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Kinematic Alignment in TKA Using the Contralateral Healthy Knee as Reference: A Combined Finite Element and Clinical
Lingce Kong1, Wei Lin1, Huijun Kang1
1Department of Orthopaedic Surgery, Third Hospital of Hebei Medical University, Shijiazhuang, Hebei, China.
Objective:
Mechanical alignment (MA) and kinematic alignment (KA) are common total knee arthroplasty (TKA) strategies. Patients with bilateral knee osteoarthritis lack a precise individualized alignment reference, whereas those with unilateral OA have a potential reference from the contralateral healthy knee. This study proposes a natural KA (NKA) strategy referencing the contralateral healthy knee and compares biomechanical and clinical outcomes of MA, KA, and NKA for TKA.
Methods:
Finite element models (neutral/mild/moderate varus) were established based on three selected patients with unilateral knee OA using bilateral CT data to simulate MA/KA/NKA implantation. This exploratory biomechanical analysis was designed to identify potential patterns. Stress distribution on the femoral component, polyethylene insert, and tibia, along with contact pressure, contact area, and implant displacement, was analyzed. Additionally, a retrospective clinical study included 101 patients who underwent TKA with a minimum 1-year follow-up. Patients were divided into MA, KA, and NKA groups based on postoperative radiographic alignment. Postoperative alignment parameters, range of motion (ROM), Knee Society Score (KSS), and Forgotten Joint Score (FJS) were compared.
Results:
Finite element analysis revealed that in the neutral and mild varus models, NKA resulted in a more balanced mediolateral biomechanical distribution, lower implant stress, and minimal component subsidence. In the moderate varus model, MA showed the most balanced mediolateral load distribution and the largest contact area. Clinical follow-up indicated that the MA group achieved lower limb alignment close to mechanical neutrality postoperatively, while the KA and NKA groups retained some physiological varus. No significant differences were observed in KSS among the three groups. However, FJS showed a statistically favorable trend in the KA and NKA groups compared with the MA group, although the clinical significance of this difference requires further investigation.
Conclusion:
The NKA strategy shows potential biomechanical advantages by optimizing stress distribution in selected neutral/mild varus models and is associated with better short-term patient-reported satisfaction than MA. NKA provides a feasible coronal alignment concept for precision TKA in patients with unilateral knee osteoarthritis without significant contralateral deformity. Long-term safety and generalizability require further validation.
