Improved Calculation Method of TAD for Intertrochanteric Fractures

PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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).