Radiographic assessment of the safe zone for medial oblique opening wedge high tibial osteotomy.

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 0º, 5º, 10º, 15º, 20º, and 25º cephalocaudal angles of the X-ray beam. RESULTS The mean internal rotation of the proximal tibia that best demonstrated the safe zone at 0º, 5º, 10º, 15º, 20º, and 25º cephalocaudal angle of the X-ray beam were 50º, 45º, 37º, 32º, 23º, and 19º, respectively. CONCLUSION The safe zone was best demonstrated with 50º and 45º internal rotation of the proximal tibia at 0º and 5º cephalocaudal angles of the X-ray beam, respectively.