Molecular Biomarkers of Knee Pathology.

The identification of biomarkers has become increasingly important in our fundamental understanding of the molecular basis for disease and subsequently in the advancement of modern medicine. Biomarkers have been identified in a plethora of normal and pathologic conditions and are most often found in blood, tissue, or synovial fluid. Orthopaedic research has more recently focused on biomarkers of cartilage and joint diseases, with an emphasis on understanding the molecular underpinnings of their pathophysiology. This article focuses on the biomarkers identified to date in several select knee pathologies and how further research can contribute to new diagnostic tools and targeted therapeutics.

Biomarker Changes in Anterior Cruciate Ligament-Deficient Knees Compared With Healthy Controls.

PURPOSE: To establish how synovial fluid biomarker concentrations change in patients after anterior cruciate ligament (ACL) tears, with and without associated cartilage injury, with comparisons made to healthy controls. METHODS: Patients were prospectively enrolled between January 2013 and December 2014. Inclusion criteria included any patient undergoing knee arthroscopy. Patients with a confirmed ACL tear were allocated to either the ACL tear with cartilage injury group or the ACL tear without cartilage injury group based on intraoperative assessment. Patients who underwent an arthroscopic procedure with no injury history or symptoms in their contralateral knee were asked to provide samples to serve as healthy controls. These subjects may or may not have been the same ones with noted ACL pathology. The concentrations of 20 biomarkers were determined using a multiplex magnetic bead immunoassay. Biomarker concentrations were then compared between the 3 study groups (ACL tears with and without cartilage injury, and uninjured contralateral knees) using an analysis of variance test with pairwise comparisons. The minimal clinically important difference was calculated based on the standard error of measurement. RESULTS: The study included synovial fluid samples from 134 knees: 34 ACL tears without cartilage injury (mean age 34.0 years), 28 ACL tears with cartilage injury (mean age 36.3 years), and 72 healthy controls (mean age 41.1 years). Analysis of variance testing showed significant differences among groups for matrix metalloproteinase-3 (F = 81.8; P < .001), tissue inhibitor of metalloproteinase (TIMP)-1 (F = 7.9; P ≤ .001), TIMP-2 (F = 4.5; P = .015); fibroblast growth factor-2 (F = 4.9; P = .011), interleukin-6 (F = 8.2; P = .001), and macrophage inflammatory protein-1 beta (F = 7.3; P = .001). Pairwise comparisons showed no significant differences between ACL tears with, and without cartilage injury, but did show that both groups of ACL tears had significantly higher concentrations of (first P value = ACL tears with and then ACL tears without cartilage injury): matrix metalloproteinase-3 (P < .001; P < .001), TIMP-1 (P < .001; P = .011), interleukin-6 (P = .009; P = .038), and macrophage inflammatory protein-1 beta (P = .003; P = .045) compared with contralateral controls. ACL tears without associated cartilage damage had significantly lower concentrations of TIMP-2 (P = .011) and fibroblast growth factor-2 (P = .014) compared with controls. All biomarker concentration differences that reached statistical significance were also larger than calculated minimal clinically important differences. CONCLUSIONS: The current study identified 6 pro- and anti-inflammatory synovial fluid biomarkers whose concentrations after ACL injury were significantly different compared with uninjured controls. No significant differences in synovial fluid biomarker concentrations were seen between ACL injured knees with and without associated cartilage damage. LEVEL OF EVIDENCE: Level III, retrospective comparative study of prospectively gathered data.

α2-Macroglobulin: Autologous Protease Inhibition Technology.

α2-Macroglobulin (A2M) is a plasma glycoprotein best known for its ability to inhibit a broad spectrum of serine, threonine, and metalloproteases as well as inflammatory cytokines by a unique bait-and-trap method. A2M has emerged as a unique potential treatment of cartilage-based pathology and inflammatory arthritides. This article describes the unique method by which A2M not only inhibits the associated inflammatory cascade but also disrupts the catabolic process of cartilage degeneration. Autologous concentrated A2M from plasma is currently in use to successfully treat various painful arthritides. Future directions will focus on recombinant variants that enhance its anti-inflammatory and disease-modifying potential.

