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Updated: Jan 11, 2026
In Vitro Application of a Wireless Sensor in Flexion-Extension Gap Balance of Unicompartmental Knee Arthroplasty
Published on: May 5, 2023
Functional alignment maintains constant medial stability and a more distinct medial pivot pattern throughout flexion
Takashi Kobayashi1, Kenichi Kono1, Tomofumi Kage1
1Department of Orthopaedic Surgery, Faculty of Medicine The University of Tokyo Tokyo Japan.
Purpose:
To investigate whether functional alignment (FA) leads to differences in in vivo kinematics and early clinical outcomes compared to mechanical alignment (MA) in patients undergoing total knee arthroplasty (TKA) using a medial pivot (MP) prosthesis.
Methods:
Forty patients (20 MA and 20 FA) who underwent TKA with a MP implant were investigated under fluoroscopy during squatting using a two-to-three-dimensional registration technique 1 year postoperatively. FA started with anatomical implant positioning plan, followed by navigation-guided adjustments of femoral and tibial cutting plan based on intraoperative varus-valgus stress testing for soft tissue balance. In MA, resections are aimed for neutral coronal alignment. External rotation, varus-valgus angle, anteroposterior translation of medial and lateral contact points and kinematic pathways were assessed from 0° to 110° of flexion. Clinical outcomes were evaluated 1 year postoperatively using the Knee injury and Osteoarthritis Outcome Score (KOOS) and 2011 Knee Society Score (KSS). The range of motion and radiographic alignment were also evaluated.
Results:
A significant group × angle interaction was observed for lateral anteroposterior translation, external rotation and valgus angulation (p < 0.001), indicating different kinematic pathways between groups. In the MA group, a significant main effect of the flexion angle on valgus angulation was detected (p < 0.001), whereas in the FA group, the varus-valgus angles remained consistent throughout flexion. The FA group demonstrated significantly greater postoperative flexion; better KOOS scores for pain, ADL and sports; and superior KSS symptom scores (p < 0.05). Radiographic analysis showed significant differences in MPTA and LDFA in the FA group (both p < 0.001).
Conclusion:
FA and MA techniques resulted in distinct in vivo kinematics. The FA approach demonstrated MP knee motion with consistent varus-valgus stability throughout flexion, leading to improved early clinical outcomes compared to MA. These findings support the kinematic benefits of FA in MP TKA.
Level Of Evidence:
Level III.
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