The septic versus nonseptic inflamed joint: MRI characteristics

Objective. To differentiate the MR features of septic versus nonseptic infl amed joints. Design and patients. Thirty patients were referred for MRI with inflamed jo ints (19 were subsequently found to be septic and 11 nonseptic). At 1.5 T e nhanced MRI five groups of signs related to joint space, synovium, cartilag e, bone and peri-articular soft tissue respectively were assessed and compa red between the septic and nonseptic groups. Results. The prevalence of MRI findings in septic versus nonseptic joints ( respectively) was as follows: effusion (79% vs 82%), fluid outpouching (79% vs 73%), fluid heterogeneity (21% vs 27%), synovial thickening (68% vs 55% ), synovial periedema (63% vs 55%), synovial enhancement (94% vs 88%), cart ilage loss (53% vs 30%), bone erosions (79% vs 38%); bone erosions enhancem ent (77% vs 43%), bone marrow edema (74% vs 38%), bone marrow enhancement ( 67% vs 50%), soft tissue edema (63% vs 78%), soft tissue enhancement (67% v s 71%), periosteal edema(11% vs. 10%). The presence of bone erosions appear ed to be an indicator for an infected joint (P=0.072); coexistence of bone marrow edema slightly improves the significance (0.068). A similar trend wa s obtained when combining bone erosions with either synovial thickening, sy novial periedema, bone marrow enhancement or soft tissue edema (P=0.075). Conclusions. The combination of bone erosions with marrow edema is highly s uggestive for a septic articulation; the additional coexistence of synovial thickening, synovial edema, soft tissue edema or bone marrow enhancement i ncreases the above level of confidence. Similar to conventional radiography , the single sign that appeared to show a significant trend was the presenc e of bone erosions. However, no single sign or combination could either be considered pathognomonic or exclude the presence of a joint infection.