This article reviews aspects of arthritis imaging that are specific to children. The pediatric skeleton is unique and responds in characteristic ways to articular inflammation. Epiphyseal and physeal cartilage are affected by joint diseases, and disturbances of growth and maturation are sometimes the cardinal manifestations of arthritis. The target joints of pediatric articular diseases differ considerably from those of diseases in adults. Imaging techniques should be tailored to the children being studied.

An analysis of 160 patients with Reiter's disease, 144 with yersinia arthritis, and 9 with salmonella arthritis was performed, Complete or incomplete Reiter's syndrome was observed in one-third of the patients with yersinia arthritis and in most of those with salmonella arthritis. During the followup period, chronic back pain and joint symptoms were frequent in all the patient groups. Patients who were HLA-B27 positive had a more severe acute disease (more frequent back pain, urologic symptoms, mucocutaneous manifestations, and a longer duration of the disease) and more frequent chronic back pain and sacroiliitis.

HLA-B27 typing of all arthritic children helped to identify and focus attention on a subset whose disease was pathogenetically related to and demonstrated clinical features of ankylosing spondylitis and Reiter syndrome, but only rarely fulfilled current diagnostic criteria for those disorders (spondyloarthritis). In contrast to other forms of childhood arthritis, enthesopathy (inflammation at the sites of attachment of ligaments and tendons to bone) was a prominent feature in 75%; a family history of similar arthritis was obtained from 60%; boys were more frequently affected (2:1); urethritis, acute iritis, conjunctivitis, or keratoderma blennorrhagicum occurred at some time in 42%; and the initial attack followed an unexplained febrile illness, known dysentery or urethritis, or severe musculoskeletal trauma in 41%. The arthritis was generally pauciarticular, asymmetric, and primarily in the feet and large joints of the lower extremities. Distinctive radiographic features included periostitis, severe osteopenia, calcaneal erosions, and heel spurs; three of 58 had rapid destruction of a single joint. Only ten patients (all boys) were found to have radiographic sacroiliitis after an average of five years of disease, and only three had the Reiter triad. The lifetime risk of sacroiliitis and spinal ankylosis can only be determined by long-term follow-up of such prospectively identified groups of spondyloarthritic children.

This study presents the frequency of severe and mild talalgias in unselected, consecutive patients with rheumatoid arthritis, ankylosing spondylitis, Reiter's syndrome, and generalized osteoarthosis. Achilles tendinitis and plantar fasciitis caused a severe talalgia and they were observed mainly in males with Reiter's syndrome or ankylosing spondylitis. On the other hand, sub-Achilles bursitis more frequently affected women with rheumatoid arthritis and rarely gave rise to severe talalgias. The simple calcaneal spur was associated with generalized osteoarthrosis and its frequency increased with age. This condition was not related to talalgias. Finally, clinical and radiological involvement of the subtalar and midtarsal joints were observed mainly in rheumatoid arthritis and occasionally caused apes valgoplanus.

Haglund syndrome is a common cause of posterior heel pain, characterized clinically by a painful soft-tissue swelling at the level of the achilles tendon insertion. On the lateral heel radiograph the syndrome is characterized by a prominent calcaneal bursal projection, retrocalcaneal bursitis, thickening of the Achilles tendon, and a convexity of the superficial soft tissues at the level of the Achilles tendon insertion, a "pump-bump." An objective method for evaluating prominence of the bursal projection is measurement using the parallel pitch lines. This measurement helps to identify patients with Haglund syndrome and patients predisposed to develop this condition, and also to differentiate local causes of posterior heel pain from systemic causes. The parallel pitch line measurement was determined in 10 symptomatic feet and 78 control feet and the results were analyzed statistically.

Differentiation of the many disorders that affect the sacroiliac joints can often be accomplished by attention to radiographic detail. By evaluating the distribution of disease, the presence of erosions and other changes as noted herein, and the course of disease over a period of time, a specific diagnosis can often be made, or at the very least, suggested (Table).

Radiographic manifestations of the seronegative spondyloarthropathies superficially resemble the findings of rheumatoid arthritis although they differ in both distribution and pattern of disease. Ankylosing spondylitis has a predilection for the axial skeleton; psoriatic arthritis may involve distal interphalangeal joints; and Reiter's syndrome is most commonly associated with asymmetrical lower extremity alterations. The absence of osteoporosis and the presence of bony proliferation are also noted in these disorders. Sacroiliitis and spondylitis, which can be observed in any of these disease, may have distinctive features. In ankylosing spondylitis, bilateral saroiliac joint alterations and typical syndesmophytes are common; in Reiter's syndrome and psoriasis, asymmetrical saroiliac joint changes and bulky spinal outgrowths may be observed. The physician should be aware of typical roentgen findings in each of the spondyloarthropathies.

Radiographs of symptomatic joints were retrospectively evaluated in 24 patients with inflammatory arthritis and human immunodeficiency virus (HIV) infection. Clinically, 20 patients had a seronegative arthritis including Reiter syndrome (54%), psoriatic arthritis (17%), and undifferentiated forms of spondyloarthropathy (13%). These patients were indistinguishable radiographically from patients with typical seronegative disorders except for the predominance of lower-extremity abnormalities. Four patients (17%) had a rheumatoidlike arthritis defined as acute symmetric polyarthritis (ASP). With the exception of extensive proliferative periostitis, ASP simulated classic rheumatoid arthritis. HIV-associated arthritis was manifest during various stages of HIV infection. It preceded acquired immunodeficiency syndrome in 64% of patients with stage IV HIV infection. Awareness of the coexistence of HIV infection in patients with the above-mentioned arthritides is important, since immunosuppressive therapy, commonly used in the treatment of arthritis, can have detrimental effects in patients with HIV infection.

Manubriosternal joint abnormalities are often undetected causes of chest pain. Twenty-five normal patients and 40 cadaver specimens were evaluated to establish the normal radiographic anatomy of this articulation. Analysis of the manubriosternal joint was carried out in rheumatoid diseases in order to ascertain the incidence and variety of abnormalities. Twenty-seven of 100 manubriosternal joints were abnormal in rheumatoid arthritis. Of 25 patients with ankylosing spondylitis 20 (80%) revealed abnormalities either with erosions or fusion. None of 25 patients with psoriatic arthritis and none of 20 with Reiter syndrome showed erosions or ankylosis. The articulation should be evaluated in rheumatoid diseases and in non-arthritic patients with chest and/or shoulder pain.