title: Relationship between CTX-II and patient characteristics, patient-reported outcome, muscle strength, and rehabilitation in patients with a focal cartilage lesion of the knee: a prospective exploratory cohort study of 48 patients.
abstract: BACKGROUND
  C-telopeptide fragments of type II collagen (CTX-II) are created during articular cartilage breakdown and CTX-II is considered useful as a biomarker of osteoarthritis. The primary objective of the present study was to explore the relationship between urinary CTX-II concentration and patient characteristics, patient-reported outcome, muscle strength, and rehabilitation in patients with isolated focal knee cartilage lesions. Furthermore, the secondary objective was to examine differences in urinary CTX-II concentration between patients with focal cartilage lesions and healthy controls.
  
  
  METHODS
  48 patients (mean age 33.4 years, standard deviation 9.0) with a focal full-thickness (International Cartilage Repair Society grade 3 or 4) cartilage lesion on the medial or lateral femoral condyle were included. After baseline assessments, the patients completed a 3-month rehabilitation program and 44 patients attended the 3 month follow-up. Baseline and follow-up assessments consisted of urinary CTX-II, the Knee Injury and Osteoarthritis Outcome Score (KOOS), and isokinetic quadriceps and hamstring muscle strength measurements. CTX-II was also analysed in urine samples from 6 healthy individuals, serving as normal controls. Correlations were classified as very weak (correlation coefficient [r] < 0.20), weak (r = 0.20 - 0.39), moderate (r = 0.40 - 0.59), strong (r = 0.60 - 0.79), and very strong (r > 0.80).
  
  
  RESULTS
  Except for age and quadriceps strength, no significant correlations were found between CTX-II concentrations and baseline characteristics, KOOS, or muscle strength. Except for age, all correlations were considered as weak or very weak. The patients with a focal cartilage lesion had significantly higher mean CTX-II concentration than the healthy control individuals both at baseline (p = 0.001) and at follow-up (p = 0.001). The mean CTX-II concentration tended to decrease during rehabilitation, but the reduction was not significant (p = 0.076).
  
  
  CONCLUSIONS
  The current exploratory study demonstrated that patients with a focal cartilage lesion of the knee had higher concentrations of urinary CTX-II than healthy individuals. In addition, CTX-II concentration tended to decrease during rehabilitation.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT00885729.
authors.affiliation: Department of Orthopedic Surgery, Akershus University Hospital, Lørenskog, Norway. janhrot@medisin.uio.no.
authors.forename: Jan Harald
authors.initials: JH
authors.lastname: Røtterud
authors.forename: Finn P
authors.initials: FP
authors.lastname: Reinholt
authors.forename: Karen Johanne
authors.initials: KJ
authors.lastname: Beckstrøm
authors.forename: May Arna
authors.initials: MA
authors.lastname: Risberg
authors.forename: Asbjørn
authors.initials: A
authors.lastname: Arøen
mesh_terms: D000293:Adolescent; D000328:Adult; D001182:Arthroscopy; D015415:Biomarkers; D015992:Body Mass Index; D002358:Cartilage, Articular / Q000473:pathology*; D024043:Collagen Type II / Q000652:urine*; D005260:Female; D006801:Humans; D007718:Knee Injuries / Q000150:complications / Q000534:rehabilitation*; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000209:etiology / Q000652:urine*; D010008:Osteochondritis Dissecans / Q000150:complications / Q000534:rehabilitation*; D010446:Peptide Fragments / Q000652:urine*; D011183:Postoperative Complications; D011446:Prospective Studies; D052097:Quadriceps Muscle / Q000503:physiopathology*; D011859:Radiography; D011795:Surveys and Questionnaires; D015599:Trauma Severity Indices; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D015415:Biomarkers; C000590554:C-terminal cross-linking telopeptide of type II collagen, human; D024043:Collagen Type II; D010446:Peptide Fragments