Unicompartmental knee arthroplasty (UKA), resulting in similar kinematics to native knees, is functionally superior to total knee arthroplasty (TKA). However, ACL deficiency is generally considered to be a contraindication. The main purpose of this study was to investigate if UKA in ACL-deficient knees would result in similar kinematics to conventional UKA with an intact ACL.
Ten conventional UKA patients were compared to eight ACL-deficient patients with a reduced tibial slope to compensate for instability, resulting from the deficient ACL. Knee kinematics was evaluated with a moving fluoroscope, tracking the knee joint during daily activities. In a standing position (baseline), posterior shift of the femur was observed for ACL-deficient UKA patients, compared to conventional UKA patients.
A significant posterior femoral shift in the ACL-deficient group was observed during the first 25% (near extension) of deep knee bend, while there was no difference in kinematic waveforms for all other activities. No significant range of motion differences across different activities between the two UKA groups were detected, except for an increase of medial AP translation in the ACL-deficient group, during deep knee bend and stair descent.
Despite the posterior femoral shift due to ACL deficiency, both UKA groups showed similar kinematic waveforms, indicating that posterior tibial slope reduction can partially compensate for ACL function. This supported our hypothesis that fixed bearing UKA can be a viable treatment option for selected ACL-deficient patients, allowing patient-specific kinematics. While anteroposterior laxity can be compensated, rotational stability was a prerequisite for this approach.
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UKA patients with intact ACL
UKA patients with deficient ACL
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The authors of this manuscript would like to thank all members of the Institute for Biomechanics for their help during the experiments or establishing the required hardware and software processes. Specifically, we would like to thank Lorena Suter and Adrian Roth for the 2D/3D registration, Luca Kiener for the validation experiments, Donato Papillo for his help with patient recruitment, and all patients for participating in this study.
This study was funded by the Mäxi Foundation, departmental grants of ETH Zurich and Schulthess Klinik, together with industry support from DePuy Synthes.
Conflict of interest
This study was partially supported by the implant manufacturer and institutional research funding was received from several medical device companies. Some of the authors are paid consultants for medical device companies not related to this study. One author was a paid employee at a medical device company not involved in this project.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional review board at ETH Zurich and the Zurich cantonal ethics committee (BASEC-No. 2016-00438) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
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This research was carried out at the Institute for Biomechanics at ETH Zurich.
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Zumbrunn, T., Schütz, P., von Knoch, F. et al. Medial unicompartmental knee arthroplasty in ACL-deficient knees is a viable treatment option: in vivo kinematic evaluation using a moving fluoroscope. Knee Surg Sports Traumatol Arthrosc 28, 1765–1773 (2020). https://doi.org/10.1007/s00167-019-05594-0
- Unicompartmental knee arthroplasty
- ACL deficiency
- Total knee arthroplasty
- In vivo kinematics
- Moving fluoroscopy