the forearm was extended distally until the pressure sensor was found. The distance from this point to the distal volar wrist crease was measured. The TCL was released, keeping the DVFF intact, and the experiment was repeated. Paired t-tests determined whether there were statistically significant differences between measurements before and after TCL release. RESULTS: Average peak pressure under the intact TCL was 57.8 +/- 10.1 mm Hg. Average peak pressure under the DVFF with the TCL intact was 61.2 +/- 43.6 mm Hg. Following release of the TCL, average peak pressure beneath the TCL significantly decreased to 14.0 +/- 9.0 mm Hg, whereas average peak pressure at the intact DVFF increased to 64.8 +/- 48.7 mm Hg. Average locations where DVFF pressure became less than 10 mm Hg with an intact TCL and with released TCL were 4.30 +/- 1.8 cm and 4.00 +/- 1.8 cm proximal to the distal volar wrist crease, respectively. There was no significant difference between DVFF pressures before or after TCL release. CONCLUSIONS: In a cadaver model of carpal tunnel syndrome, release of the TCL alone is associated with persistent pressures >30 mm Hg in the region of the DVFF. Release of the TCL did not significantly change the location of the pressure drop-off under the DVFF.     

Morphological Analysis of the Transverse Carpal Ligament

Transection of the transverse carpal ligament (TCL) for carpal tunnel syndrome is commonly performed, yet actual knowledge of TCL morphology is rudimentary and the anatomical terminology is inconsistently used. The purpose of this study was to perform a morphological analysis of the TCL, to redefine the anatomical terminology concerning the TCL and surrounding structures, and to evaluate any correlation between external, measurable hand dimensions, and TCL dimensions. A silicone casting technique and digitization were employed to measure the morphology of the TCL in cadaveric specimens and to construct a three-dimensional TCL model. The TCL was the thickest distally at the midline and ulnar segments and the thickest proximally at the radial segment. External hand dimensions did not significantly correlate with TCL dimensions. The TCL thickness distribution is variable along the radioulnar axis. The thickness of the TCL was 2.1 ± 0.8 mm, ranging from 1.3 to 3.0 mm.     

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.     

Comparative study of carpal tunnel compliance in the human,dog, rabbit,and rat

The purpose of this study was to measure the compliance of the carpal tunnel in candidate animal models of carpal tunnel syndrome (CTS), by measuring the resistance when passing a tapered metal rod through the carpal tunnel. Forepaws from 10 dogs, 10 rabbits, and 10 rats with intact carpal tunnels, and 10 fresh frozen human wrist cadavers were used. The slopes of the linear part of the force‐displacement curve (a measure of stiffness), normal force, and increasing area ratio (InAR) were significantly different among the four species (p < 0.05). Post hoc analysis indicated that the mean slopes for the human carpal tunnel were the largest, indicating the least compliance, whereas those of the rat were the least (p < 0.05). The features of the compliance for the dog carpal tunnel were closest to the human. The development of animal models of CTS should consider the compliance of the carpal tunnel, as it will be more difficult to increase pressure in a more compliant tunnel. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:652–656, 2010     

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     

Fingertip loading and carpal tunnel pressure: Differences between a pinching and a pressing task

Carpal tunnel syndrome may be caused by repeated or sustained elevated carpal tunnel pressure. This study examined the relationship between carpal tunnel pressure, posture, and fingertip load. In 20 healthy individuals, carpal tunnel pressure was measured with a catheter inserted into the carpal tunnel of the dominant hand and connected to a pressure transducer. With the wrist in a pressure-neutral position, the subjects pressed on a force transducer with the index finger to levels of 0, 5, 10, and 15 N. They then pinched the transducer at the same levels of force. For both fingertip-loading postures, the carpal tunnel pressure increased with increasing fingertip load. Carpal tunnel pressures were significantly greater (p < 0.015) for the pinching task (14.2, 29.9, 41.9, and 49.7 mm Hg [1.89, 3.99, 5.59, and 6.63 kPa] for 0, 5, 10, and 15 N force levels, respectively) than for simple finger pressing (7.8, 14.1, 20.0, and 33.8 mm Hg [1.04, 1.88, 2.67, and 4.51 kPa]). This study indicates that although the external load on the finger remained constant between the two tasks, the internal loading, as measured by carpal tunnel pressure, experienced a near 2-fold increase by using a pinch grip. These findings should be given consideration in designing work tasks and tools because relatively low fingertip forces, especially in a pinch grip, elevate carpal tunnel pressures to levels that, if prolonged, may lead to the development or exacerbation of carpal tunnel syndrome.     

