Type II collagen C2C epitope in human synovial fluid and serum after knee injury--associations with molecular and structural markers of injury.
OBJECTIVE
Investigate in a cross-sectional study time-dependent changes of synovial fluid type II collagen epitope C2C concentrations after knee injury and correlate to other joint injury biomarkers.


METHODS
Synovial fluid samples were aspirated between 0 days and 7 years after injury (n = 235). Serum was collected from 71 of the knee injured patients. Synovial fluid from 8 knee-healthy subjects was used as reference. C2C was quantified by immunoassay and structural injury was determined from magnetic resonance images (MRI) of the injured knee acquired 1-38 days after injury (n = 98). Additional joint injury biomarker results were from earlier investigations of the same samples.


RESULTS
Synovial fluid C2C concentrations were higher in injured knees than in knees of reference subjects from 1 day up to 7 years after injury. C2C concentrations in synovial fluid and serum were correlated (r = 0.403, P < 0.001). In synovial fluid from subjects early after injury (0-33 days), C2C concentrations were correlated with cross-linked C-telopeptide of type II collagen (r = 0.444, P = 0.003), ARGS-aggrecan (r = 0.337, P < 0.001), osteocalcin (r = 0.345, P < 0.001), osteopontin (r = 0.371, P < 0.001) and IL-8 (r = -0.385, P < 0.001), but not with structural joint injury as visualized on MRI.


CONCLUSIONS
The increased levels of synovial fluid C2C after injury, together with the associations seen with several other injury-related biomarkers, suggest that an acute knee injury is associated with an immediate and sustained local degradation of type II collagen.
Orthopaedics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden; Department of Orthopaedics, Shimane University, Izumo, Japan. Electronic address: n-kuma@med.shimane-u.ac.jp.
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Kumahashi
Orthopaedics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden.
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Swärd
Orthopaedics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden.
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Larsson
Orthopaedics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden; Research Unit for Musculoskeletal Function and Physiotherapy, University of Southern Denmark, Denmark; Department of Orthopaedics and Traumatology, University of Southern Denmark, Denmark.
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Lohmander
Orthopaedics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden.
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Frobell
Orthopaedics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden.
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Struglics
D000293:Adolescent; D000328:Adult; D015415:Biomarkers / Q000032:analysis* / Q000097:blood; D024043:Collagen Type II / Q000032:analysis*; D003430:Cross-Sectional Studies; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000032:analysis*; D005260:Female; D006801:Humans; D007718:Knee Injuries / Q000097:blood / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D013582:Synovial Fluid / Q000737:chemistry*; D013997:Time Factors; D055815:Young Adult
D015415:Biomarkers; D024043:Collagen Type II; D000939:Epitopes
Biomarkers; C2C; Collagen; Knee injury; Synovial fluid