The experimental of the optimal angle position of X-ray in the closed reduction of femoral neck fracture using internal fixation

Abstract

Objective To find out the display rules of the key part of the proximal femur and fracture line and obtain the best viewing position and angle by placing the femoral neck at different positions and different angles through X-ray. Meth-ods Six dry specimens of cadaveric femur were from Department of Anatomy, Tianjin Medical University. Three models of com-plete femoral neck model, tin line fracture model and steel saw fracture model were made respectively. The tin line fracture model was based on the Pauwells angle, using the tin wire(1mm) wrapped around the femoral necks to make three kinds of fracture mod-els (Pauwells angle 30°, 50° and 70°); steel saw fracture model was made by hacksaw, then reposition in situ, to make three kinds of fracture models same as the tin line fracture model. The projection manner included different positions and different angles, dif-ferent projection positions include: parallel with the femoral shaft, perpendicular to the femoral shaft, parallel to the femoral neck and perpendicular to the femoral neck; different projection angles included: from 40°, 30°, 20°, 15°, 10° and 5° in the head side to 5°, 10°, 15 °, 20 °, 30 °and 40° in the foot side and vertical angle 0°. For the complete femoral neck model, we observed the imag-ing characteristics of the key parts of the femoral head and neck (tension trabecular bone and pressure trabecular bone; lesser tro-chanter; intertrochanteric line; length of neck of femur and femoral head shape), looking for the display rules, and obtained the best viewing position. For tin line fracture model and steel saw fracture model, we tried to find the best display angle and position by the different projection position and angle. Results The results of complete femoral neck model: Lesser trochanter: in perpen-dicular to the femoral shaft position showed the best, gradually increased with the foot side deflection; tension trabecular bone and pressure trabecular bone: in parallel with the femoral shaft position 10°on the head side; intertrochanteric line: no difference be-tween parallel with the femoral shaft with perpendicular to the femoral shaft;Femoral neck shape: deflect to both sides, head of fe-mur was out of shape. The results of tin line fracture model: the Pauwells angle 30° model showed the best position in parallel with the femoral shaft position 20° on the head side; the Pauwells angle 50° model showed the best position in parallel with the femoral shaft position 5° on the head side; the Pauwells angle 70° model showed the best position in parallel with the femoral shaft position 10° on the head side. The results of steel saw fracture model were the same with the tin line fracture model. Conclusion There was the best viewing angles and positions for the key anatomy of the proximal femur and different Pauwells angle classification of femoral neck fracture. The image doctor could make more accurate projection, according to the different types of femoral neck frac-ture. Key words: Femoral neck fractures; Radiography; Diagnosis