Evaluation of Dynamic Carpal Arch Stability following Carpal Tunnel Release Using Four-Dimensional Computed Tomography

Introduction  This study aimed to assess the carpal arch dynamics during active finger and wrist motion following carpal tunnel release using four-dimensional computed tomography (4D-CT). Materials and Methods  Four patients who diagnosed with bilateral carpal tunnel syndrome and underwent unilateral carpal tunnel release were prospectively included. 4D-CT of the bilateral wrists during active finger and wrist motion was performed for 10 seconds at five frames per second. The distances between the tip of tuberosity of the scaphoid and the volar ridge of the pisiform (S–P distance) and volar ridge of trapezium and the tip of hook of hamate (T–H distance) were measured at each position and the values of S–P and T–H distances were compared between the postoperative and contralateral wrists. Results  During finger motion, the S–P and T–H distances were not different at any position between the postoperative side and contralateral side. Conversely, S–P and T–H distances gradually increased in the postoperative wrists. The differences between the sides of S–P distance were significant, with >0 degrees of wrist extension, and differences of T–H distance were significant with >15 degrees of wrist extension. Conclusion  This study demonstrated the carpal arch dynamics using 4D-CT and revealed that the carpal arch was widened with the wrist in extension after carpal tunnel release. This study suggests that the transverse carpal ligament plays an important role in maintaining carpal arch stability.     

The clinical significance of the palmaris longus tendon in the pathophysiology of carpal tunnel syndrome

Carpal tunnel syndrome is associated with increased intracarpal canal pressure. The effect of tendon loading on intracarpal canal pressures is documented in biomechanical studies. Palmaris longus loading in wrist extension induces the greatest absolute increase in intracarpal canal pressure. Despite this fact, the palmaris longus is not yet a proven independent risk factor for the development of carpal tunnel syndrome. The purpose of this prospective clinical study was to assess and quantify the association between the presence of a palmaris longus tendon and carpal tunnel syndrome. Thirty-six carpal tunnel subjects with bilateral disease were compared with 36 controls. Each subject was clinically examined for the presence of the palmaris longus tendon. The prevalence of palmaris longus agenesis was significantly lower in the carpal tunnel group. The palmaris longus tendon is a strong independent risk factor for carpal tunnel syndrome.     

Median nerve deformation in differential finger motions: ultrasonographic comparison of carpal tunnel syndrome patients and healthy controls

We investigated the median nerve deformation in the carpal tunnel in patients with carpal tunnel syndrome and controls during thumb, index finger, middle finger, and a four finger motion, using ultrasound. Both wrists of 29 asymptomatic volunteers and 29 patients with idiopathic carpal tunnel syndrome were evaluated by ultrasound. Cross‐sectional images during motion from full extension to flexion were recorded. Median nerve cross‐sectional area, perimeter, aspect ratio of the minimal enclosing rectangle, and circularity in extension and flexion positions were calculated. Additionally, a deformation index was calculated. We also calculated the intra‐rater reliability. In both controls and patients, the median nerve cross‐sectional area became significantly smaller from extension to flexion in all finger motions (p < 0.05). In flexion and extension, regardless of the specific finger motion, the median nerve deformation, circularity and the change in perimeter were all significantly greater in CTS patients than in controls (p < 0.05). We found excellent intra‐rater reliability for all measurements (ICC > 0.84). With this study we have shown that it is possible to assess the deformation of the median nerve in carpal tunnel syndrome with ultrasonography and that there is more deformation of the median nerve in carpal tunnel syndrome patients during active finger motion. These parameters might be useful in the evaluation of kinematics within the carpal tunnel, and in furthering our understanding of the biomechanics of carpal tunnel syndrome in the future. © 2011 Orthopaedic Research Society. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:643–648, 2012     

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 mm², and 1,737 ± 542 mm³, 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: \textWidt\texth_\textCT = 1.285 + 0.236 ×\textWidt\texth_\textpalm {\text{Widt}}{{\text{h}}_{\text{CT}}} = 1.285 + 0.236 \times {\text{Widt}}{{\text{h}}_{\text{palm}}} .     

