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Antero-Posterior Translation of Mobile-Bearing in Mobile-Bearing Unicompartmental Knee Arthroplasty

2023 Congress Paper Abstracts
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Antero-Posterior Translation of Mobile-Bearing in Mobile-Bearing Unicompartmental Knee Arthroplasty

Takahiro Arakawa, MD, JAPAN Kenichi Kono, MD, PhD, JAPAN Tetsuya TOMITA, MD, PhD, JAPAN Shuji Taketomi, MD, PhD, JAPAN Ryota Yamagami, MD, JAPAN Kohei Kawaguchi, MD, JAPAN Tomofumi Kage, JAPAN Ryo Murakami, MD, JAPAN Hiroshi Inui, PhD, JAPAN Sakae Tanaka, MD, PhD, JAPAN

The University of Tokyo, Bunkyo-ku, Tokyo, JAPAN


2023 Congress   ePoster Presentation   2023 Congress   Not yet rated

 

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Summary: A novel method of fluoroscopic kinematic analysis allowed us to clarify the kinematics of mobile-bearing unicompartmental knee arthroplasty for the first time, and we found that the mobile-bearing moved 1.4 mm anteriorly from extension to 40° of flexion, and then moved 4.8 mm posteriorly up to 130° of flexion during non-weight bearing knee flexion.


Introduction

In the field of knee surgery, in vivo kinematics of the knee and prosthesis is important to elucidate the causes of dysfunction, improve surgical procedures, and refine prosthesis design. A two-dimensional (2D)/three-dimensional (3D) registration technique is one method of obtaining those 3D kinematics from fluoroscopy by matching 3D computer models to 2D fluoroscopic images. There are two ways of matching, bone matching and implant matching. On the other hand, silhouettes of unicompartmental knee arthroplasty (UKA) implants are quite small, and when it comes to mobile-bearing (MB) UKA, femoral component is symmetric and single radius. Because of these reasons, there have been few studies on implant kinematics of UKA, and to the best of our knowledge, none of MB-UKA. In this study, we determined the kinematics of MB-UKA implants using novel method of fluoroscopic kinematic analysis, and estimated antero-posterior (AP) translation of the MB.

Method

We developed a new method for matching both bone and implant simultaneously. This "double-matching method" enables the analysis of implant kinematics of MB UKA. A total of 21 UKA knees in 20 patients were investigated. Each patient performed knee flexion with their feet floating in a sitting position. The lowest point of the femoral component relative to the tibial baseplate was assumed to coincide with the deepest point of the MB and its AP translation was analyzed. The AP midpoint of the tibial baseplate was defined zero position; positive and negative values were described as anterior and posterior, respectively.

Results

The deepest point of the MB was located -2.0 ± 3.1 mm at knee extension (defined as the initial position). It translated to -0.6 ± 3.4 mm (i.e., anteriorly) until 40° of flexion, then moved to -5.4 ± 5.0 mm (i.e., posteriorly) until 130° of flexion (defined as the final position). The average of total AP translation (from the initial to the final position) was 3.0 ± 4.7 mm posterior. Assuming a cutoff value of 3.0 mm posterior translation from the initial position, 11 cases moved more posterior than it (Group M, total AP translation was 6.6 ± 2.0 mm posterior) and 10 cases moved less than it (Group L, total AP translation was 1.1 ± 3.2 mm anterior). Comparison of implant alignment, inter-component kinematics, and inter-bone kinematics between the two groups showed significant differences in tibial component valgus angle (Group M, -2.1 ± 2.1°; Group L, -4.2 ± 1.8°).

Conclusion

“Double-matching method" enables the analysis of implant kinematics of MB UKA. Compared to previous studies, our method has two strong points. First, because of the fluoroscopic study, in vivo kinematics can be analyzed. Second, since 2D images are converted to 3D kinematics, there are few restrictions on the imaging direction, allowing analysis of various motions (e.g., squatting, walking, etc.). In terms of non-weight bearing knee flexion, the MB moved 1.4 mm anteriorly from its initial position up to 40° of flexion, and then moved 4.8 mm posteriorly up to 130° of flexion in MB-UKA.


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