Knee Infiltrations: Understanding Types, Procedure, Benefits, and Risks

What is a knee infiltration?

A knee infiltration, often referred to as a knee injection, is a medical procedure involving the injection of therapeutic substances directly into or around the knee joint to alleviate pain, reduce inflammation, and improve function, typically when conservative treatments have been insufficient.

Understanding Knee Pain and the Role of Infiltrations

The knee joint is a complex structure susceptible to various conditions causing pain, inflammation, and reduced mobility. Common culprits include osteoarthritis (degenerative joint disease), various forms of arthritis, tendinitis (inflammation of tendons), bursitis (inflammation of bursae), and meniscal tears. While initial management often involves rest, ice, compression, elevation (RICE), physical therapy, and oral medications, these approaches may not provide sufficient relief for all individuals. In such cases, knee infiltrations offer a targeted, non-surgical option to deliver medication directly to the affected area, bypassing systemic side effects and providing more immediate relief.

What Exactly is a Knee Infiltration?

A knee infiltration is a precise medical procedure performed by a healthcare professional (e.g., orthopedic surgeon, sports medicine physician, rheumatologist) where a needle is used to deliver medication into the joint space, a bursa, or around a tendon. The primary goal is to address localized pain and inflammation, aiming to restore comfort and function. The specific substance injected depends on the underlying condition and the desired therapeutic effect.

Types of Knee Infiltrations

Several types of substances can be infiltrated into the knee, each with a distinct mechanism of action and indication:

• Corticosteroid Injections (Steroid Shots)
  • Mechanism: Corticosteroids are potent anti-inflammatory medications. When injected, they directly reduce inflammation within the joint or surrounding tissues.
  • Uses: Commonly used for osteoarthritis flares, rheumatoid arthritis, gout, tendinitis (e.g., patellar tendinitis, quadriceps tendinitis), and bursitis (e.g., prepatellar bursitis).
  • Considerations: Provide rapid pain relief, but the effects are often temporary (weeks to months). Repeated injections are typically limited due to potential side effects like cartilage damage or weakening of tendons over time.
• Hyaluronic Acid Injections (Viscosupplementation)
  • Mechanism: Hyaluronic acid is a natural component of healthy joint fluid (synovial fluid), acting as a lubricant and shock absorber. Injections aim to supplement the depleted hyaluronic acid in arthritic joints, improving joint lubrication and cushioning.
  • Uses: Primarily indicated for mild to moderate knee osteoarthritis that has not responded to other conservative treatments.
  • Considerations: The pain relief is typically slower to onset than corticosteroids but can last longer (up to six months or more). A series of injections (e.g., 3-5 over several weeks) may be required.
• Platelet-Rich Plasma (PRP) Injections
  • Mechanism: PRP is derived from the patient's own blood. It is processed to concentrate platelets, which contain numerous growth factors and proteins that can promote tissue repair and reduce inflammation.
  • Uses: Used for various musculoskeletal conditions, including chronic tendinopathies (e.g., patellar tendinopathy), ligament injuries, and increasingly for early-stage osteoarthritis.
  • Considerations: As an autologous (from the patient's own body) treatment, it carries a low risk of allergic reaction. The evidence base is still evolving, with promising results for some conditions but variable efficacy depending on the specific application.
• Prolotherapy (Dextrose Injections)
  • Mechanism: Prolotherapy involves injecting a mild irritant solution, most commonly dextrose (sugar water), into ligaments or tendons. This is believed to stimulate a localized inflammatory response, promoting healing and strengthening of weakened connective tissues.
  • Uses: Primarily used for chronic pain associated with ligament laxity or instability, such as in certain cases of chronic knee pain where ligaments are a primary contributor.
  • Considerations: While not a direct intra-articular injection in the same way as steroids or HA, it targets structures around the knee. It often requires multiple sessions, and the evidence supporting its widespread use for knee conditions is less robust than for other injection types.

The Procedure: What to Expect

A knee infiltration is typically an outpatient procedure.

