A fluid-immersed multi-body contact finite element formulation for median nerve stress in the carpal tunnel

Carpal tunnel syndrome (CTS) is among the most important of the family of musculoskeletal disorders caused by chronic peripheral nerve compression. Despite the large body of research in many disciplinary areas aimed at reducing CTS incidence and/or severity, means for objective characterization of the biomechanical insult directly responsible for the disorder have received little attention. In this research, anatomical image-based human carpal tunnel finite element (FE) models were constructed to enable study of median nerve mechanical insult. The formulation included large-deformation multi-body contact between the nerve, the nine digital flexor tendons, and the carpal tunnel boundary. These contact engagements were addressed simultaneously with nerve and tendon fluid-structural interaction (FSI) with the synovial fluid within the carpal tunnel. The effects of pertinent physical parameters on median nerve stress were explored. The results suggest that median nerve stresses due to direct structural contact are typically far higher than those from fluid pressure.     

Involvement of tenascin-C and PG-M/versican in flexor tenosynovial pathology of idiopathic carpal tunnel syndrome

Increased intra-carpal-tunnel pressure due to swelling of the flexor tenosynovium is the most probable pathological mechanism of idiopathic carpal tunnel syndrome (CTS). To clarify the role of tenascin-C and PG-M/versican, which have often been found to be involved in tissue remodeling and vascular stenosis in the pathogenesis of CTS, we histologically and biochemically examined the production of extracellular matrix in the flexor tenosynovium from 40 idiopathic CTS patients. Tenascin-C was temporarily expressed in the vessel wall, synovial lining and fibrous tissue, with expression regulated differently in each tissue. Tenascin-C expression by vessels correlated with disease duration and appeared to be involved in vascular lesion pathology. Morphometric analysis showed that tenascin-C expression by small arteries is correlated with PG-M/versican expression in surrounding connective tissue. PG-M/versican was also present at the neointima of severely narrowed vessels. Although tenascin-C expression by synovial lining and connective tissue shows marked regional variation and seems inconsistent, in vitro examination suggested that tenascin-C production by these tissues is regulated in response to mechanical strain on the flexor tenosynovium.     

Flexor tendon and synovial gliding during simultaneous and single digit flexion in idiopathic carpal tunnel syndrome

The characteristic pathological finding in carpal tunnel syndrome (CTS) is non-inflammatory fibrosis of the subsynovial connective tissue (SSCT), which lies between the flexor tendons and the visceral synovium (VS). How this fibrosis might affect tendon function is unknown. To better understand the normal function of the SSCT, the relative motion of the middle finger flexor digitorum superficialis (FDS III) tendon and VS was observed during finger flexion in patients with CTS and cadavers with a history of CTS and compared to normal cadavers. A digital camcorder was used to monitor the gliding motion of the FDS III tendon and SSCT in eight patients with idiopathic CTS undergoing carpal tunnel release surgery (CTR), in eight cadavers with an antemortem history of CTS and compared these with eight cadaver controls. There were no significant differences noted in the total movement of the SSCT relative to the FDS III. However, the pattern of SSCT movement relative to the FDS III in the CTS patients and cadavers with an antemortem history of CTS differed from the controls in one of two patterns, reflecting either increased SSCT adherence to FDS III or increased SSCT dissociation from FDS III. In CTS, the gliding characteristics of the SSCT are qualitatively altered. These changes may be the result of increased fibrosis within the SSCT, which in some cases has ruptured, resulting in SSCT-tendon dissociation. Similar changes are also identified postmortem in the CTS patient.     

