Thickness and Stiffness Adaptations of the Transverse Carpal Ligament Associated with Carpal Tunnel Syndrome

Time-Dependent Change in Carpal Tunnel Cross-Sectional Area and Transverse Carpal Ligament Thickness Using Serial Magnetic Resonance Imaging Studies-An Anatomical Study

PURPOSE

Idiopathic carpal tunnel syndrome (CTS) is a common compressive neuropathy. Aging and female sex are risk factors, but the reasons are unclear. The purpose of this study was to evaluate whether identifiable radiographic changes resulting in a decrease in carpal tunnel area (CTA) over time exist.

METHODS

A database search of a multicenter, academic, tertiary institution from 1998 to 2021 identified 433 patients with serial wrist magnetic resonance images (MRI) at least 5 years apart. Fifty-six met the inclusion criteria with adequate films to measure CTA and transverse carpal ligament (TCL) thickness at the same slice location-the carpal tunnel inlet, hook of the hamate, and carpal tunnel outlet-independently by two observers who were blinded to each other's measurements. Rates for the change in CTA and TCL thickness were calculated at all three locations.

RESULTS

Thickness of the TCL increased, whereas that of the CTA decreased over time. Inlet CTA decreased by 0.9 mm2 per year (95% CI: 0.34-1.5), outlet CTA decreased by 1.8 mm2 per year (95% CI: 1.2-2.5), and CTA at the hook of the hamate decreased by 1.6 mm2 per year (95% CI: 1.0-2.0 per year). The TCL thickened by 0.02 mm per year at all three sections. Taller patients had a decreased rate of CTA loss.

CONCLUSIONS

In this select cohort, TCL thickened and CTA decreased with time. TCL thickening accounted for about half of the variation in CTA, suggesting that this is a possible contributor to this change. Hypertrophy of the carpal tunnel floor may account for the remaining variation in CTA. The question of whether these results are reliable and generalizable to the general population, or a major influence in the pathophysiology of CTS, is unknown.

CLINICAL RELEVANCE

Small decreases in CTA and thickening of the TCL occur with aging. Whether this is a contributing factor in the development of CTS requires further study.

Anatomical considerations of US-guided carpal tunnel release in daily clinical practice

Carpal tunnel syndrome is the most frequent compression neuropathy with an incidence of one to three subjects per thousand. As specific anatomical variations might lead to unintended damage during surgical interventions, we present a review to elucidate the anatomical variability of the carpal tunnel region with important considerations for daily clinical practice: several variants of the median nerve branches in and around the transverse carpal ligament are typical and must - similarly to the variant courses of the median artery, which may be found eccentric ulnar to the median nerve - be taken into account in any interventional therapy at the carpal tunnel. Unintended interference in these structures might lead to heavy arterial bleeding and, in consequence, even underperfusion of segments of the median nerve or, if neural structures such as variant nerve branches are impaired or even cut, severe pain-syndromes with a profound impact on the quality of life. This knowledge is thus crucial for outcome- and safety-optimization of different surgical procedures at the volar aspect of the wrist and surgical therapy of the carpal tunnel syndrome e.g., US-guided carpal tunnel release, as injury might result in dysfunction and/or pain on wrist motion or direct impact in the region concerned. For most variations, anatomical and surgical descriptions vary, as official classifications are still lacking.

Non-Surgical Carpal Arch Space Augmentation for Median Nerve Decompression

The carpal tunnel is a tightly bounded space, making the median nerve prone to compression and eventually leading to carpal tunnel syndrome. Carpal tunnel release surgery transects the transverse carpal ligament to expand the tunnel arch space, decompress the median nerve, and relieve the associated symptoms. However, the surgical procedure unavoidably disrupts essential anatomical, biomechanical and physiological functions of the wrist, potentially causing reduced grip strength, pillar pain, carpal bone instability, scar tissue formation, and perineural fibrosis. It is desirable to decompress the median nerve without surgically transecting the transverse carpal ligament. This paper is to review several approaches we have developed for nonsurgical carpal arch space augmentation (CASA), namely, radio ulnar wrist compression, muscle-ligament interaction, palmar pulling, and collagenolysis of the transverse carpal ligament. Briefly summarized is the research work on the CASA topic about theoretical considerations, in vitro and in situ experiment, computational modeling, and human subject studies with asymptomatic and carpal tunnel syndrome hands.

