Abstract
Introduction
Tibial components that match the resected proximal tibia may promote accurate rotational alignment and maximize coverage while minimizing overhang in total knee arthroplasty (TKA). Tibial component designs have traditionally been evaluated utilizing an overall anterior-posterior (AP)/medial-lateral (ML) ratio. However, since the tibial plateau is irregularly shaped, such a metric has drawbacks. Here, a detailed set of morphological metrics is used to evaluate six contemporary tibia designs against a multi-ethnic bone database.
Methods
Tibial surfaces from 347 subjects, including 97 Indian (50m/47f), 99 Japanese (44m/55f), and 151 Caucasian (85m/66f), were virtually resected following a specific TKA procedure, as previous publications have shown surgical variability minimally impacts tibial resection morphology. Medial and lateral AP dimensions (MAP and LAP), ML width (ML), and medial and lateral anterior radii (MAR and LAR) were measured in a coordinate system constructed on the resected surface based on the neutral rotational axis (Fig. 1A). These metrics, along with anterior radius asymmetry (MAR/LAR), were regressed against ML for each ethnicity. The regressions were then compared with similar measurements obtained from tibial components in six contemporary TKA systems (one asymmetric: Design A; four symmetric: Designs B-E; and one anatomic: Design F).
Results
The LAP of all six designs generally agrees well with the three ethnicities investigated. Designs A and F have MAP closer to tibial morphology (Fig. 2), while those of the symmetric designs are smaller than the morphological measurement, especially for tibiae with larger ML (Fig. 2). Across all three ethnicities, there is a positive correlation between anterior radii and ML (Fig. 3), which is reflected in each of the component designs. However, the symmetric designs tend to have bigger LAR and smaller MAR compared to the anatomic tibial morphology. Design F has the closest APs and anterior radii to the morphological measurements in all three ethnicities.
The MAR/LAR is 1.8 ± 0.6 for Indian, 1.7 ± 0.4 for Caucasian, and 1.6 ± 0.3 for Japanese, and is negatively correlated with ML (Fig. 1B). However, except for Design F, which closely matches the measured morphology, all of the other designs investigated have constant and significantly lower MAR/LAR across all sizes (1 for the symmetric designs, 1.1 for the asymmetric design).
Discussion
The ability to closely match the medial AP dimensions for Designs A and F suggests that anatomic or asymmetric designs with properly sized AP dimensions may reduce the amount of uncovered resected tibial surface compared to symmetric designs. Additionally, the current mismatch of the anterior radii in the asymmetric or symmetric component designs investigated may drive surgical compromise of coverage in order to facilitate rotational alignment or minimize overhang on the anterior regions of the resected tibia. Lastly, only the anatomic Design F accounts for the asymmetric characteristics of the tibial anterior radii, which may assist proper alignment of the tibial component, while the other five designs have either a radius ratio of 1 (Designs B-E) or a very small asymmetry (1.1, Design A). In summary, improved understanding of variations in tibial morphology across ethnicities can support continuous improvement of contemporary tibial component designs.