Single-stage Reconstruction of Elbow Flexion Associated with Massive Soft-Tissue Defect Using the Latissimus Dorsi Muscle Bipolar Rotational Transfer.

In the upper extremity, the latissimus dorsi muscle can be used as an ipsilateral rotational muscle flap for soft-tissue coverage or functional reconstruction of arm and elbow. Patients who have both major soft-tissue loss and functional deficits can be successfully treated with a single-stage functional latissimus dorsi rotational muscle transfer that provides simultaneous soft-tissue coverage and functional reconstruction. METHODS: Our data base was queried for all patients undergoing a rotational latissimus dorsi muscle transfer for simultaneous soft-tissue coverage and functional reconstruction of elbow flexion. Four patients were identified. A chart review documented the mechanism of injury, associated injuries, soft-tissue defect size, number of surgical procedures, length of follow-up, last elbow range of motion, and flexion strength. RESULTS: Four patients with loss of elbow flexion due to traumatic loss of the anterior compartment muscles and the overlying soft tissue underwent simultaneous soft-tissue coverage and elbow flexorplasty using the ipsilateral latissimus dorsi as a bipolar muscle rotational tissue transfer. All flaps survived and had a recovery of Medical Research Council Grade 4/5 elbow flexion strength. No additional procedures were required for elbow flexion. The surgical technique is described and supplemented with surgical technique video and patient outcome. CONCLUSIONS: This patient series augments the data provided in other series supporting the safety and efficacy of this procedure which provides both soft-tissue coverage and functional restoration of elbow flexion as a single-stage procedure in the setting of massive traumatic soft-tissue loss of the arm.

Correlation of Synovial Fluid Biomarkers With Cartilage Pathology and Associated Outcomes in Knee Arthroscopy.

PURPOSE: To correlate the intraoperative concentrations of 20 synovial fluid biomarkers with preoperative symptoms, intraoperative findings, and postoperative outcomes in patients undergoing knee arthroscopy, with comparisons made to samples obtained from asymptomatic knees. METHODS: Synovial fluid samples were obtained from 81 patients undergoing knee arthroscopy meeting the inclusion criteria, which included 70 samples from operative knees and 32 samples from contralateral knees. Preoperatively, baseline data obtained from clinical questionnaires including a visual analog scale (VAS) score, the Lysholm score, and the Knee Injury and Osteoarthritis Outcome Score-Physical Function Short Form were recorded. Synovial fluid was collected from both the operative knee and asymptomatic contralateral knee. Synovial fluid was stored with a protease inhibitor at -80°C until analysis. Intraoperative findings, procedures performed, and International Cartilage Repair Society (ICRS) cartilage status scores in all operative knees were documented. The concentrations of the following 20 biomarkers were measured using a multiplex magnetic bead immunoassay: matrix metalloproteinase (MMP) 3; MMP-13; tissue inhibitor of metalloproteinase (TIMP) 1; TIMP-2; TIMP-3; TIMP-4; fibroblast growth factor 2; eotaxin; interferon γ; interleukin (IL) 10; platelet-derived growth factor BB; IL-1 receptor antagonist; IL-1ß; IL-6; monocyte chemotactic protein 1 (MCP-1); macrophage inflammatory protein 1α; macrophage inflammatory protein 1ß; RANTES (regulated upon activation, normal T cell expressed and secreted); tumor necrosis factor α; and vascular endothelial growth factor. Clinical outcome scores were obtained in 83% of patients at a mean of 17 months' follow-up postoperatively. Analysis of variance and Pearson correlation analysis were performed to determine statistical significance between preoperative data, intraoperative findings, postoperative outcomes, and synovial fluid biomarker concentrations compared with asymptomatic contralateral knees. RESULTS: Analysis was performed on 70 operative and 32 contralateral samples. There were strong positive correlations between ICRS score and age, symptom duration, VAS score, and Knee Injury and Osteoarthritis Outcome Score-Physical Function Short Form. A strong positive correlation was found between MCP-1 and IL-6 concentrations, intraoperative ICRS score, and continued pain at the time of final follow-up. MCP-1 and IL-6 were the strongest predictors of severe cartilage lesions, whereas IL-1 receptor antagonist was inversely related. MMP-3 levels were consistently elevated in all operative samples and directly correlated to increased preoperative VAS scores. RANTES, vascular endothelial growth factor, and platelet-derived growth factor BB were the strongest predictors of postoperative improvement at final follow-up regardless of injury and cartilage status. CONCLUSIONS: Synovial fluid biomarkers have the capacity to reflect the intra-articular environment before surgery and potentially predict postoperative clinical outcomes. Recognition of key molecular players may yield future therapeutic targets, and large clinical trials exploring these discoveries are anticipated. LEVEL OF EVIDENCE: Level III, therapeutic case-control study.

