Knee Replacement: Understanding Why Your Operated Knee Appears Larger

Why is my knee replacement larger than my other knee?

It is common for a knee that has undergone total knee replacement (TKR) to appear larger than the unoperated knee due to a combination of factors including post-surgical swelling, the inherent bulk of the prosthetic components, and changes in surrounding tissues.

Understanding Total Knee Arthroplasty (TKA)

Total Knee Arthroplasty, commonly known as knee replacement surgery, is a procedure designed to resurface a damaged knee joint. During TKA, the damaged cartilage and bone from the thigh bone (femur), shin bone (tibia), and sometimes the kneecap (patella) are removed and replaced with artificial components. These prosthetics are typically made of metal alloys (such as cobalt-chrome or titanium) and high-grade plastics (polyethylene), meticulously shaped to restore joint function and alleviate pain. While the goal is to replicate the natural joint's mechanics, the physical presence of these implants, combined with the body's healing response, can lead to a perceived or actual increase in the knee's size.

Common Causes of Perceived Size Difference

Several factors contribute to why a knee replacement might appear larger than your other, unoperated knee:

• Initial Post-Operative Swelling (Edema)
  • Natural Inflammatory Response: Surgery is a significant trauma to the body. The immediate aftermath involves inflammation and fluid accumulation (edema) as part of the natural healing process. This swelling can be substantial and make the operated knee look significantly larger.
  • Duration: While initial swelling subsides within weeks, some degree of swelling can persist for several months, and even up to a year or more, particularly after increased activity.
• Implant Design and Materials
  • Prosthetic Bulk: The artificial components, though precisely designed, are inherently more rigid and can be slightly bulkier than the natural bone and cartilage they replace. While designed to fit within the existing anatomical space, their metallic and plastic composition can add a subtle external volume.
  • Component Placement: The femoral component, for instance, wraps around the end of the femur, and the tibial component sits on top of the tibia. Even slight variations in their contour compared to the original bone can contribute to a larger appearance.
• Surgical Alterations and Bone Reshaping
  • Bone Cuts: During TKA, precise cuts are made to the ends of the femur and tibia to accommodate the implants. This reshaping, while necessary, can alter the overall contour of the joint.
  • Osteophyte Removal: Any existing bone spurs (osteophytes) or excess bone growth from arthritis are removed, which paradoxically might make the new joint appear more defined but potentially bulkier due to the new, stable structure.
  • Bone Cement: In some cases, bone cement is used to secure the implants, which adds a minimal, but present, layer between the bone and the prosthesis.
• Scar Tissue Formation (Arthrofibrosis)
  • Fibrous Tissue Buildup: As the body heals, scar tissue forms around the joint. While necessary for repair, excessive scar tissue (arthrofibrosis) can lead to stiffness and, in some cases, add to the perceived bulk of the knee. This tissue can feel firm to the touch.
• Muscle Atrophy and Asymmetry
  • Pre-Operative Weakness: Before surgery, the affected leg often experiences muscle atrophy due to pain and disuse.
  • Post-Operative Disuse: During the recovery period, the operated leg will continue to experience some muscle loss due to reduced activity.
  • Comparative Appearance: The unoperated leg, if healthier and more muscular, might make the operated knee appear larger by contrast, even if the muscle mass around the operated knee is actually less. As rehabilitation progresses, muscle symmetry typically improves.
• Residual Swelling or Inflammation
  • Chronic Low-Grade Inflammation: For some individuals, a low level of inflammation can persist for an extended period after surgery, contributing to ongoing swelling and a larger appearance. This can be exacerbated by activity.

Distinguishing Normal Healing from Concerns

It's crucial to differentiate between expected post-operative changes and potential complications.

• Normal: Gradual reduction in swelling over weeks to months, improving range of motion, and pain that is manageable and decreasing over time. The "larger" appearance often stabilizes and becomes less noticeable as swelling fully resolves and muscle mass balances.
• Concerning: Sudden, significant increase in swelling accompanied by severe pain, redness, warmth, fever, or pus discharge could indicate an infection. Numbness or tingling might suggest nerve involvement. Any disproportionate or worsening symptoms should prompt immediate medical consultation.

Managing Swelling and Promoting Recovery

Effective management of swelling is key to reducing the perceived size difference and promoting optimal recovery:

• RICE Protocol:
  • Rest: Avoid excessive activity, especially in the early stages.
  • Ice: Apply ice packs for 15-20 minutes several times a day to reduce inflammation.
  • Compression: Use compression bandages or stockings as advised by your surgeon or physical therapist to help control swelling.
  • Elevation: Keep your leg elevated above heart level whenever possible, especially when resting.
• Medication: Take prescribed anti-inflammatory medications or pain relievers as directed.
• Gentle Movement: Follow your physical therapy program diligently. Regular, controlled movement helps pump fluid out of the joint and prevents stiffness.

The Importance of Rehabilitation

Physical therapy is paramount after TKA. A structured rehabilitation program helps to:

• Reduce Swelling: Through exercises and manual therapy techniques.
• Restore Range of Motion: Preventing stiffness and scar tissue contracture.
• Strengthen Muscles: Rebuilding quadriceps, hamstrings, and calf muscles to support the new joint and restore functional symmetry.
• Improve Proprioception: Enhancing your body's awareness of the joint's position in space.

Consistent adherence to your rehabilitation exercises is vital for long-term success and to minimize any perceived size discrepancy by balancing muscle mass and reducing residual swelling.

When to Consult Your Surgeon

While a slightly larger appearance of the operated knee is often a normal part of the healing process, you should contact your surgeon immediately if you experience:

• Sudden, severe, or worsening pain.
• Increased redness, warmth, or pus drainage from the incision site.
• Fever (over 100°F or 38°C).
• New or worsening numbness or tingling in the leg or foot.
• Inability to bear weight on the operated leg.

Understanding the reasons behind your knee's appearance post-TKA can provide reassurance and guide your recovery efforts. With time, diligent rehabilitation, and proper management, the perceived size difference often diminishes as your body fully adapts to its new joint.