Evaluation of the material properties of the subsynovial connective tissue in carpal tunnel syndrome

doi:10.1016/j.clinbiomech.2007.07.009

Clinical Biomechanics

Volume 22, Issue 9, November 2007, Pages 999-1003

https://doi.org/10.1016/j.clinbiomech.2007.07.009 Get rights and content

Abstract

Background

The purpose of this study was to determine the material properties of the normal carpal tunnel subsynovial connective tissue in response to shear stress.

Methods

The shear modulus and maximum shear strength were measured with a custom-made micro-tester in 10 specimens of subsynovial connective tissue from 10 wrists in eight patients with idiopathic carpal tunnel syndrome and in 10 specimens from five fresh frozen cadavers without a history of carpal tunnel syndrome.

Findings

The mean shear modulus was 22.8 (SD 15.4) kPa for the patient group and 2.7 (SD 1.8) kPa for the control group. The mean maximum shear strength was 54.6 (SD 20.3) kPa for the patient group and 23.3 (SD 10.7) kPa for the control group. The values for the patient group were significantly higher than the control group (P < 0.05).

Interpretation

The material properties of subsynovial connective tissue are altered in patients with idiopathic carpal tunnel syndrome. The impact, if any, of these altered properties on carpal tunnel syndrome remains to be elucidated.

Introduction

The subsynovial connective tissue (SSCT) is the most characteristic structure in the carpal tunnel. It consists of multiple thin layers of collagenous fibers, in which blood and lymphatic vessels are richly represented (Guimberteau, 2001, Ettema et al., 2004). The SSCT plays an important role as a gliding unit to diminish friction and protect the vascular system within the SSCT. Noninflammatory fibrosis of the tenosynovium is the most common finding in idiopathic carpal tunnel syndrome (CTS), but its relationship to the neuropathy is unknown. Some have suggested that the changes in the SSCT might cause the neuropathy, through altered mechanics and vascularity in the carpal tunnel (Lluch, 1992, Sud et al., 2002).

Recent studies have demonstrated alterations in the gliding mechanism of the SSCT in patients with CTS (Ettema et al., 2004), as well as increased collagen type III, TGF-beta and abnormal angiogenesis (Ettema et al., 2004, Oh et al., 2004, Oh et al., 2005, Oh et al., 2006). These changes support the hypothesis that idiopathic CTS may be caused primarily by an injury to the SSCT, with secondary nerve involvement, rather than by direct damage of the nerve itself.

If CTS is caused, or can be caused, by an injury to the SSCT, then the mechanism of that injury must be plausible. One such mechanism could be a shearing injury of the SSCT, due to excessive differential tendon motion. There are many reports describing highly repetitive work as one of the risk factors for idiopathic CTS (Finkel, 1985, Atcheson et al., 1998, Chin and Jones, 2002). One biomechanical study has reported that differential finger motion with the wrist flexed elevated the tendon gliding resistance in the carpal tunnel (Zhao et al., 2007). The thickening of the fibers, noted by Ettema et al., 2004, Oh et al., 2006 could be the result of healing of such an injury. To date, there have been no reports describing the mechanical properties of the SSCT in the carpal tunnel. The purpose of this study was to compare the mechanical properties of the SSCT of normal human cadavers in response to shear stress with those of patients with CTS.

Section snippets

Specimen preparation

This study was approved by our Institutional Review Board, and all patients gave informed consent for the use of their tissue in the study. Ten SSCT samples were obtained from 10 wrists of eight adult patients (2 males and 6 females) with idiopathic CTS undergoing open carpal tunnel release surgery. The patients’ ages ranged from 24 to 71 years (mean, 45 years). A full thickness SSCT biopsy, 5 mm wide by 10 mm long, was taken from the visceral synovium on the anterior middle finger flexor

Results

There were no surgical complications as a result of the synovial biopsy.

The mean SSCT thickness for the carpal tunnel patients; 1.46 mm (SD 0.56 mm) was significantly greater than the normal control, 0.48 mm (SD 0.12 mm) (P < 0.05).

