Scholarly article on topic 'Evaluation of plasma basic fibroblast growth factor (bFGF) in primary knee osteoarthritis patients'

Evaluation of plasma basic fibroblast growth factor (bFGF) in primary knee osteoarthritis patients Academic research paper on "Clinical medicine"

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{"Basic fibroblast growth factor" / Osteoarthritis / Knee / Ultrasonography / Kellgren–Lawrence / WOMAC}

Abstract of research paper on Clinical medicine, author of scientific article — Athar E. El-Fetiany, Elham M. Kassem, Amal M. El-Barbary, Rasha A. Gaber, Hossam A. Zyton

Abstract Aim of the work The aim of this study was to investigate plasma basic fibroblast growth factor (bFGF) levels in patients with primary knee osteoarthritis (KOA) and to correlate it with physical performance, functional status and radiological severity. Patients and methods Sixty patients with primary KOA and 30 healthy individuals were recruited into this study. Measures of physical performance were assessed using Chair Stand Test, Stair Climb Test and Six-Minute Walk Test. Functional assessment was carried out using the Western Ontario and McMaster Universities (WOMAC) index. KOA severity was determined using X-ray evaluated according to the Kellgren–Lawrence (KL) grading and all underwent sonographic examination. bFGF concentrations in plasma were determined. Results The mean age of the KOA patients was 53.67±7.99years, female:male 4:1 and disease duration of 4.17±1.74years. KOA was bilateral in 71.7% and knee effusion was present in 20.39%. The WOMAC index was 53.78±13.7. Plasma bFGF levels in KOA patients (43.82±20.18pg/ml) were significantly higher than in controls (12.40±9.12pg/ml) (p < 0.001). bFGF significantly correlated the KL radiographic grading (r =0.31, p <0.027) and negatively with cartilage thickness of medial and lateral femoral condyles (r =−0.38, p < 0.006). Conclusions Plasma bFGF levels were significantly increased in OA patients, and these elevated levels were significantly correlated with the degree of radiographic severity evaluated by KL grading scale and cartilage degeneration evaluated by ultrasound. These findings indicate that bFGF levels may be a monitor of disease severity and could play an essential part in the pathophysiology of degenerative process in OA.

Academic research paper on topic "Evaluation of plasma basic fibroblast growth factor (bFGF) in primary knee osteoarthritis patients"

The Egyptian Rheumatologist (2017) 39, 33-37

Egyptian Society of Rheumatic Diseases The Egyptian Rheumatologist

www.rheumatology.eg.net www.elsevier.com/locate/ejr

ORIGINAL ARTICLE

Evaluation of plasma basic fibroblast growth factor c^Ma* (bFGF) in primary knee osteoarthritis patients

Athar E. El-Fetiany a, Elham M. Kassema, Amal M. El-Barbary a'*, Rasha A. Gaberb, Hossam A. Zytonc

a Physical Medicine, Rheumatology and Rehabilitation Department, Faculty of Medicine, Tanta University, Egypt b Biochemistry Department, Faculty of Medicine, Tanta University, Egypt c Diagnostic Radiology Department, Faculty of Medicine, Tanta University, Egypt

Received 8 March 2016; accepted 18 March 2016 Available online 26 April 2016

KEYWORDS

Basic fibroblast growth factor;

Osteoarthritis; Knee;

Ultrasonography;

Kellgren-Lawrence;

Abstract Aim of the work: The aim of this study was to investigate plasma basic fibroblast growth factor (bFGF) levels in patients with primary knee osteoarthritis (KOA) and to correlate it with physical performance, functional status and radiological severity.

Patients and methods: Sixty patients with primary KOA and 30 healthy individuals were recruited into this study. Measures of physical performance were assessed using Chair Stand Test, Stair Climb Test and Six-Minute Walk Test. Functional assessment was carried out using the Western Ontario and McMaster Universities (WOMAC) index. KOA severity was determined using X-ray evaluated according to the Kellgren-Lawrence (KL) grading and all underwent sonographic examination. bFGF concentrations in plasma were determined.

