Data Extraction

The following data were extracted independently by two reviewers using a predefined form: first author, year of publication, country, sample size, preoperative diagnosis, age, sex, body mass index (BMI), pre‐ and post‐operative alignment, length of follow‐up, and methods used to assess knee function and survival. To ensure uniform descriptions of the coronal limb axis, the hip–knee–ankle angle (HKA) and mechanical femorotibial alignment (FTMA) were defined as the angle between the mechanical axis of the femur and the reversed extension line of the mechanical axis of the tibia. Varus was defined as positive and valgus as negative. Neutral alignment was defined as 0° ± 3° with reference to the postoperative coronal mechanical axis; mild varus alignment, 3°–6°; and severe varus alignment, >6° (Fig. 1). Alignment in one study ²⁴ was not defined as 3°–6° by the authors but the 95% confidence interval (CI) of the alignment fell within that range, so it was classified as mild varus alignment for the present meta‐analysis. When outcomes were reported for multiple time points, only data for the longest time point were included. If outcome data were unclear, the corresponding author was contacted for clarification.

Method of calculation of preoperative and postoperative alignment and illustration of preoperative alignment and the neutral, mild varus and severe varus alignment after the operation. (A) Preoperative varus alignment; (B–D) postoperative alignments; (B,C) neutral alignment; (C,D) mild varus alignment; (>D) severe varus alignment.