title: Discoid lateral meniscus and the frequency of meniscal tears.
abstract: OBJECTIVE
  To use MRI to determine the incidence of discoid lateral menisci in a large study population, and to compare those patients with those without a discoid meniscus in order to assess the impact of a discoid lateral meniscus on the frequency of meniscal tears.
  
  
  METHODS
  Results of 1,250 knee MRI studies were retrospectively reviewed. Using the criterion of three or more meniscal body segments on sequential sagittal images, 56 patients were found to have a discoid lateral meniscus. After exclusion of patients with prior knee surgery, 49 patients with a discoid lateral meniscus were compared with 1,146 patients without a discoid meniscus. Patients were categorized as having tears of the medial meniscus, lateral meniscus, or both menisci.
  
  
  RESULTS
  In our study population, there was a 4.5% incidence of discoid lateral meniscus. Seventy-one percent of patients with a discoid lateral meniscus had one or more meniscal tears, compared with 54% of the comparison group (P=0.01). The frequency of solitary lateral meniscal tears in the discoid group was also higher than in the comparison group: 20%.versus 11% (P=0.03). The frequency of solitary medial meniscal tears and concomitant tears of both menisci were not significantly different between the two groups.
  
  
  CONCLUSIONS
  The discoid lateral meniscus is an uncommon variant, but not as rare as once believed. Compared with the normal semilunar meniscus, the discoid lateral meniscus has a higher frequency of meniscal tears, and solitary tears of the lateral meniscus are more common in the discoid variant. The frequency of medial meniscal tears is not altered by the presence of a discoid lateral meniscus.
authors.affiliation: Department of Radiology, Duke University, Durham, NC 27710, USA.
authors.forename: E M
authors.initials: EM
authors.lastname: Rohren
authors.forename: F J
authors.initials: FJ
authors.lastname: Kosarek
authors.forename: C A
authors.initials: CA
authors.lastname: Helms
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D015994:Incidence; D008279:Magnetic Resonance Imaging; D008297:Male; D008592:Menisci, Tibial / Q000473:pathology*; D008875:Middle Aged; D012189:Retrospective Studies; D000070600:Tibial Meniscus Injuries; D014947:Wounds and Injuries / Q000453:epidemiology