A Biomechanical Study of Posteromedial Tibial Plateau Fracture Stability: Do They All Require Fixation?

OBJECTIVES: Although the posteromedial fragment in tibial plateau fractures is often considered unstable, biomechanical evidence supporting this view is lacking. We aimed to evaluate the stability of the fragment in a cadaver model. Our hypothesis was that under the expected small axial force during rehabilitation and the combined effects of this force with shear force, internal rotation torque, and varus moment, the most common posteromedial tibial fragment morphology could maintain stability in early flexion. METHODS: Axial compression force alone or combined with posterior shear, internal rotation torque, or varus moment was applied to the femurs of 5 fresh cadaveric knees. A Tekscan pressure mapping system was used to measure pressure and contact area between the femoral condyles, meniscus, and tibial plateau. A Microscribe 3D digitizer was used to define the 3-dimensional positions of the femur and tibia. A 10-mm and then a 20-mm osteotomy was created with a saw at an angle of 30 degrees in the axial plane with respect to the tangent of the posterior tibial plateau and 75 degrees in the sagittal plane, representing a typical posteromedial fracture fragment. At each flexion angle (15, 30, 60, 90, and 120 degrees) and loading condition (axial compression only, compression with shear force, torque, and varus moment), distal displacement of the medial femoral condyle and the tibial fracture fragments was determined. RESULTS: For the 10-mm fragment, medial femoral condyle displacement was little affected up to approximately 30-degree flexion, after which it increased. For the 20-mm fragment, there was progressive medial femoral condyle displacement with increasing flexion from baseline. However, for the 10- and 20-mm fragments themselves, displacements were noted at every flexion angle, starting at 1.7 mm inferior displacement with 15 degrees of flexion and internal rotation torque and up to 10.2 mm displacement with 90 degrees of flexion and varus bending moment. CONCLUSIONS: In this cadaveric model of a posteromedial tibial plateau fracture, both fracture fragments studied displaced with knee flexion, even at low flexion angles. Although such fragments may initially seem nondisplaced after injury, posteromedial fragments similar to these tested are likely to displace during knee range of motion exercises in non-weight-bearing conditions.

Delayed presentation of incidental durotomy.

Two case reports illustrate a delayed clinical presentation of incidental durotomy following surgical posterior decompression of the lumbar spine. The clinical presentation as well as radiographic imaging studies used in diagnosing this relatively rare surgical complication are discussed. Both nonoperative as well as surgical treatment alternatives are outlined.

Cytokine expression in the epidural space: a model of noncompressive disc herniation-induced inflammation.

