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Findings:

1) Hip films - The sacroiliac joints appear sclerotic with the left showing more sclerosis than the right. There is formation of an osteophyte at the junction of the left femoral head and neck. The left acetobulum appears sclerotic compared to the right. There is slight narrowing of the left hip joint.

2) Foot films - Diffuse osteopenia is present in the visualized bony structures.

Diagnosis: Juvenile Ankylosing Spondylitis

Discussion: Juvenile ankylosing spondylitis (JAS) is a form of arthritis that produces characteristic findings in the sacroiliac joints, spine, and, less frequently, appendicular joints. HLA-B27 gene is present in approximately 90% of patients with A S. Most patients have an increased Erythrocyte Sedimentation Rate (ESR) and C-reactive protein Rheumatoid factor and antinuclear antibodies are absent.

Radiographic findings show early changes in the sacroiliac joints. These changes involve blurring of the cortical margins of subchondral bone, followed by erosions and sclerosis. Progression of the erosions lead to widening followed by obliteration as fibrous and then bony ankylosis occur.

In the lumbar spine, progression of disease with osteitis and erosion lead to a squaring of the vertebral bodies. Ossification of the annulus fibrosis leads to an eventual formation of syndesmophytes seen as bridges connecting successive vertebral bodies.

Of the appendicular joints the hip is the most commonly involved followed by the knees, shoulders and distal joints. Deminieralization, soft tissue swelling, and synovitis are commonly present with the joint pain.

Juvenile ankylosing spondylitis has an average age of onset of greater than 10 years, usually affects males more than females, usually has negative rheumatoid factor, and has positive HLA-B27 antigen in approximately 90% of the cases. The proximal appendicular skeleton is usually the original presenting part. This disease entity must be separated from juvenile rheumatoid arthritis, both clinically and radiographically. Sacroiliac joint changes are less common in juvenile rheumatoid arthritis (JRA) as is ankylosis of the thoraco-lumbar spine. HLA-B27 is less commonly positive with rheumatoid factor being more common in juvenile rheumatoid arthritis.

Treatment of juvenile ankylosing spondylitis involves nonsteroidal anti-inflammatory drugs which reduce pain and stiffness.

References:
1) Kleinman Pet al. Juvenile ankylosing spondy/itis. Radiology 1977; 125: 775-780.
2) Harrison's Principles of Internal Medicine, 13th edition. McGraw-Hill, 1994.
3) Mitnick JS et al. Proliferative changes of the hip in juvenile rheumatoid arthritis
Radiology 1980; 136: 369-371.
4) Nelson's Essentials of Pediatrics. W.B. Saunders co. 1990.
5) Robbins Pathologic Basis of Disease, 4th edition. W.B. Saunders co. 1989.

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