Tibial subchondral trabecular bone micromechanical and microarchitectural properties are affected by alignment and osteoarthritis stage

Abstract

At advanced knee osteoarthritis (OA) stages subchondral trabecular bone (STB) is altered. Lower limb alignment plays a role in OA progression and modify the macroscopic loading of the medial and lateral condyles of the tibial plateau. How the properties of the STB relate to alignment and OA stage is not well defined. OA stage (KL scores 2-4) and alignment (HKA from 17° Varus to 8° Valgus) of 30 patients were measured and their tibial plateau were collected after total knee arthroplasty. STB tissue elastic modulus, bone volume fraction (BV/TV) and trabecula thickness (Tb.Th) were evaluated with nanoindentation and µCT scans (8.1 µm voxel-size) of medial and lateral samples of each plateau. HKA and KL scores were statistically significantly associated with STB elastic modulus, BV/TV and Tb.Th. Medial to lateral BV/TV ratio correlated with HKA angle (R = -0.53, p = 0.016), revealing a higher ratio for varus than valgus subjects. STB properties showed lower values for KL stage 4 patients. Tissue elastic modulus ratios and BV.TV ratios were strongly correlated (R = 0.81, p < 0.001). Results showed that both micromechanical and microarchitectural properties of STB are affected by macroscopic loading at late stage knee OA. For the first time, a strong association between tissue stiffness and quantity of OA STB was demonstrated.

Figure 1

Schematic of the sample acquisitions and subsequent characterisation methods used in this study. (1) Two samples, one medial and one lateral, were excised from tibial plateaus retrieved during total knee arthroplasty surgery and polished. (2) Forty indent tests were performed per sample. (3) Each sample was μCT scanned. (4) Definition of the volume of interest (VOI) used to calculate the microarchitectural parameters.

Figure 2

Scatter plots of the association between the depth from subchondral surface, namely the distance between the indented plane and the tidemark, and the per sample mean of E*, i.e., the mean nanoindentation elastic modulus of each subchondral bone sample. Best fit lines (solid lines) and 95% intervals (shaded area) for Pearson’s correlations: (left) all samples, (top right) samples stratified with sample side and (bottom right) samples stratified with loading status, with the medial samples of varus subjects considered overloaded and the lateral ones underloaded and vice-versa for the valgus subjects.

Figure 3

Plots illustrate relationships between per sample mean nanoindentation modulus (E*) and associated clinical parameters. The data were adjusted for depth from subchondral surface before plotting. For scatter plots, best fit lines (solid lines) and 95% intervals (shaded area) for Pearson’s correlations. (Left) Scatter plots of the association between the medial to lateral ratio of sample mean nanoindentation modulus (M:L mean E* ratio) and knee alignment (HKA angle). (top right) Scatter plots of per sample mean nanoindentation modulus (E*) and knee alignment (HKA angle). (bottom right) Bar plot of the per sample means of nanoindentation modulus (E*) stratified with both loading status and KL score. For KL score, subjects were separated into two groups: those rated IV by all surgeons and those not. Error bars indicate ±1 SD. For the bar plot, the horizontal lines indicate if the differences of the means are statistically significant according to Student’s t-tests.

Figure 4

Plots illustrate relationships between microarchitectural parameters and associated clinical parameters. For scatter plots, data are presented along with best-fit lines (solid lines) and 95% intervals (shaded area) for Pearson’s correlations. For bar plots, the error bars denote ±1 SD. (Top left) Scatter plots of the association of the medial to lateral ratio of bone volume fraction (M:L BV/TV) with knee alignment (HKA angle). (Bottom left) Scatter plots of the association of the medial to lateral ratio of per sample mean trabecula thicknesses (M:L Tb.Th) with knee alignment (HKA angle). (Top middle) Scatter plots of per sample mean nanoindentation modulus (E*) and knee alignment (HKA angle).(top right) Bar plot of bone volume fraction (BV/TV) data stratified with both loading status and KL score. For KL score, subjects were separated into two groups: those rated IV by all surgeons and those not. Error bars indicate ±1 SD. (bottom right), the same as top right but for the per sample mean trabecula thickness (Tb.Th) data. For the bar plots, the horizontal lines indicate if the differences of the means are statistically significant according to Student’s t-tests.

Figure 5

Scatter plots illustrate the association between nanoindentation modulus and microarchitectural parameters. Data are presented along with best-fit lines (solid lines) and 95% intervals (shaded area) for Pearson’s correlations. (left) Association between the medial to lateral ratio of sample mean nanoindentation modulus (M:L mean E*) and the medial to lateral ratio of bone volume fraction (M:L BV/TV). (right) Association between the medial to lateral ratio of sample mean nanoindentation modulus (M:L mean E*) and the medial to lateral ratio of per sample mean trabecula thicknesses (M:L Tb.Th).