Title: The relationship between knee pain and MR relaxation in medial tibial articular cartilage
Abstract: Purpose: Knee articular cartilage degeneration associated with osteoarthritis (OA) has been associated with a multitude of pathological occurrences, including joint pain. With respect to magnetic resonance imaging (MRI), T1ρ and T2 relaxation time mapping are non-invasive techniques that may provide information regarding early degenerative changes in the cartilage matrix. This study aims to investigate the relationship between degenerative biochemical changes in the cartilage matrix, as measured with T1ρ and T2 relaxation time constants and knee pain measured by The Western Ontario and McMaster Universities Arthritis Index (WOMAC) questionnaire. Methods: Patients were stratified into asymptomatic (no pain, WOMAC score = 0, n=22, mean age of 41 years (± 13.5), mean BMI of 23.6 kg/m2 (± 2.3) and 32% female) and pain (moderate to severe pain; WOMAC≥8; n=28 mean age of 59 years (± 11.5), mean BMI of 27.3 kg/m2 (± 5.3) and 70% female) groups. WOMAC questionnaires were administered to each subject prior to imaging. MR studies in 50 subjects (mean age of 51 years (± 15.3), mean BMI of 25.8 kg/m2 (± 4.7) and 52% female) were acquired on a 3T Signa HDx MR (GE Healthcare, Piscataway, NJ) scanner with an 8-channel phased array knee coil. Sagittal cartilage T1ρ and T2 maps were generated using 3D MAPSS mapping techniques (TR/TE=9.3/3.7 ms; FOV=14cm, matrix=256×128 pixels, slice thickness=4 mm, BW=31.25 kHz, views per segment=64, recovery time =1.5 s, for T1ρ: Time of Spin-Lock=0, 10, 40, 80 ms, spin-lock frequency=500 Hz; for T2: prep TE=4.1, 14.5, 25, 45.9 ms). A fat-saturated T1-weighted 3D SPGR sequence (TR/TE=15/6.7 ms, flip angle=12, FOV=14cm, matrix=512 × 512, slice thickness=1 mm, bandwidth=31.25 kHz, NEX=1) was used for cartilage segmentation. Five cartilage knee compartment regions of interest (ROIs) (lateral femoral condyle (LFC), medial femoral condyle (MFC), lateral tibia (LT), medial tibia (MT), patella (PAT)) were segmented in a MATLAB (MathWorks, Natick MA) based in-house software package. Compartments were partitioned into a bone and articular layer, using a Euclidean distance algorithm with the same in-house software. A random effects linear regression model adjusting for age, gender, and BMI was performed in JMP software version 8 (SAS Institute, Cary NC). Results: Statistically significant increases in both T1ρ and T2 (p<0.01 respectively) relaxation time constants were observed in the MT for the pain group (Figure 1, Figure 2) when compared to the asymptomatic cohort. In analysis of the cartilage layers, MT bone layer T1ρ (p<0.01), MT bone and articular layer T2 (p<0.01 respectively), and LT bone layer T2 (P<0.05) were also significantly elevated in the pain cohort. Conclusions: This study shows a significant relationship between knee pain and cartilage T1ρ and T2 relaxation time mapping, metrics for early cartilage degeneration. Subjects reporting moderate to severe knee pain as determined by the WOMAC questionnaire displayed elevated T1ρ and T2 relaxation time constant in the MT, indicating that cartilage degeneration in this compartment may be related to noticeable pain symptoms. Furthermore, the laminar analysis shows that the elevation of T1ρ and T2 in the pain group is more dominant in the bone layer, implying the cartilage and bone interaction may contribute to the association between cartilage degeneration and pain.Figure 2Medial tibia whole compartment, bone, and articular layer T2 relaxation time constants for both asymptomatic and arthralgic groups. Single asterisk denotes p<0.05 and double asterisk denotes p<0.01.View Large Image Figure ViewerDownload Hi-res image Download (PPT)