[Slope and frontal axis: three-dimensional analysis and correction with patient-specific cutting guides for the proximal tibia].

Objective: Three-dimensional correction of the bony alignment in the frontal and sagittal plane of the proximal tibia; surgery is performed via an open- or closing-wedge osteotomy to improve ligament stability and reduce joint degeneration.

Indications: Chronic anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) instability and ligament revision surgeries; subjective knee instability in patients who are ambitious athletes and people who do physical labor; moderate joint degeneration with meniscus and cartilage damage, post-traumatic deformities.

Contraindications: Time pressure (immediate meniscus surgery, since planning and production of patient-specific tools is time-consuming), lack of compliance (need for partial weight bearing, crutches), excessive smoking, vascular pathologies.

Surgical technique: Planning based on computed tomography (CT) data, determination of the axis of rotation with open or closing wedge, or dome osteotomy; production of corresponding patient-specific cutting blocks. Surgery is performed using the known standard approaches for a high tibial osteotomy (HTO). Exact positioning of cutting guides on the exposed bone. Sawing and adjusting the correction using an osteotomy chisel so that the reduction guide can be attached. Fixation of the achieved correction with angle-stable plate fixator.

Postoperative management: Partial weight bearing based on the extent of the correction for 6 weeks, free range of motion if no additional ligamentous reconstruction was performed. Subsequent full weight bearing after X‑ray and, if necessary, CT control.

Results: No general results can be presented, since the surgical procedure, the indication, and the patient group are extremely heterogeneous. Accuracy of the cutting blocks used has been presented in other studies and is given as 0.8° ± 1.5° in relation to the frontal axis. However, the intraoperative change in the correction and adaptation to the surgical site that is presented depends on the surgeon and can greatly influence the extent of correction in terms of accuracy in complex corrections.