Changes in Tip-Apex Distance by Position and Film Distance Measured by Picture Archiving and Communication System (PACS) / 대한고관절학회지

ABSTRACT

PURPOSE: 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). MATERIALS AND METHODS: We used a femur replica with a 10degrees femoral neck anteversion and a 130degrees 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 10degrees, 20degrees, 30degrees, 40degrees internal/external rotation, 10degrees abduction, and 10degrees and 40degrees 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. CONCLUSION: 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.