Results: The mean age of the KOA patients was 53.67 ± 7.99 years, female:male 4:1 and disease duration of 4.17 ± 1.74 years. KOA was bilateral in 71.7% and knee effusion was present in 20.39%. The WOMAC index was 53.78 ± 13.7. Plasma bFGF levels in KOA patients (43.82 ± 20.18 pg/ml) were significantly higher than in controls (12.40 ± 9.12pg/ml) (p < 0.001). bFGF significantly correlated the KL radiographic grading (r = 0.31, p < 0.027) and negatively with cartilage thickness of medial and lateral femoral condyles (r = —0.38, p < 0.006).

Conclusions: Plasma bFGF levels were significantly increased in OA patients, and these elevated levels were significantly correlated with the degree of radiographic severity evaluated by KL grading scale and cartilage degeneration evaluated by ultrasound. These findings indicate that bFGF levels may be a monitor of disease severity and could play an essential part in the pathophysiology of degenerative process in OA.

© 2016 Egyptian Society of Rheumatic Diseases. Publishing services provided by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

* Corresponding author. Tel.: +20 1001264626.

E-mail address: ml_barbary@yahoo.com (A.M. El-Barbary).

Peer review under responsibility of Egyptian Society of Rheumatic Diseases.

http://dx.doi.org/10.1016/j.ejr.2016.03.006

1110-1164 © 2016 Egyptian Society of Rheumatic Diseases. Publishing services provided by Elsevier B.V.

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

A.E. El-Fetiany et al.

1. Introduction

Osteoarthritis (OA) is a common chronic disease that affects all joint tissues, causing progressive irreversible damage. Pathological changes in OA not only include joint cartilage degeneration but also subchondral bone thickening, osteo-phyte formation and synovial inflammation, all of which are associated with capsule laxity and decreased muscle strength [1].

Many factors have been implicated in the pathogenesis of Egyptian patients with Knee OA (KOA) as interleukin-1b, tumor necrosis factor-a, leptin, matrix metalloproteinase, nitric oxide [2] hyaluronic acid, cartilage oligomeric cartilage protein [3,4], and oxidative stress [5]. Vascular endothelial growth factor significantly correlated with clinical manifestations, functional impact, as well as radiological changes of KOA [6]. Osteopontin was found to serve as another biomar-ker of disease severity in KOA and could be predictive to the progression of the disease [7] and with radiological grading [8]. Osteoarthritis patients are frequently associated with subclini-cal atherosclerosis [9] and obese KOA patients were found to represent a high risk group for renal dysfunction [10].

Basic fibroblast growth factor (bFGF), also known as FGF-2, is a polypeptide with pleiotropic effects when applied to diverse tissues, including mitogenesis, cell migration and cell differentiation [11]. FGF-2 plays an important role in tissue repair and angiogenesis. It is responsible for wound healing and modulates many cellular functions, including proliferation, differentiation and neovascularization [12,13]. However, in systemic sclerosis, another rheumatic disease, the serum level of FGF-23 showed no significant difference between patients and normal subjects with no role in the clinical manifestations of the disease [14].

Ultrasound (US) imaging is a non-invasive technique that can be used to image soft tissues. With the advancement of technology, the newer US machine models can be equipped with high frequency probes that are very useful for muscu-loskeletal imaging to study the peri-articular and intra-articular structures [15,16].

The aim of this study was to investigate plasma basic fibroblast growth factor (bFGF) levels in patients with primary knee osteoarthritis and to evaluate the correlation between it and clinical and radiographic parameters including conventional X-ray and ultrasonography.

2. Patients and methods

Sixty patients with primary KOA selected from the outpatient clinic of Physical Medicine, Rheumatology and Rehabilitation Department, Tanta University Hospitals. Patients fulfilled the criteria of the American College of Rheumatology (ACR) [17] for diagnosis of osteoarthritis knee. Thirty healthy volunteers matched in age, sex and body mass index (BMI) were selected as controls. The study was approved by the local research ethics committee of Faculty of Medicine, Tanta University and the patients gave an informed consent before being enrolled. Patients with other forms of arthritis, chronic inflammatory diseases, diabetes, cancer and patients with past history of knee trauma or corticosteroid injection within the past three months were excluded from the study.

The following were clinically assessed for the patients: BMI, pain using Visual Analogue Scale (VAS) [18], and duration of morning stiffness and knee effusion. Measures of physical performance were assessed using Chair Stand Test (CST), Stair Climb Test (SCT) and Six-Minute Walk Test (6MWT) [19]. Functional assessment was carried out using the WOMAC (Western Ontario and McMaster Universities) index [20].

