DOI: 10.1097/io9.0000000000000409 ISSN: 2405-8572

Historical control trial: safe tibia varus cut in kinematic total knee arthroplasty using mechanical instrument combined 3D-printed tibia recut guide

Nguyen Phuc Thinh, Pham Thi Cam Van, Bui Hong Thien Khanh
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Background:

Kinematic alignment total knee arthroplasty (KA TKA) has the potential to restore native knee kinematics and improve functional outcomes compared with conventional mechanical alignment (MA) techniques; however, controlling tibial varus cuts remains a challenge, particularly in resource-limited settings.

Methods:

This study aimed to evaluate a modified KA TKA technique using conventional mechanical instruments combined with a 3D-printed tibial recut guide to control tibial varus alignment, and to compare its radiologic measures with those of MA TKA performed with navigation assistance. A historical control trial was conducted involving 100 patients. Fifty patients underwent KA TKA using mechanical instruments and a 3D-printed tibial recut guide (2020–2022), and 50 historical controls underwent MA TKA with navigation (2016–2019). Radiologic assessments included joint-line obliquity, femoral and tibial mechanical angles (TMAs), and the hip-knee-ankle (HKA) angle, measured using EOS imaging pre- and postoperatively.

Results:

Postoperative femoral mechanical angles showed no significant difference between groups (KA: 89.6° ± 2.9, MA: 89.3° ± 2.4; P = 0.497). TMAs indicated slight varus alignment in the KA group (86.9° ± 2.5) versus neutral alignment in the MA group (89.8° ± 2.0; P < 0.001). Postoperative HKA was more varus in the KA group than in the MA group (2.5°± 3.1 vs 1.1° ± 2.9; P = 0.020), but the difference was not significant after adjustment for preoperative HKA ( P = 0.161). Nine patients exhibited HKA varus > 6°; four were from the navigation mechanical group and five from the manual kinematic group. The most extreme tibial varus observed in the kinematic TKA group was 9°, corresponding to a HKA angle of 6°. Knee joint line obliquity was maintained near neutral in the KA group (−0.8° ± 2.6) and significantly increased laterally in the MA group (4.0° ± 2.6; P < 0.001).

Conclusions:

The modified KA TKA technique, using conventional instruments combined with a 3D-printed tibial recut guide, achieves reliable joint line restoration and controlled tibial varus cuts comparable to navigation-assisted MA TKA.

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