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Abstract

Background:

Ghrelin, an amino acid hormone secreted primarily from the stomach, can regulate bone metabolism, regulate inflammation via suppressing proinflammatory cytokines, and suppress expression of matrix metalloproteinases (MMPs).

Purpose:

To measure synovial fluid levels of ghrelin in young patients with anterior cruciate ligament (ACL) tear to assess the role of ghrelin as a potential biomarker for cartilage injury.

Study Design:

Controlled laboratory study.

Methods:

This study included 120 patients who underwent ACL reconstructionbetween January 1, 2016, and May 31, 2021. We categorized 60 patients with acute cartilage injury (International Cartilage Regeneration & Joint Preservation Society grade 2 or 3) as the acute group and 60 patients with no acute cartilage injury as the nonacute group, with the healthy contralateral knee of each patient acting as the control group (n = 120). Synovial fluid samples were collected from the knees in the operating room before ACL reconstruction. We assessed the inflammatory biomarkers interleukin (IL)-6, MMP-1, MMP-9, and MMP-13, as well as serum ghrelin level and Mankin score, and results were compared between the 3 study groups with the Mann-Whitney U test.

Results:

Lower serum ghrelin levels in the synovial fluid were found in the acute group compared with the nonacute group and healthy controls (232.4 vs 434.4 vs 421.5 pg/mL, respectively; P < .001). Ghrelin level in the synovial fluid was significantly and positively correlated with IL-6 (r = 0.4223; P < .0001), MMP-13 (r = 0.3402; P < .0001), and Mankin score (r = 0.1453; P = .0244).

Conclusion:

In patients with ACL injury, ghrelin synovial fluid was significantly differently expressed in patients with cartilage injury and no cartilage injury.

Clinical Relevance:

Ghrelin synovial fluid has the potential to be a biomarker to predict acute cartilage injury in patients with ACL injury.

Keywords

ACL injury IL-6 Mankin score MMP-13 synovial fluid ghrelin

The anterior cruciate ligament (ACL) is crucial to stabilizing the knee joint, connecting the femur to the tibia. Around 40% of sports injury is caused by ACL injury,²² which leads to knee instability³⁰ and results in poor knee-related quality of life.^25,39 Treatment for ACL injuries in athletes often involves reconstructing the ACL, including removing the torn ligament and replacing it with a tendon graft that is usually taken from another part of the knee.^7,12,25

ACL rupture leads to tibial anterior displacement.³⁷ A considerable proportion of patients with collision injury have bone marrow edema,^10,18 during which the articular cartilage secretes proinflammatory cytokines into the joint space.^2,28,41 These inflammatory biomarkers at the time of ACL injury, as well as the chondral impaction, contribute to the development of osteoarthritis (OA).¹ Articular cartilage is hyaline cartilage, which lacks blood supply and nerve tissue nutrition, resulting in a weak ability to repair itself, making it difficult to heal after injury. Diagnosing acute cartilage injury has been a challenging problem. In most cases, the diagnosis is according to the imaging (such as magnetic resonance imaging [MRI]) as well as knee pain symptoms, instability of the knee, and functional restrictions.^3,5 Early-stage cartilage injury is particularly difficult to diagnose, resulting in a longer time to treatment.⁴⁰ Thus, it is of interest to find a reliable parameter to detect early acute cartilage injury in patients.

Inflammatory biomarkers in the synovial fluid are specific to the joint and are also common in people who have some forms of inflammatory arthritis, such as rheumatoid arthritis and osteoarthritis.²¹ Inflammatory markers of the knee joint are important in diagnosing early cartilage metabolism after ACL injury.²⁹ Thus, a synovial fluid biomarker profile characteristic is a possible approach to identify highly clinically relevant cartilage injury.