Area and shape changes of the carpal tunnel in response to tunnel pressure

Carpal tunnel mechanics is relevant to our understanding of median nerve compression in the tunnel. The compliant characteristics of the tunnel strongly influence its mechanical environment. We investigated the distensibility of the carpal tunnel in response to tunnel pressure. A custom balloon device was designed to apply controlled pressure. Tunnel cross sections were obtained using magnetic resonance imaging to derive the relationship between carpal tunnel pressure and morphological parameters at the hook of hamate. The results showed that the cross‐sectional area (CSA) at the level of the hook of hamate increased, on average, by 9.2% and 14.8% at 100 and 200 mmHg, respectively. The increased CSA was attained by a shape change of the cross section, displaying increased circularity. The increase in CSA was mainly attributable to the increase of area in the carpal arch region formed by the transverse carpal ligament. The narrowing of the carpal arch width was associated with an increase in the carpal arch. We concluded that the carpal tunnel is compliant to accommodate physiological variations of the carpal tunnel pressure, and that the increase in tunnel CSA is achieved by increasing the circularity of the cross section. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:1951–1956, 2011     

Segmental carpal canal pressure in patients with carpal tunnel syndrome

PURPOSE: To clarify which part of the median nerve is the most compressed and to compare carpal canal pressure with the latency of the sensory nerve potential and the duration of symptoms. METHODS: Fifteen patients with idiopathic carpal tunnel syndrome were studied using a pressure guidewire system to record canal pressure. The wire was introduced from the distal end of the carpal canal to 2 cm proximal to the distal wrist crease (DWC) and then retracted in 5-mm increments using an image intensifier to guide the progress. A nerve conduction study was performed, and all patients were asked how long the symptoms lasted. RESULTS: Carpal canal pressure was significantly higher 5 to 15 mm distal to the DWC. The most compressed point was 10 mm distal to the DWC, with a pressure of 44.9 +/- 26.4 mm Hg. The correlation coefficient between the highest canal pressure and the latency was 0.393 and between highest canal pressure and duration of symptoms was 0.402. CONCLUSIONS: Our study showed that the most compressed part of the median nerve in the carpal canal is 10 mm distal to the DWC. The carpal canal pressure was related to the latency and to the duration of symptoms.     

Effect of grip type,wrist motion,and resistance level on pressures within the carpal tunnel of normal wrists

Elevated carpal tunnel pressure (CTP) has been associated with carpal tunnel syndrome. This study systematically evaluated the effect of wrist motion resistance and grip type on CTP during wrist motion typical of occupational tasks. CTP during four wrist motion patterns, with and without resistance, and with and without gripping, was measured in vivo in 14 healthy individuals. CTP measured during compound motions fell between that measured in the cardinal planes of wrist flexion/extension and radial/ulnar deviation. Generally, with no active gripping there was little pressure change due to wrist angular displacement or resistance level. However, concurrent active pinch or power grip increased CTP particularly in motions including extension. CTP typically did not increase during wrist flexion, and in fact often decreased. Extension motions against resistance when employing a pinch or power grip increase CTP more than motions with flexion. Results could help inform design or modification of wrist motion intensive occupational tasks. © 2014 The Authors. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:524–530, 2014.     

Postoperative changes of carpal canal pressure in carpal tunnel syndrome: a prospective study with follow-up of 1 year

Carpal canal pressures were measured in 103 patients with idiopathic carpal tunnel syndrome, before and after open release, with a postoperative follow-up of 1 year. Twenty-five normal subjects were used as controls. Pressures were measured with the wrists in three positions: neutral, full passive flexion and full passive extension. At each wrist position, the mean pre-operative pressures in the study group were significantly higher than in the control group. In both groups, the pressures were maximal with full passive extension and minimal in the neutral wrist position. Immediately after surgical release, there was a marked decrease of the carpal canal pressures. However, during the second postoperative month, there was a significant increase of the pressures at each wrist position, although these were still within the normal control range. This rise in pressures persisted to 12 months. These findings suggest that the carpal ligament reconstitutes by normal scar formation, but with lengthening such that the volume of the carpal canal is enlarged, so preventing a rise in pressure with return of the pre-operative problem.     

Gliding resistance of flexor tendon associated with carpal tunnel pressure: A biomechanical cadaver study

The purpose of this study was to investigate the effect of carpal tunnel pressure on the gliding characteristics of flexor tendons within the carpal tunnel. Eight fresh human cadaver wrists and hands were used. A balloon was inserted into the carpal tunnel to elevate the pressure. The mean gliding resistance of the middle finger flexor digitorum superficialis tendon was measured with the following six conditions: (1) as a baseline, before balloon insertion; (2) balloon with 0 mmHg pressure; (3) 30 mmHg; (4) 60 mmHg; (5) 90 mmHg; (6) 120 mmHg. The gliding resistance of flexor tendon gradually increased as the carpal tunnel pressure was elevated. At pressures above 60 mmHg, the increase in gliding resistance became significant compared to the baseline condition. This study helps us to understand the relationship between carpal tunnel pressure, which is elevated in the patient with carpal tunnel syndrome (CTS) and tendon gliding resistance, which is a component of the work of flexion. These findings suggest that patients with CTS may have to expend more energy to accomplish specific motions, which may in turn affect symptoms of hand pain, weakness and fatigue, seen commonly in such patients. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:58–61, 2011