Ankylosed Knee: Understanding, Types, Causes, Symptoms, Diagnosis, and Treatment

What is ankylosed knee?

Ankylosed knee refers to a pathological condition where the knee joint loses its normal range of motion and becomes stiff or fused, often due to abnormal bone growth, fibrous tissue formation, or severe inflammation, leading to significant functional impairment.

Understanding Joint Ankylosis

Ankylosis is a medical term describing the stiffness and immobility of a joint due to fusion of the bones. While it can occur in any joint, when it affects the knee, it profoundly impacts mobility and quality of life. A healthy knee is a synovial joint, meaning it's highly mobile, allowing for flexion, extension, and slight rotation, facilitated by articular cartilage, synovial fluid, and a complex network of ligaments and muscles. In an ankylosed knee, this intricate system is compromised, leading to a restricted or completely absent range of motion.

Types of Ankylosis Affecting the Knee

Ankylosis can manifest in different forms, each with varying degrees of severity and underlying causes:

• Fibrous Ankylosis: This type involves the formation of fibrous tissue within the joint capsule, leading to significant stiffness and limited movement, but not complete bony fusion. There may still be some residual, albeit painful and restricted, motion. It often results from chronic inflammation, infection, or prolonged immobilization.
• Bony Ankylosis (Synostosis): Considered the most severe form, bony ankylosis occurs when the bones of the joint (femur and tibia, and sometimes patella) completely fuse together, forming a single, solid bone structure. This results in the complete absence of movement at the joint, effectively eliminating the joint space. This can be a natural progression of severe inflammatory diseases, a complication of trauma, or an intentional surgical outcome (arthrodesis).

Causes of Ankylosed Knee

The development of an ankylosed knee is typically a consequence of severe and chronic pathological processes within the joint. Common causes include:

• Inflammatory Arthritis: Conditions like rheumatoid arthritis, psoriatic arthritis, and, less commonly affecting the knee, ankylosing spondylitis, can cause chronic inflammation that damages articular cartilage and bone, eventually leading to fibrous or bony fusion.
• Severe Osteoarthritis (OA): While OA primarily involves cartilage degeneration, in its most advanced stages, particularly after severe trauma or long-standing joint damage, the joint can become completely destroyed, leading to bone-on-bone contact and eventual fusion.
• Trauma and Injury: Severe fractures involving the joint surface, extensive ligamentous injuries, or deep burns around the knee can lead to significant scarring, heterotopic ossification (abnormal bone formation in soft tissues), or joint incongruity, predisposing to ankylosis.
• Infection (Septic Arthritis): A severe bacterial or fungal infection within the joint can rapidly destroy cartilage and bone, leading to inflammation and subsequent fusion if not promptly and effectively treated.
• Surgical Complications: While rare, complications from knee surgeries, such as excessive scar tissue formation or infection, can contribute to joint stiffness and, in severe cases, ankylosis. Intentional surgical fusion (arthrodesis) is also a treatment option for intractable pain and instability.
• Prolonged Immobilization: While immobilization alone rarely causes true bony ankylosis, prolonged periods of non-weight-bearing or casting, especially after injury or surgery, can lead to severe joint stiffness and fibrous contractures that mimic ankylosis.

Signs and Symptoms

The primary hallmark of an ankylosed knee is the progressive loss of its range of motion. Other common signs and symptoms include:

• Severe and Persistent Stiffness: Especially noticeable after periods of rest or in the morning.
• Pain: Chronic pain is common, though it may decrease once complete bony fusion occurs, as the pain-generating joint surfaces are no longer moving.
• Fixed Deformity: The knee may become stuck in a bent (flexion) or straightened (extension) position, making walking or sitting extremely difficult.
• Functional Limitations: Significant difficulty with daily activities such as walking, climbing stairs, standing up from a chair, or putting on shoes.
• Muscle Atrophy: Muscles surrounding the knee (quadriceps, hamstrings) may waste away due to disuse.
• Crepitus: Though less common in true ankylosis, some grinding or popping may be present in fibrous ankylosis.

