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

Osteochondritis Dissecans (OCD) of the Knee: A Rare Condition Explained

Osteochondritis Dissecans (OCD) of the knee is a relatively rare condition characterized by the separation of a segment of bone and its overlying cartilage from the surrounding bone, primarily affecting adolescents and young adults.

What is Osteochondritis Dissecans (OCD)?

Osteochondritis Dissecans (OCD) is a joint disorder in which cracks form in the articular cartilage and the underlying subchondral bone. This condition arises when a small segment of bone, along with the cartilage covering it, loses its blood supply, leading to the death of the bone tissue (avascular necrosis). Over time, this dead segment, known as the "osteochondral fragment," may separate from the surrounding healthy bone, potentially causing pain, swelling, and mechanical symptoms within the joint.

While OCD can affect various joints, including the ankle and elbow, the knee is the most commonly involved site, particularly the medial femoral condyle (the inner part of the lower thigh bone). Its rarity, affecting an estimated 15-30 per 100,000 individuals, especially in the younger, physically active population, makes it a notable, albeit uncommon, cause of knee pain.

Anatomy and Biomechanics of the Affected Knee Joint

To understand OCD, it's crucial to grasp the basic anatomy of the knee. The knee joint is formed by the articulation of three bones: the femur (thigh bone), tibia (shin bone), and patella (kneecap). The ends of the femur and tibia, as well as the back of the patella, are covered with articular cartilage – a smooth, slippery tissue that allows the bones to glide effortlessly against each other during movement. Beneath this cartilage lies the subchondral bone, which provides support and receives blood supply.

In OCD, the disruption of blood flow primarily affects the subchondral bone. This leads to bone necrosis, weakening the foundation beneath the cartilage. The weakened bone, unable to withstand normal stresses, can then fracture, causing the overlying cartilage to crack and eventually separate. The medial femoral condyle is particularly susceptible due to its weight-bearing role and specific vascular supply.

Causes and Risk Factors

The exact cause of OCD is often multifactorial and not fully understood, but several theories and risk factors are commonly cited:

• Repetitive Microtrauma: This is the most widely accepted theory. Repeated stress and minor injuries to the joint, often from athletic activities involving jumping, cutting, and twisting, can disrupt the blood supply to the subchondral bone, leading to its demise.
• Ischemia (Lack of Blood Supply): Any event that compromises the blood flow to a specific area of the subchondral bone can initiate OCD. This could be due to small vessel damage or blockages.
• Rapid Growth: In adolescents, periods of rapid bone growth may outpace the development of adequate blood supply, making certain areas vulnerable.
• Genetic Predisposition: While not directly inherited, some familial patterns suggest a genetic component may increase susceptibility.
• Anatomical Factors: Variations in knee alignment or patellar tracking might place abnormal stress on certain areas of the joint.
• Endocrine Factors: Hormonal imbalances have been explored as potential contributing factors, though their role is less clear.

OCD predominantly affects active boys and young men between the ages of 10 and 20, though it can occur in girls and adults as well.

Recognizing the Symptoms

The symptoms of OCD can vary depending on the stage of the condition, from subtle discomfort to severe mechanical issues. Common signs include:

• Pain: This is the most frequent symptom. It's often a vague, deep ache in the knee, typically worsened by physical activity, especially impact sports. The pain may improve with rest.
• Swelling: Intermittent swelling of the knee joint, particularly after exercise or activity.
• Catching or Locking: If the osteochondral fragment becomes unstable or detaches and moves freely within the joint (a "loose body"), it can cause the knee to catch, click, or lock, preventing full extension or flexion.
• Giving Way: A sensation of instability or the knee buckling, often due to pain or mechanical interference.
• Decreased Range of Motion: Stiffness in the knee, making it difficult to fully straighten or bend the leg.
• Tenderness: Localized tenderness when pressing on the affected area of the joint, such as the medial femoral condyle.

Symptoms may be present for months before a diagnosis is made, as they can initially be mild and mistaken for general overuse injuries.

Diagnosis: A Multi-Modal Approach

Diagnosing OCD requires a thorough clinical evaluation combined with advanced imaging techniques.

