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. 2023 Apr 17;109(5):1158–1168. doi: 10.1097/JS9.0000000000000369

Figure 5.

Figure 5

Clinical significance of axial safe target area (ASTA). (A) Schematic of preoperative design of individualized screws spatial configuration based on the individualized ASTA. Recommend three screws should be arranged parallel to the central axis and distributed in the three vertices of the ASTA triangle with scattered welt. A1: The ASTA and its coordinate system were projected to the lateral side of the proximal femur to facilitate a visual understanding of the spatial location and orientation of the ASTA. A2: There was an individual angle between the anterior base of ASTA (AB-ASTA) and the coronal plane of proximal femur (PFCP). A3: Comparing with the actual ASTA, the hypothetical oval safe zone (HOSZ) used in the navigation system had a certain error, which could cause IOI screws. A4: The spatial configuration of the screws scattered at the three vertices of the ASTA was projected to the lateral wall of the proximal femur to facilitate a visual understanding of the spatial location and layout of the screws. A5: The inverted triangular distribution of the screws was projected to the lateral wall of the proximal femur. A6: The triangular distribution of the screws was projected to the lateral wall of the proximal femur. A7: Axial computed tomography (CT) of the spatial configuration of screws scattered at three vertices of ASTA corresponding to A4, and its fixed cross-sectional area was larger than those of the inverse-triangular and triangular configuration. A8: Axial CT of the distribution configuration of the inverted triangular screws, corresponding to A5. A9: Axial CT of the distribution configuration of the triangular screws, corresponding to A6. (B–D) Taking the screw guide pin S2 as an example, the process of calculating their coordinates in ASTA through intraoperative anteroposterior and lateral x-rays was demonstrated. (B) Measure the distances from S2 center to the superior–inferior borders respectively in anteroposterior x-ray (a1, a2), y2=(a2−a1)×d1/[2×(a1+a2)]. d1 was superior–inferior diameter (D-SI) of ASTA measured in CT. (C) Measure the distances from S2 center to the anterior–posterior edges respectively in lateral x-ray (b1, b2), z2=(b2−b1)×d2/[2×(b1+b2)]. d2 was anterior–posterior diameter (D-AP) of ASTA measured in CT. (D) In ASTA on the YOZ coordinate system, the coordinates point S2 (y2, z2) calculated above was marked to obtain the coordinate position of S2 center in ASTA and to judge whether the screw or guild pin penetrates cortical bone or not intuitively. The same as S1 and S3. (E) Axial CT postoperative showed the coordinate position of each guide pin, which was consistent with the calculation result in (D). Due to metal interference, there were guide pin diameter enlargement and artifacts.