Osteochondritis Dissecan’s of the Knee

 

Osteochondritis Dissecans (OCD) is a condition that affects the articular cartilage and the subchondral bone of the knee. The lesion usually occurs in the knee on the lateral and posterior aspect of the medial femoral condyle (70% of lesions are in the postero-lateral aspect of the knee). OCD lesions are distributed around the knee, 85% medial femoral condyle, 13% lateral femoral condyle, 1% patella, 1% trochlea. The chances of the lesion occurring at the lateral femoral condyle and patellar aspect of the knee is rare. Lateral condyle and patellar lesions will have a bad prognosis. The mechanisms and causes of injury for OCD lesions may be multifactorial. It is usually caused by repetitive overloading causing fragmentation and separation of bony fragments. It can occur in juveniles with an open epiphysis usually during the ages 10-15 years old. Prognosis is usually very good when the patient has an open epiphysis. It can also occur in adults with a less favorable prognosis. Osteochondritis Dissecans of the knee is classified in four stages. Stage I is depressed OCD with intact cartilage and a small area of compressed subchondral bone. Stage II is a partially detached fragment. Stage III is the most common type and has a completely detached but non-displaced fragment. Stage IV is completely detached and displaced. The displaced fragment can be a loose body. Symptoms include activity related pain, poorly localized tenderness, effusion, and swelling and stiffness with or without mechanical symptoms. Mechanical symptoms indicate an advanced problem. The Wilson’s Test is a test used to detect the presence of Osteochondritis Dissecans of the knee. To perform the Wilson’s test, ask the patient to sit on a table with his legs dangling over the edge. The patient’s knee should be flexed at a 90-degree angle. Grasp the patient’s leg and internally rotate the tibia. Instruct the patient to extend the leg until pain is felt. The test is positive when the patient reports pain in the knee about 30-degrees from full extension. When rotating the leg back to its normal position, the pain disappears. Internal rotation causes impingement of the tibial eminence on the OCD lesion of the medial femoral condyle which causes the pain. external rotation moves the eminence away from the lesion, which relieves the pain. For x-ray images, do weight-bearing AP and lateral view radiographs and use the Tunnel View (intercondylar notch view). On MRI, check the size of the lesion, signal intensity surrounding the lesion, and the presence of any loose bodies. Prognosis correlates with age; the younger the age, the better the prognosis. Adults have a worse prognosis. Lesions in the lateral femoral condyle and patella have a worse prognosis. Synovial fluid appearing behind the lesion on MRI correlates with a worse prognosis. Fluid signal on MRI behind the lesion indicates that the fragment is unstable and is less likely to heal. Nonoperative treatment is observation, limitation of activity, crutches, trial of non-weight bearing for six weeks, and close follow-up. Stable lesions in children with open physis are an indication of nonoperative treatment. The majority will heal as long as the physis is open (good prognosis). Operative treatment is indicated if the fragment is detached, unstable or loose in patients where the physis has already closed, is near closing, or if there is failure of the non-operative treatment. Surgical treatment usually includes arthroscopy and removal of the loose fragment, fixation of the unstable lesion, or microfracture (drilling of the lesion). Arthroscopic drilling of the subchondral bone is done in children who approach skeletal maturity. Drilling of the lesion has a high success rate especially if the lesion is stable.