Hip Pelvis.  2015 Mar;27(1):36-42. 10.5371/hp.2015.27.1.36.

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

• Lee KY
• Kim SS
• Kim HJ
• Ha DH
• Yoon HM
• Do HS

• KMID: 2156018
• DOI: http://doi.org/10.5371/hp.2015.27.1.36

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.

Keyword

Intertrochanteric fractures; Tip-apex distance; Picture Archiving and Communication System

MeSH Terms

Axis
Femur
Femur Neck
Fracture Fixation
Hip Fractures
Neck
Orthopedics

Figure

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  Fig. 1 Proximal femoral nail antirotation nail and a helical blade inserted into the femur replica. (A) Anteroposterior and (B) lateral views.

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  Fig. 2 (A) Radiograph is taken after applying internal/external rotation to the mechanical axis. (B) Anteroposterior radiograph in neutral position. (C) Radiograph is taken after applying abduction/adduction to the mechanical axis. (D) Lateral radiograph in 15° external rotation.

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  Fig. 3 Radiographs are taken at replica-film distances of 10 cm and 20 cm under same conditions.

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  Fig. 4 Tip-apex distance (TAD) is the summation of the distance, in millimeters, from the tip of the lag screw to the apex of the femoral head on the anteroposterior (ap) and lateral (lat) radiographs.

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  Fig. 5 Tip-apex distance (TAD) on the anteroposterior view.

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  Fig. 6 Tip-apex distance (TAD) on the lateral view.

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