Comparison of kinematic and mechanical alignment techniques in primary total knee arthroplasty

Background: This meta-analysis compared clinical and radiographic outcomes and complications of kinematic alignment (KA) and mechanical alignment (MA) techniques in primary total knee arthroplasty (TKA). Methods: All studies comparing the operation time, change in hemoglobin, length of hospital stay, postoperative complications, and clinical and radiographic outcomes as assessed with various measurement tools, from direct interview to imaging methods, in patients who underwent primary TKA through the KA or MA technique were included. Results: Six studies were included in the meta-analysis. The proportion of patients who developed postoperative complications (OR: 1.10, 95% CI: 0.49-2.46; P=.69) did not differ significantly between the KA and MA techniques. The 2 groups were also similar in terms of change in hemoglobin (95% CI:-0.38 to 0.34; P=.91), length of hospital stay (95% CI:-0.04 to 0.55; P=.10), hip-knee-ankle angle (95% CI:-1.76 to 0.75; P=.43), joint line orientation angle (95% CI:-4.27 to 4.23; P=.99), tibial component slope (95% CI:-0.53 to 3.56; P=.15), and femoral component flexion (95% CI:-2.61 to 7.57; P=.34). In contrast, operation time (95% CI:-27.16 to-3.71; P=.01), overall functional outcome (95% CI: 6.59-11.51; P<.0001), knee anatomical axis (95% CI:-1.38 to-0.01; P=.05), femoral component relative to the mechanical axis (95% CI:-2.47 to-1.40; P<.0001), and tibial component relative to the mechanical axis (95% CI: 1.56-2.95; P<.0001) were significantly different between the 2 groups. Conclusions: There were no significant differences in postoperative complications, change in hemoglobin, length of hospital stay, hip-knee-ankle angle, joint line orientation angle, tibial component slope, or femoral component flexion between the KA and MA techniques for primary TKA. However, the KA technique resulted in a significantly shorter operation time and better overall functional outcome than the MA technique, even though the femoral component was placed in a slightly more valgus position relative to the mechanical axis and the tibial component in a slightly more varus position with the KA technique.