title: Quantitative Magnetic Resonance Imaging UTE-T2* Mapping of Cartilage and Meniscus Healing After Anatomic Anterior Cruciate Ligament Reconstruction.
abstract: BACKGROUND
  An anterior cruciate ligament (ACL) injury greatly increases the risk for premature knee osteoarthritis (OA). Improved diagnosis and staging of early disease are needed to develop strategies to delay or prevent disabling OA.
  
  
  OBJECTIVE
  Novel magnetic resonance imaging (MRI) ultrashort echo time (UTE)-T2(*) mapping was evaluated against clinical metrics of cartilage health in cross-sectional and longitudinal studies of human participants before and after ACL reconstruction (ACLR) to show reversible deep subsurface cartilage and meniscus matrix changes.
  
  
  METHODS
  Cohort study (diagnosis/prognosis); Level of evidence, 2.
  
  
  METHODS
  Forty-two participants (31 undergoing anatomic ACLR; 11 uninjured) underwent 3-T MRI inclusive of a sequence capturing short and ultrashort T2 signals. An arthroscopic examination of the medial meniscus was performed, and modified Outerbridge grades were assigned to the central and posterior medial femoral condyle (cMFC and pMFC, respectively) of ACL-reconstructed patients. Two years after ACLR, 16 patients underwent the same 3-T MRI. UTE-T2(*) maps were generated for the posterior medial meniscus (pMM), cMFC, pMFC, and medial tibial plateau (MTP). Cross-sectional evaluations of UTE-T2(*) and arthroscopic data along with longitudinal analyses of UTE-T2(*) changes were performed.
  
  
  RESULTS
  Arthroscopic grades showed that 74% (23/31) of ACL-reconstructed patients had intact cMFC cartilage (Outerbridge grade 0 and 1) and that 90% (28/31) were Outerbridge grade 0 to 2. UTE-T2(*) values in deep cMFC and pMFC cartilage varied significantly with injury status and arthroscopic grade (Outerbridge grade 0-2: n = 39; P = .03 and .04, respectively). Pairwise comparisons showed UTE-T2(*) differences between uninjured controls (n = 11) and patients with arthroscopic Outerbridge grade 0 for the cMFC (n = 12; P = .01) and arthroscopic Outerbridge grade 1 for the pMFC (n = 11; P = .01) only and not individually between arthroscopic Outerbridge grade 0, 1, and 2 of ACL-reconstructed patients (P > .05). Before ACLR, UTE-T2(*) values of deep cMFC and pMFC cartilage of ACL-reconstructed patients were a respective 43% and 46% higher than those of uninjured controls (14.1 ± 5.5 vs 9.9 ± 2.3 milliseconds [cMFC] and 17.4 ± 7.0 vs 11.9 ± 2.4 milliseconds [pMFC], respectively; P = .02 for both). In longitudinal analyses, preoperative elevations in UTE-T2(*) values in deep pMFC cartilage and the pMM in those with clinically intact menisci decreased to levels similar to those in uninjured controls (P = .02 and .005, respectively), suggestive of healing. No decrease in UTE-T2(*) values for the MFC and new elevation in UTE-T2(*) values for the submeniscus MTP were observed in those with meniscus tears.
  
  
  CONCLUSIONS
  This study shows that novel UTE-T2(*) mapping demonstrates changes in cartilage deep tissue health according to joint injury status as well as a potential for articular cartilage and menisci to heal deep tissue injuries. Further clinical studies of UTE-T2(*) mapping are needed to determine if it can be used to identify joints at risk for rapid degeneration and to monitor effects of new treatments to delay or prevent the development of OA.
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California, USA chucr@stanford.edu.
authors.forename: Constance R
authors.initials: CR
authors.lastname: Chu
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California, USA.
authors.forename: Ashley A
authors.initials: AA
authors.lastname: Williams
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Robin V
authors.initials: RV
authors.lastname: West
authors.affiliation: Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Yongxian
authors.initials: Y
authors.lastname: Qian
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Freddie H
authors.initials: FH
authors.lastname: Fu
authors.affiliation: Department of Radiology, Veterans Affairs Palo Alto Health Care System, Palo Alto, California, USA.
authors.forename: Bao H
authors.initials: BH
authors.lastname: Do
authors.affiliation: Division of Pulmonology Allergy and Critical Care Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Bruno
mesh_terms: D000293:Adolescent; D000328:Adult; D059549:Anterior Cruciate Ligament Reconstruction / Q000379:methods*; D002358:Cartilage, Articular / Q000601:surgery; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D005269:Femur / Q000601:surgery; D006801:Humans; D007718:Knee Injuries / Q000601:surgery*; D007719:Knee Joint / Q000601:surgery*; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D013977:Tibia / Q000601:surgery; D000070600:Tibial Meniscus Injuries; D055815:Young Adult
keywords: ACL reconstruction; MRI; UTE-T2*; anterior cruciate ligament tear; articular cartilage; joint injury; mapping; osteoarthritis; posttraumatic OA; quantitative MRI