Background Pain in the knee joints is a common rheumatologic complaint among patients with benign joint hypermobility syndrome (BJHS). There structural causes of artralgia in BJHS are unclear. Usually any structural abnormalities are not found during physical examinations. We used the ultrasonografó (US) to examine of knee tissues in individuals with BJHS and symptomatic or asymptomatic knee joints.

Methods 26 women (w), age 16–25, with BJHS were examined. The first group consisted of 13 w with BJHS and the knee pain (Beigthon score > 5; 6 bilateral and 7 unilateral pain, 19 painful joints); the second group consisted of 13 w with BJHS without knee pain at the moment of the US examinations (26 joints). BJHS individuals were then compared with 10 healthy w (third group) of the same age without joint hypermobility and without knee pain (Beigthon score < 4; 20 joints). The US examinations were performed using a 7,5 MHz linear probe. The following knee tissues were examined: synovia, fluid in the joint, cartilage of the femur condyles, collateral ligaments (CL), tendon of the m.semimembranosus.

Results In the 1st group (BJHS+, pain+) following abnormalities were found: oedema of the CL ? 8, tenosynovitis of the m.semimembranosus (TMS) ? 9, thickness of the synovia > 3 mm ? 1 and small poplyteal cyst ? 1 case per 19 painful joints. In 4 cases there was a combination of the 2 US features. In only 3 out of 19 symptomatic knee joints did the US not find any abnormalities. In the 2nd group (BJHS+, pain-) oedema of the CL was found in 8, TMS in 8 cases. A combination of both was detected in 2 cases. Overall, in 14 out of 26 asymptomatic knee joints, the US found the same morphologic changes as those in the painful joints. The was no difference between 1st and 2nd BJHS groups in prevalence oedema of the CL or TSM (ð >0,05). In only 1 case out of 20 controlled joints (BJHS-, pain-) was the TMS detected. The differences between 1st and 3rd, 2nd and 3rd groups were highly significant (p = 0,000 and p = 0,0005 accordingly). There were no differences between the groups regarding to thickness of the cartilage, fluid in the joint and thickness of the synovia.

Conclusion The characteristic US morphologic changes of the periarticular tissues are detected in knee joints in patients with BJHS. These abnormalities are typical of BJHS itself but not of painful joints. This fact may reflect the possible presence of subclinical soft tissues injuries in some individuals with BJHS.