Venous blood samples were collected from all participants with sterile disposable syringes in sterile EDTA vacuum tube, and samples were centrifuged at 1000g for 15 min for plasma separation by means of dry clean Pasteur pipette. The plasma samples were frozen at —70 C until used for assay of plasma basic fibroblast growth factor (bFGF) level by ELISA technique [21]. (Quantikine ELISA Human FGF basic Immunoassay kit Catalog Number DFB50 supplied by Clini Lab Scientific Service Company).

Osteoarthritis severity was determined using weight-bearing anteroposterior and lateral radiographs of the affected knee and was evaluated according to the Kellgren Lawrence (KL) grading system [22]. All the patients underwent sonographic examination at ultrasound unit of Physical Medicine, Rheumatology and Rehabilitation Department of Tanta University Educational Hospital using SAMSUNG MEDI-SON (UGEO H60) by an expert radiologist blinded to the clinical and radiological data, using linear array transducers (with frequencies ranging between 7.5 and 12 MHz). Power Colour Doppler was used to check for blood flow in the synovium. The following were considered during the ultrasound assessment: supra-patella recess effusion (mm), synovitis, synovial thickness (mm), cartilage thickness at medial and lateral femoral condyles (maximal and minimal thickness in mm), medical and lateral menisci (positive or negative degeneration) and presence of osteophytes [23].

2.1. Statistical analysis

Statistical analysis was carried out using the SPSS software, version 16.0. Demographic data between patients and controls were compared by chi-square tests and unpaired Student's t tests where appropriate. Pearson's correlation coefficient (r) was employed to determine correlation between concentrations of bFGF in plasma and clinical and radiographic parameters. Data are expressed as mean ± standard deviation (SD). p values <0.05 were considered statistically significant for differences and correlation.

3. Results

Sixty knee OA patients and thirty healthy controls were enrolled in this study. There was no significant difference in demographic data between OA patients and controls. However, there was a significant difference between OA patients and controls regarding physical performance assessments and plasma bFGF levels as demonstrated in Table 1.

Regarding KL criteria; 35.9% and 32% of KOA patients revealed KL grades 1 and 3 respectively, while 25.3% and 6.8% revealed grades 2 and 4 respectively. Ultrasound findings in OA patients were demonstrated in Table 2. The decreased cartilage thickness of medial and lateral femoral condyle in knee osteoarthritis patient is shown in Fig. 1.

Table 1 Demographic, clinical and laboratory data in knee osteoarthritis patients and controls.

Mean ± SDor n (%) KOA patients (n = 60) Control (n = 30) p-value

Age (years) 53.67 ± 7.99 51.53 0.11

± 4.46

Sex (female/male) 48/12 20/10 0.17

BMI 33.94 ± 7.07 32.67 0.22

± 2.48

Disease duration 4.17 ± 1.74 -

(years)

Bilateral 43 (71.7)

Unilateral 17 (28.3)

VAS 6.53 ± 1.56 -

Morning stiffness 7.42 ± 5.78 -

(min.)

Knee effusion 21(20.39) -

WOMAC index 53.78 ± 13.7 -

CST (times/30 s) 5.65 ± 1.72 11.07 <0.001*

± 0.78

SCT (/s) 12.98 ± 6.37 6.47 ± 1.01 <0.001*

6MWT (/m) 93.5 ± 22.16 187.33 <0.001*

± 37.5

Plasma bFGF level 43.82 ± 20.18 12.40 <0.001*

(Pg/ml) ± 9.12

KOA: knee osteoarthritis; BMI: body mass index; VAS: Visual Analogue Scale; WOMAC: Western Ontario and McMaster Universities; CST: Chair Stand Test; 6MWT: Six-Minute Walk Test; SCT: Stair Climb Test; bFGF: basic fibroblast growth factor. Significantly different at p < 0.05.

Table 2 Ultrasound findings in the knees of knee osteoarthri-tis patients.

Ultrasound findings n (%) - mean ± SD KOA patients (n = 60) Findings in 103 knees

Effusion (ml) 25 (24.3)

0.61 ± 0.85

Synovial thickening (mm) 24 (23.3)

3.92 ± 2.48

Synovial activity 0

Osteophytes 66 (64.08)

Meniscal degeneration 4 (3.88)

Cartilage thickness (mm)

Medial femoral condyle

Minimal 1.16 ± 0.59

Maximum 1.72 ± 0.77

Lateral femoral condyle

Minimal 1.41 ± 0.58

Maximum 2.15 ± 0.52

KOA: knee osteoarthritis.

