With advances in technology and particularly locked screws, patients with high tibial osteotomy (HTO) are frequently allowed full weight bearing for a  unilateral procedure. We are aware of no reports comparing the safety of a simultaneous bilateral HTO with staged bilateral HTO. The purpose of this study was to retrospectively compare these two strategies.
Ninety patients were treated with bilateral HTO surgery for osteoarthritis from 2009 to 2013; they had opening-wedge HTO and fixed with the same plate fixation and locked screws. A comparison of the outcomes after simultaneous bilateral HTO (35 patients) and after sequential staged bilateral HTO (55 patients) was performed. We considered four measures of medical safety: hypotension, serious intra-operative adverse event, heterologous blood transfusion, and thrombophlebitis. We considered also four measures of orthopaedic safety: infection, patient's inability to walk full weight bearing, changes in correction, and nonunion.
For the same duration of operation, the duration of anaesthesia and the time in the operating room were 35% longer for patients having a staged bilateral HTO. Blood loss was higher in patients undergoing simultaneous bilateral HTO compared with those who underwent a staged bilateral HTO. For patients undergoing simultaneous bilateral HTO, thrombophlebitis frequency and length of anticoagulation were lower than the sum of each event in the staged bilateral HTO. The patients with simultaneous bilateral HTO had a longer total period of time for crutches than patients with staged bilateral HTO. Patients in the simultaneous bilateral cohort did not develop an infection within one year as patients in the planned-stage cohort. The simultaneous bilateral cohort had a lower rate of delayed union than the planned-stage cohort did.
On the basis of this analysis, simultaneous bilateral HTO is a reasonable treatment option. Individuals who undergo staged bilateral HTO face the risk of complications twice, in addition to two hospitalizations. Patients who undergo simultaneous bilateral HTO have a higher risk of blood transfusion.