Modified kinematic alignment better restores plantar pressure distribution than mechanical alignment in total knee arthroplasty: a randomized controlled trial

Kinematic alignment (KA) in the short to medium term clinical outcomes is superior to the mechanical alignment (MA), but whether it will improve patients' postoperative gait is still controversial. Understanding whether and how KA influences postoperative gait mechanics could provide insights into optimizing alignment philosophy to improve functional outcomes. To investigate the impact of KA versus MA in total knee arthroplasty (TKA) on the operated and contralateral native lower limbs by analyzing plantar pressure distribution during walking gait. This study was designed as a secondary analysis from a randomized controlled trial. Thirty-seven patients were included, nineteen underwent KA-TKA and eighteen underwent MA-TKA, each with a native knee in the contralateral limb. Pressure-sensitive insoles were used to collect plantar pressure distribution of both limbs simultaneously during walking defined as medial-lateral load ratio (MLR). Perioperative characteristics including radiographic metrics (Hip-Knee-Ankle angle (HKA), mechanical lateral distal femoral angle (mLDFA), and mechanical medial proximal tibial angle (mMPTA) and clinical outcomes (Oxford Knee Scores (OKS)) were compared between the two groups pre-operatively and 2-year postoperatively. Significant differences were found in postoperative radiographic metrics, with KA showing better OKS 1 year postoperatively (p = 0.021), lower mean HKA (p = 0.009) and mMPTA (p < 0.001). Other perioperative characteristics were similar between groups. In the pedobarographic analysis, the MA group demonstrated greater medial pressure distribution in forefoot compared to both the KA group (p < 0.001) and the contralateral native knee (p = 0.002). Besides, the MA group revealed a more lateral pressure distribution in rearfoot compared to the KA group (p = 0.007) and the contralateral native knee (p = 0.001). While there was no significant difference between KA and native group (p = 0.064 and p = 0.802, respectively). KA offered advantages over MA in restoring a more physiologic plantar pressure distribution at two years postoperatively. These results underscore the potential clinical benefits of adopting KA techniques in TKA procedures.