title: A new quantitative radiographic measurement of patella for patellar instability using the lateral plain radiograph: 'patellar width ratio'.
abstract: OBJECTIVE
  Patellar width ratio, a new measurement of anterior-posterior patellar width, was developed using lateral radiographs. The hypothesis was that patellar width ratio would increase with increasing patellar tilt angle and that patients with patellar instability would have larger patellar width ratio compared to controls.
  
  
  METHODS
  Fifty knees who underwent surgery for patellar instability were enrolled as Group P. The fifty knees without patellar instability were enrolled as controls (Group C). Patellar width ratio was measured using preoperative lateral radiographs. The width between proximal and distal apexes of patella was defined as A. The width between anterior and posterior margins of patella was defined as B. Patellar width ratio was defined as the ratio B/A. Patellar tilt angle was measured on preoperative computed tomography images. Values were compared between groups and their correlation examined, and a receiver operating characteristic (ROC) curve was generated to identify the threshold value.
  
  
  RESULTS
  Mean patellar width ratio in Groups C and P was 0.54 ± 0.04 and 0.66 ± 0.11 (P < 0.01). Mean patellar tilt angle in Groups C and P was 12.8° ± 4.9° and 32.0° ± 10.3° (P < 0.01). Patellar width ratio was strongly correlated with patellar tilt angle (R = 0.83, P < 0.01). For patellar width ratio, the area under ROC curve was 0.86, and the cut-off value was 0.59 (sensitivity 76.0 %, specificity 90.0 %).
  
  
  CONCLUSIONS
  Patellar width ratio in Group P was significantly larger than in Group C. Patellar width ratio would allow clinicians to evaluate patellar tilt on lateral radiographs.
  
  
  METHODS
  III.
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1, Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan. kurodar@med.kobe-u.ac.jp.
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Kuroda
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1, Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Kanto
authors.initials: K
authors.lastname: Nagai
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1, Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Matsushita
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1, Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Araki
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1, Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Matsumoto
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1, Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Takayama
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1, Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kurosaka
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging* / Q000601:surgery; D007719:Knee Joint / Q000000981:diagnostic imaging; D008297:Male; D010329:Patella / Q000000981:diagnostic imaging*; D031222:Patellar Dislocation / Q000000981:diagnostic imaging*; D057071:Patellofemoral Joint / Q000000981:diagnostic imaging*; D055815:Young Adult
keywords: Knee; Patellar dislocation; Patellar instability; Patellar tilt; Patellar width ratio; Radiograph