Quantitative assessment of bone marrow edema-like lesion and overlying cartilage in knees with osteoarthritis and anterior cruciate ligament tear using MR imaging and spectroscopic imaging at 3 Tesla

Abstract

Purpose: To quantitatively assess bone marrow edema-like lesion (BMEL) and the overlying cartilage in osteoarthritis (OA) or anterior cruciate ligament (ACL)-injured knees using magnetic resonance imaging (MRI) and spectroscopic imaging (MRSI).

Materials and methods: Eight healthy controls and 30 patients with OA and other injuries who showed BMEL were scanned at 3.0T. A regression model was constructed to automatically calculate the volume of BMEL. Normalized T(1rho) z-scores were calculated within BMEL-overlying cartilage. Three-dimensional (3D) MRSI was acquired in the BMEL and surrounding bone marrow.

Results: The mean T(1rho) z-score was significantly higher in BMEL-overlying cartilage than that in surrounding cartilage in the lateral tibia of patients with ACL tears (P < 0.001). Significantly elevated water and unsaturated lipids, and decreased saturated lipids were observed in BMEL. The volume of elevated water correlated with the volume of BMEL. Water content was significantly higher within BMEL than that outside BMEL. The unsaturation index outside BMEL was significantly higher in patients with ACL tears than that in OA.

Conclusion: 3D MRSI and T(1rho) mapping provide tools to quantitatively evaluate BMEL in OA and knee injury. This may allow us to better understand pathophysiology and evolution of injuries and degenerative conditions of the knee.

(c) 2008 Wiley-Liss, Inc.

Figures

Figure 1

Definition of BMEL and overlying cartilage vs. surrounding cartilage. a: The T2-weighted fat-saturated FSE image. Yellow contour: BMEL; blue contour: normal-appearing bone marrow in the same compartment. Mean and SD of signal intensity within normal-appearing bone marrow were measured and used to calculate threshold for BMEL segmentation. The T2-weighted image is aligned to SPGR image. b: The SPGR image with cartilage segmented and defined as BMEL-overlying cartilage (red) and surrounding cartilage (green).

Figure 2

T1ρ Z-score maps for an ACL tear patient who showed BMEL in both LFC and LT (a) and for an OA patient who showed BMEL in MFC (b). Significant elevated T1ρ values were found in BMEL-overlying cartilage in LT (a: white arrow) but not in BMEL-overlying cartilage in LFC (a: yellow arrow) in the ACL-injured knee. No significant difference in T1ρ values was found between BMEL-overlying vs. surrounding cartilage in the OA patient.

Figure 3

MR spectral data in bone marrow in a healthy volunteer (a), a patient with OA (b), and a patient with ACL tear (c). In healthy controls, saturated lipids at 1.3 ppm dominated the signal. Significantly elevated unsaturated lipids peaks at 5.35 ppm and water peaks at 4.65 ppm were observed in patients with OA and ACL tear. Significantly elevated water peaks were more focused within BMEL, while significantly elevated unsaturated lipid peaks extended outside the BMEL. Saturated lipids decreased within BMEL.

Figure 4

Scatter plot of volumes of significantly elevated water vs. BMEL volumes.

Figure 5

Water content (%) and unsaturation index (%) within and outside BMEL for patient with OA and ACL tears. Bright: within BMEL; dark: outside BMEL. (a) Water content for patients with OA and ACL tears, (b) unsaturation index for patients with OA and ACL tears, (c) water content for patients with ACL tears, and (d) unsaturation index for patients with ACL tears; with BMEL located in LT and LFC, respectively. Stars indicate where the difference is significant (P < 0.05).

Figure 6

A patient with ACL tear showed BMEL in lateral tibia. a: Color coded T1ρ relaxation time maps. T1ρ values were significantly elevated in BMEL-overlying cartilage in posterolateral tibia plateau (white arrow) vs. surrounding cartilage in the same compartment (60.2 ± 13.7 msec vs. 37.5 ± 14.3 msec). b: Arthroscopic picture demonstrating grade I softening of the posterolateral tibial plateau with linear partial fissures along the articular cartilage overlying the region of the BMEL (black arrow). Regenerated from Ref with permission.