title: Radiographic Reference Points Are Inaccurate With and Without a True Lateral Radiograph: The Importance of Anatomy in Medial Patellofemoral Ligament Reconstruction.
abstract: BACKGROUND
  Studies have reported methods for radiographically delineating medial patellofemoral ligament (MPFL) femoral tunnel position on a true lateral knee radiograph. However, obtaining a true lateral fluoroscopic radiograph intraoperatively can be challenging, rendering radiographic methods for tunnel positioning potentially inaccurate.
  
  
  OBJECTIVE
  To quantify the magnitude of MPFL femoral tunnel malposition that occurs on true lateral and aberrant lateral knee radiographs when using a previously reported radiographic technique for MPFL femoral tunnel localization.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  Ten fresh-frozen cadaveric knees were dissected to expose the MPFL femoral insertion and surrounding medial knee anatomy. True lateral and aberrant lateral knee radiographs at 2.5°, 5°, and 10° off-axis were obtained with a standard mini C-arm in 4 orientations: anterior to posterior, posterior to anterior, caudal, and cephalad. A previously reported radiographic method for MPFL femoral localization was performed on all radiographs and compared in reference to the anatomic MPFL attachment center.
  
  
  RESULTS
  The radiographic point, as previously described, was a mean distance of 4.1 mm from the anatomic MPFL attachment on a true lateral knee radiograph. The distance between the anatomic MPFL attachment center and the radiographic point significantly increased on aberrant lateral knee radiographs with as little as 5° of rotational error in 3 of 4 orientations of rotation when a standard mini C-arm was used. This corresponded to a malposition of 7.5, 9.2, and 8.1 mm on 5°-aberrant radiographs in the anterior-posterior, posterior-anterior, and cephalad orientations, respectively (P < .005). In the same 3 orientations of rotation, MPFL tunnel malposition on the femur exceeded 5 mm on 2.5° aberrant radiographs.
  
  
  CONCLUSIONS
  The commonly utilized radiographic point, as previously described for MPFL femoral tunnel placement, results in inaccurate tunnel localization on a true lateral radiograph, and this inaccuracy is perpetuated with aberrant radiography. Aberrant lateral knee imaging of as little as 5° off-axis from true lateral has a significant effect on placement of a commonly used radiographic point relative to the anatomic MPFL femoral attachment center and results in nonanatomic MPFL tunnel placement.
  
  
  CONCLUSIONS
  This study demonstrates that radiographic localization of the MPFL femoral tunnel results in inaccurate tunnel placement on a true lateral radiograph, particularly when there is deviation from a true lateral fluoroscopic image, which can be difficult to obtain intraoperatively. Assessing anatomy directly intraoperatively, rather than relying solely on radiographs, may help avoid MPFL tunnel malposition.
authors.affiliation: Department of Orthopaedic Surgery, University of Connecticut Health Center, Farmington, Connecticut, USA connor.ziegler@gmail.com.
authors.forename: Connor G
authors.initials: CG
authors.lastname: Ziegler
authors.affiliation: Orthopedic Associates of Hartford, Hartford, Connecticut, USA.
authors.forename: John P
authors.initials: JP
authors.lastname: Fulkerson
authors.affiliation: Orthopedic Associates of Hartford, Hartford, Connecticut, USA.
authors.forename: Cory
authors.initials: C
authors.lastname: Edgar
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000601:surgery; D005471:Fluoroscopy; D006801:Humans; D008023:Ligaments, Articular / Q000000981:diagnostic imaging* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D057071:Patellofemoral Joint / Q000000981:diagnostic imaging* / Q000601:surgery*; D012399:Rotation
keywords: adductor tendon tubercle; medial patellofemoral ligament; medial patellofemoral ligament reconstruction; patellar instability; radiographic landmarks; tunnel placement