Fig. 2

Illustration of the key steps of the novel technology group. a–c The distal femoral osteotomy. The red dot in a was the position where the anatomical axis of the distal femur penetrated the distal femur cortex on the preoperative 3D model, i.e., the femoral entry point; b the accurate positioning of the femoral entry point during surgery; c the intramedullary positioning rod was inserted from the femoral entry point into the medullary cavity for about 20 cm, and the distal femur osteotomy was performed according to the projection angle of the HKS on the coronal plane. d–g The positioning of the proximal end of the tibial extramedullary rod. The red dot in d was the position where the tibial anatomical axis penetrated the tibial plateau cortex, i.e., the fix point of the tibial plateau extramedullary guide pin; e the accurate positioning of the above anchor point during surgery; f, g the tibial extramedullary guide pin was fixed to the anchor point to ensure the accurate positioning of the extramedullary positioning rod at the proximal end of the tibia during the surgery and on the preoperative 3D models, respectively. h–j The coronal positioning of the distal end of the tibial extramedullary rod; h distance between the midpoint of the ankle mortise and the midpoint of medial and lateral malleolus; i, j the accurate positioning of the distal end of the tibial extramedullary rod on the coronal plane with reference to the above preoperative design during the surgery and on the preoperative 3D model, respectively. k–n The sagittal positioning of the distal end of the tibial extramedullary rod. k the thickness of the anterior tibial soft tissue at 3 cm above the ankle mortise; l the distance between the anterior tibial cortex and the distal tibial extramedullary positioning rod; m, n the accurate positioning of the distal end of the tibial extramedullary rod on the sagittal plane was ensured with reference to the distance between the anterior tibial skin and the distal tibial extramedullary positioning rod (the distance between the anterior tibial cortex and the distal tibial extramedullary positioning rod minus the thickness of the anterior tibial soft tissue) during the surgery and on the preoperative 3D model, respectively