The fewer joint affected type of arthritis (oligoarticular) is characterised by having four or fewer joints affected, with the larger joints more typically affected such as the knees and ankles. These children usually appear well even though they may limp on walking. If only one hip seems affected this is very unusual for this type of arthritis and a different condition such as Perthes disease should be suspected. If the joints, such as the knees, are affected over a long period then the large extensor muscles of the thighs can weaken and waste, with tight hamstrings leading the flexion contractures of the knees. If the legs are affected asymmetrically then the length of the legs can develop a discrepancy.