STUDY DESIGN: Animal study. OBJECTIVE: Development of an animal model for the study of biochemical changes that occur in the epidural space after intervertebral disc herniation. SUMMARY OF BACKGROUND DATA: Although strong evidence for an inflammatory component exists, the biochemical processes underlying pain after disc herniation remain unknown. METHODS: Epidural lavage was performed in 48 rats after L5 dorsal root ganglion exposure at baseline and 3, 6, or 24 hours after placement of autologous nucleus pulposus (NP) (N = 15), saline (N = 15), or NP + an interferon-γ antibody (anti-IFN-γ; N = 18) directly onto the dorsal root ganglion. Multiplex assays quantifying interleukin (IL)-1α, IL-1ß, IL-2, IL-4, IL-6, IL-10, tumor necrosis factor α (TNF-α), IFN-γ, and granulocyte-macrophage colony-stimulating factor (GM-CSF) were performed. NP (N = 7) was also analyzed for these cytokines by placing NP into saline and measuring the relative concentration. RESULTS: Cytokines measured low at baseline (0-100 pg/mL) in all groups. Compared with saline, NP application caused IL-6 elevation, peaking at T = 3 hours, that was prevented by anti-IFN-γ. NP induced elevation of TNF-α, peaking at T = 24 hours and was prevented by anti-IFN-γ. IFN-γ was elevated after NP at T = 3 hours and T = 24 hours. IL-1α was similar after saline versus NP. The concentrations of IL-1ß and IL-10 were elevated at T = 3 hours, 6 hours, and 24 hours in all groups without between-groups difference. The level of IL-4 peaked at T = 3 hours in the NP group and was different than saline and NP + anti-IFN-γ groups, but the time effect was insignificant. There was no change for GM-CSF. The concentration of cytokines measured in normal NP was less than 2 pg/mL for all cytokines except TNF-α. CONCLUSION: In this model of acute noncompressive disc herniation, NP caused the elevation of epidural IL-6, TNF-α, and IFN-γ--all attenuated by IFN-γ blockade. IL-1ß and IL-10 were both significantly elevated by saline alone and their response was not prevented by IFN-γ blockade. This model may prove useful for the study of the biochemical processes by which NP induces inflammation-induced nerve root irritation and radiculopathic pain.

Long-term expression of human coagulation factor VIII in a tolerant mouse model using the φC31 integrase system.

We generated a mouse model for hemophilia A that combines a homozygous knockout for murine factor VIII (FVIII) and a homozygous addition of a mutant human FVIII (hFVIII). The resulting mouse, having no detectable FVIII protein or activity and tolerant to hFVIII, is useful for evaluating FVIII gene-therapy protocols. This model was used to develop an effective gene-therapy strategy using the φC31 integrase to mediate permanent genomic integration of an hFVIII cDNA deleted for the B-domain. Various plasmids encoding φC31 integrase and hFVIII were delivered to the livers of these mice by using hydrodynamic tail-vein injection. Long-term expression of therapeutic levels of hFVIII was observed over a 6-month time course when an intron was included in the hFVIII expression cassette and wild-type φC31 integrase was used. A second dose of the hFVIII and integrase plasmids resulted in higher long-term hFVIII levels, indicating that incremental doses were beneficial and that a second dose of φC31 integrase was tolerated. We observed a significant decrease in the bleeding time after a tail-clip challenge in mice treated with plasmids expressing hFVIII and φC31 integrase. Genomic integration of the hFVIII expression plasmid was demonstrated by junction PCR at a known hotspot for integration in mouse liver. The φC31 integrase system provided a nonviral method to achieve long-term FVIII gene therapy in a relevant mouse model of hemophilia A.

Accelerated degeneration after failed cervical and lumbar nucleoplasty.

