title: Greater Mechanical Loading During Walking Is Associated With Less Collagen Turnover in Individuals With Anterior Cruciate Ligament Reconstruction.
abstract: BACKGROUND
  Individuals who have sustained an anterior cruciate ligament (ACL) injury and undergo ACL reconstruction (ACLR) are at higher risk of developing knee osteoarthritis. It is hypothesized that altered knee loading may influence the underlying joint metabolism and hasten development of posttraumatic knee osteoarthritis.
  
  
  OBJECTIVE
  To explore the associations between serum biomarkers of cartilage metabolism and peak vertical ground-reaction force (vGRF) and vGRF loading rate in the injured and uninjured limbs of individuals with ACLR.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  Patients with a history of a primary unilateral ACLR who had returned to unrestricted physical activity (N = 19) participated in the study. Resting blood was collected from each participant before completing 5 walking gait trials at a self-selected comfortable speed. Peak vGRF was extracted for both limbs during the first 50% of the stance phase of gait, and the linear vGRF loading rate was determined between heel strike and peak vGRF. Sera were assessed for collagen breakdown (collagen type II cleavage product [C2C]) and synthesis (collagen type II C-propeptide [CPII]), as well as aggrecan concentrations, via commercially available specific enzyme-linked immunosorbent assays. Pearson product-moment correlations (r) and Spearman rank-order correlations (ρ) were used to evaluate associations between loading characteristics and biomarkers of cartilage metabolism.
  
  
  RESULTS
  Lower C2C:CPII ratios were associated with higher peak vGRF in the injured limb (ρ = -0.59, uncorrected P = .007). There were no significant associations between peak vGRF or linear vGRF loading rate and CPII, C2C, or aggrecan serum concentrations.
  
  
  CONCLUSIONS
  Lower C2C:CPII ratios were associated with higher peak vGRF in the ACLR limb during gait, suggesting that higher peak loading in the ACLR limb is related to lower type II collagen breakdown relative to type II collagen synthesis.
  
  
  CONCLUSIONS
  These data suggest that type II collagen synthesis may be higher relative to the amount of type II collagen breakdown in the ACLR limb with higher lower extremity loading. Future study should determine if metabolic compensations to increase collagen synthesis may affect the risk of developing osteoarthritis after ACLR.
authors.affiliation: Department of Exercise and Sport Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA Human Movement Science Curriculum, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA brian@unc.edu.
authors.forename: Brian
authors.initials: B
authors.lastname: Pietrosimone
authors.affiliation: Department of Exercise and Sport Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA Human Movement Science Curriculum, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA Department of Orthopaedics, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: J Troy
authors.initials: JT
authors.lastname: Blackburn
authors.affiliation: Department of Exercise and Sport Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA Human Movement Science Curriculum, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Harkey
authors.affiliation: Department of Exercise and Sport Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA Human Movement Science Curriculum, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Brittney A
authors.initials: BA
authors.lastname: Luc
authors.affiliation: Department of Exercise and Sport Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA Human Movement Science Curriculum, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA Department of Nutrition, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, North Carolina, USA.
authors.forename: Anthony C
authors.initials: AC
authors.lastname: Hackney
authors.affiliation: Department of Exercise and Sport Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA Human Movement Science Curriculum, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Darin A
authors.initials: DA
authors.lastname: Padua
authors.affiliation: Division of Rheumatology, Tufts Medical School, Boston, Massachusetts, USA.
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Driban
authors.affiliation: Department of Orthopaedics, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Spang
authors.affiliation: Division of Rheumatology, Allergy, and Immunology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA Thurston Arthritis Research Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Joanne M
authors.initials: JM
authors.lastname: Jordan
mesh_terms: D053674:Aggrecans / Q000378:metabolism; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction; D002135:Calcium-Binding Proteins / Q000378:metabolism; D024043:Collagen Type II / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005684:Gait / Q000502:physiology; D006801:Humans; D007718:Knee Injuries / Q000378:metabolism / Q000503:physiopathology / Q000601:surgery; D035002:Lower Extremity / Q000502:physiology; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000209:etiology / Q000378:metabolism; D012421:Rupture / Q000378:metabolism / Q000601:surgery; D016138:Walking / Q000502:physiology*
chemical_list: D053674:Aggrecans; D002135:Calcium-Binding Proteins; D024043:Collagen Type II; C040072:chondrocalcin
keywords: cartilage; ground-reaction force; knee; osteoarthritis; posttraumatic