Agreement of self-reported hormone receptor status with cancer registry data in young breast cancer patients

BackgroundThough breast cancer subtype is a key determinant of treatment choice and prognosis, few studies have assessed breast cancer patients’ knowledge of estrogen and progesterone receptor (ER/PR) status.MethodsWomen diagnosed with invasive breast cancer at age 18–64 years in 2007 were recruited from the Pennsylvania Cancer Registry, and mailed a questionnaire that asked respondents to identify their ER/PR status. There were 2191 respondents included in the analysis. Agreement between self-report and cancer registry ER/PR status was assessed using kappa statistic. Logistic regression was used to assess the association of demographic, socioeconomic, and tumor factors with inaccurate self-report of ER/PR status.ResultsFifty-nine percent of respondents reported ER/PR positive status, 15% reported ER/PR negative status, 17% responded ‘don’t know’, and 9% did not respond. Overall, there was 69% agreement between self-report and cancer registry data, and fair agreement as measured by kappa (0.36). After excluding women who did not know or did not report their ER/PR status, there was 93% agreement, and substantial agreement as measured by kappa (0.76). Women who were older, non-white, less educated, lower income, and had ER/PR negative disease were significantly more likely to inaccurately report their ER/PR status.ConclusionsThough a significant proportion of women do not know their hormone receptor status, women who reported their ER/PR status were accurate. Our results suggest room for improvement in patient knowledge of tumor subtypes, but also that self-reported ER/PR status may be a useful surrogate when medical record or cancer registry data is unavailable.     

Apparent transverse compressive material properties of the digital flexor tendons and the median nerve in the carpal tunnel

Carpal tunnel syndrome is a frequently encountered peripheral nerve disorder caused by mechanical insult to the median nerve, which may in part be a result of impingement by the adjacent digital flexor tendons. Realistic finite element (FE) analysis to determine contact stresses between the flexor tendons and median nerve depends upon the use of physiologically accurate material properties. To assess the transverse compressive properties of the digital flexor tendons and median nerve, these tissues from ten cadaveric forearm specimens were compressed transversely while under axial load. The experimental compression data were used in conjunction with an FE-based optimization routine to determine apparent hyperelastic coefficients (μ and α) for a first-order Ogden material property definition. The mean coefficient pairs were μ=35.3 kPa, α=8.5 for the superficial tendons, μ=39.4 kPa, α=9.2 for the deep tendons, μ=24.9 kPa, α=10.9 for the flexor pollicis longus (FPL) tendon, and μ=12.9 kPa, α=6.5 for the median nerve. These mean Ogden coefficients indicate that the FPL tendon was more compliant at low strains than either the deep or superficial flexor tendons, and that there was no significant difference between superficial and deep flexor tendon compressive behavior. The median nerve was significantly more compliant than any of the flexor tendons. The material properties determined in this study can be used to better understand the functional mechanics of the carpal tunnel soft tissues and possible mechanisms of median nerve compressive insult, which may lead to the onset of carpal tunnel syndrome.     

Expression of sex steroid receptors and IGF-1 mRNA in breast tissue--effects of hormonal treatment

The mechanisms behind increased breast tissue proliferation and a possibly increased breast cancer risk in women using hormonal contraception (HC) and hormonal replacement therapy (HRT) are incompletely understood. We analyzed breast tissue from 20 premenopausal and seven postmenopausal women undergoing reduction mammoplasties for estrogen receptor (ER) and progesterone receptor (PR) content as well as mRNA levels for ER, PR and insulin-like growth factor-1 (IGF-1). The receptor values were correlated to IGF-1 mRNA concentrations and levels of steroid and peptide hormones and SHBG. In women using HC, we found significantly lower ER values (p=0.02) but non-significantly lower ER mRNA levels compared to those in naturally cycling women. PR and PR mRNA were no different. Women on HC displayed a higher breast tissue proliferation (p=0.05) expressed as Ki-67, MIB-1 positivity, which was correlated with IGF-1 mRNA (r_s=0.82, p=0.04). Since the concentration of sex steroid receptors in breast tissue is comparatively low and steroid receptors are down-regulated during hormonal treatment, mechanisms other than direct sex steroid receptor action are likely to be present. Our results suggest a role for IGF-1 in the proliferative response of breast tissue during exogenous hormonal treatment.     