STUDY DESIGN: Observational cohort study. SUMMARY OF BACKGROUND DATA: Studies evaluating the treatment of presumed discogenic spine pain using nucleoplasty have reported variable success rates. It has been suggested that these procedures lower the intradiscal pressure, reduce disk protrusion, improve disk hydration, and restore disk height. It is proposed that such structural changes in treated disks correspond to the clinical improvement in patients. Radiographic and clinical evidence showing the efficacy of nucleoplasty remains inadequate. OBJECTIVE: To document the comparative changes in magnetic resonance imaging (MRI) the appearance of disk morphology as reflected by Pfirrmann classification scores before and after the nucleoplasty treatment in patients with continued symptoms. METHODS: Twenty-eight consecutive patients with persistent symptoms after nucleoplasty within 1 year of treatment were evaluated. Prenucleoplasty and postnucleoplasty MRIs were evaluated and Pfirrmann scores of the symptomatic level were determined. RESULTS: In all the treated patients, comparison between the prenucleoplasty and the postnucleoplasty MRI of the targeted disks failed to show increased signal hydration, disk space height improvement, or shrinkage of the preoperative disk bulge at a mean time of 6 months after the procedure. Of the 17 cervical levels treated in 12 patients, 5 seemed to show progressive degeneration at treated levels (42% of the patients). Of the 17 lumbar procedures in 16 patients, 4 seemed to show progressive degeneration (25% of the patients) and 1 developed a new spondylolisthesis (6.3%). Thus, 32% of the patients in our cohort showed progressive degeneration at the treated level. The median Pfirrmann score in both prenucleoplasty and postnucleoplasty was 2, and the mean Pfirrmann classification prenucleoplasty and postnucleoplasty was 1.8 and 2.1, respectively (P<0.05, 2-tailed t test). CONCLUSION: This study failed to detect any morphologic improvement of disk abnormalities by MRI evaluation in patients with persistent pain, who then underwent nucleoplasty. Thirty-two percent showed progressive degeneration in less than 1 year after nucleoplasty, a rate greater than expected by natural progression during the interval of examination.

Cytokine profiling in acute anterior cruciate ligament injury.

PURPOSE: To evaluate the presence and relative concentrations of cytokines, known to be involved in the inflammatory cascade, in acute anterior cruciate ligament (ACL) injury. METHODS: We evaluated an extensive cytokine profile in synovial fluid from 12 patients with acute ACL injury undergoing arthroscopy compared with 15 control subjects using a BioPlex assay (Bio-Rad Laboratories, Hercules, CA) to measure the concentration of 17 inflammatory cytokines. RESULTS: In patients with acute ACL injury compared with asymptomatic control subjects, the following cytokines were identified at significantly increased concentrations (P < .001, Mann-Whitney U test) compared with control samples: interleukin 6 (105 ± 72 v 0 ± 0 pg/ml), interferon γ (1,544 ± 608 v 9 ± 7.5 pg/ml), macrophage inflammatory protein 1ß (16 ± 3.8 v 0.3 ± 0.2 pg/ml), and monocyte chemotactic protein 1 (35 ± 13 v 0.5 ± 0.4 pg/ml). There was no case of a cytokine exhibiting increased levels in asymptomatic compared with symptomatic knee samples. CONCLUSIONS: This investigation identified 4 specific cytokines (interleukin 6, interferon γ, monocyte chemotactic protein 1, and macrophage inflammatory protein 1ß) out of a panel of 17 inflammatory molecules for which the levels were consistently elevated in the context of ACL injury compared with non-painful, non-acutely injured knees in a volunteer population. LEVEL OF EVIDENCE: Level IV, prognostic case series.

Identification of a complex between fibronectin and aggrecan G3 domain in synovial fluid of patients with painful meniscal pathology.

