title: T1ρ imaging demonstrates early changes in the lateral patella in patients with patellofemoral pain and maltracking.
abstract: BACKGROUND
  Patellofemoral pain (PFP) is a common condition and often presents without evidence of arthritis on radiographs. Magnetic resonance imaging (MRI) has shown good correlation between T1ρ and T2 relaxation times and changes in the cartilage matrix, but as of yet, there are limited data in the literature utilizing these modalities to evaluate the patellofemoral joint.
  
  
  OBJECTIVE
  Patients with PFP and patellar tilt will show longer T1ρ relaxation times in the lateral facets of their patella but no difference in T2 values.
  
  
  METHODS
  Cross-sectional study; Level of evidence, 3.
  
  
  METHODS
  A total of 20 patients aged 18 to 45 years with anterior knee pain, patellar tilt, and no evidence of osteoarthritis were identified and consented to undergo MRI including axial T1ρ and T2 relaxation time mapping sequences. Knee cartilage was segmented on spoiled gradient recalled acquisition in steady state (SPGR) images using a spline-based algorithm. These results were then compared with those of 10 age-matched controls.
  
  
  RESULTS
  The mean T1ρ values of the lateral facets were significantly elevated in patients with PFP compared with controls (46.33 ± 4.92 ms vs. 42.32 ± 3.67 ms, respectively; P = .031), while no significant difference was observed in the medial facets (42.20 ± 5.55 ms vs. 41.42 ± 4.09 ms, respectively; P = .69). Significantly higher mean T1ρ values were noted in the lateral facets of the patients with PFP (46.33 ms) compared with the medial facets (42.20 ms) (P = .0001), while no significant differences in T1ρ values were observed between the medial and lateral facets of the controls (P = .502). No significant differences were noted in T2 relaxation times. A high correlation was noted between the mean T1ρ values of the whole patella of patients with PFP and the degree of patellar tilt (r = 0.72).
  
  
  CONCLUSIONS
  There were significantly higher T1ρ values in the lateral facets of patients with PFP and patellar tilt that were not seen in control patients. These higher values approach the numbers seen in patients with early osteoarthritis.
authors.affiliation: Department of Orthopaedic Surgery, University of California, San Francisco, 500 Parnassus Avenue, MUW 3rd Floor, Box 0728, San Francisco, CA 94143, USA. daniel.thuillier@ucsf.edu
authors.forename: Daniel U
authors.initials: DU
authors.lastname: Thuillier
authors.forename: Richard B
authors.initials: RB
authors.lastname: Souza
authors.forename: Samuel
authors.initials: S
authors.lastname: Wu
authors.forename: Anthony
authors.initials: A
authors.lastname: Luke
authors.forename: Xiaojuan
authors.initials: X
authors.lastname: Li
authors.forename: Brian T
authors.initials: BT
authors.lastname: Feeley
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D018771:Arthralgia / Q000209:etiology*; D017760:Bone Malalignment / Q000150:complications / Q000175:diagnosis*; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010329:Patella / Q000473:pathology / Q000503:physiopathology; D057071:Patellofemoral Joint / Q000473:pathology / Q000503:physiopathology; D055815:Young Adult
keywords: MRI; T1ρ; T2; cartilage; knee; osteoarthritis; patella; patellofemoral maltracking; patellofemoral pain