• Clinical Examination: The physician will take a detailed medical history, inquiring about the onset of symptoms, activity levels, and any previous knee injuries. A physical examination will assess range of motion, joint stability, and specific tests like Wilson's Sign (pain with internal rotation of the tibia during knee extension), which can be indicative of OCD of the medial femoral condyle.
• Imaging Studies:
  • X-rays: Initial X-rays (AP, lateral, tunnel views) can reveal characteristic changes such as flattening, lucency (darker areas indicating bone loss), or the presence of a detached fragment. However, early-stage OCD may not be visible on X-rays.
  • Magnetic Resonance Imaging (MRI): MRI is considered the gold standard for diagnosing OCD. It provides detailed images of both bone and cartilage, allowing for precise staging of the lesion (e.g., stable vs. unstable), assessment of the integrity of the overlying cartilage, and detection of bone edema (swelling) or fluid accumulation beneath the fragment.
  • Computed Tomography (CT) Scan: While not typically used for initial diagnosis, a CT scan may be employed for surgical planning, as it offers superior bony detail and can accurately measure the size and location of the lesion.

Treatment Options

Treatment for OCD depends on several factors, including the patient's age (especially whether growth plates are open), the size and stability of the lesion, and the severity of symptoms.

• Conservative Management (Non-Surgical): This approach is often the first line of treatment, particularly for younger patients with open growth plates and stable, intact lesions.
  • Activity Modification: Limiting or avoiding high-impact activities, jumping, and running is crucial to reduce stress on the affected area and allow for healing.
  • Immobilization: In some cases, a brace or cast may be used to immobilize the knee for a period, promoting rest and healing.
  • Physical Therapy: Once initial pain subsides, a structured physical therapy program focuses on restoring range of motion, strengthening the muscles around the knee (quadriceps, hamstrings), and improving proprioception (balance and joint awareness).
  • Pain Management: Over-the-counter anti-inflammatory medications (NSAIDs) may be used to manage pain and swelling.
• Surgical Intervention: Surgery is typically recommended for:
  • Patients who fail to improve with conservative management.
  • Older adolescents or adults with closed growth plates.
  • Unstable lesions (where the fragment is partially or completely detached).
  • Large lesions or those causing mechanical symptoms (locking, catching).
  • Surgical techniques vary widely:
    • Drilling/Microfracture: Small holes are drilled into the subchondral bone to stimulate bleeding and promote the growth of fibrocartilage (a type of repair cartilage).
    • Internal Fixation: If the fragment is still viable and not completely detached, it can be reattached to the underlying bone using screws, pins, or other fixation devices.
    • Bone Grafting: For lesions with significant bone loss, bone grafts (from the patient or a donor) may be used to fill the defect.
    • Osteochondral Autograft/Allograft Transplantation (OATS/Allograft): Healthy bone and cartilage plugs are taken from a less weight-bearing area of the patient's own knee (autograft) or from a donor (allograft) and transplanted into the OCD lesion.

Rehabilitation and Recovery

Regardless of whether the treatment is conservative or surgical, a structured rehabilitation program is critical for optimal recovery and return to activity. This typically involves a phased approach:

• Protection Phase: Focus on pain control, reducing swelling, and protecting the healing tissue. This often includes limited weight-bearing (crutches) and gentle range of motion exercises.
• Mobility Phase: Gradually restoring full, pain-free range of motion through stretching and passive/active exercises.
• Strengthening Phase: Progressive strengthening of the quadriceps, hamstrings, glutes, and calf muscles to improve knee stability and support.
• Functional and Sport-Specific Phase: Incorporating balance training, agility drills, plyometrics, and sport-specific movements to prepare for a safe return to desired activities.

Adherence to the rehabilitation protocol is paramount, as premature return to high-impact activities can jeopardize healing and lead to recurrence or further damage.

Prognosis and Long-Term Outlook

The prognosis for OCD of the knee varies significantly. Factors influencing the outcome include:

• Age of the Patient: Younger patients with open growth plates generally have a better prognosis, as their bones have greater healing potential.
• Lesion Stability: Stable lesions that remain attached typically heal better than unstable or detached fragments.
• Size and Location of the Lesion: Smaller lesions in less weight-bearing areas tend to have better outcomes.
• Adherence to Treatment: Compliance with activity restrictions and rehabilitation protocols significantly impacts success.

While many individuals recover fully, especially with early diagnosis and appropriate management, there is an increased risk of developing osteoarthritis in the affected knee later in life, particularly with larger, unstable, or recurrent lesions. Regular follow-up with a healthcare professional is often recommended to monitor long-term joint health.

When to Consult a Professional

If you or someone you know experiences persistent knee pain, swelling, clicking, or a sensation of the knee catching or locking, especially if it's activity-related and does not resolve with rest, it's crucial to consult a healthcare professional. Early diagnosis of Osteochondritis Dissecans can significantly improve the chances of successful non-surgical treatment and lead to better long-term outcomes, preserving knee joint health and function.