Osteochondritis dissecans is a condition in which a piece of cartilage, along with a thin layer of the bone separates from the end of the bone because of inadequate blood supply. The separated fragments are sometimes called “joint mice”. These fragments may be localized, or may detach and ‘dislodge’ into the joint space causing pain, locking and joint instability.
The knee, mostly the femoral condyles are most commonly affected. The two femoral condyles make up the rounded end of femur (thigh bone). Each knee has two femoral condyles, the medial femoral condyle on the inside of the knee and the lateral femoral condyle on the outside of the knee. Osteochondritis dissecans occurs characteristically within the lateral aspect of the medial femoral condyle. The condition can also occur in other joints, including your elbows, ankles, shoulders and hips.
Osteochondritis dissecans is more common among boys and young men between 10 and 20 years who take part in sports. Athletes participating in a variety of sports may develop osteochondritis dissecans.
The exact cause for osteochondritis dissecans remains unknown and certain factors such as trauma, fractures, sprains, or injury to the joint are considered to increase the risk of developing the condition. Osteochondritis dissecans may be caused by restricted blood flow to the bone-cartilage junction of the affected bone that usually occurs in conjunction with repetitive trauma. Following the injury or trauma, the bones in the area may be deprived of blood flow leading to necrosis (tissue death) and finally the bone fragment may become loose and break off. This may initiate the healing process. However, by this time, articular cartilage will be compressed, flattened, and a subchondral cyst (under the cartilage) may have developed. These changes, in addition to increased joint pressures, can cause failure of healing of the damaged area of joint surface.
The appearance of osteochondritis dissecans in several family members may indicate that the condition is inherited.
Patients with osteochondritis dissecans usually have joint pain, swelling, stiffness, decreased range of motion, and will often describe mechanical features such as ‘popping’ or ‘locking’. Pain and swelling usually increases after activity.
Your surgeon will order an X-ray of the knee to see the abnormality in the joint space and to assess any displacement. You may also have a CT or MRI scan that is useful in determining the location and stability of the lesion.
Your surgeons may recommend various treatments depending on the diagnostic scans, age, severity, stability of the cartilage and other factors. Goals of treatment are to relieve the symptoms and stop or impede the progression of degeneration of the joint. Conservative treatment approaches such as a ‘watch and wait’ approach, pain medications, and immobilization for 1-2 weeks are recommended if the condition is diagnosed at early stages and if the severity is mild. However surgery is required if the condition is diagnosed at advanced stage or if the condition is severe.
Surgical correction of osteochondritis dissecans can be achieved using open or arthroscopic techniques. Some of the surgical procedures include drilling, bone grafting, open reduction internal fixation, osteochondral grafting, or autologous chondrocyte implantation (ACI).
- Retrograde Drilling – In this method multiple small holes are drilled into the bone which allows the growth of new blood vessels in the defect area. This promotes blood flow into the defect thereby initiating the healing response and formation of new cartilage cells inside the lesion
- Open reduction internal fixation – Open surgery is performed in cases where the affected area is difficult to reach with an arthroscope. In this procedure an incision is made in front of the joint to allow your surgeon to see the joint and any loose fragments are removed. Internal fixation involves fixing the ostechondral fragment using internal fixators such as metal screws, pins, or wires
- Bone grafting – It helps to fill the gap after removal of the dead or necrotic bone. In this procedure, bone graft is placed on the damaged site. This procedure may be performed to repair the damaged area or replace the missing bone. Autograft (harvested from the same individual) or allograft (taken from a bone bank) may be required to help in the growth of new bone
- Osteochondral grafting – The procedure involves transfer of healthy cartilage plugs from the non-weight bearing areas of the joint and transferring them into the damaged areas of the joint in a ‘mosaic’ pattern. It allows the newly implanted bone and cartilage to grow into the damaged area. Grafts may be taken from the same individual (autograft) or from a donor or bone bank (allograft)
- Autologous chondrocyte implantation (ACI) – In this procedure, healthy cartilage cells are harvested from the non-weight bearing parts of the joint of the patient and cultured in a laboratory. Cultured cartilage tissue can then be implanted into the defected area which promotes the growth of a new cartilage covering.