Ghrelin is an amino acid hormone that is secreted primarily in the stomach.⁴⁴ Widely known as the “hunger hormone,” ghrelin is the endogenous ligand of receptors for the growth hormone secretagogue.²⁰ In addition to the growth hormone–releasing function, ghrelin has a broad variety of other functions,¹³ such as regulation of dietary intake, stimulation of insulin secretion, and regulation of glucose balance and immune system.³³ Ghrelin can regulate bone metabolism by an autocrine/paracrine mode³¹ and via the direct effect on the bone cells,⁶ promoting the proliferation and inhibiting apoptosis of osteoblasts.^4,8,19 Furthermore, ghrelin increases the level of chondroitin sulfate type 4, and it enhances proteoglycan synthesis by promoting hypertrophy and participating in chondrocyte metabolism.⁴ It has been confirmed previously that ghrelin regulates inflammation via suppressing proinflammatory cytokines, such as interleukin (IL)-6 and IL-1β,¹¹ and that ghrelin suppresses expression of matrix metalloproteinases (MMPs), including MMP-1, MMP-9, and MMP-13, in human chondrocytes.²⁴ Thus, ghrelin may be an important diagnostic marker for cartilage injury.

Currently, there is no published literature explaining the relationship between ghrelin concentrations in synovial fluid in patients after ACL injury. The purpose of this study was to measure synovial fluid levels of ghrelin in young patients with ACL injury to assess its potential role as a diagnostic biomarker for cartilage injury. We hypothesized that ghrelin levels would be lower in patients with cartilage injury than in those with healthy knees.

Methods

Study Patients

The protocol for this study was approved by a medical ethics review committee, and all study participants provided written informed consent. A total of 120 patients scheduled for ACL reconstruction between January 1, 2016, and May 31, 2021, were recruited prospectively in this study. All patient diagnoses of ACL injury were confirmed according to clinical and MRI examinations. Our inclusion criteria were patients scheduled to undergo isolated arthroscopic ACL reconstruction. Excluded were patients <18 years, those with primary OA of any joint or severe systemic or chronic disease, those who had previous knee surgery or an intra-articular injection 3 months before surgery, and those with an insufficient amount of synovial fluid after aspiration. In this study, patients were not allowed to receive steroids or hyaluronic acid injection during the analysis.

The patients were divided into those with acute cartilage injury (acute group; n = 60) and those without acute cartilage injury (nonacute group; n = 60), with the healthy contralateral knee of each patient acting as the control group (n = 120). Acute cartilage injury was defined as International Cartilage Regeneration & Joint Preservation Society (ICRS) grade 2 or 3 at 1 month before study enrollment.

Intraoperative Procedures

Synovial Fluid Collection

Synovial fluid samples (5 mL) were collected with the help of the superolateral portal location using a local anesthetic injection or a numbing spray before knee debridement and ACL reconstruction. We collected the maximum amount of synovial fluid that egressed for evaluation. All samples were stored on ice during transport. After synovial fluid samples were collected, the samples were centrifuged immediately to remove cells and joint debris and then stored at -80°C until analysis.

Degree of Cartilage Injury

Cartilage injury was assessed intraoperatively by 2 reviewers (D.J. and R.L.) using the ICRS score.

Analysis of Cartilage Injury Markers

Blood samples were taken from all patients and the serum was frozen at a temperature of -80°C before surgery. Radioimmunoassay kit was used to evaluate the serum and synovial fluid ghrelin levels. We chose inflammatory biomarkers that are commonly found in ACL injury and cartilage degeneration (IL-6, MMP-1, MMP-9, MMP-13) and measured their levels using enzyme-linked immunosorbent assay. Serum markers, including albumin, aspartate aminotransferase (AST), and alanine aminotransferase (ALT), were also analyzed. The precision of the intra-assay was ≤5% and interassay is ≤4%. All parameters were measured twice by 2 reviewers (D.J. and R.L.). The coefficient of variation between the reviewers ranged from 2.8% to 5.4%.

We assessed the histopathological gradation of the severity using the grading system proposed by Mankin et al.²⁷ This is a reliable test of histological scoring of cartilage changes with evaluations of structure, matrix staining, cellular abnormalities, as well as tidemark integrity. The total score ranges from 0 to 14, with 0 meaning normal and 14 meaning most severe injury.⁴³

Statistical Analysis

Statistical analyses were performed with SPSS 23 (IBM) and GraphPad Prism (Version 9.0.1). Baseline characteristics were compared for all continuous variables with mean values and categorical variables with numbers. We compared ghrelin levels between the acute group, the nonacute group, and healthy controls using Mann-Whitney U test with P < .05 considered statistically significant. The association of ghrelin levels in synovial fluid and serum with inflammatory biomarkers and Mankin score were assessed with the Spearman correlation coefficient (r).

