title: Quantitative analysis of dynamic patellar tracking in patients with lateral patellar instability using a simple video system.
abstract: BACKGROUND
  As patellar dislocation occurs during activity, it is more important to assess the behavior of the patellofemoral joint under dynamic conditions. The aim of this study was to compare patellar tracking between knees with and without patellar dislocation in patients with an unstable patella and healthy controls using a simple video technique.
  
  
  METHODS
  Twenty-three knees with patellar dislocation (dislocated group), 23 contralateral knees without dislocation (non-dislocated group), and 23 healthy knees (control group) were examined. Those with skin markers on anatomical landmarks were made to extend their knees actively, and skin markers were attached to the examiner's fingertips and the patella was followed by pinching. The knee during active knee extension was recorded with digital video cameras. The patella was tracked on imaging software, and the mediolateral patellar position (% patellar position: %PP) was calculated in reference to the knee width consecutively.
  
  
  RESULTS
  %PP was significantly different between the dislocated and control groups, from 30° (mean±SD: 58.9±6.2%, 54.6±4.7%) to 5° (64.2±5.2%, 55.2±5.2%). It was also significantly different between the non-dislocated and control groups, from 25° (58.9±7.1%, 54.5±4.6%) to 5° (63.8±6.5%, 55.2±5.2%). No significant difference in %PP was found between the dislocated and non-dislocated groups.
  
  
  CONCLUSIONS
  With the new video system, patellar tracking during active knee extension was successfully quantified. The tracking patterns were the same in knees with and without patellar dislocation, and the tracking in patients significantly differed from that in the controls at lower knee flexion angles.
  
  
  CONCLUSIONS
  The development of a quantitative examination technique for dynamic patellar tracking, which is easy to use and repeatedly applicable in a clinical situation, could help to follow-up the time-dependent changes and analyze the treatment effect on an unstable patella.
authors.affiliation: Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, 5 Zaifu-cho, Hirosaki, Aomori 036-8562, Japan. Electronic address: yuki2jp@hirosaki-u.ac.jp.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Fujita
authors.affiliation: Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, 5 Zaifu-cho, Hirosaki, Aomori 036-8562, Japan.
authors.forename: Eiichi
authors.initials: E
authors.lastname: Tsuda
authors.affiliation: Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, 5 Zaifu-cho, Hirosaki, Aomori 036-8562, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Yamamoto
authors.affiliation: Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, 5 Zaifu-cho, Hirosaki, Aomori 036-8562, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Naraoka
authors.affiliation: Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, 5 Zaifu-cho, Hirosaki, Aomori 036-8562, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Kimura
authors.affiliation: Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, 5 Zaifu-cho, Hirosaki, Aomori 036-8562, Japan.
authors.forename: Shizuka
authors.initials: S
authors.lastname: Sasaki
authors.affiliation: Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, 5 Zaifu-cho, Hirosaki, Aomori 036-8562, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Ishibashi
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008297:Male; D010329:Patella / Q000000981:diagnostic imaging* / Q000503:physiopathology; D031222:Patellar Dislocation / Q000000981:diagnostic imaging* / Q000503:physiopathology; D057071:Patellofemoral Joint / Q000000981:diagnostic imaging* / Q000503:physiopathology; D016059:Range of Motion, Articular; D014741:Video Recording; D055815:Young Adult
keywords: Dynamic patellar tracking; Kinematics; Unstable patella; Video analysis