Covariation between shape and bone microstructure in the proximal tibia in humans

Prosthetic knee replacement is a surgical procedure designed to restore knee joint function in cases of advanced osteoarthritis and fracture. Since tibial morphology and microstructure vary among different individuals, the surgeon’s anatomical expertise and knowledge of various implant designs is essential. In order to contribute to the pre-surgical diagnosis of bone degradation, we investigate patterns of variation and covariation between the shape of the proximal tibia and its microstructure. The general objective of this pilot study is the prediction of bone microstructure in relation to the shape of the proximal tibia, thereby delivering an estimation of bone microstructure based on the geometry of the knee. Our sample comprises dried bone samples of 20 human tibiae including cases of osteoarthritis. The shape of the tibia is represented by anatomical landmarks as well as curve and surface semilandmarks. Microstructural parameters are relative bone volume, trabecular thickness, number, and spacing obtained from high resolution X-ray computed tomography (XCT) images with an isometric voxel size of 50 μm. Geometric Morphometric techniques are used to study the covariation between proximal tibial shape and structural parameters using partial least squares analysis. Our results indicate that a decrease in bone volume fraction, as seen in older individuals, is moderately correlated (>0.6) with a flattening and broadening of the tibial plateau. Using this approach it is possible to estimate structural parameters in the knee according to its shape, allowing the three-dimensional visualization of covariation patterns in relation to aging. This method can potentially function as an aid in the clinical diagnosis of tibial bone degradation and delivers anatomical information that may be valuable in the design of custom knee implant components.