title: Comparison of Insall-Salvati ratios in children with an acute anterior cruciate ligament tear and a matched control population.
abstract: OBJECTIVE
  An anterior cruciate ligament (ACL) injury is an increasingly recognized cause of knee pain in young patients and in athletes in particular and can be detected non-invasively with MRI. Anecdotal information suggests that patella alta may be more common in the setting of this injury, but no study has documented this phenomenon. This study sought to test whether an ACL tear is associated with an increased Insall-Salvati ratio suggestive of patella alta.
  
  
  METHODS
  Measurements of patellar height, patellar tendon length, and the Insall-Salvati ratio obtained from MRI of the knee were compared for 34 children with an arthroscopically proven ACL tear (mean age ± SD, 12.4 ± 1.4 years) and 36 control subjects with normal knee examinations (12.8 ± 2.1 years); these measurements were performed independently by two observers.
  
  
  RESULTS
  Patellar tendon length (47.6 ± 6.6 mm vs 40.4 ± 5.7 mm) and patellar position calculated as the Insall-Salvati ratio (1.16 ± 0.16 vs 0.99 ± 0.14) were significantly greater in the knees with an ACL injury than in those without an internal injury, respectively, on MRI (p < 0.001). Patella length was not significantly different between the two groups (patients vs control subjects, 41.1 ± 4.2 mm vs 40.6 ± 2.7 mm, respectively; p = 0.523). There was good to excellent interobserver and intraobserver correlation for all measurements.
  
  
  CONCLUSIONS
  There is a significant association between an ACL tear and increased patellar tendon length with a greater Insall-Salvati ratio. The mechanism for this finding is unclear, but this association provides support to suggest relative patella alta may be a risk factor for ACL injuries in pediatric patients.
authors.affiliation: 1 Department of Radiology, University of Pittsburgh Medical Center, 200 Lothrop St, 3950 South Tower, Pittsburgh, PA 15213.
authors.forename: Andrew Joseph
authors.initials: AJ
authors.lastname: Degnan
authors.forename: Catherine
authors.initials: C
authors.lastname: Maldjian
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Adam
authors.forename: Freddie H
authors.initials: FH
authors.lastname: Fu
authors.forename: Marica
authors.initials: M
authors.lastname: Di Domenica
authors.forename: Marica
authors.initials: M
authors.lastname: Didomenico
mesh_terms: D000293:Adolescent; D000465:Algorithms; D016118:Anterior Cruciate Ligament / Q000473:pathology*; D000070598:Anterior Cruciate Ligament Injuries; D002648:Child; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007718:Knee Injuries / Q000473:pathology*; D022125:Lacerations / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D010329:Patella / Q000473:pathology*; D017847:Patellar Ligament / Q000473:pathology*; D015203:Reproducibility of Results; D012421:Rupture / Q000473:pathology; D012680:Sensitivity and Specificity
keywords: MRI; anterior cruciate ligament tear; knee joint injury; patella alta; patellar tendon injury