ACL Surgery: Persistent Knee Swelling, Causes, and Treatment

Why is my knee still swollen 5 months after ACL surgery?

Persistent knee swelling 5 months after ACL surgery is not typical and warrants immediate medical evaluation, as it often signals underlying complications such as arthrofibrosis, infection, or issues with graft healing or other intra-articular structures.

Understanding Normal Post-Operative Swelling

Following Anterior Cruciate Ligament (ACL) reconstruction, some degree of swelling is an expected part of the healing process. This initial inflammation is a natural physiological response to surgical trauma, the presence of the new graft, and the body's repair mechanisms.

• Acute Phase (First 2-6 weeks): Swelling is most prominent during this period. It is managed through RICE (Rest, Ice, Compression, Elevation) principles, anti-inflammatory medications, and controlled mobilization as guided by your physical therapist.
• Resolution: Typically, by 2-3 months post-surgery, significant swelling should have substantially diminished, allowing for improved range of motion and progression in rehabilitation. By 5 months, residual swelling, if any, should be minimal and not impacting daily function or exercise.

When swelling persists or recurs at the 5-month mark, it's a clear indication that something is impeding the normal healing process or that a new issue has developed.

Reasons for Persistent Swelling at 5 Months Post-ACL Surgery

Several factors can contribute to prolonged or recurrent knee swelling long after ACL surgery. Identifying the specific cause is crucial for appropriate management.

• Arthrofibrosis (Scar Tissue Formation): This is one of the most common causes of persistent swelling and stiffness. Arthrofibrosis occurs when excessive scar tissue forms within the joint, limiting range of motion and often causing a chronic inflammatory response that manifests as swelling.

  • Mechanism: The body overproduces collagen in response to injury and surgery, leading to dense, restrictive fibrous tissue.
  • Symptoms: Besides swelling, common signs include a feeling of tightness, difficulty fully straightening (extension loss) or bending (flexion loss) the knee, and pain with movement.

• Infection: While less common, a deep joint infection is a serious complication that can occur after surgery, even months later.

  • Symptoms: Swelling accompanied by increased pain, redness, warmth, fever, chills, or drainage from the incision site strongly suggests an infection and requires urgent medical attention.

• Graft-Related Issues:

  • Graft Impingement: The newly placed ACL graft may be impinging on other structures within the joint, such as the intercondylar notch or the PCL, leading to chronic irritation and swelling.
  • Graft Failure/Re-rupture: Although less likely to present solely as swelling without instability, a partial or complete re-rupture of the graft can cause acute or persistent swelling due to renewed trauma and inflammation.
  • Cyclops Lesion: A nodule of fibrous tissue can form in front of the graft, often causing an extension block and persistent inflammation.

• Meniscal Tear or Cartilage Damage: If a concomitant meniscal tear or articular cartilage injury was present at the time of surgery and not fully addressed, or if a new injury has occurred, it can cause ongoing irritation and swelling.

  • Mechanism: Torn meniscal fragments or damaged cartilage can irritate the joint lining (synovium), leading to fluid accumulation.

• Synovitis: This refers to inflammation of the synovial membrane, the lining of the joint capsule. Persistent synovitis can be a standalone issue or secondary to other problems like impingement, arthrofibrosis, or chronic irritation.

  • Symptoms: Pain, warmth, and joint effusion (fluid buildup).

• Overactivity or Premature Return to Activity: Pushing the knee too hard, too soon, or engaging in activities beyond the current stage of rehabilitation can overwhelm the healing tissues and lead to a flare-up of inflammation and swelling.

  • Mechanism: Repeated stress on healing tissues can cause micro-trauma and perpetuate the inflammatory cycle.

• Complex Regional Pain Syndrome (CRPS): A rare but severe neurological condition that can develop after limb injury or surgery. It involves chronic pain, swelling, changes in skin temperature and color, and hypersensitivity.

• Deep Vein Thrombosis (DVT): While typically presenting with calf pain, redness, and swelling, a blood clot in the leg veins can occasionally cause knee swelling. This is a medical emergency.

The Importance of Medical Evaluation

Given that persistent swelling at 5 months is an atypical and concerning symptom, it is imperative to consult your orthopedic surgeon or physical therapist without delay. Self-diagnosing or waiting it out can lead to further complications or delay appropriate treatment.

What Your Doctor Will Look For

During your evaluation, your healthcare provider will likely:

• Conduct a thorough physical examination: Assessing range of motion, stability, tenderness, and signs of inflammation.
• Review your surgical history and rehabilitation progress: Understanding your journey since surgery.
• Order imaging studies:
  • X-rays: To assess bone alignment and look for signs of impingement or hardware issues.
  • MRI (Magnetic Resonance Imaging): The gold standard for visualizing soft tissues, including the ACL graft, menisci, cartilage, and detecting fluid accumulation or scar tissue.
• Consider joint aspiration: If infection is suspected, fluid may be drawn from the knee joint for analysis.

Potential Treatment Approaches

Treatment for persistent swelling depends entirely on the underlying cause identified:

• Physical Therapy Adjustments: For issues related to range of motion deficits or muscle imbalances, your physical therapy program may be modified to include specific mobilization techniques, stretching, strengthening, or activity modification.
• Medications: Non-steroidal anti-inflammatory drugs (NSAIDs) may be prescribed to manage inflammation and pain. If an infection is present, antibiotics will be necessary.
• Injections: Corticosteroid injections may be used to reduce localized inflammation, particularly in cases of synovitis or arthrofibrosis, though this is often a temporary measure.
• Surgical Intervention:
  • Arthroscopic Debridement: For significant arthrofibrosis or cyclops lesions, a minimally invasive procedure may be performed to remove scar tissue and restore range of motion.
  • Revision Surgery: In rare cases of graft failure or severe impingement, a second surgery may be required to address the underlying structural issue.

Proactive Steps and Rehabilitation Considerations

While waiting for your medical appointment, continue to follow your prescribed physical therapy exercises, but avoid activities that exacerbate swelling or pain.

• RICE Principles (Judiciously): Continue to use ice and elevation to manage swelling, but understand this is a symptomatic treatment, not a cure for the underlying problem. Compression with a sleeve can also be helpful.
• Adhere to Your PT Program: Consistent, controlled rehabilitation is key to recovery. Do not skip sessions or attempt to accelerate your progress without professional guidance.
• Communicate with Your Team: Maintain open communication with your surgeon and physical therapist about all your symptoms and concerns.

Conclusion and Next Steps

Persistent knee swelling 5 months after ACL surgery is a significant red flag that should not be ignored. It's not "normal" and indicates an underlying issue that requires professional medical diagnosis and intervention. Early identification and treatment of the cause are critical to preventing further complications, preserving knee function, and optimizing your long-term recovery trajectory. Consult your orthopedic surgeon or physical therapist immediately to determine the cause and establish an appropriate treatment plan.