The design of TKA implants is defined by manufacturers according to a specific alignment philosophy; however, in-vivo performance strongly depends on the surgeon’s decisions regarding component position, orientation, and soft tissue management. Mechanical Alignment (MA) and Kinematic Alignment (KA) are the most widely used strategies. Several studies have compared their clinical outcomes, but no definitive conclusions exist, and long-term multicentric follow-ups are lacking. Surgeons sometimes select the surgical alignment independently of the implant’s design rationale, meaning components designed for MA may be implanted following KA, potentially affecting outcomes and complicating interpretation. The aim of this study is therefore to compare different alignment philosophies in various TKA designs using a validated finite element model. Four implanted knee configurations were obtained by modifying accordingly a TKA starting design: standard MA with symmetric polyethylene (MA-Std, obtaining an orthogonal joint line), MA with asymmetric polyethylene (MA-Asymm, obtaining a physiological joint line), KA with tibial stem orthogonal to the tibial cut, and KA with tibial stem aligned to the tibial axis. Each model underwent a 2500 N vertical load simulating peak walking force. Polyethylene and bone stresses were extracted and compared in multiple regions of interest. Tibio-femoral interaction showed distinct contact area and pressure patterns for each configuration. Differences were minor, but KA configurations exhibited larger contact areas medially and laterally than MA configurations. The MA-Std configuration showed a medial-to-lateral force ratio close to physiological (> 50%), while MA-Asymm and KA-Std exhibited slightly higher lateral forces. Bone-implant interaction differences were minimal, primarily localized in the proximal region, reflecting variations in medio-lateral load distribution. Each combination of alignment approach and prosthesis design produces a specific stress distribution at both tibio-femoral and prosthesis-bone interfaces. Surgeons should consider these biomechanical effects when selecting an implant and determining the alignment strategy to adopt.
Innocenti et al. (Thu,) studied this question.