Diagnosis

Diagnosing an ankylosed knee involves a comprehensive assessment by a healthcare professional, typically an orthopedic surgeon or rheumatologist:

• Clinical Examination: The doctor will physically assess the knee's range of motion, evaluate for swelling, tenderness, and any visible deformities. They will also observe the patient's gait and functional abilities.
• Medical History: A detailed history of past injuries, surgeries, inflammatory conditions, or infections is crucial.
• Imaging Studies:
  • X-rays: The most common initial imaging, X-rays can clearly show joint space narrowing, bone spurs (osteophytes), and complete bony fusion.
  • Magnetic Resonance Imaging (MRI): Provides detailed images of soft tissues, cartilage, ligaments, and can identify inflammation or fibrous tissue contributing to stiffness.
  • Computed Tomography (CT) Scan: Offers excellent bony detail and can precisely delineate the extent of bone fusion.
• Blood Tests: If an inflammatory or autoimmune condition is suspected, blood tests such as erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor, or anti-CCP antibodies may be ordered.

Treatment Approaches

Treatment for an ankylosed knee depends heavily on the type of ankylosis, its underlying cause, the patient's overall health, and their functional goals.

• Non-Surgical Management (primarily for fibrous ankylosis or early stages):
  • Physical Therapy: Intensive physical therapy is paramount. It focuses on maintaining any residual range of motion, stretching tight tissues, strengthening surrounding muscles, and improving functional independence.
  • Medications: Non-steroidal anti-inflammatory drugs (NSAIDs) or corticosteroids may be used to manage pain and inflammation. Disease-modifying anti-rheumatic drugs (DMARDs) or biologic agents are prescribed for underlying autoimmune conditions.
  • Assistive Devices: Crutches, walkers, or braces may be used to aid mobility and support the joint.
• Surgical Interventions (for severe cases, especially bony ankylosis):
  • Arthroplasty (Joint Replacement): For severe bony ankylosis, particularly in older, less active individuals, a total knee replacement (TKR) can be performed to remove the fused bones and replace them with prosthetic components, restoring significant motion and alleviating pain. This is a complex procedure in an ankylosed joint.
  • Arthrodesis (Joint Fusion): In cases where joint replacement is not feasible (e.g., severe infection, very young patients, or high-demand individuals who need a stable, pain-free limb), intentional surgical fusion of the knee joint may be performed. While it eliminates all motion, it provides a stable, pain-free limb, albeit with a permanent stiff-legged gait.
  • Arthrolysis: This procedure involves surgically releasing adhesions, scar tissue, or bone spurs that are restricting joint movement. It is typically used for fibrous ankylosis or post-operative stiffness.
  • Osteotomy: In some cases, bone cutting may be performed to correct a fixed deformity and improve alignment, though it doesn't restore joint motion.

Prognosis and Living with Ankylosis

The prognosis for an ankylosed knee varies widely depending on the cause, severity, and success of treatment. Without intervention, an ankylosed knee leads to significant long-term disability, impacting ambulation, balance, and the ability to perform activities of daily living. Surgical interventions like total knee replacement can dramatically improve function and reduce pain, but require dedicated rehabilitation. Patients with an ankylosed knee often need to adapt their lifestyle, modify their home environment, and utilize assistive devices to maintain independence.

The Role of Physical Activity and Rehabilitation

Regardless of the treatment path, physical activity and rehabilitation are critical. For those not undergoing surgery, a consistent exercise program helps to maximize any remaining joint mobility, strengthen supporting muscles, and prevent further stiffness. For surgical patients, pre-operative conditioning and post-operative physical therapy are essential for optimal recovery, regaining strength, and adapting to the new joint mechanics. This includes range-of-motion exercises, strengthening exercises, balance training, and gait re-education.

Prevention Strategies

While not all cases of ankylosis are preventable, certain strategies can reduce the risk or mitigate its severity:

• Early and Aggressive Treatment of Inflammatory Arthritis: Prompt diagnosis and effective management of conditions like rheumatoid arthritis can prevent severe joint damage and subsequent fusion.
• Appropriate Management of Joint Injuries: Thorough evaluation and proper treatment of knee fractures, ligament tears, and other traumas can minimize complications that lead to stiffness.
• Early Mobilization Post-Surgery: When medically appropriate, early and controlled movement after knee surgery can help prevent excessive scar tissue formation and joint stiffness.

When to See a Doctor

If you experience persistent knee pain, progressive stiffness, or a noticeable decrease in your knee's range of motion, it is crucial to consult a healthcare professional. Early diagnosis and intervention can significantly impact the outcome, potentially preventing or delaying the onset of severe ankylosis and preserving joint function. Seek immediate medical attention for sudden, severe knee pain accompanied by swelling, redness, and fever, as these could indicate a joint infection requiring urgent treatment.