Robot and ultrasound assisted needle insertion to the transverse carpal ligament

BACKGROUND

A potential alternative treatment to surgery for carpal tunnel syndrome is to inject enzymes into the transverse carpal ligament to decrease its stiffness and alleviate pressure off the median nerve. An accurate injection is needed for delivery to achieve the effects of tissue degradation. The purposes of this study were to 1) determine injection sites using 3D reconstructed anatomy, and 2) insert the needle to the middle of the transverse carpal ligament thickness in situ.

METHODS

Six fresh-frozen cadaveric hands were used in this study. Five injection sites were determined in the sagittal plane along the center of the transverse carpal ligament thickness ulnar to the thenar muscle attachment using 3D ultrasonographic reconstruction. Each injection was delivered by rigidly fixing a 27-gauge needle to a six degrees of freedom robot arm programmed to insert the needle tip to the intended target. Ultrasound images were taken of the needle after insertion to measure accuracy and precision of the needle placement.

FINDINGS

The needle tip was successfully delivered to the middle region of the transverse carpal ligament thickness and visualized using ultrasound imaging. The accuracy and precision of the needle insertion were 0.83 and 0.31 mm, respectively.

INTERPRETATION

Methodology was established for robot-assisted needle insertion to the transverse carpal ligament using 3D ultrasonographic reconstructed anatomy. This methodology can be used in the future to deliver enzymatic injections to the transverse carpal ligament as a potential treatment for carpal tunnel syndrome.

A finite element analysis of the carpal arch with various locations of carpal tunnel release

Objective

The purpose of this study was to investigate the effects of the location of transverse carpal ligament (TCL) transection on the biomechanical property of the carpal arch structure. It was hypothesized that carpal tunnel release would lead to an increase of the carpal arch compliance (CAC) in a location-dependent manner.

Methods

A pseudo-3D finite element model of the volar carpal arch at the distal carpal tunnel was used to simulate arch area change under different intratunnel pressures (0-72 mmHg) after TCL transection at different locations along the transverse direction of the TCL.

Results

The CAC of the intact carpal arch was 0.092 mm²/mmHg, and the simulated transections ranging from 8 mm ulnarly to 8 mm radially from the center point of the TCL led to increased CACs that were 2.6-3.7 times of that of the intact carpal arch. The CACs after radial transections were greater than those ulnarly transected carpal arches.

Conclusion

The TCL transection in the radial region was biomechanically favorable in reducing carpal tunnel constraint for median nerve decompression.

Dose- and time-dependent effects of collagenase clostridium histolyticum injection on transverse carpal ligament elastic modulus and thickness in vitro

A potential treatment for carpal tunnel syndrome is to biochemically alter the mechanical properties of the transverse carpal ligament (TCL) through Collagenase Clostridium Histolyticum (CCH) injection. The purpose of this study was to determine the time- and dose-dependent effects of CCH injection on TCL elastic modulus and thickness. Nine TCLs were dissected from cadaveric hands for this study. CCH doses of 50U, 100U, 150U, 200U, and 250U were injected into five points on the TCL, respectively. B-mode and shear wave elastography images were taken of each injection point using robot-assisted ultrasound imaging immediately after injection, as well as 2, 4, 6, 8, and 24 hours after injection. TCL thickness and mean shear wave speed were measured for each CCH dose at each time point. CCH doses of 200U and 250U decreased shear wave speed by 18.70% and 30.01% (p<0.05), respectively, after 24 hours. CCH doses of 150U, 200U, and 250U decreased TCL thickness by 7.28%, 10.97%, and 14.92%, respectively, after 24 hours (p<0.05). Our findings suggest that CCH injection may be effective in degrading TCL tissue, with higher doses of CCH resulting in greater tissue degradation up to 24 hours after injection.

