Knee Osteochondritis Dissecans (OCD): Understanding Causes, Symptoms, Diagnosis, and Treatment

What is Knee OCD?

Knee Osteochondritis Dissecans (OCD) is a condition where a segment of cartilage and underlying bone detaches or partially detaches from the joint surface, most commonly affecting the femoral condyles within the knee joint.

Understanding Osteochondritis Dissecans (OCD)

Osteochondritis Dissecans (OCD) is a joint disorder in which cracks form in the articular cartilage and the subchondral bone (the bone just beneath the cartilage). While OCD can occur in various joints, the knee is one of the most common sites, particularly affecting the femoral condyles – the rounded ends of the thigh bone (femur) that form the upper part of the knee joint.

In OCD, the affected segment, often referred to as a lesion, loses its blood supply, causing the bone and cartilage to soften and potentially die (avascular necrosis). This necrotic tissue can then separate from the surrounding healthy bone, forming a loose body within the joint. Depending on the severity, the lesion may remain in place, partially detach, or fully detach and float freely within the joint space, leading to pain, instability, and mechanical symptoms.

Causes and Risk Factors

The exact cause of OCD is not always clear, but it is generally believed to be multifactorial, involving a combination of factors:

• Repetitive Microtrauma: The most widely accepted theory suggests that repetitive stress and microtrauma to the joint, often from athletic activities involving jumping, cutting, and pivoting, can disrupt blood flow to the subchondral bone.
• Ischemia: A disruption of blood supply (ischemia) to the affected area of bone is a critical component, leading to the death of bone cells.
• Genetic Predisposition: There may be an inherited component, as OCD can sometimes run in families.
• Rapid Growth: Adolescents, especially those undergoing rapid growth spurts, are particularly susceptible. During growth, the cartilage and bone may be more vulnerable to injury or disruption of blood flow.
• Anatomical Factors: Some individuals may have anatomical variations that predispose them to increased stress on certain parts of the joint.
• Age and Activity Level: OCD predominantly affects children and adolescents, typically between the ages of 10 and 20, who are physically active. It is more common in males than females.

Signs and Symptoms

The symptoms of knee OCD can vary depending on the size and stability of the lesion. Common signs include:

• Pain: Often the primary symptom, located deep within the knee and typically worsened by activity, especially weight-bearing or impact activities. The pain may be diffuse or localized to the specific area of the lesion.
• Swelling: Intermittent or persistent swelling around the knee joint, especially after activity.
• Clicking, Popping, or Grinding: Sounds or sensations within the knee, particularly during movement.
• Catching or Locking: If a piece of cartilage or bone has fully detached and is floating freely (a "loose body"), it can get caught between the joint surfaces, causing the knee to momentarily lock or give way.
• Weakness or Instability: A feeling of the knee giving out or feeling unstable.
• Reduced Range of Motion: Difficulty fully straightening or bending the knee.

Diagnosis

Diagnosing knee OCD typically involves a thorough clinical evaluation and imaging studies:

• Physical Examination: The physician will assess pain, swelling, range of motion, and stability of the knee. Specific tests may be performed to reproduce symptoms or identify the location of the lesion.
• X-rays: Initial X-rays can often show the bone defect, especially if the lesion is calcified or detached. Multiple views are usually taken.
• Magnetic Resonance Imaging (MRI): MRI is the most definitive non-invasive imaging technique for OCD. It provides detailed images of both cartilage and bone, allowing for assessment of the size, stability, and extent of the lesion, as well as any associated bone marrow edema.
• Computed Tomography (CT) Scan: A CT scan may be used to provide more detailed images of the bone structure, particularly useful for surgical planning.
• Arthroscopy: In some cases, a diagnostic arthroscopy (a minimally invasive surgical procedure where a small camera is inserted into the joint) may be performed to directly visualize the lesion, assess its stability, and potentially perform treatment.

Treatment Approaches

Treatment for knee OCD depends on several factors, including the patient's age, the size and stability of the lesion, and the presence of loose bodies.

Non-Surgical Management

Non-surgical approaches are often the first line of treatment, especially for younger patients with open growth plates and stable lesions:

• Rest and Activity Modification: Limiting or avoiding activities that aggravate the knee, particularly high-impact or twisting movements.
• Immobilization: In some cases, a brace or cast may be used to restrict knee movement and allow the lesion to heal.
• Physical Therapy: A structured rehabilitation program focusing on:
  • Restoring full range of motion.
  • Strengthening the muscles around the knee (quadriceps, hamstrings, glutes).
  • Improving proprioception and balance.
  • Gradual return to activity.
• Pain Management: Over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs) may be used to manage pain and inflammation.

Surgical Interventions

Surgery is considered when non-surgical treatments fail, for unstable lesions, or for larger lesions in older patients. Surgical goals include restoring blood flow, securing the fragment, or replacing damaged cartilage. Common surgical procedures include:

• Drilling: Small holes are drilled into the subchondral bone to stimulate blood flow and promote healing of the overlying cartilage.
• Internal Fixation: If the fragment is still attached but unstable, it can be reattached to the underlying bone using pins, screws, or other fixation devices.
• Microfracture: For lesions where the cartilage has been lost, small holes are made in the subchondral bone to stimulate the formation of fibrocartilage (a type of scar tissue) to fill the defect.
• Osteochondral Autograft Transplantation (OATS) / Mosaicplasty: Healthy cartilage and bone plugs are harvested from a less weight-bearing area of the patient's own knee and transplanted into the OCD defect.
• Osteochondral Allograft Transplantation: Similar to OATS, but the cartilage and bone plugs are taken from a deceased donor.
• Autologous Chondrocyte Implantation (ACI): A two-stage procedure where healthy cartilage cells are harvested from the patient, grown in a lab, and then reimplanted into the defect.

Rehabilitation and Prognosis

Regardless of the treatment method, a structured rehabilitation program is crucial for optimal recovery. This typically involves:

• Initial Phase: Protecting the knee, managing pain and swelling, and maintaining passive range of motion.
• Intermediate Phase: Gradual increase in active range of motion, light strengthening exercises, and proprioceptive training.
• Advanced Phase: Progressive strengthening, sport-specific drills, and a carefully monitored return to full activity.

The prognosis for knee OCD varies. Younger patients with smaller, stable lesions that are treated non-surgically often have a good outcome. However, larger, unstable lesions or those requiring surgery may have a longer recovery period and a higher risk of developing osteoarthritis in the affected joint later in life.

Prevention

While not always entirely preventable, several strategies can help reduce the risk of developing knee OCD:

• Proper Training Techniques: Emphasize correct biomechanics and movement patterns in sports and exercise.
• Gradual Progression: Avoid sudden increases in training volume or intensity, allowing the body to adapt.
• Adequate Rest and Recovery: Ensure sufficient time for tissues to repair and rebuild between training sessions.
• Balanced Nutrition: Support bone and cartilage health through a diet rich in essential nutrients.
• Early Recognition of Symptoms: Seek medical attention promptly if knee pain or other symptoms develop, especially in active adolescents. Early diagnosis and intervention can significantly improve outcomes.