Plasma bFGF level significantly correlated with the KL radiographic grading of KOA (r = 0.31, p = 0.027) (Fig. 2). In additions, plasma bFGF levels negatively correlated with cartilage thickness of medial and lateral femoral condyles measured by ultrasonography. (r = —0.38, p = 0.006) (Table 3). However, there was no significant correlation between plasma bFGF levels and other sonographic findings. Moreover, no

significant correlation was found between plasma bFGF levels and clinical data and physical performance.

4. Discussion

Knee osteoarthritis was more frequent in females in the present study. In another study on Egyptian patients with primary KOA, females were significantly more involved [2].

Fibroblast growth factors (FGFs) represent a large cytokine family of structurally related multifunctional polypeptide mitogens of widespread tissue distribution.[24] Basic FGF is one of the most well-characterized members of the family and one of the most powerful angiogenic polypeptides [25].

Our study demonstrated that the plasma basic fibroblast growth factor (bFGF) levels in OA patients were significantly higher than the control group. These results were in agreement with, Honsawek et al. [26] who measured plasma and synovial bFGF levels in thirty-five patients with primary KOA and found that their levels were significantly elevated compared with that of healthy controls. Jingushi et al. [27] showed that when radiolabeled FGF-2 was injected into knee joints of C57Bl/10 mice, a transient binding was observed in the superficial and intermediate zones of the articular cartilage as well as in the synovium and perichondrium. FGF-2 injection (5 ig) caused synovial hyperplasia adjacent to the articular cartilage on day 7, cartilage formation adjacent to the articular cartilage on day 14, and osteophyte on day 21. These changes were dose-dependent. No destructive changes in the joints were observed. Im et al. [28] documented that FGF-2 induces matrix metalloproteinase-13 (MMP-13), the most potent collagen-type II degrading enzyme in human articular cartilage, resulting in collagen breakdown. They used chondrocytes isolated from human adult articular cartilage 24 h after death. Treatment of cells in monolayer with bFGF significantly stimulated MMP-13 production, and the induction occurred in both mRNA and protein levels in a dose-dependent manner. bFGF stimulates MMP-13 via molecular cross-talk between mitogen-activated protein kinases and protein kinase C delta pathways in articular chondrocytes. Li et al. [29] provide a biochemical explanation for the conflicting effects induced by FGF-2 on articular cartilage human and mice, using human articular cartilage (ex vivo) and a medial meniscal destabiliza-tion animal model (in vivo). The differences in the expression patterns of FGFR receptors (FGFRs) explain these conflicting effects. In normal human cartilage, FGFR1 and FGFR3 are predominantly expressed, with negligible levels of FGFR2 and FGFR4. In OA cartilage, FGFR3 expression level is markedly reduced, and this is closely linked with enhanced catabolic signaling in the presence of FGF-2. FGF-2 highly up regulates FGFR3 in murine chondrocytes, whereas FGF-2 significantly down regulates FGFR3 in human articular chondrocytes. Thus, in mice, FGFR3 may also play an anabolic role in articular cartilage after injection with FGF-2.

The WOMAC index was used for functional assessment of the present KOA patients and a non-significant correlation was found with the plasma bFGF levels. The severity of KOA in our patients was detected by KL grading and ultrasonogra-phy of knee joint to assess cartilage thickness, effusion, synovial thickening and meniscal degeneration. KL grades 1, 2, 3 and 4 were found in 35.9%, 25.3%, 32% and 6.8%. The US revealed

Figure 2 Correlation between plasma bFGF levels and KL grades in KOA patients (n = 60; 103 knees).

Table 3 Correlation between plasma bFGF levels and ultrasound (US) findings in KOA.

KOA patients (n = 60) OA knee (n = 103)

US readings r (p) Plasma bFGF (pg/ml)

Effusion (ml) 0.12 (0.39)

Synovial thickening (mm) 0.15 (0.29)

Cartilage thickness (mm)

Medial femoral condyle

Minimal -0.38 (0.006)*

Maximum -0.38 (0.006)*

Lateral femoral condyle

Minimal -0.38 (0.006)*

Maximum -0.3 (0.03)*

KOA: knee osteoarthritis; US: ultrasound; bFGF: basic fibroblast growth factor. Significant at p < 0.05.

