PMC6755290_01
Preoperative CT scan femoral torsion measurements are shown. In the left leg, the femoral torsion is 32 ; the right leg has a torsion of 23 . Measurements were made according to the technique described by Jarrett et al..
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CT measurements are summarised in Table 1, and an increased femoral internal rotation was the main finding (Figure 1).
Illustrations that represent the surgery in the left femur. (a) The lateral cortex of the distal third of the femoral shaft was marked with a parallel line to the long axis to guide the correction (black line). A transverse bone cut (red line) parallel to the shaft axis was performed in the middle of the black line. (b) By a percutaneous approach to the knee, a retrograde femoral nail (T2, Stryker ) was placed. To begin with, a proximal blocking screw was placed in the dynamic hole. (c) The distal end of the osteotomy was externally rotated, as planned. (d) The parallel line to the axis of the diaphysis was the guide (black line), and the rotation was performed until both lines were separated by 0.8 cm. Immediately after the derotational maneuver, two distal locking screws were placed in the distal end of the nail.
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Immediately after the derotational maneuver, two distal locking screws were placed in the distal end of the nail (Figure 2).
The enlarged image of the left knee of the full-length standing AP radiography before surgery (a) and enlarged image 8 months after surgery (b) are shown. Both were taken with 15  of internal rotation of the foot. The perimeter of the patella is highlighted in red, and the medialization of the patella due to the derotational osteotomy is observed.
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The eight-month postsurgery radiographs are shown in Figure 3 and are compared with the preoperative radiographs. It is remarkable how the patella looks medialised compared to the preoperative study (Figure 3), and as planned, the coronal alignment was not changed (Figure 4(a)) achieving a femoral-tibial mechanical angle after surgery of 0.51  of valgus.
Radiographs at eight months after surgery are shown. (a) Full-length standing AP radiography of the lower extremity six months after surgery. Coronal alignment is symmetrical. (b) Femoral-tibial mechanical angle is 0.51  of valgus and mDLFA is 86 . (c) Lateral radiography of the femur. It shows complete healing of the osteotomy (red arrow). Also, the proximal locking of the nail and the entry point chosen in the distal femur for the LPFM can be observed.
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It is remarkable how the patella looks medialised compared to the preoperative study (Figure 3), and as planned, the coronal alignment was not changed (Figure 4(a)) achieving a femoral-tibial mechanical angle after surgery of 0.51  of valgus. At the eight-month follow-up, the osteotomy was completely healed (Figures 4(b) and 4(c)).
13-month postsurgery CT scan. The final femoral torsion that was achieved is shown, measuring 6.4 . Femoral torsion according to the method described by Jarrett et al. was used.
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At the 18-month follow-up, a CT scan was performed, and femoral torsion was 6.4  (Figure 5).