Matrix metalloproteinase (MMP-2 and MMP-9) and steroid receptor expressions in feline mammary tumors

We evaluated the presence of estrogen (ER) and progesterone (PR) receptors, and matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) enzymes in 18 feline mammary tubulopapillary carcinomas. Immunohistochemistry was performed to localize ER, PR, MMP-2 and MMP-9 in situ. Western blotting and zymographic analyses also were performed to investigate the presence and activities of MMP-2 and MMP-9 enzymes in fresh tissue homogenates. ER immune expression was detected in five samples (27.7%) and PR was positive in sixteen (88.8%) samples. Diffuse cytoplasmic staining of MMP-2 and MMP-9 in neoplastic mammary epithelial cells, stromal fibroblasts and inflammatory cell was evident. MMP-2 and MMP-9 staining was observed also in metastasizing neoplastic cells within lymphatic vessels. MMP-2 and MMP-9 enzymes and their activities in fresh tumor homogenates were demonstrated by zymography. Comparison of MMP-9 gelatinolytic bands from tumor samples and controls revealed a statistically significant difference. We demonstrated elevated MMP-9 and MMP-2 levels in tumor samples by Western blotting; analysis of protein bands revealed 1.9-to-3 fold increase in MMP-9 in tumor samples and the difference was statistically significant. Our results suggest that the expression of MMP-9 can be an important indicator for tumor progression and the possible metastatic nature of feline tubulopapillary carcinomas.     

雌、孕激素受体及C-erbB2在子宫内膜癌中的表达和意义

目的探讨雌、孕激素受体（Estrogen Receptor ER、Progesterone Receptor PR）及C-erbB2在子宫内膜癌中的表达与临床病理参数的关系。方法采用免疫组织化学技术检测56例子宫内膜癌患者子宫内膜中ER、PR及C-erbB2的表达,并对56例患者的临床病理资料进行回顾性分析。结果子宫内膜癌患者内膜ER、PR及C-erbB2阳性率分别为41.07%、57.14%、53.57%。子宫内膜癌中ER表达与肿瘤分化程度、年龄、有无淋巴结转移呈负相关;PR表达与肿瘤组织学类型、分化程度、年龄、浸润肌层深度及有无淋巴结转移均呈负相关;而C-erbB2的表达与内膜癌分化程度、有无淋巴结转移呈正相关。结论激素依赖型子宫内膜癌ER、PR及C-erbB2表达水平均反映了子宫内膜癌的生物学行为,三者的测定对估计预后和指导术后辅助治疗具有重要意义。     

ER/PR阳性和阴性乳腺癌的定量蛋白质组学和生物信息学比较研究

目的:建立雌/孕激素受体(ER/PR)阴性和阳性乳腺癌的蛋白质表达谱,寻找ER/PR阴性和阳性乳腺癌中差异表达蛋白,为乳腺癌患者提供新的预后预测指标和治疗新靶点。方法:应用蛋白质组学i TRAQ技术建立ER/PR阳性和阴性乳腺癌的蛋白质差异表达谱,鉴定两组乳腺癌的差异表达蛋白,对部分差异表达蛋白进行生物信息学分析,包括蛋白功能注释和分类GO分析和KEGG通路分析。结果:应用i TRAQ蛋白质组学技术对乳腺癌组织进行了蛋白组学分析,鉴定出ER/PR阳性和阴性组间有差异表达的蛋白4999种,以ER/PR阳性:ER/PR阴性≥3为上调标准,确定ER/PR阳性组上调蛋白101种。以ER/PR阳性:ER/PR阴性≤0.5为下调标准,ER/PR阳性组下调蛋白122种。GO分析结果显示ER/PR受体阴性和阳性乳腺癌的差异表达蛋白的分子功能、生物过程、细胞定位较为复杂,并且在上调蛋白和下调蛋白上存在分布差异。KEGG通路分析发现部分差异表达蛋白涉及201条信号通路。结论:ER/PR阳性和阴性乳腺癌间存在差异表达蛋白,这些蛋白涉及复杂的分子功能、生物过程和信号通路。     

A fine structural study of the development of the chick flexor digital tendon: a model for synovial sheathed tendon healing.