Results

Baseline Characteristics of the Study Groups

The 120 study patients were between 21 and 38 years of age, and the interval between injury and surgery was 4 to 6 weeks. Baseline patient characteristics; albumin, AST, and ALT levels; and Mankin score according to the study groups are summarized in Table 1.

Table 1

Baseline Characteristics of the Study Patients ^a

	Acute Group (n = 60)	Nonacute Group (n = 60)
Age, years, median (range)	29 (22-38)	28 (21-36)
Sex, female/male, n	24/36	22/38
BMI	23.5 ± 1.2	23.9 ± 1.4
Albumin level, g/L, mean	33.7	32.5
ALT level, IU/L	32 ± 1.5	33 ± 1.4
AST level, IU/L	38 ± 1.8	37 ± 1.8
Mankin score	11.9 ± 0.9	1.4 ± 0.3

^a Data are reported as mean ± SD unless otherwise indicated. ALT, alanine aminotransferase; AST, aspartate aminotransferase; BMI, body mass index; IU, international units.

Ghrelin Levels and Inflammatory Biomarkers

Ghrelin levels and inflammatory biomarkers in the acute, nonacute, and control groups are summarized in Table 2. There was no statistical difference in the serum ghrelin level between the acute and nonacute groups (263.9 vs 328.8). Patients in the acute group had higher levels of IL-6 (12.8 ± 3.4 vs 5.0 ± 3.4 pg/mL; P = .012) and MMP-13 (48.5 vs 13.6 pg/mL; P = .015) than patients in the nonacute group. Patients in the acute group also had lower synovial fluid ghrelin level compared with patients in the nonacute group as well as with their own healthy knees (232.4 vs 434.4 vs 421.5 pg/mL; P < .001) (Figure 1). Synovial fluid ghrelin levels in the knees with and without acute cartilage injury compared with healthy control knees. Synovial fluid ghrelin level was significantly and positively correlated with IL-6 (r = 0.4223; P < .0001), MMP-13 (r = 0.3402; P < .0001), and Mankin score (r = 0.1453; P = .0244) (Figure 2).

Table 2

Baseline Ghrelin Level and Synovial Fluid Inflammatory Biomarkers According to Study Groups ^a

	Acute Group(n = 60 knees)	Nonacute Group(n = 60 knees)	Control Group(n = 120 knees)	P
Ghrelin level, pg/mL
Serum	263.9 ± 12.2	328.8 ± 9.8	311.4 ± 10.3	.472
Synovial fluid	232.4 ± 11.5	434.4 ± 6.3	421.5 ± 15.1	.001
IL-6, pg/mL	12.8 ± 3.4	5.0 ± 3.4	3.8 ± 2.9	.012
MMP-1, pg/mL	48.5 ± 5.4	39.1 ± 4.8	41.3 ± 4.9	.412
MMP-9, pg/mL	21.2 ± 2.9	11.4 ± 1.8	14.9 ± 2.2	.218
MMP-13, pg/mL	48.5 ± 5.9	13.6 ± 2.3	11.8 ± 1.9	.015

^a Values presented as mean and standard deviation if not otherwise stated. Boldface P values indicate statistically significant differences among the 3 groups (P < .05). IL, interleukin; MMP, matrix metalloproteinase.

Figure 1.

Synovial fluid ghrelin levels in patients ACL reconstruction with or without acute cartilage injury compared with the levels in their own healthy knees (N = 240).

Figure 2.

Correlation of synovial fluid ghrelin with (A) IL-6, (B) MMP-13, and (C) Mankin score. IL, interleukin; MMP, matrix metalloproteinase.

Discussion

Patients in the acute cartilage injury group had higher levels of IL-6 (12.8 ± 3.4 vs 5.0 ± 3.4 pg/mL; P = .012), and MMP-13 (48.5 vs 13.6 pg/mL; P = .015) than patients in no acute cartilage injury group. Patients with acute cartilage injury had lower synovial fluid ghrelin level compared with patients with no acute cartilage injury and with their own healthy knees (232.4 pg/mL versus 434.4 pg/mL versus 421.5 pg/mL; P < .001). Ghrelin level in the synovial fluid was correlated with IL-6 (r = 0.4223; P < .0001), MMP-13 (r = 0.3402; P < .0001), and Mankin score (r = 0.1453; P = .0244).