Fig. 2 shows representative shear stress–shear strain curves. Typically, no load (i.e., a “toe” region) was observed during the initial strain phase. The failure mode during testing included mid-substance rupture (n = 5 patients, n = 9 controls) or avulsion from the plastic

Discussion

Recently, several immunohistological (Ettema et al., 2004, Oh et al., 2005) and biochemical studies (Freeland et al., 2002, Hirata et al., 2004, Hirata et al., 2005, Tsujii et al., 2006) have been reported describing the SSCT in carpal tunnel syndrome patients. The SSCT of CTS patients is fibrotic, with increased amounts of type III collagen, tenascin-C, versican, VEGF, PGE-2, MMP-2, IL-6, and TGF-beta, and decreased elastin. Sud et al. (2002) have shown that the in vitro tenosynovial

Acknowledgement

This study was funded by grants from NIH (NIAMS AR49823) and Mayo Foundation.

References (21)

A.L. Lluch
Thickening of the synovium of the digital flexor tendons: Cause or consequence of the carpal tunnel syndrome?
Journal of Hand Surgery [Br].
(1992)
J. Oh et al.
Immunolocalization of collagen types in the subsynovial connective tissue within the carpal tunnel in humans
Journal of Orthopaedic Research
(2005)
N. Osamura et al.
Permeability of the subsynovial connective tissue in the human carpal tunnel: A cadaver study
Clinical Biomechanics
(2007)
S.G. Atcheson et al.
Concurrent medical disease in work-related carpal tunnel syndrome
Archives of Internal Medicine
(1998)
C.K. Becker et al.
In vitro mechanical properties of the accessory ligament of the deep digital flexor tendon in horses in relation to age
Equine Veterinary Journal
(1994)
P.W. Brand et al.
Clinical Mechanics of the Hand
(1993)
D.H. Chin et al.
Repetitive motion hand disorders
Journal of the California Dental Association
(2002)
A.M. Ettema et al.
A histological and immunohistochemical study of the subsynovial connective tissue in idiopathic carpal tunnel syndrome
Journal of Bone and Joint Surgery. American volume
(2004)
M.L. Finkel
The effects of repeated mechanical trauma in the meat industry
American Journal of Industrial Medicine
(1985)
A.E. Freeland et al.
Biochemical evaluation of serum and flexor tenosynovium in carpal tunnel syndrome
Microsurgery
(2002)

There are more references available in the full text version of this article.

Cited by (54)