The development of the synovial sheathed flexor digital tendon in the chick was studied by light and electron microscopy in 12-day embryos to 22-day post-hatched chickens. Areas of specialized connective tissue differentiation were identified in this complex structure consisting of a lubricated synovial sheath, elastic vincula and fibrocartilaginous adaptations on the surface of the tendon. The presence of some of these specialized adaptations may be related to the specific types of mechanical forces and stresses applied to the developing connective tissue system. This model system appears to be appropriate for the experimental study of tendon injuries related to the human hand.     

Cell-based immunotherapy with suppressor CD8+ T cells in rheumatoid arthritis

The chronic persistence of rheumatoid synovitis, an inflammation driven by activated T cells, macrophages, and fibroblasts causing irreversible joint damage, suggests a failure in physiologic mechanisms that down-regulate and terminate chronic immune responses. In vitro CD8(+)CD28(-)CD56(+) T cells tolerize APCs, prevent the priming of naive CD4(+) T cells, and suppress memory CD4(+) T cell responses. Therefore, we generated CD8(+)CD28(-)CD56(+) T cell clones from synovial tissues, expanded them in vitro, and adoptively transferred them into NOD-SCID mice engrafted with synovial tissues from patients with rheumatoid arthritis. Adoptively transferred CD8(+)CD28(-)CD56(+) T cells displayed strong anti-inflammatory activity. They inhibited production of IFN-gamma, TNF-alpha, and chemokines in autologous and HLA class I-matched heterologous synovitis. Down-regulation of costimulatory ligands CD80 and CD86 on synovial fibroblasts was identified as one mechanism of immunosuppression. We propose that rheumatoid synovitis can be suppressed by cell-based immunotherapy with immunoregulatory CD8(+) T cells.     

Immunocytochemical analysis of estrogen and progestin receptors in uteri of steroid-treated and pregnant cats.

The purpose of this study was to determine the distribution of estrogen receptors (ER) and progestin receptors (PR) in specific uterine cell populations during various steroid hormone treatment regimens, and to determine if ER and PR distribution in the uterus is altered during implantation and the establishment of pregnancy in the cat. The tissues were processed for indirect immunocytochemical localization of receptors using specific monoclonal antibodies against ER and PR. ER were present in the nuclei of all epithelial cells and stromal fibroblasts in endometrium obtained from ovariectomized animals, whereas PR were only detectable in the nuclei of stromal fibroblasts. There was an apparent increase in the staining intensity and number of nuclei that stained positively for both ER and PR in all cell populations after 14 days of estradiol treatment. The administration of progesterone for 14 and 21 days, in the presence or absence of continuous estradiol, reduced the apparent intensity of staining and the number of nuclei staining positively for both ER and PR. ER were undetectable in the luminal epithelium, but remained in the glandular epithelial cells and stromal fibroblasts, whereas PR were only detectable in stromal fibroblasts. ER and PR localization in the endometrium obtained from estrus animals was similar to that observed in the estradiol-treated animals. A general decrease in intensity of staining for both ER and PR was evident by Day 5 postcoitus in pregnant animals. This decrease in intensity of staining continued until Day 12 postcoitus, when the distributions of ER and PR were similar to those observed in the ovariectomized estradiol-primed, progesterone-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of oestrogen,progesterone receptor and human epidermal growth factor receptor 2 expression in mediastinal metastases of breast cancer obtained by endobronchial ultrasound‐guided transbronchial needle aspiration

Background

In breast cancer patients, the expression statuses of oestrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) are crucial in the choice of treatment. Receptor expression in metastatic lesions can differ from the primary tumour. The aim of our study was to analyse the utility of endobronchial ultrasound‐guided transbronchial needle aspiration (EBUS‐TBNA) to obtain samples allowing the identification of ER, PR and HER2 expression in patients with mediastinal metastases of breast cancer.

Patients and methods

The clinical files of all patients with a final diagnosis of breast cancer mediastinal metastases diagnosed by EBUS‐TBNA in our institution were retrospectively analysed. The ability of EBUS‐TBNA to obtain samples that allowed hormone receptor and HER2 expression analysis was calculated.