Ghrelin is brain-gut peptide secreted largely in the stomach⁹ and functions in growth plate chondrocyte regulation.⁴² A study by Wu et al⁴⁵ indicated an increase of ghrelin in OA patients and suggested its association with knee symptoms. This study was in accordance with a previous study suggesting that synovial fluid ghrelin is expressed differently between knees with cartilage injury or with no cartilage injury and contralateral controls.⁴² Thus, synovial fluid, which is accessible during ACL injury, was found to be a reliable intra-articular parameter.³⁶ The results of the current study indicated that synovial fluid ghrelin was significantly differently expressed in patients with cartilage injury and no cartilage injury. The most meaningful thing is that no differences were found from serum samples, which illustrates that synovial fluid ghrelin is a better biomarker in predicting cartilage injury, with higher sensitivity. The reason for its sensitivity might be that synovial fluid ghrelin is derived directly from the knee.

Ghrelin is important in the regulation of cartilage-specific genes on chondrocytes.^23,34 This analysis showed that ghrelin level in the synovial fluid was correlated with IL-6 as well as MMP-13. Furthermore, IL-6 has been proved to play a vital role in the pathogenesis of bone diseases.^14,16 High levels of IL-6 were associated with greater prevalence of osteophytes in the whole tibiofemoral compartment.³⁸ Serum levels of IL-6 are associated with knee cartilage loss in the elderly population, indicating that low level inflammation plays a role in the pathogenesis of knee OA.³⁸ In accordance with previous publications,^16,17 the level of IL-6 was much higher in patients with cartilage injury than in patients with no cartilage injury.

MMP-13 is an important enzyme that targets cartilage for degradation.¹⁵ It has the function of degrading proteoglycan, type 4 collagen, and type 9 collagen. MMP-13 can regulate the activation of other MMPs. Synovial fibroblasts are among a variety of cells that produce MMP-13.^32,35 The level of MMP-13 in the synovial fluid of patients with OA was correlated with disease severity, suggesting that MMP-13 is indicating cartilage destruction.²⁶ This study indicated that MMP-13 was higher in the ACL reconstruction with cartilage injury group than in the no cartilage injury group. Synovial fluid ghrelin was correlated with MMP-13. This study also suggested that ghrelin level in the synovial fluid was correlated with Mankin score, proving its prognostic function.

Limitations

As this was an observational study, the sample size was relatively small. Thus, further large-scale clinical studies in the field are needed. A biomarker has the potential to be used widely only when it can be reversed using interventions; for ghrelin synovial fluid, this seems to be the situation. When patients are diagnosed with cartilage injury at an early stage, more effective interventions are needed to help patients with the recovery process.

Conclusion

Based on study findings in patients with ACL injury, ghrelin synovial fluid has the potential to be a biomarker to predict acute cartilage injury and is correlated with levels of IL-6, MMP-13, and Mankin score. More clinical trials are needed to further confirm this.

Footnotes

Acknowledgement

The authors thank all patients and all research team members for their contribution to this study.

Final revision submitted January 28, 2023; accepted February 22, 2023.

The authors declared that there are no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

Ethical approval for this study was obtained from The Affiliated Changzhou No.2 People’s Hospital of Nanjing Medical University (reference No. C2016150).

References

Akesen

Demirag

Budak

Evaluation of intra-articular collagenase, TIMP-1, and TNF-alpha levels before and after anterior cruciate ligament reconstruction. Acta Orthop Traumatol Turc. 2009;43(3):214–218.

Anderson

Chubinskaya

Guilak

, et al. Post-traumatic osteoarthritis: improved understanding and opportunities for early intervention. J Orthop Res. 2011;29(6):802–809.

Brown

Johnston

Saltzman

Marsh

Buckwalter

. Posttraumatic osteoarthritis: a first estimate of incidence, prevalence, and burden of disease. J Orthop Trauma. 2006;20(10):739–744.

Caminos

Gualillo

Lago

, et al. The endogenous growth hormone secretagogue (ghrelin) is synthesized and secreted by chondrocytes. Endocrinology. 2005;146(3):1285–1292.

Chen

Shi

Xue

Chen

. Application value of magnetic resonance arthrography of the shoulder in nursing and diagnosis of patients with shoulder joint injury. J Healthc Eng. 2021;2021:3051578.

