- Anatomy:
    - varus or valgus angulation of arthritic knee usually results from 3 components:
         - geometric alignment of femur & tibia;
         - narrowing or loss of bone & cartilage in one compartment;
         - widening of other compartment's joint space because of slack ligamentous and soft-tissue structures;
               - detected by measuring difference between involved knee and the opposite, uninvolved knee;
               - each millimeter of excessive joint space separation causes an apparent 1 deg of angular deformity on weightbearing x-ray;
               - if widening is not taken into consideration, an excessive lateral tibial wedge may be removed, and therefore malalignment may be 
                      overcorrected;

- Planning the Osteotomy:
    - management of fibula:
    - closing-wedge osteotomy:
         - most commonly performed HTO procedure;
         - may be contra-indicated when the affected leg is shorter than the unaffected leg;
    - opening wedge osteotomy:
         - requires bone grafting, w/ delay in mobilizing knee & possibility of collapse of graft & loss of correction;
         - indicated when the affected side is shorter than the non affected side;
    - osteotomy site:
         - osteotomy distal to tibial tubercle is more slow to heal than osteotomy above the tubercle;
         - osteotomy proximal to tibial tubercle;
               - quadriceps can exert compressive effect at osteotomy site;
               - cancellous bone allows faster healing;
               - osteotomy is generally performed 2 cm distal to joint line;
                     - more proximal resection causes proximal frag to be too thin & at risk for intraoperative fracture or avascular necrosis;
                     - osteotomy that is too distal disrupts extensor mech at tibial tubercle;
    - size of the wedge:
         - see: radiographs for HTO:
         - measured by transposing measurements from the radiograph to the tibia and by accurately measuring the base of the wedge.
         - as a rule of thumb, removing 1 mm of tibial wedge will provide 1 deg of correction;
                - this is precisely true for a tibia which is 56 mm wide
         - references:
                - Serial Assessment of Weight-Bearing Lower Extremity Alignment Radiographs After Open-Wedge High Tibial Osteotomy
                - Standing radiographs cannot determine the correction in high tibial osteotomy.

Standing radiographs cannot determine the correction in high tibial osteotomy.

High Tibial Valgus Osteotomy: Closing, Opening or Combined? Patellar Height as a Determining Factor

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