Background The knee is commonly affected in inflammatory as in mechanical joint conditions. It has been shown that the amount of synovitis correlates with pain and the risk of future structural damage. Ultrasound (US) is widely available and useful to study the synovial tissue. It allows the evaluation of the synovial membrane thickening and the degree of inflammation. However, current US scoring methods are global, assessing the effusion and synovitis as a whole. Moreover, the cut-off value for normal synovial thickening and the best site to study synovial changes and inflammation remains to be determined.
Objectives The goal of this work was to assess by US the changes of the synovial tissues in different compartment of the anterior knee in patients with inflammatory and mechanical diseases.
Methods This was a monocentric cross-sectional study. All patients seen in our unit for a pain associated with an effusion of the knee were included. They were diagnosed as inflammatory and non-inflammatory diseases according the clinical data and the results of the synovial fluid analysis. A comprehensive US study of 5 synovial recesses of the anterior knee has been carried out suprapatellar recess (midline, lateral, medial), parapatellar (lateral and medial) with assessment of joint effusion, synovial thickening and Doppler signal intensity.
Results Sixty-one patients (68 knees) were included, mean age 60 years (range 17-93). Final diagnosis was inflammatory arthritis in 29 knees (42.6%), crystal induced arthritis in 21 (30.9%), OA in 12 (17.6%) and septic arthritis in 6 (8.8%). A significant effusion was detected in 98.5% of the patients, more frequently in the supra patellar recess (64 knees (94.1%)) than in the parapatellar medial or lateral recesses (45 knees (66.2%) and 46 knees (67.6%) respectively; p<0.001). The synovial thickness was absent in 10 knees (14.7%), mild (between 2 and 4 mm) in 28 knees (41, 2%), moderate (between 4 and 6 mm) in 16 knees (23.5%), and severe (over 6 mm) in 14 knees (20. 6%). The thickening was mostly diffuse (46 knees (79.3%)) and limited to one compartment in only 9 cases (13%). The thickness of the synovial tissue was homogenous although significantly thinner in the medial suprapatellar and parapatellar recesses when compared to the midline suprapatellar recess (3.4 versus 3.1 and 2.9 mm respectively; p=0,002; p=0,044). A positive Doppler signal was detected in at least in one recess in 25% (17) of the knees. It was found less frequently in the midline suprapatellar recess (4.5%) than is the other recesses (p<0.05). Finally, no difference has been found in the effusion, thickening or Doppler signal pattern between the different groups of diseases.
Conclusions Our study shows that knee effusion was more frequently detected in the suprapatellar recess. Synovial thickening was usually mild and uniformly distributed. Synovial thickness was most of the time less than 4 mm, cut-off usually used to define a significant synovitis. This was even true in long standing inflammatory disease. Therefore, a cut-off of 2 mm could be more sensitive to define a significant synovial thickening. Finally, Doppler signal was more frequently detected in the superficial recesses than in the midline suprapatellar recess.
Disclosure of Interest None declared