Objective: To examine the relationship between longitudinal fluctuations in synovitis with change in pain and cartilage in knee osteoarthritis.
Methods: Study subjects were patients 45 years of age and older with symptomatic knee osteoarthritis from the Boston Osteoarthritis of the Knee Study. Baseline and follow-up assessments at 15 and 30 months including knee magnetic resonance imaging (MRI), BMI and pain assessment (VAS) over the last week. Synovitis was scored at 3 locations (infrapatellar fat pad, suprapatellar and intercondylar regions) using a semi-quantitative scale (0-3) at all 3 time points on MRI. Scores at each site were added to give a summary synovitis score (0-9).
Results: We assessed 270 subjects whose mean ± SD age was 66.7 ± 9.2 years, BMI 31.5 ± 5.7kg/m2; 42% were female. There was no correlation of baseline synovitis with baseline pain score (r=0.09, p=0.17). Change in summary synovitis score was correlated with change in pain (r = 0.21, p=0.0003). An increase of one unit in summary synovitis score resulted in 3.15mm increase in VAS pain score (0-100 scale). Effusion change was not associated with pain change. Of the 3 locations for synovitis, changes in the infrapatellar fat pad were most strongly related to pain change. Despite cartilage loss occurring in over 50% of knees, synovitis was not associated with cartilage loss in either tibiofemoral or patellofemoral compartment.
Conclusions: Change in synovitis was correlated with change in knee pain, but not loss of cartilage. Treatment of pain in knee OA needs to consider treatment of synovitis.