Assessment of synovitis with contrast-enhanced MRI using a whole-joint semiquantitative scoring system in people with, or at high risk of, knee osteoarthritis: the MOST study

Abstract

Objectives: To introduce a comprehensive and reliable scoring system for the assessment of whole-knee joint synovitis based on contrast-enhanced (CE) MRI.

Methods: Multicenter Osteoarthritis Study (MOST) is a cohort study of people with, or at high risk of, knee osteoarthritis (OA). Subjects are an unselected subset of MOST who volunteered for CE-MRI. Synovitis was assessed at 11 sites of the joint. Synovial thickness was scored semiquantitatively: grade 0 (<2 mm), grade 1 (2-4 mm) and grade 2 (>4 mm) at each site. Two musculoskeletal radiologists performed the readings and inter- and intrareader reliability was evaluated. Whole-knee synovitis was assessed by summing the scores from all sites. The association of Western Ontario and McMaster Osteoarthritis Index pain score with this summed score and with the maximum synovitis grade for each site was assessed.

Results: 400 subjects were included (mean age 58.8±7.0 years, body mass index 29.5±4.9 kg/m(2), 46% women). For individual sites, intrareader reliability (weighted κ) was 0.67-1.00 for reader 1 and 0.60-1.00 for reader 2. Inter-reader agreement (κ) was 0.67-0.92. For the summed synovitis scores, intrareader reliability (intraclass correlation coefficient ( ICC)) was 0.98 and 0.96 for each reader and inter-reader agreement (ICC) was 0.94. Moderate to severe synovitis in the parapatellar subregion was associated with the higher maximum pain score (adjusted OR (95% CI), 2.8 (1.4 to 5.4) and 3.1 (1.2 to 7.9), respectively).

Conclusions: A comprehensive semiquantitative scoring system for the assessment of whole-knee synovitis is proposed. It is reliable and identifies knees with pain, and thus is a potentially powerful tool for synovitis assessment in epidemiological OA studies.

Figure 1

Eleven anatomical sites evaluated in the proposed scoring system. (A) Sagittal T1-weighted contrast-enhanced (CE) image at the location of the anterior cruciate ligament (ACL). Definition of the suprapatellar site: 0.5–1 cm cranial to the superior patellar pole (black arrow). Definition of infrapatellar site: directly adjacent to the inferior patellar pole (black arrowhead). Definition of the intercondylar site: at the surface of Hoffa’s fat pad 1.5–2 cm distal to inferior patellar pole (grey arrowhead). Definition of ‘adjacent to the ACL’ site: directly anterior to the ACL close to its femoral attachment (white arrow). (B) Axial T1-weighted CE image at the location of the maximum medial-lateral patellar diameter. Definition of the medial parapatellar site: 0.5–1 cm posterior to the medial patellar pole. Definition of the lateral parapatellar site: 0.5–1 cm posterior to the lateral patellar pole. (C) Sagittal T1-weighted CE image at the location of the tibiofibular joint. Definition of the lateral parameniscal site: directly adjacent posterior to the posterior horn of the lateral meniscus (white arrow). (D) Sagittal T1-weighted CE image at the location of the tibial semimembranosus attachment. Definition of the medial parameniscal site: directly adjacent to the posterior horn of the medial meniscus (white arrowhead). (E) Sagittal T1-weighted CE image at the location of the femoral posterior cruciate ligament (PCL) attachment. Definition of ‘adjacent to the PCL’ site: Directly adjacent to the PCL at its mid-portion (white arrow). (F) Axial T1-weighted CE image at the location of the Baker cyst with peripheral enhancement indicating synovitis (white arrow). (G) Sagittal T1-weighted CE image showing a loose body (white arrow), located posteriorly to the PCL, surrounded by enhancing synovitis.

Figure 2

Semiquantitative synovitis scoring. (A) Grade 0—normal enhancement (<2 mm) of the intercondylar synovium (arrow). (B) Grade 1—enhancement of the suprapatellar and intercondylar synovium (white arrows) and grade 2 enhancement around the anterior cruciate ligament (black arrow).