Results

Twenty‐four patients were included. ER, PR and HER2 assessments could be performed in 22, 20 and 22 patients, respectively. In 20 of the 24 patients it was possible to investigate all three types of receptor expression. In the remaining four cases, where ER, PR or HER2 expression tests could not be performed, it was due to a lack of tissue. In cases with adequate results for EBUS‐TBNA and the primary tumour agreement was greater for ER (16/19) and HER2 (12/14) than PR (8/17). Based on receptor status, there was a change in the choice of treatment for five patients.

Conclusion

In patients with breast cancer mediastinal metastases, ER, PR and HER2 expression can be assessed in samples obtained by EBUS‐TBNA whenever a sufficient tissue sample is collected.     

Attachment and extracellular matrix differences between tendon and synovial fibroblastic cells

Summary Fibroblasts of the synovium of sheathed tendons were isolated, and their biochemical properties were compared with those of the fibroblasts of the remaining tendon. The synovial cells had a lower attachment efficiency than did the tendon cells. On the day of cell isolation the synovial cells synthesized collagen as 10% of their total protein, whereas the tendon cells synthesized 30% collagen. After growth in fetal bovine serum (FBS), the percentage of collagen synthesized by both populations decreased; however, the synovial cells still made less collagen than did the tendon cells (5 versus 11%). On the basis of cyanogen bromide peptide analysis, the synovial cells were found to synthesize Types I and III collagen in primary culture, whereas the tendon cells synthesized only Type I. The synovial cells aslo synthesized two to three times less sulfated glycosaminoglycans in culture than did the tendon cells. Thus, the two cell, populations differed in attachment efficiency and in their biosynthesis of collagen and sulfated glycosaminoglycans. These differences reflect extracellular matrix differences that have been observed in the tendon in vivo. In addition, the results augment existing data showing that not all fibroblasts have identical phenotypes. This investigation was supported by National Institutes of Health Grant AM 25749.     

TNFα modulates protein degradation pathways in rheumatoid arthritis synovial fibroblasts

Introduction

Rheumatoid arthritis (RA) is a chronic inflammatory and destructive disease of the joint. The synovial lining consists of two main types of cells: synovial fibroblasts and macrophages. The macrophage-derived cytokine TNFα stimulates RA synovial fibroblasts to proliferate and produce growth factors, chemokines, proteinases and adhesion molecules, making them key players in the RA disease process. If proteins are not correctly folded, cellular stress occurs that can be relieved in part by increased degradation of the aberrant proteins by the proteasome or autophagy. We hypothesized that the activity of the protein degradation pathways would be increased in response to TNFα stimulation in RA synovial fibroblasts compared with control fibroblasts.

Methods

Endoplasmic reticulum (ER) stress markers were examined in synovial fibroblasts by immunoblotting and PCR. Use of the autophagy and proteasome protein degradation pathways in response to TNFα stimulation was determined using a combination of experiments involving chemical inhibition of the autophagy or proteasome pathways followed by immunoblotting for the autophagy marker LC3, measurement of proteasome activity and long-lived protein degradation, and determination of cellular viability.

Results

RA synovial fibroblasts are under acute ER stress, and the stress is increased in the presence of TNFα. Autophagy is the main pathway used to relieve the ER stress in unstimulated fibroblasts, and both autophagy and the proteasome are more active in RA synovial fibroblasts compared with control fibroblasts. In response to TNFα, the autophagy pathway but not the proteasome is consistently stimulated, yet there is an increased dependence on the proteasome for cell viability. If autophagy is blocked in the presence of TNFα, an increase in proteasome activity occurs in RA synovial fibroblasts but not in control cells.

Conclusions

TNFα stimulation of synovial fibroblasts results in increased expression of ER stress markers. Survival of synovial fibroblasts is dependent on continuous removal of proteins by both the lysosome/autophagy and ubiquitin/proteasome protein degradation pathways. Both pathways are more active in RA synovial fibroblasts compared with control fibroblasts. These results may provide a better understanding of the mechanism of TNFα on prolonging the survival of synovial fibroblasts in RA tissue.     

