Relationship between trabecular bone structure and articular cartilage morphology and relaxation times in early OA of the knee joint using parallel MRI at 3 T

Abstract

Objective: To evaluate trabecular bone structure in relationship with cartilage parameters in distal femur and proximal tibia of the human knee at 3Tesla (3T) using high-resolution magnetic resonance imaging (MRI) with parallel imaging.

Method: Sixteen healthy controls and 16 patients with mild osteoarthritis (OA) were studied using a 3T magnetic resonance (MR) scanner and an eight-channel phased-array knee coil. Axial 3D GeneRalized Autocalibrating Partially Parallel Acquisition (GRAPPA)-based phase cycled Fast Imaging Employing Steady State Acquisition (FIESTA-c) images were acquired in order to quantify the trabecular bone structure. For assessing cartilage morphology (thickness, volume), sagittal high-resolution 3D spoiled gradient echo (SPGR) images were acquired. In a subset of the subjects, sagittal images were acquired for measuring T1rho and T2 relaxation times, using 3D T1rho and T2 mapping techniques.

Results: Good measurement reproducibility was observed for bone parameters, the coefficients of variations (CVs) ranging from 1.8% for trabecular number (app. Tb.N) to 5.5% for trabecular separation (app. Tb.Sp). Significant differences between control and OA groups were found for bone volume fraction bone volume over total volume (app. BV/TV) and app. Tb.Sp in all compartments. Significantly increased values in T1rho and T2 were demonstrated in OA patients compared with controls at the femur, but not at the tibia. T1rho was negatively correlated with app. BV/TV, app. Tb.N and app. Tb.Sp both at the medial femoral condyle (MFC) and lateral tibia (LT), while T2 was only correlated at the LT. Also, medial tibia (MT) T1rho was negatively correlated with app. BV/TV (R(2)=-0.49, P<0.05) and app. Tb.N (R(2)=-0.42, P<0.05) from the opposite side of lateral femoral condyle (LFC). Significant correlations were found between trabecular bone parameters and cartilage thickness and normalized volume, mainly at LT, tibia (T) and femur (F).

Conclusion: At this early stage of OA, an overall decrease in bone structure parameters and an increase in cartilage parameters (T1rho, T2) were noticed in patients. Trabecular bone structure correlated with articular cartilage parameters suggesting that loss of mineralized bone is associated with cartilage degeneration.

Figure 1

Trabecular bone structure post-processing: bone and marrow regions of interest (ROI) were outlined for the femur (A), lateral and medial condyles (B), tibia (C) and lateral and medial tibia (D); the tibial grid was derived from the epicondylar distance (Unit [mm] = Epicondylar Distance × 100/9).

Figure 2

A graphical representation of the segmented trabecular bone regions. The femur, tibia, lateral femoral condyle (LFC), medial femoral condyle (MFC), lateral tibia (LT), and medial tibia (MT) are shown; the ROIs were defined similarly with a previous described method

Figure 3

Representative T1ρ and T2 maps for a control subject (A, C) and for an OA patient (B, D).

Figure 4

Trabecular bone structure data: apparent measures of trabecular bone fraction (BV/TV), trabecular number (Tb.N), trabecular separation (Tb.Sp), and trabecular thickness (Tb.Th) were computed in OA patients compared with controls, using the ANOVA F-test; *P<0.05.

Figure 5

Articular cartilage data: T1ρ and T2 relaxation times as well as thickness and normalized volume were computed in OA patients compared with controls, using the ANOVA F-test; to account for the variation in joint size, the calculated volume was normalized to the epicondylar distance of each respective subject; the epicondylar distance was used to standardize the volume due to its invariance to osteoarthritic changes; *P<0.05.