Saarakkala, et al. [30] investigated the diagnostic performance of non-invasive knee US to detect degenerative changes of articular cartilage compared to arthroscopic grading as the gold standard. They concluded that the sum of cartilage grades significantly correlated between both modalities and that knee US is a promising technique for screening but a negative finding does not rule out degenerative changes of articular cartilage.

Our study found that plasma bFGF levels significantly correlated with KL grades of OA knees and negatively with cartilage thickness of both medial and lateral femoral condyles in OA knees detected by US. This was in agreement with Hon-sawek et al. [26] who found that plasma and synovial bFGF levels were significantly increased in OA patients and correlated with radiographic severity using KL grading. They observed that plasma bFGF levels were more pronounced in end-stage compared with early OA patients. The correlation of plasma bFGF levels with OA severity was explained by Li et al. [29] who documented that bFGF plays a catabolic and anti-anabolic role in cartilage homeostasis, driving homeosta-sis toward degeneration.

In conclusion, the study revealed that plasma bFGF in patients with primary knee OA was significantly elevated compared with that of healthy controls. Plasma bFGF levels significantly correlated with the degree of radiographic severity evaluated by KL grading scale and negatively with cartilage thickness of both medial and lateral femoral condyles. These findings suggest that bFGF could be a useful biochemical parameter to reflect disease severity in KOA. Further studies are needed to explore the role of bFGF in the pathogenesis and progression of primary KOA and the possibility of being a novel therapeutic target.

Conflict of interest

None. References

effusion in 24.3%, synovial thickening in 23.3%, osteophytes in 64.08% and meniscal degeneration in 3.88%. The cartilage thickness was more reduced over the medial condyle.

[1] Roman-Blas J, Castafieda S, Largo R, Herrero-Beaumont G. Osteoarthritis associated with estrogen deficiency. Arthritis Res Ther 2009;11:241.

[2] Hussein NA, Sharara G. Correlation between serum leptin, cytokines, cartilage degradation and functional impact in obese knee osteoarthritis patients. Egypt Rheumatol 2016;38 (2):117-22.

[3] Darwish AF, Abdel-Ghany HS, El-Sherbini YM. Diagnostic and prognostic value of some biochemical markers in early knee osteoarthritis. Egypt Rheumatologist 2012;34(1):1-8.

[4] Fawzy SM, El Sherbeni HH, Rashad A, El demellawy HH. Serum COMP and their correlations with various disease parameters in patients with systemic lupus erythematosus and osteoarthritis. Egypt Rheumatologist 2011;33(1):13-9.

[5] El-barbary AM, Abdel Khalek MA, Elsalawy AM, Hazaa SM. Assessment of lipid peroxidation and antioxidant status in rheumatoid arthritis and osteoarthritis patients. Egypt Rheuma-tologist 2011;33(4):179-85.

[6] Gaballah A, Hussein NA, Risk M, Elsawy N, Elabasiry S. Correlation between synovial vascular endothelial growth factor, clinical, functional and radiological manifestations in knee osteoarthritis. Egypt Rheumatologist 2016;38:29-34.

[7] Haider HM, Amin IR, Ahmad KA. Plasma and synovial osteopontin levels, are they associated with disease severity of primary knee osteoarthritis in Egyptian patients? Egypt Rheumatologist 2015;37(1):29-34.

[8] Mohammed FI, Abd El-Azeem MI, KamalElDin AM. Plasma and synovial fluid osteopontin levels in patients with knee osteoarthritis: relation to radiological grade. Egypt Rheumatol-ogist 2012;34(3):131-6.

[9] Fouda N, Abd-Elaziz H, Fouda EM. Assessment of subclinical carotid atherosclerosis in patients with primary osteoarthritis: correlation with disease severity and insulin resistance. Egypt Rheumatologist 2014;36(2):85-91.

[10] Zayed HS, Younis G, Bader R, Amin A. Prevalence of preclinical renal dysfunction in obese Egyptian patients with primary knee osteoarthritis, preliminary data. Egypt Rheumatologist 2013;35 (4):239-44.

[11] Okada-Ban M, Thiery JP, Jouanneau J. Fibroblast growth factor-2. Int J Biochem Cell Biol 2000;32:263-7.