OBJECTIVES: We previously described a panel of four cytokines biomarkers in knee synovial fluid for acute knee pain associated with meniscal pathology. The cytokine biomarkers included interferon gamma (IFN-gamma), interleukin 6 (IL-6), monocyte chemotactic protein 1 (MCP-1), and macrophage inflammatory protein-1 beta (MIP-1beta). Validation studies using other immunologic techniques confirmed the presence of IL-6, MCP-1 and MIP-1beta, but not IFN-gamma. Therefore we sought the identity of the IFN-gamma signal in synovial fluid. METHODS: Knee synovial fluid was collected from patients with an acute, painful meniscal injury, as well as asymptomatic volunteers. A combination of high-pressure chromatography, mass spectrometry and immunological techniques were used to enrich and identify the protein components representing the IFN-gamma signal. RESULTS: A protein complex of fibronectin and the aggrecan G3 domain was identified in the synovial fluid of patients with a meniscal tear and pain that was absent in asymptomatic controls. This protein complex correlated to the IFN-gamma signal. A novel enzyme-linked immunosorbent assay (ELISA) was developed to specifically identify the complex in synovial fluid. CONCLUSIONS: We have identified a protein complex of fibronectin and aggrecan G3 domain that is a candidate biomarker for pain associated with meniscal injury.

Cytokine evaluation in individuals with low back pain using discographic lavage.

BACKGROUND CONTEXT: The pathophysiology underlying degenerative disc disease and its implication in painful syndromes remain unclear. However, spine magnetic resonance imaging (MRI) can demonstrate changes in disc water content and the annulus; provocative discography purportedly identifies degenerate discs causing serious low back pain; and biochemical assays have identified local inflammatory markers. No study to date has correlated pain on disc injection during discography evaluation with relevant MRI findings and biochemical markers. PURPOSE: The purpose of this study was to correlate concordant pain on during discography to biochemical markers obtained by disc lavage and MRI findings. STUDY DESIGN: This is a Phase 1 Diagnostic Test Assessment Cohort Study (Sackett and Haynes). PATIENT SAMPLE: The patient sample included 21 symptomatic patients with suspected discogenic pain and three Phase 1 control subjects. OUTCOME MEASURES: The outcome measures included discography pain scores, MRI degenerative grades, and immunoreactivity to various inflammatory cytokine concentrations present in disc lavage samples. METHODS: Twenty-one symptomatic patients with lumbar degenerative disc disease and three control subjects underwent discography, MRI, and biochemical analysis of disc lavage fluid. Lumbar MRI was scored for Pfirrmann grading of the lumbar discs, and annular disruption was identified by nuclear disc lavage. Disc lavage samples were analyzed for biochemical markers by high-sensitivity immunoassay. RESULTS: Eighty-three discs from 24 patients were studied: 67 discs from 21 patients with axial back pain (suspected discogenic pain group) and 16 discs from 3 scoliosis patients without back pain (Phase 1 control subjects). Among the biochemical markers surveyed, interferon gamma (IFN-gamma) immunoreactivity was most consistently identified in patients with axial back pain. Discs with annular disruption and concordant pain reproduction at a visual analog scale of 7 to 10/10 had greater IFN-gamma immunoreactivity than those without this finding (p=.003); however, at least some IFN-gamma immunoreactivity was found in all but one disc in the symptomatic group. CONCLUSIONS: Among the potential inflammatory markers tested in this Phase 1 study, IFN-gamma immunoreactivity was most commonly elevated in discogram "positive" discs but absent in asymptomatic controls. However, this marker was also frequently elevated in degenerative but "negative" discography discs. From these findings, Phase 2 and Phase 3 validity studies are reasonable to pursue. Phase 4 utility studies may be performed concurrently to assess this method's predictive value in outcome studies.

Epidural interferon gamma-immunoreactivity: a biomarker for lumbar nerve root irritation.

