Causes / typical injury mechanism:

• Osteochondritis dissecans (OCD) is defined as an area of osteonecrosis in subchondral bone that supports overlying cartilage.
• If the patient's growth plates are still open, the lesion is considered juvenile OCD (JOCD) and has a better prognosis for healing than adult OCD, where the growth plates are closed.
• Separation of cartilage from the underlying necrotic subchondral bone may result in a stable or unstable fragment of bone with attached overlying cartilage in the knee.
• OCD is caused by many factors including genetics, ischemia, altered local growth, inflammation, ossification, and repetitive microtrauma of the joint. It may also be idiopathic.

Classic history and presentation: This most commonly presents as a chronic knee pain in children and adolescents active in sports. Adult OCD usually arises from JOCD.

Prevalence:

• Prevalence is 15-29 cases of OCD per 100 000 people.
• Most frequently seen in patients aged 10-19 years.
• Males are at 4 times increased risk compared to females.
• 69% of cases involve the lateral aspect of medial femoral condyle.
• 15% of cases involve the weight-bearing portion of the lateral femoral condyle.

Risk factors:

• Male
• Active in sports
• Black race or Hispanic or Asian descent
• Obese

Pathophysiology: The disease process is thought to begin by a disturbance in blood supply to the knee, resulting in a piece of subchondral bone loosening from its surrounding tissue because of the osteonecrosis. Over time, this extends and the bone with overlying cartilage loosens. This can result in a completely separated osteochondral (bone and associated overlying cartilage) fragment into the knee joint space. Additionally, repetitive microtrauma interferes with healing of the bony trabeculae and can result in disruption.

Intraoperative Clanton and DeLee grading system:

• Grade 1 – normal articular cartilage
• Grade 2 – fragmentation in situ
• Grade 3 – partial detachment
• Grade 4 – complete detachment, loose body present