Total knee replacement designs have differing stability under novel robotic testing method in vitro
Author(s)
Type
Journal Article
Abstract
Purpose:
This study implemented a novel robotic test method to quantify the effect of three distinct total knee arthroplasty (TKA) designs on knee kinematics and stability. It was hypothesised that the implant geometries would affect stability and rollback, with differences between the native and replaced knees, as well as between implant designs.
Methods:
Eight fresh-frozen cadaveric knees were tested across the arc of flexion-extension under 710 N compressive load, combined with either no anterior-posterior (AP) tibial force, 90 N anterior or 90 N posterior drawer force using a robotic actuator. The same testing protocol was used post-TKA using three distinct implant designs (gradually reducing femoral condylar radius medially stabilised, multi-radius medially conforming and single-radius symmetrical), matched to the same bone cuts. Laxity and rollback were analysed using statistical parametric mapping and implant designs were compared to the intact knee and each other.
Results:
No significant differences in AP laxity were found between the intact knee (4.7 ± 0.7 mm), gradually reducing radius (6.3 ± 1.3 mm) and multi-radius designs (5.7 ± 1.1 mm). The single-radius implant showed significantly larger average AP laxity envelope (11.6 ± 2.3 mm) than the intact knee, the multi-radius design and the gradually reducing radius design and was more variable between knees. The rollback among the intact knee and TKAs were not significantly different: gradual radius 81% of native, multi-radius 85% and single-radius 90%.
Conclusions:
Significant differences of AP laxity were found between the pre- and post TKA knee and between implant designs. Rollback did not differ significantly. Implanted knee behaviour also showed differences of sensitivity to cadaveric specimen and implantation variation among the prosthesis designs.
Clinical relevance:
Instability post-TKA remains an issue for good patient outcomes. Robotic testing of implanted knees shows the effects of implant design on knee stability and motion, potentially improving outcomes by providing the surgeon with objective data on which to base their choice of TKA.
Level of Evidence:
Controlled laboratory study.
This study implemented a novel robotic test method to quantify the effect of three distinct total knee arthroplasty (TKA) designs on knee kinematics and stability. It was hypothesised that the implant geometries would affect stability and rollback, with differences between the native and replaced knees, as well as between implant designs.
Methods:
Eight fresh-frozen cadaveric knees were tested across the arc of flexion-extension under 710 N compressive load, combined with either no anterior-posterior (AP) tibial force, 90 N anterior or 90 N posterior drawer force using a robotic actuator. The same testing protocol was used post-TKA using three distinct implant designs (gradually reducing femoral condylar radius medially stabilised, multi-radius medially conforming and single-radius symmetrical), matched to the same bone cuts. Laxity and rollback were analysed using statistical parametric mapping and implant designs were compared to the intact knee and each other.
Results:
No significant differences in AP laxity were found between the intact knee (4.7 ± 0.7 mm), gradually reducing radius (6.3 ± 1.3 mm) and multi-radius designs (5.7 ± 1.1 mm). The single-radius implant showed significantly larger average AP laxity envelope (11.6 ± 2.3 mm) than the intact knee, the multi-radius design and the gradually reducing radius design and was more variable between knees. The rollback among the intact knee and TKAs were not significantly different: gradual radius 81% of native, multi-radius 85% and single-radius 90%.
Conclusions:
Significant differences of AP laxity were found between the pre- and post TKA knee and between implant designs. Rollback did not differ significantly. Implanted knee behaviour also showed differences of sensitivity to cadaveric specimen and implantation variation among the prosthesis designs.
Clinical relevance:
Instability post-TKA remains an issue for good patient outcomes. Robotic testing of implanted knees shows the effects of implant design on knee stability and motion, potentially improving outcomes by providing the surgeon with objective data on which to base their choice of TKA.
Level of Evidence:
Controlled laboratory study.
Date Issued
2025-11-01
Date Acceptance
2025-05-22
Citation
Knee Surgery, Sports Traumatology, Arthroscopy, 2025, 33 (11), pp.3896-3905
ISSN
0942-2056
Publisher
Wiley
Start Page
3896
End Page
3905
Journal / Book Title
Knee Surgery, Sports Traumatology, Arthroscopy
Volume
33
Issue
11
Copyright Statement
© 2025 The Author(s). Knee Surgery, Sports Traumatology, Arthroscopy published by John Wiley & Sons Ltd on behalf of European Society of Sports Traumatology, Knee Surgery and Arthroscopy. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
License URL
Identifier
10.1002/ksa.12761
Subjects
ACL, anterior cruciate ligament
ANOVA, analysis of variance
AP, anterior-posterior
ASTM, American Society for the Testing of Materials
ATT, anterior tibial translation
DOF, degrees of freedom
MC, medially congruent
MS, medially stabilised
PE, polyethylene
PMMA, polymethylmethacrylate
PTT, posterior tibial translation
SD, standard deviation
TEA, trans-epicondylar axis
TKA, total knee arthroplasty
TKR, total knee replacement kinematics, prosthesis articular geometry, robot testing, stability testing, total knee arthroplasty
Publication Status
Published
Article Number
ksa.12761
Date Publish Online
2025-07-07