title: Length change behavior of virtual medial patellofemoral ligament fibers during in vivo knee flexion.
abstract: BACKGROUND
  In vivo length change behavior of native medial patellofemoral ligament (MPFL) fibers throughout the range of knee motion has not been reported in vivo.
  
  
  OBJECTIVE
  To measure the length changes of various fibers of the MPFL and to determine their length change patterns during in vivo passive knee flexion.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  The right knees of 11 living subjects were scanned with a high-resolution computed tomography scanner at 0°, 30°, 60°, 90°, and 120° of knee flexion, and 3-dimensional (3D) models were constructed using customized software. Five patellar points were determined: 20% (point 20), 30% (point 30), 40% (point 40), 50% (point 50), and 60% (point 60) from the superior pole of the patella. The Schöttle femoral point (point F) was marked on a translucent 3D model of a true lateral view. Five virtual fibers connecting these points on the 3D knee model were created, and the lengths of various fibers were digitally measured.
  
  
  RESULTS
  The average length changes were 9.1±2.5 mm in F20, 9.1±2.5 mm in F30, 8.1±2.6 mm in F40, 6.9±2.4 mm in F50, and 6.9±1.7 mm in F60. There were significant differences in length changes of these 5 fibers (P<.001). The lengths of 2 superior fibers (F20 and F30) increased as the knee flexed from 0° to 30° and decreased as the knee flexed over 30°. The lengths of a middle fiber (F40) and an inferior fiber (F50) increased from 0° to 30°, reached a plateau from 30° to 60°, and then decreased from 60° to 120°. F60 showed an increase from 0° to 30°, and then a plateau pattern from 30° to 90°, followed by a decrease during further flexion.
  
  
  CONCLUSIONS
  Superior fibers exhibited their maximum lengths at low flexion angles, and inferior fibers exhibited their maximum lengths at midflexion angles. The MPFL is a complex of functionally various fibers with some taut and others slack over the whole range of knee motion.
  
  
  CONCLUSIONS
  The results for lengths and length change patterns of various MPFL fibers are expected to serve as a theoretical background for anatomic double-bundle MPFL reconstruction.
authors: Department of Orthopaedic Surgery, Dongtan Sacred Heart Hospital, Hallym University College of Medicine, Hwaseong, Republic of Korea kneearthro@gmail.com.
authors: Si Young
authors: SY
authors: Song
authors: Department of Orthopaedic Surgery, Dongtan Sacred Heart Hospital, Hallym University College of Medicine, Hwaseong, Republic of Korea.
authors: Chae-Hyun
authors: CH
authors: Pang
authors: Department of Orthopaedic Surgery, Dongtan Sacred Heart Hospital, Hallym University College of Medicine, Hwaseong, Republic of Korea.
authors: Chan Hyoek
authors: CH
authors: Kim
authors: Department of Orthopaedic Surgery, Seoul Sacred Heart General Hospital, Seoul, Republic of Korea.
authors: Jeehyoung
authors: J
authors: Kim
authors: Department of Data Statistics, Korea Culture & Tourism Institute, Seoul, Republic of Korea.
authors: Mi Lim
authors: ML
authors: Choi
authors: Department of Orthopaedic Surgery, Dongtan Sacred Heart Hospital, Hallym University College of Medicine, Hwaseong, Republic of Korea.
authors: Young-Jin
authors: YJ
authors: Seo
mesh_terms: D000328:Adult; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008022:Ligaments / Q000000981:diagnostic imaging / Q000502:physiology*; D008297:Male; D010329:Patella / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D014057:Tomography, X-Ray Computed
keywords: 3-dimensional knee model; fiber length change; medial patellofemoral ligament; patella