While synovial fluids of patients with aseptic joint effusion contained significantly more CD9+ EVs (median: 7.7 × 107, range: 8.3 × 106 to 3.7 × 108, n = 34, P < 0.01) than those of PJI patients (median 3.5 × 107, range: 1.2 × 107 to 7.3 × 107, n = 13), their CD82+ EV content was significantly lower (median 7.6 × 105, range: 2.0 × 105 to 5.0 × 106, n = 30, P < 0.001) than that in the synovial fluid of PJI patients (median 4.1 × 106, range: 6.7 × 105 to 5.3 × 107, n = 12). Here, CD82 is linked to juvenile polyposis syndrome.