Isolated high tibial osteotomy is appropriate in less than two-thirds of varus knees if excessive overcorrection of the medial proximal tibial angle should be avoided

Purpose To perform a detailed deformity analysis of patients with varus alignment and to define the ideal osteotomy level (tibial vs. femoral vs. double level) to avoid an oblique joint line. Methods A total of 303 digital full-leg standing radiographs of patients aged 18-60 years and varus alignment [mechanical tibiofemoral varus angle (mFTA) >= 3 degrees] were included. All legs were analyzed regarding mFTA, mechanical medial proximal tibia angle (mMPTA), mechanical lateral distal femur angle (mLDFA), and joint line convergence angle. Based on mFTA, varus alignment was categorized as "mild" (3 degrees-5 degrees), "moderate" (6 degrees-8 degrees), or "severe" (>= 9 degrees). Deformity location was determined according to the malalignment test described by Paley. Two osteotomy simulations were performed with different upper limits for mMPTA: anatomic correction (mMPTA <= 90 degrees, mLDFA >= 85 degrees) and overcorrection (mMPTA <= 95 degrees, mLDFA >= 85 degrees). If a single osteotomy exceeded these limits at the intended mFTA of 2 degrees valgus, a double-level osteotomy was simulated. If even a double-level osteotomy resulted in deviations from the defined limits, the leg was categorized as "uncorrectable". Results Mean mFTA was 6 degrees +/- 11 degrees of varus (range 3 degrees-15 degrees). A tibial deformity was observed in 28%, a femoral deformity in 23%, a combined tibial and femoral deformity in 4%, and no bony deformity in 45%. The prevalence of a tibial deformity did not differ between varus severity groups, whereas a femoral and bifocal deformity was significantly more prevalent in knees with more distinct varus (p < 0.001). Osteotomy simulation revealed that isolated high tibial osteotomy (HTO) was appropriate in only 12% for anatomic correction, whereas a double-level osteotomy was necessary in 63%. If overcorrection of mMPTA was tolerated, the number of HTOs significantly increased to 57% (p < 0.001), whereas the number of double-level osteotomies significantly decreased to 33% (p < 0.001). Isolated DFO was considered ideal in 8% for both simulations. Significantly more knees were considered "uncorrectable" by simulating anatomic correction (18 vs. 2%;p < 0.001). A double-level osteotomy was significantly more often necessary in knees with "severe" varus (p < 0.001). Conclusion Less than one-third of patients (28%) with mechanical varus >= 3 degrees have a tibial deformity. If anatomic correction (mMPTA <= 90 degrees) is intended, only 12% of patients can be corrected via isolated HTO, whereas 63% of patients require a double-level osteotomy. If slight overcorrection is accepted (mMPTA <= 95 degrees), 57% of patients can be corrected via isolated HTO, whereas 33% of patients would still require a double-level osteotomy.