• Preparation: The physician will review your medical history, current medications, and imaging (e.g., X-rays, MRI) to confirm the diagnosis and determine the appropriate injection type.
• During the Procedure:
  1. The skin around the knee is thoroughly cleaned with an antiseptic solution.
  2. A local anesthetic may be injected to numb the skin and underlying tissues.
  3. The physician carefully inserts a thin needle into the targeted area (joint space, bursa, or around a tendon).
  4. Imaging Guidance: Often, ultrasound or fluoroscopy (a type of real-time X-ray) is used to ensure precise needle placement, maximizing efficacy and minimizing risks.
  5. Once the needle is correctly positioned, the therapeutic substance is slowly injected.
• Post-Procedure: The needle is withdrawn, and a small bandage is applied. You may be advised to rest the knee for a short period and avoid strenuous activities for 24-48 hours. Ice packs can help manage any discomfort or swelling at the injection site.

Benefits and Expected Outcomes

The primary benefits of knee infiltrations include:

• Significant Pain Reduction: Direct delivery of medication to the source of pain can provide rapid and localized relief.
• Reduced Inflammation: Especially with corticosteroid injections, inflammation can be effectively quelled.
• Improved Mobility and Function: By reducing pain and inflammation, infiltrations can improve the knee's range of motion and allow for better participation in physical therapy and daily activities.
• Delaying or Avoiding Surgery: For some individuals, injections can provide sufficient relief to delay or potentially avoid the need for more invasive surgical interventions.

Potential Risks and Side Effects

While generally safe, knee infiltrations carry some potential risks:

• Common Side Effects:
  • Temporary increase in pain or swelling at the injection site.
  • Bruising.
  • "Steroid flare" (with corticosteroid injections), a temporary increase in pain for 1-2 days after the injection.
• Less Common/Serious Risks:
  • Infection (rare but serious).
  • Allergic reaction to the injected substance or anesthetic.
  • Nerve damage or bleeding (very rare).
  • Skin discoloration or fat atrophy at the injection site (with corticosteroids).
  • Repeated corticosteroid injections may, over time, potentially contribute to cartilage damage or weakening of tendons.

Who is a Candidate for Knee Infiltration?

Knee infiltrations are typically considered for individuals who:

• Experience persistent knee pain that significantly impacts their quality of life.
• Have a confirmed diagnosis (e.g., osteoarthritis, tendinitis, bursitis) amenable to injection therapy.
• Have not achieved adequate relief from more conservative treatments like oral medications, physical therapy, or bracing.
• Do not have contraindications such as active infection in or around the knee, uncontrolled bleeding disorders, or severe joint damage that would necessitate surgical intervention.

Recovery and Follow-up

Following a knee infiltration, it's crucial to follow your healthcare provider's specific instructions. You may be advised to:

• Rest and Ice: Apply ice to the knee for 15-20 minutes several times a day for the first 24-48 hours to minimize swelling and discomfort.
• Activity Modification: Avoid strenuous activities, heavy lifting, or high-impact exercises for a few days to a week, depending on the type of injection and your response.
• Monitor Symptoms: Report any signs of infection (e.g., severe pain, redness, warmth, fever) to your doctor immediately.
• Physical Therapy: Infiltrations are often used in conjunction with physical therapy. Once pain is reduced, therapy can focus on strengthening surrounding muscles, improving flexibility, and restoring proper biomechanics to maintain long-term benefits.
• Follow-up: Your doctor will schedule a follow-up to assess your response to the injection and discuss further management if needed.

Conclusion: A Component of Comprehensive Knee Care

Knee infiltrations are valuable tools in the comprehensive management of various knee conditions. They offer a targeted approach to reduce pain and inflammation, improve function, and can significantly enhance quality of life for many individuals. However, they are rarely a standalone cure. Instead, they are best viewed as one component of a broader treatment plan that often includes physical therapy, lifestyle modifications, and, when appropriate, surgical considerations. Always consult with a qualified healthcare professional to determine if a knee infiltration is the right option for your specific condition.