Evaluation of the Transverse Carpal Ligament in Carpal Tunnel Syndrome by Shear Wave Elastography: A Non-Invasive Approach of Diagnosis and Management

OBJECTIVES

The goal of this work is to determine the clinical value of the transverse carpal ligament (TCL) in carpal tunnel syndrome (CTS) for guiding subsequent treatment.

METHODS

This study analyzed patients who underwent median nerve (MN) ultrasound (US) examination of the wrist from April 2020 to April 2021. The cross-sectional area and anteroposterior diameter of the MN, as well as the TCL thickness and stiffness, were measured from images. The intra-group and intra-patient subgroup differences were compared using a t-test and a rank test. We also utilized receiver operating characteristic (ROC) curves to diagnose CTS and evaluate the severity.

RESULTS

The final cohort consisted of 120 wrists (bilateral) from 60 samples, evenly balanced across the patient and control groups according to their CTS diagnosis. In the unilateral positive patient subgroup, the MN and TCL of the positive hand were significantly thicker and stiffer than the negative counterparts (both, p < 0.05). The values from the right were also thicker and stiffer than the left (both, p < 0.05) in patients with bilateral CTS. The MN and TCL of the patient group were also significantly thicker and stiffer than those of the control group (both, p < 0.001). For diagnosing CTS, the area under the curve (AUC) of TCL thickness and stiffness at the distal carpal tunnel (DCT) ranged between 0.925 and 0.967. For evaluating CTS severity, we found that the optimal TCL stiffness is sufficient for diagnosing mild and non-mild patient cases (AUC: Emean = 0.757, Emax = 0.779).

CONCLUSIONS

Shear wave elastography is therefore an effective method for CTS diagnosis and management.

Thenar and Hypothenar Muscle Coverage on the Transverse Carpal Ligament

Background  The purpose of the study was to examine the coverage of thenar and hypothenar muscles on the transverse carpal ligament (TCL) in the radioulnar direction through in vivo ultrasound imaging of the carpal tunnel. We hypothesized that the TCL distance covered by the thenar muscle would be greater than that by the hypothenar muscle, and that total muscle coverage on the TCL would be greater than the TCL-alone region. Methods  Ultrasound videos of human wrist were collected on 20 healthy subjects. Automated algorithms were used to extract the distal cross-sectional image of the trapezium-hamate level. Manual tracing of the anatomical features was conducted. Results  Thenar muscles covered a significantly larger distance (11.9 ± 1.8 mm) as compared with hypothenar muscles (1.7 ± 0.8 mm) ( p  < 0.001). The TCL covered by thenar and hypothenar muscles was greater than the TCL-alone length ( p  < 0.001). The thenar and hypothenar muscle coverage on the TCL, as normalized to the total TCL length, was 61.0 ± 7.5%. Conclusions  More than 50% of the TCL at the distal carpal tunnel is covered by thenar and hypothenar muscles. Knowledge of muscular attachments to the TCL improves our understanding of carpal tunnel syndrome etiology and can guide carpal tunnel release surgery.

Use of conservative therapy before and after surgery for carpal tunnel syndrome

Background

Conservative therapies are typically offered to individuals who experience mild or intermittent symptoms of carpal tunnel syndrome (CTS) or postoperatively to subjects who have undergone carpal tunnel release. Although long-term studies report mostly positive results for carpal tunnel release, knowledge on the need for conservative treatments following surgery is scarce. The aim of this retrospective cohort study was to examine the use of conservative therapies before and after carpal tunnel releasing surgery.

Methods

Of 528 patients who underwent carpal tunnel release surgery in the study hospital during the study period, 259 provided sufficiently completed questionnaires (response rate 49 %). The patients completed a questionnaire battery including a sociodemographic, medical history and symptom questionnaire, the Boston Carpal Tunnel Syndrome Questionnaire, 6-item CTS symptoms scale and EuroQoL 5D. Frequencies of conservative therapies pre- and postoperatively were calculated. Association between Pain VAS and satisfaction with treatment were examined in patient groups according to the use of conservative therapies.

