title: Changes in Tip-Apex Distance by Position and Film Distance Measured by Picture Archiving and Communication System (PACS).
abstract: OBJECTIVE
  The tip-apex distance (TAD) is used to predict the clinical outcome of intertrochanteric fracture fixation. We aimed to measure the changes in TAD by position and film distance using Picture Archiving and Communication System (PACS).
  
  
  METHODS
  We used a femur replica with a 10° femoral neck anteversion and a 130° neck shaft angle. Proximal femoral nail antirotation nail and a helical blade were inserted into the replica. Radiographs were taken at the neutral position and after applying 10°, 20°, 30°, 40° internal/external rotation, 10° abduction, and 10° and 40° adduction to the mechanical axis. Radiographs were taken at the replica-film distance of 10 cm and 20 cm under the same conditions, mimicking the differences in Focus-film distance (FFD), which reflect the patient's contour in clinical settings. A radiologist and an orthopedic surgeon measured the TAD twice using PACS. The average error was 2 mm (4.5%) and the standard error was ±3.04. TADs in the neutral position constituted the standard values to measure the relative errors.
  
  
  RESULTS
  TADs increased with an increase in the external rotation and abduction of the replica. TADs decreased with an increase in the internal rotation and adduction of the replica. For comparable measurements, relative errors were higher at FFDs of 20 cm compared to FFDs of 10 cm.
  
  
  CONCLUSIONS
  Since the femur is internally rotated and adducted for reduction, orthopedic surgeons would assess the lag screw to be closer to the apex of femur on intraoperative radiographs. To have a correct measurement of the TAD after fixation of intertrochanteric fractures, radiographs should be taken in neutral position and measurement errors should be considered based on the patient's size.
authors.affiliation: Department of Orthopaedic Surgery, Dong-A University College of Medicine, Busan, Korea.
authors.forename: Kyu Yeol
authors.initials: KY
authors.lastname: Lee
authors.affiliation: Department of Orthopaedic Surgery, Dong-A University College of Medicine, Busan, Korea.
authors.forename: Sung Soo
authors.initials: SS
authors.lastname: Kim
authors.affiliation: Department of Orthopaedic Surgery, Dong-A University College of Medicine, Busan, Korea.
authors.forename: Hyeon Jun
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Department of Diagnostic Radiology, Dong-A University College of Medicine, Busan, Korea.
authors.forename: Dong Ho
authors.initials: DH
authors.lastname: Ha
authors.affiliation: Department of Orthopaedic Surgery, Dong-A University College of Medicine, Busan, Korea.
authors.forename: Hyung Min
authors.initials: HM
authors.lastname: Yoon
authors.affiliation: Department of Orthopaedic Surgery, Dong-A University College of Medicine, Busan, Korea.
authors.forename: Hyun Su
authors.initials: HS
authors.lastname: Do
keywords: Intertrochanteric fractures; Picture Archiving and Communication System; Tip-apex distance