How is leg length assessed in a child? Why is the affected leg often longer in a child with oligoarticular JIA?
Leg length is measured from the anterior superior iliac spine to the medial malleolus. In a child with a joint contracture, the functional leg length may be shorter than the actual leg length, and therefore both must be measured.
Leg length discrepancy (LLD) reflects a chronic disease process. The affected leg is often longer in a child with chronic arthritis (in particular, that affecting the knee) as a result of increased blood flow to the joint in response to localized inflammation and cytokine release. This increased blood flow may also lead to development of a “macroepiphysis.” LLD may result in an abnormal gait, and correction with a lift on the bottom of the shoe of the shorter leg is recommended when the LLD is >2cm. The shorter, unaffected leg will usually “catch up” to the affected leg and may overgrow the affected leg since the epiphysis of the inflamed joint will undergo accelerated fusion. In addition, muscle bulk of the thigh or the calf may be reduced in the affected leg and will rarely “catch up” to that of the unaffected leg, particularly if the arthritis has an onset at <6 years of age.