Results

Of all patients, 41 (16 %) reported receiving only preoperative, 18 (7 %) reported receiving only postoperative, 157 (60 %) reported receiving both pre- and postoperative conservative therapies and 43 (17 %) did not receive any therapies. Preoperative use of conservative therapies was more common in females than males (82 % vs. 64 %; p = 0.002), but postoperatively no significant gender difference was observed. The patients who received conservative therapies were younger than non-users in both the preoperative (median age 59 vs. 66; p < 0.001) and postoperative (59 vs. 66; p = 0.04) phases. The patients reported high satisfaction with their treatment and simultaneous improvement in Pain VAS scores. Those receiving conservative therapies only preoperatively reported the highest satisfaction.

Conclusions

While the use of conservative therapies decreased after surgery, a large proportion of the patients received these adjunct interventions. Patients reported high satisfaction with their treatment one year post surgery. Pain outcome seems to be closely related to satisfaction with treatment.

Level of Evidence

Level III.

The Influence of Transverse Carpal Ligament Thickness on Treatment Decisions for Idiopathic Mild to Moderate Carpal Tunnel Syndrome

PURPOSE

The main cause of carpal tunnel syndrome (CTS) is pathological changes in the flexor synovium, which is a known cause of pressure elevation in the carpal tunnel. The importance of the transverse carpal ligament (TCL) in the pathogenesis of CTS has hitherto been overlooked. However, the TCL significantly affects carpal biomechanics; the TCL is known to affect the carpal bone to a greater extent when intra carpal tunnel pressure is high. In addition, the effect of TCL properties on the progression course of idiopathic CTS is unknown.Therefore, we hypothesized that TCL thickness, measured using ultrasonography, would influence the results of conservative treatment for CTS patients with mild to moderate symptoms. We aimed to investigate the relationship between the ultrasound-measured TCL thickness and idiopathic carpal tunnel conservative treatment surgery rate.

MATERIALS AND METHODS

We analyzed the wrists of 127 patients with mild to moderate symptoms of CTS. The patients were diagnosed on the basis of electrophysiological assessment outcomes, median nerve cross-sectional area in the carpal tunnel, and clinical symptoms. The Boston carpal tunnel questionnaire score was also measured. Patients with a TCL thinner than 1.5 mm were classified into group A (n = 62), and those with a TCL thicker than 1.5 mm were classified into group B (n = 65). Patients with severe symptoms or other diseases were excluded. The patients were initially treated with night splinting after diagnosis. If symptoms were not ameliorated, steroid injection and surgical treatment were performed consecutively. The procedures were determined by a single surgeon.

RESULTS

The mean TCL thickness was 1.51 mm: 0.98 mm in group A and 2.28 mm in group B. The percentages of patients who underwent surgery were 43.0% in group A and 67.7% in group B. Group B was 1.77 times more likely to have surgery, and the interval between diagnosis and surgery and/or steroid injection was shorter. The TCL thickness in group B was also related to cross-sectional area and symptom duration.

CONCLUSIONS

Transverse carpal ligament thickness affects disease progression and may affect treatment efficacy, depending on the treatment method. Transverse carpal ligament thickness may be a criterion for deciding between surgical and conservative treatments based on a thickness threshold of 1.5 mm.

Sonoelastography in the Diagnosis of Carpal Tunnel Syndrome: A Systematic Review of Diagnostic Values Compared With the Normative Population

BACKGROUND

Sonoelastography (SEL) is widely used for assessing tissue stiffness and pathophysiology. It has also been used to diagnose carpal tunnel syndrome (CTS). However, the current criteria to diagnose CTS in SEL are diverse. The aim of this study was to systematically review the literature and assess the diagnostic value of SEL for CTS.

METHODS

A literature review was performed using MEDLINE (PubMed), EMBASE, and the Cochrane Collaboration Library for primary research articles using the keywords sonoelastography and carpal tunnel syndrome. Data related to diagnostic and cutoff value were extracted. Bias assessment was performed.

