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, 13 (12), e0209317
eCollection

A Proposed New Rotating Reference Axis for the Tibial Component After Proximal Tibial Resection in Total Knee Arthroplasty

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A Proposed New Rotating Reference Axis for the Tibial Component After Proximal Tibial Resection in Total Knee Arthroplasty

Takaaki Ohmori et al. PLoS One.

Abstract

Purpose: During total knee arthroplasty, few rotating reference axes can be reliably used after tibial resection. We speculated that a line that passes through the lateral edge of the posterior cruciate ligament (PCL) at its tibial attachment after resection and the most prominent point of the tibial tubercle [after-tibial resection (ATR) line] will provide a good reference axis. In this study, we aimed to evaluate the association between ATR and Akagi's lines.

Materials and methods: In this case-control simulation study, we retrospectively evaluated 38 patients with varus knee and 28 patients with valgus knee. We defined the reference cutting plane as 10 mm distal from the lateral articular surface of the tibia in varus group and as 7 mm distal from the medial articular surface in the valgus group. We measured angles between Akagi's line and the ATR line (ATR line angle) as well as between Akagi's line and 1/3 Akagi's line (1/3 Akagi's line angle), which passes through the midpoint of PCL and the medial third of the patellar tendon. We used paired t-tests to determine the significance of differences between these angles, with p < 0.05 indicating statistical significance. Intra- and interclass correlation coefficients for the reproducibility of 1/3 Akagi's line angle and ATR line angle were analyzed by two surgeons.

Results: We found that 1/3 Akagi's line angle was 10.2° ± 1.3° in the varus group and 10.9° ± 1.3° in the valgus group (p = 0.017). The ATR line was positioned externally compared with Akagi's line in all patients. Mean ATR line angles at 0°, 3° and 7° posterior slopes were 6.1° ± 1.9°, 5.8° ± 2.0° and 6.0° ± 1.7° in the varus group and 6.3° ± 2.3°, 6.2° ± 2.3° and 5.4° ± 2.1° in the valgus group, respectively. There were no significant differences in the ATR line angle between the varus and valgus groups. (p = 0.34-0.67) Intra- and interclass correlation coefficients for the reproducibility of 1/3 Akagi's line angle were 0.936 and 0.986 and those for the reproducibility of ATR line angle were 0.811 and 0.839.

Conclusions: The ATR line was positioned between Akagi's line and 1/3 Akagi's line in all patients and was a valid option for evaluating rotational tibial alignment after tibial resection.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Flowchart of patient selection.
Fig 2
Fig 2. Definitions of the axes in the tibial reference plane.
Left Upper: Tibial surface before resection 〇: Medial and lateral eminentia intercondylaris ☆: Centre of the medial and lateral eminentia intercondylaris △: Midpoint of the posterior cruciate ligament Lower: 2D plane of the ankle joint 〇: Medial and lateral edge of the ankle joint ☆: Centre of the ankle joint Middle: YZ plane The Z-axis was defined as the line connecting the centre of the medial and lateral eminentia intercondylaris and the centre of the ankle. The Y-axis was defined as the line perpendicular to the Z-axis from the midpoint of the PCL. Right: XZ plane The X-axis was defined as the line perpendicular to the YZ plane bisecting the Y-axis.
Fig 3
Fig 3. Definition of Akagi’s line.
Left (〇): Midpoint of the PCL at the tibial attachment before resection Middle (△): Medial edge of the patellar tendon at the tibial attachment Right: Akagi’s line on 3D model.
Fig 4
Fig 4. Definition of 1/3 Akagi’s line.
Left (〇): Midpoint of the PCL at the tibial attachment before resection Middle (△): Medial third of the patellar tendon at the tibial attachment Right: 1/3 Akagi’s line on 3D model.
Fig 5
Fig 5. Definition of the ATR line.
Left (〇): The lateral edge of the PCL at the tibial attachment after resection Middle (△): The most prominent point of the tibial tubercle Right: The ATR line on 3D model.
Fig 6
Fig 6. Clinical photo of the ATR line.
Left: The tibial surface after osteotomy ①: The most prominent point of the tibial tubercle ②: The lateral edge of the PCL at the tibial attachment Right: The ATR line.
Fig 7
Fig 7. The three lines and their projections (p) on the tibial XY plane.
Left: Akagi’s line, 1/3 Akagi’s line and the ATR line in the 3D model Right: Definitions of ‘p Akagi’s line’, ‘p 1/3 Akagi’s line’ and ‘p ATR line’.
Fig 8
Fig 8. Relationship between Akagi’s line and the ATR line.
①: The line parallel to Akagi’s line ②: The ATR line.

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The authors received no specific funding for this work.
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