title: MPFL graft fixation in low degrees of knee flexion minimizes errors made in the femoral location.
abstract: OBJECTIVE
  To evaluate the appropriate amount of knee flexion in which to secure the graft during medial patellofemoral ligament (MPFL) reconstruction.
  
  
  METHODS
  Heavy suture was used to simulate graft tissue during MPFL reconstruction on eight fresh-frozen cadaveric knees. The sutures were passed through two transverse patellar tunnels and draped over a Kirschner wire at Schöttle's point on the femur. Suture displacement at the location of the wire was measured during knee range of motion from 0 to 135°. The wire's location was then moved to 3 additional locations (1 cm proximal, 1 cm distal, and 1 cm anterior), and the measurements were repeated.
  
  
  RESULTS
  Using Schöttle's point, the suture length did not vary throughout all ranges of knee flexion. The distal location resulted in a greater distance between attachment points (i.e. graft tightened) if the measurements began with the knee flexed and then brought into extension. Conversely, with the proximal location, the opposite occurred as the knee was extended (i.e. graft loosened). For all locations other than Schöttle's point, the amount of initial knee flexion for fixation was directly related to the amount of suture length change when the knee was brought into extension.
  
  
  CONCLUSIONS
  For non-anatomic femoral MPFL graft fixation locations, suture length (and thus graft length) in full extension becomes increasingly altered if the graft is secured in high degrees of knee flexion. Thus, graft fixation in lower degrees of knee flexion is recommended to minimize over or under tensioning the graft when the knee goes into extension if the graft position is placed in a non-anatomic location. To avoid this problem, fluoroscopy should be used to locate the anatomic footprint of the MPFL insertion. While recognizing the limitations of cadaveric research, this study is the first to provide any data to corroborate the widely used practice of securing the MPFL in lower degrees of knee flexion.
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia Health System (HSC), PO Box 800159, Charlottesville, VA, 22908, USA. tyrrellburrus@gmail.com.
authors.forename: M Tyrrell
authors.initials: MT
authors.lastname: Burrus
authors.affiliation: Sports Medicine and Shoulder Surgery, Hospital For Special Surgery, New York, NY, USA.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Werner
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia Health System (HSC), PO Box 800159, Charlottesville, VA, 22908, USA.
authors.forename: Jourdan M
authors.initials: JM
authors.lastname: Cancienne
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia Health System (HSC), PO Box 800159, Charlottesville, VA, 22908, USA.
authors.forename: F Winston
authors.initials: FW
authors.lastname: Gwathmey
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia Health System (HSC), PO Box 800159, Charlottesville, VA, 22908, USA.
authors.forename: David R
authors.initials: DR
authors.lastname: Diduch
mesh_terms: D000368:Aged; D002102:Cadaver; D005260:Female; D005471:Fluoroscopy; D006801:Humans; D008023:Ligaments, Articular / Q000601:surgery*; D008297:Male; D019300:Medical Errors / Q000517:prevention & control*; D057071:Patellofemoral Joint / Q000601:surgery*; D016059:Range of Motion, Articular / Q000502:physiology; D013514:Surgical Procedures, Operative / Q000379:methods*; D013537:Sutures; D019737:Transplants / Q000601:surgery*
keywords: Cadaver; Knee flexion; MPFL; Schöttle’s point