Total Knee Replacement: Procedure, Components, Recovery, and Longevity

How do they fit a new knee?

Total knee arthroplasty, commonly known as total knee replacement, is a sophisticated surgical procedure where damaged bone and cartilage in the knee joint are removed and replaced with artificial components designed to restore function and alleviate pain.

Understanding Total Knee Arthroplasty (TKA)

Total Knee Arthroplasty (TKA) is one of the most successful and frequently performed orthopedic procedures worldwide. It's primarily indicated for individuals suffering from severe knee pain and disability caused by conditions such as osteoarthritis, rheumatoid arthritis, or post-traumatic arthritis, where conservative treatments have failed. The overarching goal of TKA is to alleviate chronic pain, correct deformity, and restore mobility and stability to the knee joint, significantly improving a patient's quality of life.

Anatomy of the Knee Joint

To appreciate the complexity of fitting a new knee, it's essential to understand the joint's natural structure. The knee is a hinge joint, formed by the articulation of three bones:

• Femur: The thigh bone.
• Tibia: The shin bone.
• Patella: The kneecap.

These bones are covered at their ends by articular cartilage, a smooth, slippery tissue that allows for effortless gliding movement. Surrounding the joint is the synovial membrane, which produces lubricating fluid, and a network of ligaments and tendons that provide stability and enable movement. In conditions like osteoarthritis, this articular cartilage erodes, leading to bone-on-bone friction, pain, swelling, and stiffness.

Pre-Surgical Preparation

Before a TKA, a thorough evaluation is conducted to ensure the patient is a suitable candidate and to plan the surgery meticulously.

• Medical Evaluation: This includes a comprehensive physical exam, blood tests, urine tests, and an electrocardiogram (ECG). The orthopedic surgeon will assess the knee's range of motion, stability, and strength.
• Imaging Studies: X-rays are crucial for assessing the extent of damage and deformity. MRI or CT scans may also be used for more detailed planning.
• Patient Education: Patients receive detailed information about the procedure, potential risks, expected recovery, and the importance of rehabilitation. "Pre-habilitation" exercises may be prescribed to strengthen muscles and improve flexibility, optimizing post-operative outcomes.
• Medication Review: All current medications are reviewed, and some, like blood thinners, may need to be stopped before surgery.

The Surgical Procedure: Step-by-Step

The process of "fitting a new knee" involves several precise steps, typically lasting 1 to 2 hours.

1. Anesthesia: The patient receives either general anesthesia (rendering them unconscious) or regional anesthesia (spinal or epidural block, numbing the lower body) combined with sedation.
2. Incision: An incision, usually 6-10 inches long, is made down the front of the knee to expose the joint.
3. Bone Resection and Preparation:
   • Femur: Specialized instruments and cutting guides are used to precisely remove the damaged cartilage and a small amount of underlying bone from the end of the femur. The end of the femur is then shaped to fit the femoral component of the artificial knee.
   • Tibia: The top surface of the tibia is similarly prepared. Damaged cartilage and a small portion of bone are removed, creating a flat surface for the tibial component.
   • Patella: In many cases, the undersurface of the patella (kneecap) is also resurfaced. The damaged cartilage is removed, and a plastic "button" component is prepared for implantation.
4. Implant Placement:
   • Femoral Component: A metal alloy component (typically cobalt-chromium or titanium) is fitted onto the end of the femur. This component is designed to mimic the natural curve of the femoral condyles.
   • Tibial Component: A flat metal tray is secured to the top of the tibia. A durable polyethylene (medical-grade plastic) insert, which acts as the new articular cartilage, is then snapped or cemented into this metal tray.
   • Patellar Component: If the patella was resurfaced, a polyethylene button is cemented to its posterior surface.
5. Balancing and Testing: The surgeon carefully checks the new joint's alignment, stability, and range of motion. Ligament tension is adjusted to ensure proper tracking and function. The joint is flexed and extended multiple times to confirm smooth movement.
6. Closure: Once the surgeon is satisfied with the fit and function, the incision is closed layer by layer, and a sterile dressing is applied. A drain may be temporarily placed to remove excess fluid.

The Components of a "New Knee"

A total knee replacement typically consists of three main components, made from biocompatible materials:

• Femoral Component: A highly polished metal cap (cobalt-chromium or titanium alloy) that fits over the end of the thigh bone.
• Tibial Component: A flat metal platform (titanium alloy) with a polyethylene (plastic) insert that replaces the top surface of the shin bone. The polyethylene acts as the new smooth gliding surface.
• Patellar Component: A dome-shaped polyethylene "button" that replaces the undersurface of the kneecap.

These components are typically fixed to the bone using bone cement (polymethyl methacrylate). In some cases, a "press-fit" technique is used, where the components have a porous coating that allows bone to grow into them, providing biological fixation.

Post-Operative Recovery and Rehabilitation

The success of a total knee replacement relies heavily on diligent post-operative rehabilitation.

• Immediate Post-Op: Pain management is crucial. Patients are encouraged to begin gentle movement of the knee almost immediately, often with the help of a Continuous Passive Motion (CPM) machine.
• Hospital Stay: Physical therapy begins in the hospital. Patients learn exercises to improve range of motion, strengthen muscles, and practice walking with assistance.
• Rehabilitation Phases:
  • Phase 1 (Early Recovery): Focuses on pain and swelling control, restoring full knee extension, improving flexion, and initiating muscle activation (quadriceps sets, ankle pumps).
  • Phase 2 (Intermediate): Progresses to more aggressive strengthening exercises, balance training, and gait re-education.
  • Phase 3 (Advanced/Functional): Aims to restore higher-level function, including stair climbing, light impact activities, and a return to appropriate sports or hobbies.
• Long-Term Considerations: Adherence to a home exercise program is vital for maintaining strength and flexibility. Patients are educated on joint protection strategies and activity modifications to ensure the longevity of their new knee.

Potential Risks and Complications

While TKA is a safe and effective procedure, like all surgeries, it carries potential risks:

• Infection: Though rare, infection can be serious and may require further surgery.
• Blood Clots: Deep vein thrombosis (DVT) in the leg or pulmonary embolism (PE) in the lung can occur. Blood thinners are often prescribed to prevent this.
• Implant Loosening or Wear: Over time, the components can loosen or the plastic insert can wear out, potentially requiring revision surgery.
• Nerve or Blood Vessel Damage: Rare but possible during surgery.
• Stiffness or Persistent Pain: Some patients may experience ongoing stiffness or pain despite a successful surgery.

Longevity of a "New Knee"

Modern knee implants are highly durable. Most total knee replacements are expected to last 15 to 20 years or more for the majority of patients. Factors influencing longevity include the patient's activity level, body weight, the quality of the surgical technique, and the adherence to post-operative care.

Conclusion

Fitting a new knee is a meticulously planned and executed orthopedic procedure that fundamentally replaces the damaged surfaces of the knee joint with advanced prosthetic components. This transformative surgery, coupled with dedicated rehabilitation, offers a profound improvement in pain relief, mobility, and overall quality of life for individuals suffering from severe knee arthritis. Understanding the process empowers patients and healthcare professionals alike in navigating the journey to a more active and pain-free future.