RESULTS

A total of 121 publications were reviewed. Nineteen primary case series met the inclusion criteria and were selected for full analysis. Different diagnostic approaches were identified, with units/expressions including kilopascals, conduct velocity, and strain ratio. The kilopascals and conduct velocity were measured using shear wave elastography, whereas strain ratio was calculated by relative compression quantification. A mean shear modulus cutoff value from 38.25 to 86 kPa and an acoustic radiation force impulse cutoff value of 3.0 to 3.23 m/s were used to diagnose CTS. Eight articles reported strain ratio between the median nerve and nearby tissues with diverse results due to different reference points. The other 3 additional diagnostic values were reported.

CONCLUSIONS

Sonoelastography is a useful noninvasive and promising modality to diagnose CTS. It may reflect both the condition of soft tissue scarring and quantitative values for CTS and median nerve stiffness. A diversity of examination values was found in different modalities. A high level of evidence was absent.

Biometry of thenar muscle origins on the flexor retinaculum

The transverse carpal ligament (TCL), the main part of the flexor retinaculum, serves as an anchor for the thenar muscles: abductor pollicis brevis (APB), superficial head of the flexor pollicis brevis (sFPB), and opponens pollicis (OPP). Biomechanically, the thenar muscles rely on their TCL anchoring to transmit muscle contractions distally for thumb force and motion production, and reciprocally, muscle contraction interacts with the TCL at the proximal end through the origins. However, scarce knowledge exists regarding the distribution pattern of the thenar muscle origins. The purpose of this study was to understand the anatomical interface between the thenar muscles and TCL by examining the origin distributions of the individual muscles. Ten cadaveric specimens were dissected for digitization of the muscle origins and TCL volar surface. Digitized data were used for mesh reconstruction and calculation of surface areas and centroids. The origin areas for APB, sFPB, and OPP were 105.8 ± 30.3, 64.6 ± 15.2, and 245.9 ± 70.7 mm² , respectively. The surface area of the TCL was 386.2 ± 86.9 mm² . The origin areas of APB and OPP on the TCL were comparable, 18.4 ± 4.8% and 17.3 ± 9.6% of the TCL area, respectively. The origin locations for APB, sFPB, and OPP were in proximal-radial quadrant of the TCL, on distal aponeurosis outside the TCL, and around the ridge of trapezium, respectively. The knowledge of the anatomical interface provides a foundation for the understanding of biomechanical interactions between the muscles and ligaments and pathomechanical implications.

Wrist and Hand Ultrasound: Reliability of Side-to-Side Comparisons of Very Small (<2-mm) Clinically Relevant Anatomic Structures

OBJECTIVES

In ultrasound (US) examinations of clinically relevant very small structures of the wrist and hand, the healthy contralateral side can be used as a reference to identify subtle abnormalities. Intraindividual side-to-side variability must be minimal. The aim of this study was to assess the reliability of side-to-side US evaluations of very small structures of the wrist and hand.

METHODS

Forty-one healthy volunteers were prospectively studied. Small structures of the wrist and hand were evaluated bilaterally by 2 musculoskeletal radiologists in separate sessions. The first annular pulleys of the second finger and the thumb, sagittal band of the third finger, extensor and flexor retinacula, ulnar collateral ligament of the thumb, radial collateral ligament of the second finger, and palmar cutaneous branches of the median and ulnar nerves were considered. To assess intra- and inter-reader agreement, 10 of 41 (24%) examinations were repeated. Nonparametric statistics were used.

RESULTS

Data were not normally distributed (P > .001). Intra-reader agreement was κ = 0.674 (95% confidence interval [CI], 0.57-0.78), and inter-reader agreement was κ = 0.935 (95% CI, 0.92-0.95). The mean value ± SD for all of the structures was 0.78 ± 0.44 mm. The overall coefficient of variation was 9.8% ± 0.07%. The intraclass correlation coefficient was 0.97 (95% CI, 0.96-0.98).

CONCLUSIONS

In clinical practice, the healthy contralateral side can be used as a reference during a real-time musculoskeletal US evaluation of small (<2-mm) structures.

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

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