STUDY DESIGN: Prospective observational cohort. OBJECTIVE: Correlate epidural inflammatory cytokines with the clinical response to epidural steroid injection in patients with lumbar nerve root irritation. SUMMARY OF BACKGROUND DATA: Some back pain syndromes are thought to be associated with activation of inflammatory pathways and others may be associated with primary mechanical derangements. Human studies providing detailed evidence for the primary inflammatory causation, which may be best treated with anti-inflammatory strategies, are lacking. There are currently no accurate diagnostic tests to predict the response to epidural steroid injection or surgical intervention in back pain and sciatica syndromes. METHODS.: Forty-seven consecutive patients with lumbar degenerative changes and low back and/or leg pain were prospectively enrolled. An epidural lavage was performed, followed by injection of marcaine/depo-medrol. Subjects scored their pain before and 3 months after the procedure. The immunoreactivity of an array of cytokines was measured in lavage samples and compared with clinical response to the therapeutic injection. Ten subjects underwent repeat epidural lavage sampling 3 months after the steroid injection. RESULTS: Interferon gamma (IFNgamma) was the most consistently detected cytokine. IFNgamma-immunoreactivity also highly correlated with reported reduction of pain 3-months after the epidural steroid injection. In subjects reporting significant pain relief (>50%) from the injection, mean [IFNgamma] was significantly greater compared with patients experiencing no significant relief. The IFNgamma-immunoreactivity in repeat lavage samples decreased to trace residual concentrations in patients who reported pain relief from the steroid injection. CONCLUSION: The presence of epidural IFNgamma-immunoreactivity corresponding to >10 pg/mL predicted significant pain relief after epidural steroid injection with >95% accuracy. These results suggest that IFNgamma may be part of a biochemical cascade triggering pain in sciatica; IFNgamma-immunoreactivity may aid as a biomarker for predicting the response to steroid therapy and/or surgical intervention, and may serve as a future therapeutic target.

Diagnostic utility of cytokine biomarkers in the evaluation of acute knee pain.

BACKGROUND: The diagnosis of clinically important meniscal tears of the knee remains challenging, and it is unknown why only some injuries become painful. The role of inflammatory cytokines in generating pain following meniscal injury remains unclear. This study aimed to investigate the cytokine profile in patients with acute knee pain believed to be secondary to meniscal damage. METHODS: This prospective cohort study included thirty-two patients without rheumatoid arthritis who had knee pain for less than six months, with either an acute or insidious onset, and elected to have arthroscopic treatment after nonoperative management had failed. Twenty-three of these patients elected to have the contralateral, nonoperatively treated knee lavaged at the time of arthroscopy. Fifteen asymptomatic control subjects also contributed samples of knee joint fluid, for a total of seventy samples from forty-seven subjects. Lavage of the operatively treated, contralateral, and control knees was performed with the patient under regional anesthesia prior to arthroscopy, if applicable, by the infusion of sterile saline solution into the knee followed by the immediate withdrawal into a syringe. The concentrations of seventeen inflammatory cytokines and chemokines were measured with use of a multiplexed immunoassay panel. Preoperative magnetic resonance imaging findings and cytokine assay results were compared with intraoperative findings. RESULTS: Multivariate analysis of variance detected significantly greater concentrations of interferon gamma (IFN-gamma); interleukins 2, 4, 6, 10, and 13 (IL-2, IL-4, IL-6, IL-10, and IL-13); monocyte chemotactic protein-1 (MCP-1); and macrophage inflammatory protein-1 beta (MIP-1beta) in fluid samples from painful knees than in samples from nonpainful knees. Correlation analysis demonstrated a significant positive correlation between patient-reported pain scores and concentrations of IL-6 (Spearman rho = 0.7), MCP-1 (rho = 0.8), MIP-1beta (rho = 0.6), and IFN-gamma (rho = 0.6). These four cytokines also demonstrated a positive correlation with each other (rho = 0.5 to 0.7). The presence of IFN-gamma, IL-6, MCP-1, or MIP-1beta performed as well as magnetic resonance imaging in the prediction of intraoperative findings. CONCLUSIONS: Intra-articular concentrations of four inflammatory cytokines IFN-gamma, IL-6, MCP-1, and MIP-1beta correlated to pain in patients with symptomatic meniscal tears in the knee but were markedly lower in asymptomatic normal knees and in asymptomatic knees with meniscal tears. These cytokines may be involved in the generation of pain following meniscal injury.