Costa

Naot

Lin

, et al. Ghrelin is an osteoblast mitogen and increases osteoclastic bone resorption in vitro. Int J Pept. 2011;2011:605193.

Daniel

Stone

Dobson

, et al. Fate of the ACL-injured patient: a prospective outcome study. Am J Sports Med. 1994;22(5):632–644.

Delhanty

van der Eerden

van Leeuwen

. Ghrelin and bone. BioFactors (Oxford, England). 2014;40(1):41–48.

Delporte

. Structure and physiological actions of ghrelin. Scientifica. 2013;2013:518909.

10.

Dimond

Fadale

Hulstyn

Tung

Greisberg

. A comparison of MRI findings in patients with acute and chronic ACL tears. Am J Knee Surg. 1998;11(3):153–159.

11.

Dixit

Schaffer

Pyle

, et al. Ghrelin inhibits leptin- and activation-induced proinflammatory cytokine expression by human monocytes and T cells. J Clin Invest. 2004;114(1):57–66.

12.

Ferretti

Conteduca

De Carli

Fontana

Mariani

. Osteoarthritis of the knee after ACL reconstruction. Int Orthop. 1991;15(4):367–371.

13.

Gil-Campos

Aguilera

Cañete

Gil

. Ghrelin: a hormone regulating food intake and energy homeostasis. Br J Nutr. 2006;96(2):201–226.

14.

Guerne

Carson

Lotz

IL-6 production by human articular chondrocytes. Modulation of its synthesis by cytokines, growth factors, and hormones in vitro. J Immunol. 1990;144(2):499–505.

15.

Hasty

Reife

Kang

Stuart

. The role of stromelysin in the cartilage destruction that accompanies inflammatory arthritis. Arthritis Rheum. 1990;33(3):388–397.

16.

Higuchi

Shirakura

Kimura

, et al. Changes in biochemical parameters after anterior cruciate ligament injury. Int Orthop. 2006;30(1):43–47.

17.

Kaplan

Cuellar

Jazrawi

Strauss

. Biomarker changes in anterior cruciate ligament-deficient knees compared with healthy controls. Arthroscopy. 2017;33(5):1053–1061.

18.

Kijowski

Sanogo

Lee

, et al. Short-term clinical importance of osseous injuries diagnosed at MR imaging in patients with anterior cruciate ligament tear. Radiology. 2012;264(2):531–541.

19.

Kim

Her

Park

, et al. Ghrelin stimulates proliferation and differentiation and inhibits apoptosis in osteoblastic MC3T3-E1 cells. Bone. 2005;37(3):359–369.

20.

Kojima

Hosoda

Date

, et al. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999;402(6762):656–660.

21.

Kraus

Nevitt

Sandell

. Summary of the OA biomarkers workshop 2009 -biochemical biomarkers: biology, validation, and clinical studies. Osteoarthritis Cartilage. 2010;18(6):742–745.

22.

Lam

Fong

Yung

, et al. Knee stability assessment on anterior cruciate ligament injury: clinical and biomechanical approaches. Sports Med Arthrosc Rehabil Ther Technol. 2009;1(1):20.

23.

Liang

Rong

, et al. Ghrelin up-regulates cartilage-specific genes via the ERK/STAT3 pathway in chondrocytes of patients with adolescent idiopathic scoliosis. Biochem Biophys Res Commun. 2019;518(2):259–265.

24.

Liu

Cao

Gao

, et al. Ghrelin prevents articular cartilage matrix destruction in human chondrocytes. Biomed Pharmacother. 2018;98:651–655.

25.

Lohmander

Englund

Dahl

Roos

. The long-term consequence of anterior cruciate ligament and meniscus injuries: osteoarthritis. Am J Sports Med. 2007;35(10):1756–1769.

26.

Lohmander

Hoerrner

Lark

. Metalloproteinases, tissue inhibitor, and proteoglycan fragments in knee synovial fluid in human osteoarthritis. Arthritis Rheum. 1993;36(2):181–189.

27.

Mankin

Dorfman

Lippiello

Zarins

Biochemical and metabolic abnormalities in articular cartilage from osteo-arthritic human hips. II. Correlation of morphology with biochemical and metabolic data. J Bone Joint Surg Am. 1971;53(3):523–537.

28.

Martin

Buckwalter

. Post-traumatic osteoarthritis: the role of stress induced chondrocyte damage. Biorheology. 2006;43(3-4):517–521.

