title: Incidence of medial plica in 3,889 knee joints in the Japanese population.
abstract: OBJECTIVE
  This study aimed to document the incidence of medial plicae (plica synovialis mediopatellaris) in a large sample of the Japanese population and classify them in a type-dependent manner.
  
  
  METHODS
  The incidence of medial plicae was investigated during arthroscopic surgery of 3,889 knee joints in 3,563 patients (mean age, 35 years); medial plicae were classified according to Sakakibara's classification (type A, a cord-like elevation in the synovial wall; type B, a shelf-like appearance; type C, a large shelf-like appearance covering the anterior surface of the medial femoral condyle; and type D, double insertions into the medial wall or having a central defect). Of all the knee joints examined, 2,006 knees belonged to male patients and 1,883 to female patients. Both knee joints were examined in 326 patients. From these data, the incidence of medial plicae was calculated.
  
  
  RESULTS
  The overall incidence rate of medial plicae was 79.9%. The incidence of Sakakibara type A, B, C, and D medial plicae was 35.2%, 22.4%, 12.3%, and 10.0%, respectively. This pattern was reflected in all age groups in both genders, except in women aged 20 to 39 years. The κ coefficient was moderate, at 0.407, in the patients in whom both knee joints were examined.
  
  
  CONCLUSIONS
  In a large cohort of Japanese patients undergoing arthroscopic knee surgery, the incidence of medial plica was 79.9%. The same pattern was seen in almost all age groups and in both genders (type A > type B > type C > type D).
  
  
  METHODS
  Level IV, prognostic case series.
authors.affiliation: Tohoku Orthopaedic Clinic, Sendai, Japan.
authors.forename: Akari
authors.initials: A
authors.lastname: Nakayama
authors.forename: Takehiko
authors.initials: T
authors.lastname: Sugita
authors.forename: Toshimi
authors.initials: T
authors.lastname: Aizawa
authors.forename: Atsushi
authors.initials: A
authors.lastname: Takahashi
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Honma
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D001182:Arthroscopy; D002648:Child; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D007719:Knee Joint / Q000002:abnormalities* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009139:Musculoskeletal Abnormalities / Q000453:epidemiology*; D012189:Retrospective Studies; D017678:Sex Distribution; D055815:Young Adult