Kinematic alignment achieves a tibial joint line angle that is more parallel to the floor in single-leg stance than mechanical alignment : a radiological analysis of a randomized controlled trial.

Aims: Previous research on knee kinematics has demonstrated that achieving a tibial joint line angle (TJLA) parallel to the floor in the single-leg stance phase of gait may restore native knee kinematics and optimize compartmental compressive loads in total knee arthroplasty (TKA). However, it is currently unclear which surgical alignment strategy best achieves this. Therefore, this study sought to determine whether kinematically aligned (KA) or mechanically aligned (MA) TKAs produce a TJLA closer to parallel.

Methods: A total of 95 patients were randomized to KA (n = 46) or MA (n = 49). Constitutional joint line obliquity (JLO) was measured from preoperative radiographs; TJLA was measured from postoperative radiographs. The primary outcome was the mean difference in TJLA between KA and MA in single-leg stance. Secondary outcomes included differences in TJLA between apex distal and neutral JLO knees, the proportion of patients with TJLA within approximately 2° of neutral, and changes in constitutional JLO between alignment groups.

Results: In single-leg stance, the mean TJLA was closer to parallel with KA (-2.0° (SD 2.6°)) than MA (-4.5° (SD 1.9°); p < 0.001). Similar mean differences were observed in patients with apex distal JLO (KA -1.4° (SD 2.1°); MA -4.9° (SD 1.8°); p < 0.001) but not neutral JLO (KA -3.7° (SD 2.8°); MA -3.7° (SD 1.9°); p = 0.776). More patients had a TJLA within 2° of parallel with KA (n = 24; 52.2%) than MA (n = 4; 8.2%; p < 0.001), and KA resulted in significantly less change to constitutional JLO.

Conclusion: A TJLA parallel to the floor in single-leg stance is achieved more readily with KA than MA, but is dependent on constitutional JLO. A parallel TJLA during this phase of gait is more likely achieved when alignment is individualized to the patient's native anatomy.