title: MRI criteria for patella alta and baja.
abstract: OBJECTIVE
  To determine the range of the patellar tendon length to patellar length ratio on magnetic resonance imaging (MRI) of the knee in order to aid in the establishment of MRI criteria for patella alta and baja.
  
  
  METHODS
  Two hundred and forty-five patients ages 6-85 (mean 44) years who went through 262 consecutive 1.5 MRI studies of the knee performed during November 2000 through February 2001 were evaluated, regardless of their clinical symptoms.
  
  
  METHODS
  Patellar length (PL) and patellar tendon length (TL) were measured by a single musculoskeletal radiologist on sagittal images by a line connecting the superior and inferior patellar poles and the shortest length of the inner margin of the tendon respectively. TL/PL ratio was subsequently calculated. The distribution of ratios was evaluated; the extreme 2.5% at each end of the distribution was defined as patella alta and baja.
  
  
  RESULTS
  The TL/PL ratio ranged between 0.56 and 1.71 (mean 1.05). After plotting the ratios, we noted an asymmetric curve skewed to the left. Based upon calculation of the extreme 2.5% of the ratio at each end of the plot, we determined that the MRI definition of patella alta and baja is a ratio of TL/PL of more than 1.50 and less than 0.74 respectively. We found that females had significantly higher TL/PL ratio than males (1.0878 and 1.0032 respectively). Ratios defined for patella alta and baja were 1.52 and 0.79 respectively in females and 1.32 and 0.74 respectively in males ( p<0.0001).
  
  
  CONCLUSIONS
  Patella alta and baja are determined as TL/PL of more than 1.50 and less than 0.74 respectively, somewhat different than traditionally quoted radiographic and previously described MRI criteria.
authors.affiliation: Department of Diagnostic Imaging, Chaim Sheba Medical Center, 52621, Tel-Hashomer, Israel. shabshin@yahoo.com
authors.forename: Nogah
authors.initials: N
authors.lastname: Shabshin
authors.forename: Mark E
authors.initials: ME
authors.lastname: Schweitzer
authors.forename: William B
authors.initials: WB
authors.lastname: Morrison
authors.forename: Laurence
authors.initials: L
authors.lastname: Parker
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D010329:Patella / Q000033:anatomy & histology* / Q000473:pathology; D017847:Patellar Ligament / Q000033:anatomy & histology* / Q000473:pathology; D012016:Reference Values