Most patients who opt for osteotomy correction of a bow-leg (varus) deformity will be offered a simple high tibial osteotomy. Adequate digital planning on long leg weight-bearing X-rays will usually guide the surgeon as to the amount of correction that can be safely provided by correction in just the one bone.
If correction is likely to be compromised with a single level osteotomy, however, then the planning can be revised to calculate what corrections would be needed in both tibia and femur simultaneously to provide adequate safe realignment.
The safety concern in correcting just the one bone in a severe alignment problem is because of the size of the opening wedge that would be needed to correct the alignment. Such a large wedge may lead to the lateral tibial plateau having an abnormal inclination with the articular cartilage being under a severe sheer force. Also the femur may tend to sublux and strain the joint capsule, making things difficult for any future total knee replacement.
So in these severe cases of bow legs, the surgeon may opt instead for a double-level osteotomy.
"....Multiple studies published more than 30 years ago advocated against the [double level osteotomy]....[but surgeons]...lacked the detailed preoperative planning associated with [this procedure] today...."
"...The main advantage [of double level osteotomy] is to maintain a horizontal joint line and avoid creating secondary anatomic deformities...."