| Summary: | Purpose. To compare different cephalocaudal angles of the X-ray beam in measuring internal rotation of the proximal tibia that best demonstrates the safe zone. Methods. 10 pairs of embalmed, disarticulated knee joints from 10 cadavers were used. Soft tissues around the proximal tibia and the proximal tibiofibular joint (PTFJ) were dissected to reveal the articular cartilage. A narrow area between the end of the articular cartilage of the posterolateral proximal tibia and of the PTFJ was identified as the safe zone with a U-shape metal used as a radiographic marker. Translation of the proximal tibia was controlled during internal rotation of the proximal tibia. Internal rotation of the proximal tibia that best demonstrated the safe zone (the U-shape metal at its most outermost point) was measured at 0°, 5°, 10°, 15°, 20°, and 25° cephalocaudal angles of the X-ray beam. Results. The mean internal rotation of the proximal tibia that best demonstrated the safe zone at 0°, 5°, 10°, 15°, 20°, and 25° cephalocaudal angle of the X-ray beam were 50°, 45°, 37°, 32°, 23°, and 19°, respectively. Conclusion. The safe zone was best demonstrated with 50° and 45° internal rotation of the proximal tibia at 0° and 5° cephalocaudal angles of the X-ray beam, respectively.
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