The purpose of this study was to investigate the benefits of three different post-operative limb positions in primary total knee arthroplasty (TKA).
The trial was a single-surgeon, randomized, controlled trial, and 135 patients following primary TKA were randomized into three groups: group A (45 patients who were treated with the hip fixed at 50° and knee flexed at 90° for 6 hours post-operatively), group B (45 patients who were treated with the hip elevated at 30° and knee flexed at 45° for 6 hours  post-operatively), and group C (45 patients in whom the affected knee was fully extended after surgery). Tranexamic acid was used in all patients.
The total blood loss and hidden blood loss in group A (921 ± 209 mL, 597 ± 213 mL) were significantly less than in groups B (1125 ± 222 mL, 784 ± 229 mL) and C (1326 ± 291 mL, 915 ± 301 mL) and less in group B compared with group C. The drain volume in groups A (158 ± 35 mL) and B (174 ± 45 mL) was significantly lower than in group C (249 ± 31 mL). The maximum haemoglobin drop in group A (3.1 ± 0.5 g/dL) was statistically significantly less than in groups B (3.6 ± 0.7 g/dL) and C (4.3 ± 0.4 g/dL). The range of motion (ROM) in groups A (102 ± 3°, 105 ± 2°) and B (100 ± 3°, 104 ± 2°) was significantly better than in group C (98 ± 3°, 102 ± 2°) at the time of discharge and one  month after surgery; it was also significantly less for group A (104.9 ± 2.1%, 108.0 ± 2.4%) compared with groups B (106.7 ± 3.1%, 108.3 ± 2.7%) and C (108.4 ± 3.2%, 110.6 ± 3.0%) with post-operative knee swelling. No differences in transfusion requirements and complications were observed among the three groups.
The affected knee flexion position was superior to the use of a fully extended position for blood management, but it only contributed to better early functional recovery up to three  months post-operatively in TKA. In addition, by fixing the affected knee at a high flexion position of 90°, patients could achieve less blood loss, lower knee swelling, and better early results for ROM and patient satisfaction than the other two groups.