29.

Meulenbelt

Kraus

Sandell

Loughlin

. Summary of the OA biomarkers workshop 2010–-genetics and genomics: new targets in OA. Osteoarthritis Cartilage. 2011;19(9):1091–1094.

30.

Myklebust

Bahr

. Return to play guidelines after anterior cruciate ligament surgery. Br J Sports Med. 2005;39(3):127–131.

31.

Nikolopoulos

Theocharis

Kouraklis

. Ghrelin, another factor affecting bone metabolism. Med Sci Monit. 2010;16(7):RA147–RA162.

32.

Okada

Shinmei

Tanaka

, et al. Localization of matrix metalloproteinase 3 (stromelysin) in osteoarthritic cartilage and synovium. Lab Invest. 1992;66(6):680–690.

33.

Pusztai

Sarman

Ruzicska

, et al. Ghrelin: a new peptide regulating the neurohormonal system, energy homeostasis and glucose metabolism. Diabetes Metab Res Rev. 2008;24(5):343–352.

34.

Chen

Wang

, et al. Ghrelin protects against osteoarthritis through interplay with Akt and NF-κB signaling pathways. FASEB J. 2018;32(2):1044–1058.

35.

Ruan

Wang

, et al. Associations between knee structural measures, circulating inflammatory factors and MMP13 in patients with knee osteoarthritis. Osteoarthritis Cartilage. 2018;26(8):1063–1069.

36.

Ruiz-Romero

Blanco

. Proteomics role in the search for improved diagnosis, prognosis and treatment of osteoarthritis. Osteoarthritis Cartilage. 2010;18(4):500–509.

37.

Sabesan

Danielsky

Childs

Valikodath

. Multiligament knee injuries with associated tibial plateau fractures: a report of two cases. World J Orthop. 2015;6(3):363–368.

38.

Stannus

Jones

Cicuttini

, et al. Circulating levels of IL-6 and TNF-α are associated with knee radiographic osteoarthritis and knee cartilage loss in older adults. Osteoarthritis Cartilage. 2010;18(11):1441–1447.

39.

Swirtun

Jansson

Renström

. The effects of a functional knee brace during early treatment of patients with a nonoperated acute anterior cruciate ligament tear: a prospective randomized study. Clin J Sport Med. 2005;15(5):299–304.

40.

Takahashi

Naito

Abe

Sawada

Nagano

. Relationship between radiographic grading of osteoarthritis and the biochemical markers for arthritis in knee osteoarthritis. Arthritis Res Ther. 2004;6(3):R208–R212.

41.

Theologis

Kuo

Cheng

, et al. Evaluation of bone bruises and associated cartilage in anterior cruciate ligament-injured and -reconstructed knees using quantitative t(1ρ) magnetic resonance imaging: 1-year cohort study. Arthroscopy. 2011;27(1):65–76.

42.

Ueberberg

Unger

Saeger

Mann

Petersenn

. Expression of ghrelin and its receptor in human tissues. Horm Metab Res. 2009;41(11):814–821.

43.

van der Sluijs

Geesink

van der Linden

, et al. The reliability of the Mankin score for osteoarthritis. J Orthop Res. 1992;10(1):58–61.

44.

Verdeş

DuŢă

Popescu

, et al. Correlation between leptin and ghrelin expression in adipose visceral tissue and clinical-biological features in malignant obesity. Rom J Morphol Embryol. 2017;58(3):923–929.

45.

Wang

, et al. Associations between serum ghrelin and knee symptoms, joint structures and cartilage or bone biomarkers in patients with knee osteoarthritis. Osteoarthritis Cartilage. 2017;25(9):1428–1435.

Decreased Synovial Fluid Ghrelin Level Is Associated With Acute Cartilage Injury in Patients With Anterior Cruciate Ligament Tear

Abstract

Background:

Purpose:

Study Design:

Methods:

Results:

Conclusion:

Clinical Relevance:

Keywords

Methods

Study Patients

Intraoperative Procedures

Synovial Fluid Collection

Degree of Cartilage Injury

Analysis of Cartilage Injury Markers

Statistical Analysis

Results

Baseline Characteristics of the Study Groups

Ghrelin Levels and Inflammatory Biomarkers

Discussion

Limitations

Conclusion

Footnotes

Acknowledgement

References