Tenocyte response to cyclical strain and transforming growth factor beta is dependent upon age and site of origin

The effect of strain and transforming growth factor beta on equine tendon fibroblasts (tenocytes) was assessed in vitro. Tenocytes were isolated from flexor and extensor tendons of horses from foetal to 10 years of age. These cells were cultured until confluent on collagen-coated silicone dishes. Cyclic biaxial strain of 9+/-1% was applied at 0.5 Hz for 24 hours with or without added TGFbeta1 or 3 (10 ng/ml). Proliferation and synthetic responses were dependent on the tendon of origin. Neither strain nor TGFbeta caused flexor tenocytes to proliferate significantly, while strain alone did proliferate extensor tenocytes. TGFbeta, with or without strain, increased the incorporation of [3H]-proline and the production of types I and III collagen and COMP in both cell types, although the effect on COMP production was more marked in flexor tenocytes, perhaps reflecting the higher levels found in this tendon in vivo. Immature flexor tenocytes synthesised more collagen and COMP than those from mature animals, while age had little effect in extensor tenocytes. Our results suggest that tenocytes become differentiated at an early age and present tendon-specific responses.     

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.     

Volar/dorsal compressive mechanical behavior of the transverse carpal ligament

Mechanical insult to the median nerve caused by contact with the digital flexor tendons and/or carpal tunnel boundaries may contribute to the development of carpal tunnel syndrome. Since the transverse carpal ligament (TCL) comprises the volar boundary of the carpal tunnel, its mechanics in part govern the potential insult to the median nerve. Using unconfined compression testing in combination with a finite element-based optimization process, nominal stiffness measurements and first-order Ogden hyperelastic material coefficients (μ and α ) were determined to describe the volar/dorsal compressive behavior of the TCL. Five different locations on the TCL were tested, three of which were deep to the origins of the thenar and hypothenar muscles. The average (± standard deviation) low-strain and high-strain TCL stiffness values in compression sites outside the muscle attachment region were 3.6 N/mm (±2.7) and 28.0 N/mm (±20.2), respectively. The average stiffness values at compression sites with muscle attachments were notably lower, with low-strain and high-strain stiffness values of 1.2 N/mm (±0.5) and 9.7 N/mm (±4.8), respectively. The average Ogden coefficients for the muscle attachment region were 51.6 kPa (±16.5) for μ and 16.5 (±2.0) for α, while coefficients for the non-muscle attachment region were 117.8 kPa (±86.8) for μ and 17.2 (±1.6) for α. These TCL compressive mechanical properties can help inprove computational models, which can be used to provide insight into the mechanisms of median nerve injury leading to the onset of carpal tunnel syndrome symptoms.     

Attachment and extracellular matrix differences between tendon and synovial fibroblastic cells

Fibroblasts of the synovium of sheathed tendons were isolated, and their biochemical properties were compared with those of the fibroblasts of the remaining tendon. The synovial cells had a lower attachment efficiency than did the tendon cells. On the day of cell isolation the synovial cells synthesized collagen as 10% of their total protein, whereas the tendon cells synthesized 30% collagen. After growth in fetal bovine serum (FBS), the percentage of collagen synthesized by both populations decreased; however, the synovial cells still made less collagen than did the tendon cells (5 versus 11%). On the basis of cyanogen bromide peptide analysis, the synovial cells were found to synthesize Types I and III collagen in primary culture, whereas the tendon cells synthesized only Type I. The synovial cells also synthesized two to three times less sulfated glycosaminoglycans in culture than did the tendon cells. Thus, the two cell populations differed in attachment efficiency and in their biosynthesis of collagen and sulfated glycosaminoglycans. These differences reflect extracellular matrix differences that have been observed in the tendon in vivo. In addition, the results augment existing data showing that not all fibroblasts have identical phenotypes.