Severe and pronounced X-leggedness requires aggressive treatment. Severe deformities not only cause abnormal forces on the knee joint they also cause compensatory deformities in other adjacent joints. Therefore, early detection and treatment is essential. Pathological knee valgus in childhood is caused by a variety of bone diseases and should be treated early. For less severe knee valgus in adults, the decision to treat is based on symptoms. Many patients who do not normally have pain but experience pain in the lateral aspect of the knee after exercise or into the evening suggest the presence of lateral knee hypertension and should be treated. This protects the lateral meniscus, treating post-exercise pain as well as preventing lateral meniscal damage and subsequent lateral osteoarthritis. If the patient has developed a lateral meniscus injury, it is even more important to treat the external knee in order to stop the progression of the lateral lesion and prevent the development of osteoarthritis.