Improved Calculation Method of TAD for Intertrochanteric Fractures

To investigate the relative position of femur fixed screws using intramedullary systems for intertrochanteric fractures and to improve the accurate measurement method of the tip-to-apex distance (TAD) while providing a theoretical basis for the clinical treatment of such fractures.

In the anteroposterior (AP) radiographs of the hip joint, the femoral neck axis through the femoral head geometry point was designated as the X-axis, while the line perpendicular to the X-axis passing through the femoral head geometry point was designated as the Y-axis. In the lateral radiographs of the hip joint, the line perpendicular to the X-axis passing through the femoral head geometry point was identified as the Z-axis. The head of the nail tip's location projected on the three axes was described as A _AP, B in the AP radiographs; and A _LAT, C in the lateral radiograph. The TAD was described as X _AP and X _LAT. The radius of the femoral head was D. All distance units were expressed in mm.

When the lateral projection angle was standardized, the A _AP was equal to the A _LAT, while the X _AP ²=B ²+(D - A _AP)² and X _LAT ²=C ²+(D - A _LAT)². When the lateral projection angle was not standardized, the value of C had no significant change; however, the (D - A _LAT) value changed.

The measurement value did not match the actual values of TAD when the lateral projection angle was not standardized, possibly leading to a misinterpretation during clinical work. The X _LAT should be amended using the formula X _LAT ²=C ²+(D - A _AP)².