Paraneurium – A veiled threat to peripheral nerve function
2024, Journal of Plastic, Reconstructive and Aesthetic Surgery
Ultrasound measurement of subsynovial connective tissue thickness in the carpal tunnel: An intrarater/interrater reliability and agreement study
2023, Hand Surgery and Rehabilitation
Non-inflammatory thickening of the subsynovial connective tissue (SSCT) in the carpal tunnel is commonly found in subjects with carpal tunnel syndrome (CTS), and quantification may shed light on CTS pathogenesis. To date, information on the reliability of ultrasound quantification of SSCT is scarce. Therefore, we investigated intrarater and interrater reliability/agreement for ultrasound quantification of SSCT thickness in subjects with and without CTS, and predictors for tissue thickness.
Two investigators quantified SSCT thickness and thickness ratio on ultrasound in 16 healthy subjects (age, 24–65 years; 16 left/14 right wrists) and 17 subjects with CTS (age, 37–83 years; 14 left/14 right wrists). Intra- and inter-rater reliability/agreement were assessed on intraclass correlation coefficients, standard error of measurement and minimal detectable change. A mixed-effects model was used to evaluate potential predictors for SSCT thickness.
Intra- and inter-rater reliability analysis showed good to excellent intraclass correlation coefficients in both groups, ranging from 0.772 to 0.965. The maximum percentage standard error of measurement was 8%. The maximum minimal detectable change was 14% within raters, and 20% between raters. Both intra- and inter-rater reliability values for thickness ratio were poor. Presence of CTS (ß = 0.180; p = 0.015) correlated positively with SSCT thickness.
Ultrasound is a reliable method for quantification of SSCT thickness, but not for thickness ratio. Presence of CTS correlates positively with SSCT thickness.
Carpal tunnel mechanics and its relevance to carpal tunnel syndrome
2023, Human Movement Science
Citation Excerpt :
In addition, a fibrotic synovium was found to hinder the smooth and separate motion of the tendon relative to the subsynovial connective tissue (Ettema, Zhao, Amadio, O'Byrne, & An, 2007), which may predispose the tissue to further injury. The hindrance to the tendon and median nerve motion caused by the fibrotic synovium has been speculated to be a consequence of the increase in synovium stiffness, which has been measured to be greater in patients with CTS (22.8 kPa) than in controls (2.7 kPa) (Osamura, Zhao, Zobitz, An, & Amadio, 2007). The increase in stiffness could affect the transfer of load between the synovium, the median nerve and the tendons, leading to motion hindrance.
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.
Carpal tunnel syndrome treatment and the subsequent alterations in tendon and connective tissue dynamics
2021, Clinical Biomechanics
Carpal tunnel syndrome patients demonstrate diminished motion of the median nerve and fibrotic changes in the subsynovial connective tissue within the carpal tunnel. Currently, there are few prognostic factors to help predict the outcome of commonly performed treatments including surgical carpal tunnel release and corticosteroid injections. This study aimed to non-invasively assess the changes in the dynamic response of the subsynovial tissue relative to tendon motion after the intervention and to correlate this with disease severity.
A total of 145 patients with carpal tunnel syndrome were recruited into this study. Clinical and demographic data, electrophysiological severity and dynamic ultrasound images were collected before and after treatment, either by injection or surgery. The relative motion of the subsynovial tissue with the underlying middle finger flexor digitorum superficialis tendon was measured using a speckle tracking algorithm and was expressed as a shear index (SI). Baseline and follow-up data, the association between change in SI and severity, and the role of treatment modality were analyzed and statistically compared.
Overall, there was a significant increase (more relative motion) after treatment in the mean shear index from 79.9% (±15.4% SD) to 82.9% (±14.8% SD) (p = 0.03). Secondary analyses showed that this change was mostly present in those with mild disease severity undergoing surgery (p = 0.01).
This study shows that the relative subsynovial tissue movement increases in patients after intervention. The present study lays a foundation for future studies to non-invasively assess the role of carpal tunnel dynamics in response to treatment.
Subsynovial connective tissue thickness in carpal tunnel syndrome: A systematic review
2020, Clinical Biomechanics
Citation Excerpt :
As the SSCT in CTS has a higher shear modulus, this decreased force may be attributed to the thickening of the SSCT in CTS. Osamura et al. (2007a, 2007b) also noted a low permeability of the SSCT, meaning most leaked interstitial fluid will be retained (Osamura et al., 2007b). They did not investigate the change in permeability in CTS, but as the SSCT becomes stiffer in CTS, the permeability will probably decrease further.
Non-inflammatory thickening of the subsynovial connective tissue is a common histological finding in carpal tunnel syndrome. This subsynovial connective tissue thickening may precede changes in electrodiagnostic testing. Therefore, measuring subsynovial connective tissue thickness may help in detecting early changes in carpal tunnel syndrome.
To provide an overview of subsynovial connective tissue thickness characteristics in subjects with and without carpal tunnel syndrome, a systematic review of articles, assessing human subsynovial connective tissue, was performed using MEDLINE, CENTRAL and EMBASE.
Seven studies were included for qualitative analysis. Measurements were done ex vivo (laser (n = 3), photographic (n = 1), micrometric (n = 1)) and in vivo (ultrasound (n = 3)). All four case-control studies showed a significant difference in subsynovial connective tissue thickness between subjects with and without carpal tunnel syndrome. One study showed good correlation between ultrasound and anatomical measurements. No correlation was found between subsynovial connective tissue thickness and symptom duration, electrodiagnostic changes, age and sex.
Subsynovial connective tissue thickness may be a valuable aid in diagnosing carpal tunnel syndrome. No factors influencing subsynovial connective tissue thickness are identified, although they are not well investigated.
The biomechanics of subsynovial connective tissue in health and its role in carpal tunnel syndrome
2018, Journal of Electromyography and Kinesiology
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.

View all citing articles on Scopus

View full text

Evaluation of the material properties of the subsynovial connective tissue in carpal tunnel syndrome

Abstract

Background

Methods

Findings

Interpretation

Introduction

Section snippets

Specimen preparation

Results

Discussion

Acknowledgement

Journal of Hand Surgery [Br].

Journal of Orthopaedic Research

Clinical Biomechanics

Concurrent medical disease in work-related carpal tunnel syndrome

Archives of Internal Medicine

In vitro mechanical properties of the accessory ligament of the deep digital flexor tendon in horses in relation to age

Equine Veterinary Journal

Clinical Mechanics of the Hand

Repetitive motion hand disorders

Journal of the California Dental Association

A histological and immunohistochemical study of the subsynovial connective tissue in idiopathic carpal tunnel syndrome

Journal of Bone and Joint Surgery. American volume

The effects of repeated mechanical trauma in the meat industry

American Journal of Industrial Medicine

Biochemical evaluation of serum and flexor tenosynovium in carpal tunnel syndrome

Microsurgery