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. 2023 Jan 9:9:1054351.
doi: 10.3389/fsurg.2022.1054351. eCollection 2022.

Pre-operative predictive factors of residual varus on the mechanical axis after Oxford unicompartmental knee arthroplasty

Songjie Ji  1 , Ye Huang  1 , Yixin Zhou  1 , Chao Wang  2 , Xiaokai Wang  3 , Chaoyi Ma  3 , Xu Jiang  1
Affiliations

Pre-operative predictive factors of residual varus on the mechanical axis after Oxford unicompartmental knee arthroplasty

Songjie Ji et al. Front Surg. .

Abstract

Background: Residual varus after Oxford unicompartmental knee arthroplasty (UKA) happens frequently. This study aims to evaluate the pre-operative contributing factors of residual varus.

Methods: A total of 1,002 knees (880 patients, 201 patients were male, and 679 were female) underwent Oxford UKA in the Orthopedic Surgery Department of the Beijing Jishuitan Hospital from March 2018 to April 2021. The mean age of the patient was 64.7 ± 7.7 years. To assess residual varus, the full-length lower extremity is placed upright for EOS imaging, with the knee fully extended. The angle of post-operative residual varus was measured as described by Noyes et al. Of the knees studied, they were either categorized into an under-corrected group (post-operative Noyes angle >5°) or a corrected group (post-operative Noyes angle ≤5°). Age, gender, body mass index (BMI), range of motion (ROM), Clinical American Knee Society Score (Clinical AKSS), and Function American Knee Society Score (Function AKSS) were compared. The following additional parameters were measured: pre-operative Noyes angle, lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), the posterior slope of the proximal tibia angle (PPTA), joint line converge angle (JLCA), and fixed flexion deformity (FFD).

Results: There was no statistically significant difference between the two groups in regards to gender (p = 0.428), surgical leg (p = 0.937), age (p = 0.851), BMI (p = 0.064), pre-operative Clinical AKSS (p = 0.206) and Function AKSS (p = 0.100). However, pre-operative ROM statistically differed between the two groups (p < 0.001). The contributing factors of post-operative residual varus were determined to be the following parameters: pre-operative MPTA (p < 0.001, OR = 4.522, 95% CI: 2.927-6.984), pre-operative Noyes (p < 0.001, OR = 3.262, 95% CI: 1.802-5.907) and pre-operative FFD (p = 0.007, OR = 1.862, 95% CI: 1.182-2.934). The effects of pre-operative LDFA (p = 0.146), JLCA (p = 0.942), and pre-operative PPTA (p = 0.899) on the post-operative mechanical axis did not show statistical significance.

Conclusions: Patients with severe pre-operative varus, particularly varus deformity mainly from the tibial side or pre-operative FFD, are more prone to get extremity mechanical axis residual varus after UKA with Oxford.

Keywords: biplanar radiograph; lower limb alignment; moblie-bearing; predictor; unicompartemtal knee arthroplasty.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
In the coronal plane, the hip joint center point is the center of the circular femoral head, and the center of the distal femur is the top of the intercondylar notch. The mechanical axis of the femur passes through these two points. The center of the proximal tibia is the center of the tibial spines, and the center of the ankle is the mid-width of the tibia and fibula at the level of the plafond. The mechanical axis of the femur passes through these two points (23). Pre-operative Noyes angle: the angle between the femoral mechanical axis and the tibial mechanical axis. In the EOS software, it is designated as “varus.” In this image, the Noyes angle is 7°.
Figure 2
Figure 2
Medial proximal tibial angle (MPTA): the proximal medial angle formed between the tibial mechanical axis and the knee joint line of the tibia in the frontal plane. In this image, the MPTA is 84.7°.
Figure 3
Figure 3
Lateral distal femoral angle (LDFA): the lateral angle formed between the femoral mechanical axis and the knee joint line of the femur in the frontal plane. In this image, the LDFA is 88.2°.
Figure 4
Figure 4
Posterior slope of the proximal tibia angle (PPTA): the angle formed between tibial plateaus and the anatomic axis of the tibia in the sagittal plane. In this image, the PPTA is 80.2°.
Figure 5
Figure 5
The joint line converge angle (JLCA): the angle between the distal femoral joint line and the proximal tibial joint line in the coronal plane. In this image, the JLCA is 2.2°.
Figure 6
Figure 6
Fixed flexion deformity (FFD): in the sagittal plane, the hip joint center is the center of the femoral head, the center of the distal femur is the junction of the anterior 1/3 and the posterior 2/3 of t trace of the closed femoral growth plate. The mechanical axis of the femur passes through these two points. The proximal tibia center is the junction of the anterior 1/5 and the posterior 4/5 of the tibial plateaus; the ankle joint center is the midpoint of the tibial distal plate. The mechanical axis of the tibia passes through these two points. The angle formed between the femoral mechanical axis and the tibial mechanical axis in the sagittal plane when knees are fully extended. In this image, the FFD is −4°.
Figure 7
Figure 7
Post-operative noyes angle. It is designated as “varus” in EOS software. In this image, the Noyes angle is 5°.
See this image and copyright information in PMC

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