[12] Bikfalvi A, Klein S, Pintucci G, Rifkin DB. Biological roles of fibroblast growth factor-2. Endocr Rev 1997;18:26-45.

[13] Uchino M1, Izumi T, Tominaga T, Wakita R, Minehara H, Sekiguchi M, et al. Growth factor expression in the osteophytes of the human femoral head in osteoarthritis. Clin Orthop Relat Res 2000;377:119-25.

[14] Shenavandeh S, Radmanesh S, Sarvestani EK, Nazarinia MA, Omrani GR. Fibroblast growth factor-23 in patients with systemic sclerosis: a case-control study. Egypt Rheumatol 2016;38 (2):105-9.

[15] Monteforte P, Sessarego P, Rovetta G. Sonographic assessment of soft tissue alternations in osteoarthritis of the knee. G Ital Med Lav Ergon 2008;30:75-7.

[16] de Miguel Mendieta E, Cobo Ibanez T, Uson Jaeger J, Bonilla Hernan G, Martin Mola E. Clinical and ultrasonographic findings

related to knee Pain in osteoarthritis. Osteoarthritis Cartilage 2006;14:540-4.

[17] Altman R, Asch E, Bloch D, Bole G, Borenstein D, Brandt K, et al. Development of criteria for the classification and reporting of osteoarthritis: classification of osteoarthritis of the knee. Diagnostic and therapeutic criteria committee of the American rheumatism association. Arthritis Rheum 1986;29:1039-49.

[18] McCormack HM, Horne DJ, Sheather S. Clinical applications of visual analogue scales: a critical review. Psychol Med 1988;18:1007-19.

[19] Bennell K, Dobson F, Hinman R. Measures of physical performance assessments. Arthritis Care Res 2011;63(Suppl. 11): S350-70.

[20] Guermazi M, Poiraudeau S, Yahia M, Mezganni M, Fermanian J, Habib Elleuch M, et al. Translation, adaptation and validation of the Western Ontario and McMaster Universities osteoarthritis index (WOMAC) for an Arab population: the Sfax modified WOMAC. Osteoarthritis Cartilage 2004;12:459-68.

[21] Grose R, Dickson C. Fibroblast growth factor signaling in tumorigenesis. Cytokine Growth Factor Rev 2005;16:179-86.

[22] Kellgren JH, Lawrence JS. Radiological assessment of osteoarthrosis. Ann Rheum Dis 1957;16:494-502.

[23] Chan KK, Sit RW, Wu RW, Ngai AH. Clinical, radiological and ultrasonographic findings related to knee pain in osteoarthritis. PLoS ONE 2014;9:e92901.

[24] Alzheimer C, Werner S. Fibroblast growth factors and neuroprotection. Adv Exp Med Biol 2002;513:335-51.

[25] Yun YR, Won JE, Jeon E, Lee S, Kang W, Jo H, et al. Fibroblast growth factors: biology, function, and application for tissue regeneration. J Tissue Eng 2010;2010:218142.

[26] Honsawek S, Yuktanandana P, Tanavalee A, Saetan N, Ano-masiri W, Parkpian V. Correlation between plasma and synovial fluid basic fibroblast growth factor with radiographic severity in primary knee osteoarthritis. Int Orthop 2012;36:981-5.

[27] Jingushi S, Shida J, Iwamoto Y, Kinoshita T, Hiyama Y, Tamura M, et al. Transient exposure of fibroblast growth factor-2 induced proliferative but not destructive changes in mouse knee joints. Connect Tissue Res 2006;47:242-8.

[28] Im HJ, Muddasani P, Natarajan V, Schmid TM, Block JA, Davis F, et al. Basic fibroblast growth factor stimulates matrix metal-loproteinase-13 via the molecular cross-talk between the mitogen-activated protein kinases and protein kinase C delta pathways in human adult articular chondrocytes. J Biol Chem 2007;282:11110-21.

[29] Li X, Ellman MB, Kroin JS, Chen D, Yan D, Mikecz K, et al. Species-specific biological effects of FGF-2 in articular cartilage: implication for distinct roles within the FGF receptor family. J Cell Biochem 2012;113:2532-42.

[30] Saarakkala S, Waris P, Waris V, Tarkiainen I, Karvanen E, Aarnio J, et al. Diagnostic performance of knee ultrasonography for detecting degenerative changes of articular cartilage. Osteoarthritis Cartilage 2012;20:376-81.