Fig. 3.

Illustrative case example 4. a Deformity analysis revealed a tibial-based varus deformity of 10° with a high-normal mLDFA and a pathologic mMPTA. b, c First osteotomy simulation tolerating mLDFA ≥ 85° and mMPTA ≤ 90° (anatomic correction): by simulating HTO alone, 4.4° of varus alignment remains with the mMPTA set at 90°. By simulating a double-level osteotomy to the desired alignment of 2° of valgus, the lower limit of the mLDFA is exceeded. This case is, therefore, considered “uncorrectable”. d, e Second osteotomy simulation tolerating mLDFA ≥ 85° and mMPTA ≤ 95° (overcorrection): by simulating HTO alone, neutral alignment remains with the mMPTA set at 95°. By simulating a double-level osteotomy, the deformity can be corrected to the desired alignment of 2° of valgus without exceeding the upper and lower limit of the mMPTA and mLDFA, respectively