Insight into the 3D-trabecular architecture of the human patella

The subchondral bone plate (SBP), a dynamic component of the osteochondral unit, shows functional adaptation to long-term loading by distribution of the mineral content in a manner best serving the mechanical demands. Since the received joint-load is transmitted into the trabecular system, the spongy bone also exhibits differences in strain energy density which models it for optimal support. To evaluate the regional variations in trabecular architecture, in accordance with the density distribution of the SBP revealing its long-term load intake, CT- and muCT-datasets of ten physiologic patellae were analysed for defined parameters of bony structure. For the SBP, the density distributions as well as area measurements were used. The trabecular architecture was described using parameters of bone morphology comprising the first 5mm (examined in 1mm steps) below the SBP. The obtained measurements are: Bone volume fraction (BV/TV); Bone surface density (BS/TV); Trabecular number (Tb.N); Trabecular separation (Tb.Sp); Trabecular thickness (Tb.Th); structure model index (SMI); and the Degree of anisotropy (DA). The evaluated architectural parameters varied within the trabecular system and showed an inhomogeneous distribution pattern. It proved to be distinctive with maxima of material and stability situated below areas of the highest long-term load intake. With increasing depth, the pattern of distribution was persistent but lessened in intensity. The parameters significantly correlated with the density distribution of the SBP within the first and second millimetres. With increasing depth down to the fifth millimetre, the coefficients of correlation decreased for all values. The trabecular network adapts to its mechanical needs and is therefore not homogenously built. Dependent upon the long-term load intake, the trabecular model optimizes the support with significant correlation to the density distribution of the SBP.