The morphometry of soft tissue insertions on the tibial plateau: data acquisition and statistical shape analysis

Abstract

This study characterized the soft tissue insertion morphometrics on the tibial plateau and their inter-relationships as well as variabilities. The outlines of the cruciate ligament and meniscal root insertions along with the medial and lateral cartilage on 20 cadaveric tibias (10 left and 10 right knees) were digitized and co-registered with corresponding CT-based 3D bone models. Generalized Procrustes Analysis was employed in conjunction with Principal Components Analysis to first create a geometric consensus based on tibial cartilage and then determine the means and variations of insertion morphometrics including shape, size, location, and inter-relationship measures. Step-wise regression analysis was conducted in search of parsimonious models relating the morphometric measures to the tibial plateau width and depth, and basic anthropometric and gender factors. The analyses resulted in statistical morphometric representations for Procrustes-superimposed cruciate ligament and meniscus insertions, and identified only a few moderate correlations (R2: 0.37-0.49). The study provided evidence challenging the isometric scaling based on a single dimension frequently employed in related morphometric studies, and data for evaluating cruciate ligament reconstruction strategies in terms of re-creating the native anatomy and minimizing the risk of iatrogenic injury. It paved the way for future development of computer-aided personalized orthopaedic surgery applications improving the quality of care and patient safety, and biomechanical models with a better population or average representation.

Figure 1. The digitized cartilage and insertion site outlines mapped onto the CT-based 3D tibia model.

The digitized points (asterisks) were spline-fitted, generating 100 equidistant points (circles on the close-up view of ACL insertion outline) on the fitted outlines to facilitate the subsequent analyses. The coordinate system shown was defined based on Principal Components Analysis (PCA) of the cartilage outline points.

Figure 2. The effect of Procrustes Superimposition illustrated by one pair of tibias.

One cartilage configuration served as the base (thick) and another as the target (thin). Six tissue structure insertions in various views before (left column) and after (right column) superimposition are shown as well.

Figure 3. The outlines of tibial cartilage and six insertion sites before and after cartilage-based GPA.

The number of tibia samples is 20.

Figure 4. Statistical representations of tibial cartilage, cruciate ligament and meniscus insertion location and shape variability.

The thick outlines are the mean or “most representative” shapes (the black thick outlines for tibial cartilage and the colored thick lines in the upper and lower subplots for six insertion sites); the color ellipses are 99% confidence ellipses for the insertion centroid locations resulting from PCA; the thin ellipses centered at the equidistant landmarks (20 on each outline) quantify the landmark position variability individually and the shape variability collectively.