Rydholm, Urban M.D., Ph.D.
From the Arthritis Unit, Department of Orthopaedics, University Hospital, Lund, Sweden.
Summary: Control of hip disease is very important for maintaining mobility and independence in patients with juvenile idiopathic arthritis (JIA). Hip deformity and pain must be treated early by drugs and physiotherapy and, if necessary, by arthroscopic joint lavage and corticosteroids. Core decompression is a minor procedure that can provide considerable relief from aching pain. Soft tissue releases as well as intertrochanteric osteotomy can affect the loading situation of the whole lower extremity, and also give the possibility of regeneration of cartilage in children with clinical deformities and radiographic growth disturbances of the hip. Minor surgical procedures should always be considered if they can delay the requirement for total joint replacement. Hip involvement in children with juvenile idiopathic arthritis (JIA) is seldom present at onset, but is commonly preceded by other manifestations of the disease, including arthritis of other lower limb joints, most commonly the knee. The rate of affection of the hip is highest in children with systemic or polyarticular disease. Hip involvement is usually bilateral but asymmetric, 1 hip often being more severely affected than the other. Approximately 80% of patients with the systemic form of JIA have hip involvement within 10 years of disease. 9 The long-term functional outcome in patients with JIA is in more than one third, associated with active disease persisting into adulthood, increasing residual disability and the need for surgery, 14 commonly of the hip. Hip involvement is a major cause of disability and is accompanied by significant loss of quality of life. It is the most important reason for losing independence and mobility in children with JIA. Many children have only mild disability and slight radiographic changes or episodic disability that correlates with the activity of the disease. Some patients, however, show progressive disability and radiographic changes. The common hip contracture is one of flexion, adduction, and inward rotation, but abduction contracture can also be seen, probably as a result of a tight iliotibial band. Depending on the age of onset of disease at the hip, both abnormal muscle forces and growth disturbance are involved in the failure of normal development of the hip. Early radiographic findings are osteopenia and growth disturbance of the proximal femur and the acetabulum, which in young children can result in coxa magna with a short, wide femoral neck and varus deformity. Growth disturbance can also give rise to elongation and increased valgus and anteversion of the femoral neck (Figs. 1 and 2). Radiographic changes vary considerably. Later on, narrowing and irregularities of the joint space, as well as bony erosions, subchondral cysts, and acetabular cranial protrusion, become evident (Fig. 2). Protrusion can be rapidly progressive and regular radiographic check-ups are strongly recommended in those children. Lateral subluxation of the femoral head (Fig. 3) probably caused by intense synovitis, soft tissue contractures, or thickening of the cartilage by hypermetabolism is not unusual and can sometimes result in flattening of the femoral head. In older children, premature closure of the femoral and acetabular growth plates can result in retarded growth with a hypoplastic femoral neck and a dysplastic acetabulum. A small femoral head in a normal or enlarged acetabulum results in a mismatch in size between the femoral head and acetabulum (Fig. 4). The femoral head grows in circumference by endochondral ossification of the articular cartilage. If the rheumatoid process destroys that articular cartilage, growth of the femoral head ceases. The intact triradiate cartilage, however, permits continuing acetabular growth. 2