title: Persistent Biomechanical Alterations After ACL Reconstruction Are Associated With Early Cartilage Matrix Changes Detected by Quantitative MR.
abstract: BACKGROUND
  The effectiveness of anterior cruciate ligament (ACL) reconstruction in preventing early osteoarthritis is debated. Restoring the original biomechanics may potentially prevent degeneration, but apparent pathomechanisms have yet to be described. Newer quantitative magnetic resonance (qMR) imaging techniques, specifically T1ρ and T2, offer novel, noninvasive methods of visualizing and quantifying early cartilage degeneration.
  
  
  OBJECTIVE
  To determine the tibiofemoral biomechanical alterations before and after ACL reconstruction using magnetic resonance imaging (MRI) and to evaluate the association between biomechanics and cartilage degeneration using T1ρ and T2.
  
  
  METHODS
  Cohort study; Level of evidence, 2.
  
  
  METHODS
  Knee MRIs of 51 individuals (mean age, 29.5 ± 8.4 years) with unilateral ACL injuries were obtained prior to surgery; 19 control subjects (mean age, 30.7 ± 5.3 years) were also scanned. Follow-up MRIs were obtained at 6 months and 1 year. Tibial position (TP), internal tibial rotation (ITR), and T1ρ and T2 were calculated using an in-house Matlab program. Student t tests, repeated measures, and regression models were used to compare differences between injured and uninjured sides, observe longitudinal changes, and evaluate correlations between TP, ITR, and T1ρ and T2.
  
  
  RESULTS
  TP was significantly more anterior on the injured side at all time points (P < .001). ITR was significantly increased on the injured side prior to surgery (P = .033). At 1 year, a more anterior TP was associated with elevated T1ρ (P = .002) and T2 (P = .026) in the posterolateral tibia and with decreased T2 in the central lateral femur (P = .048); ITR was associated with increased T1ρ in the posteromedial femur (P = .009). ITR at 6 months was associated with increased T1ρ at 1 year in the posteromedial tibia (P = .029).
  
  
  CONCLUSIONS
  Persistent biomechanical alterations after ACL reconstruction are related to significant changes in cartilage T1ρ and T2 at 1 year postreconstruction. Longitudinal correlations between ITR and T1ρ suggest that these alterations may be indicative of future cartilage injury, leading to degeneration and osteoarthritis.
  
  
  CONCLUSIONS
  Newer surgical techniques should be developed to eliminate the persistent anterior tibial translation commonly seen after ACL reconstruction. qMR will be a useful tool to evaluate the ability of these newer techniques to prevent cartilage changes.
authors.affiliation: Department of Orthopaedic Surgery, University of California, San Francisco, San Francisco, California, USA.
authors.forename: Keiko
authors.initials: K
authors.lastname: Amano
authors.affiliation: Department of Radiology, University of California, San Francisco, San Francisco, California, USA.
authors.forename: Valentina
authors.initials: V
authors.lastname: Pedoia
authors.affiliation: Department of Radiology, University of California, San Francisco, San Francisco, California, USA.
authors.forename: Favian
authors.initials: F
authors.lastname: Su
authors.affiliation: Department of Radiology, University of California, San Francisco, San Francisco, California, USA.; Department of Physical Therapy and Rehabilitation, University of California, San Francisco, San Francisco, California, USA.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Souza
authors.affiliation: Department of Radiology, University of California, San Francisco, San Francisco, California, USA.
authors.forename: Xiaojuan
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Orthopaedic Surgery, University of California, San Francisco, San Francisco, California, USA.
authors.forename: C Benjamin
authors.initials: CB
authors.lastname: Ma
keywords: ACL; MRI; T1rho; osteoarthritis