The association of CT-detected intra-articular calcification with MRI-detected effusion-synovitis and Hoffa-synovitis in knee OA: The Multicenter Osteoarthritis study

CT-detected intra-articular (IA) calcification from calcium crystal deposition is associated with worsening cartilage damage and knee pain in osteoarthritis (OA); whether there is associated joint inflammation is unclear. We studied the relation of CT-detected IA calcification to imaging evidence of inflammation (i.e., effusion-synovitis and/or Hoffa-synovitis) on knee MRI in middle-aged and older adults, focusing on tissue-specific relationships. Participants from the Multicenter Osteoarthritis study with knee CTs and MRIs were included. Presence of IA calcification on CT was defined as Boston University Calcium Knee Score >0 in hyaline cartilage, meniscus, and capsule anywhere in the knee. Effusion-synovitis and Hoffa-synovitis were scored on MRI using MOAKS at baseline and two years later. We evaluated the relation of IA calcification (overall and in specific tissues) to presence of effusion-synovitis and/or Hoffa-synovitis longitudinally, using Poisson regression with generalized estimating equations, adjusting for age, sex, race, and body mass index. We included 1669 participants with available knee CT and MRI (mean age 60.6±9 years, 56% female, mean BMI 28.5±5 kg/m; 21.6% knees with radiographic OA). Overall, at baseline, 9.2% had any IA calcification, 30.0% had effusion-synovitis, 37.0% Hoffa-synovitis, and 50% either effusion-synovitis and/or Hoffa-synovitis. The presence of any IA calcification was associated with 30% higher risk of effusion-synovitis and/or Hoffa-synovitis longitudinally (risk ratio 1.30, 95% CI 1.16, 1.46). Results were similar for IA calcification in the cartilage, meniscus, and capsule. CT-detected IA calcification in various tissues was associated with the presence of joint inflammation on MRI over 2 years.