Involvement of the proximal tibiofibular joint in ankylosing spondylitis

Ankylosing spondylitis (AS) may affect peripheral joints, with the shoulder, hip, and knee being well known involved sites. However, involvement of the proximal tibiofibular (PTF) joint has not yet been investigated.

To evaluate PTF joint abnormalities in patients with AS.

From July 1997 to June 2005, 16 patients (15 male, one female; mean age 25 years), who were clinically diagnosed with AS, underwent magnetic resonance imaging (MRI) to evaluate knee pain. All patients also underwent plain radiographs of the knee, lumbar spine, and pelvis. Twenty knee MRIs (bilateral in four patients) and 16 sets of knee, lumbar spine, and pelvic radiographs were retrospectively reviewed in order to evaluate possible AS involvement. The presence of abnormalities suggesting AS involvement were recorded separately in the sacroiliac joints, lumbar spine, hip, and femorotibial and PTF joints. If the PTF joint showed any pathologic findings, the radiologic findings were recorded.

Three of 16 patients (18.7%) had pathologic features of the PTF joint observed by plain radiographs or MRI. One of these three patients showed bilateral involvement of the PTF joints on plain radiographs, while the other two patients showed unilateral involvement on MRI. Subchondral sclerosis, cartilage abnormality, erosion, and abnormal bone marrow signal intensity were identified on MRI. Plain radiographs of two patients revealed subchondral sclerosis and spur formation in the PTF joint. The frequencies of involvement of other joints in the 16 patients were as follows: lumbar spine, n=5 (31%), hip joint, n=1 (6%) (identified by plain radiographs), and femorotibial joints, n=10 (62.5%) (identified by knee MRI).

MR imaging of the PTF joint can depict synovial changes and their effect on joint structures in patients with AS. The MRI findings of AS involving the PTF joints are subchondral sclerosis, cartilage abnormality, erosion, and abnormal bone marrow signal intensity.