Inverted knee is commonly known as “O-leg”. Not only does it affect the appearance of the knee, but it also disrupts the normal way the knee joint is stressed, causing accelerated wear and tear of the medial joint space and premature development of osteoarthritis. Prompt diagnosis and treatment of entropion can help prevent the development or progression of arthritis. There are various causes of knee entropion in adults, including developmental abnormalities, sequelae of trauma, and certain bone metabolic diseases (e.g., rickets). Most causes are the result of imbalances in medial and lateral growth during growth and development. By adulthood, internal derangement of the knee usually does not progress. However, when secondary osteoarthritis develops, progressive intra-articular wear and tear, as well as loss of balance of the periarticular ligaments, may lead to further progression of the deformity. The development of osteoarthritis in the later stages of internal knee valgus is primarily due to abnormal stresses on the knee joint, resulting in premature wear and tear. Under normal circumstances, the body’s weight passes through the lower extremity with force transmission passing right through the center of the knee joint, with even forces on the inside and outside of the knee joint. When an inversion deformity exists, the force is transmitted too much down the medial side of the knee, resulting in premature osteoarthritis as the cartilage on the medial surface of the knee joint is overloaded and wears out at an accelerated rate. When osteoarthritis develops, the patient will begin to experience pain on the medial side of the knee. This pain often occurs after activity and progresses over time, making it difficult to walk and significantly reducing the patient’s quality of life. Although degenerative changes can occur in the knee without deformity as we age, osteoarthritis of the knee can appear prematurely in patients with internal derangement of the knee. If a patient wants to determine for themselves if they have an inversion of the knee, they can stand with both lower extremities naturally straight, with their feet together, and under normal circumstances the bilateral inner ankles and the medial side of the knee can be tightened at the same time. If the two knees cannot be brought together after the ankles have been brought together, the knee is inversion; the greater the distance that cannot be brought together, the greater the degree of knee inversion. Of course, inversion of the knee is not considered a disease until it reaches a certain level. Patients or family members do not need to be nervous about this, but can seek medical help at the Orthopedic Orthopaedic Lower Extremity Deformity Clinic. In order to assess the extent of the inversion and the presence of osteoarthritis, as well as to determine how to treat it later, the doctor will conduct a detailed interview and physical examination, as well as full-length x-rays of both lower extremities to assist in the evaluation. Treatment options for internal derangement include regular outpatient observation, medication and bracing, orthopedic osteotomy, partial compartment knee replacement, and total knee arthroplasty. The choice of the various modalities is based on the following points: 1) the patient’s age; 2) the patient’s lifestyle and activity needs; and 3) the presence and degree of osteoarthritis. In mild cases of internal knee roll, if no osteoarthritis is present, regular outpatient observation is usually chosen. If the knee inversion is not severe, but osteoarthritis is present, medication and brace therapy is often chosen first. If the internal knee roll is severe, whether or not osteoarthritis has started, orthopedic osteotomy is often chosen. If the osteoarthritis is very severe, partial compartment replacement of the knee with a straightened total knee arthroplasty, and sometimes even a simultaneous osteotomy, is required. In conclusion, the exact diagnosis and treatment options for internal knee valgus is an extremely specialized area and requires consultation with a team of specialized physicians. Early diagnosis and intervention can effectively prevent the premature appearance of arthritis as well as significantly delay having to undergo joint replacement surgery.