Knee Replacement: Procedure, Recovery, Risks, and Long-Term Outlook

How does a knee replacement happen?

Knee replacement surgery, formally known as total knee arthroplasty (TKA), is a highly effective orthopedic procedure designed to alleviate chronic knee pain and restore function by replacing damaged bone and cartilage with artificial components.

Understanding Knee Anatomy and the Need for Replacement

The knee is a complex hinge joint, crucial for mobility, formed by the lower end of the thigh bone (femur), the upper end of the shin bone (tibia), and the kneecap (patella). Healthy articular cartilage covers the ends of these bones, allowing for smooth, frictionless movement. When this cartilage deteriorates, most commonly due to conditions like osteoarthritis (degenerative "wear and tear" arthritis), rheumatoid arthritis (an inflammatory autoimmune disease), or post-traumatic arthritis (following an injury), bone-on-bone friction occurs, leading to pain, stiffness, swelling, and loss of mobility. A knee replacement becomes necessary when conservative treatments fail to provide adequate relief and the quality of life is significantly impacted.

Pre-Operative Assessment and Preparation

Before undergoing a knee replacement, a thorough evaluation by an orthopedic surgeon is essential. This phase ensures the patient is a suitable candidate and optimizes their health for surgery and recovery.

• Medical History and Physical Examination: The surgeon will review your complete medical history, including past surgeries, medications, allergies, and lifestyle habits. A comprehensive physical exam assesses the knee's range of motion, stability, strength, and overall functional limitations.
• Diagnostic Imaging: X-rays are standard to visualize the extent of joint damage, bone spurs, and alignment issues. In some cases, an MRI or CT scan may be used for more detailed imaging or surgical planning.
• Blood Tests and Medical Clearances: Blood work is performed to check general health, blood counts, and kidney function. Patients with pre-existing conditions (e.g., heart disease, diabetes) will require clearance from their primary care physician or specialists to ensure they are stable enough for surgery.
• Pre-Operative Education: Patients typically attend a class or receive materials explaining the surgical process, potential risks, hospital stay, pain management, and the crucial role of post-operative physical therapy.
• Optimizing Health: Patients are often advised to stop smoking, manage chronic conditions, and, if overweight, lose weight to reduce surgical risks and improve recovery outcomes.

The Surgical Procedure: Step-by-Step

Total knee replacement surgery typically takes 1 to 2 hours, though the overall process from anesthesia to recovery room is longer.

• Anesthesia: You will receive either general anesthesia (putting you completely to sleep) or regional anesthesia (an epidural or spinal block that numbs you from the waist down, often combined with sedation). The choice depends on your health, the surgeon's preference, and your input.
• Incision: Once anesthesia is administered, the surgical team cleans and drapes the operative area. The surgeon makes an incision, usually 6 to 10 inches long, down the front of the knee.
• Exposing the Joint: Muscles, ligaments, and the patella are carefully moved aside to expose the damaged knee joint. The patella is typically everted (flipped over) to allow full access.
• Bone Resection: Using specialized instruments and precise guides, the surgeon removes the damaged cartilage and a small amount of underlying bone from the ends of the femur and tibia. If the patella's undersurface is also damaged, a portion of it will be prepared for resurfacing.
• Trial Implants: Before inserting the permanent components, trial implants are placed to test the fit, alignment, and stability of the new joint. This allows the surgeon to make any necessary adjustments to ensure optimal sizing and ligament balance.
• Implant Placement: The permanent prosthetic components, made of metal alloys and high-grade plastics, are then secured.
  • Femoral Component: A curved metal component is fitted onto the end of the femur, designed to mimic the natural curve of the thigh bone.
  • Tibial Component: A flat metal plate is placed on top of the tibia. A durable plastic (polyethylene) insert is then snapped into or cemented onto this metal plate, acting as the new cartilage surface between the femur and tibia.
  • Patellar Component (Optional): If the patella was resurfaced, a plastic button-shaped component is cemented onto its back surface.
  • Implants can be secured with bone cement (cemented fixation) or designed to allow bone to grow into their porous surfaces (uncemented or press-fit fixation).
• Balancing the Joint: The surgeon carefully assesses the new joint's range of motion, stability, and ligament tension. Adjustments may be made to ensure the knee is well-balanced and moves smoothly through its full arc.
• Closure: Once the components are securely in place and the joint is functioning optimally, the surgical site is thoroughly irrigated. The muscles and tissues are repositioned, and the incision is closed with sutures or staples. A drainage tube may be inserted temporarily to prevent fluid buildup.

Post-Operative Recovery and Rehabilitation

Recovery begins immediately after surgery and is a critical phase for the success of the knee replacement.

• Immediate Post-Op: In the recovery room, your vital signs are monitored, and pain management begins, often with a combination of oral medications, nerve blocks, or patient-controlled analgesia (PCA) pumps. Measures to prevent blood clots, such as compression stockings or blood thinners, are initiated.
• Hospital Stay: Most patients stay in the hospital for 1 to 3 days. Early mobilization is encouraged, with physical therapy often beginning on the same day or the day after surgery. You'll learn to use walking aids (walker, crutches) and perform initial exercises to restore range of motion and strength.
• Rehabilitation Phases:
  • Phase 1 (Early Mobility and Pain Control): Focuses on managing pain and swelling, achieving full knee extension, and regaining initial flexion. This often occurs in the hospital and immediately after discharge, either at home with outpatient therapy or in a rehabilitation facility.
  • Phase 2 (Progressive Strengthening and Range of Motion): Typically begins a few weeks post-op. Exercises become more challenging, focusing on strengthening the quadriceps, hamstrings, and glutes, and progressively increasing knee flexion.
  • Phase 3 (Functional Integration and Return to Activity): Aims to restore higher-level functions, balance, and endurance. This phase prepares you for returning to daily activities, work, and approved recreational pursuits.
• Adherence to PT Protocol: Consistent and dedicated participation in physical therapy is paramount. The exercises are designed to prevent stiffness, strengthen surrounding muscles, and improve the function of the new joint.

Potential Risks and Complications

While knee replacement surgery is generally safe and successful, like any major surgery, it carries potential risks:

• Infection: Though rare, infection can occur around the implant, sometimes requiring further surgery.
• Blood Clots: Deep vein thrombosis (DVT) in the leg or pulmonary embolism (PE) in the lung are serious but preventable risks.
• Nerve or Blood Vessel Damage: Infrequent, but can occur during surgery.
• Implant Loosening or Wear: Over time, the components can loosen or the plastic insert can wear out, potentially requiring revision surgery.
• Stiffness or Limited Range of Motion: Despite therapy, some patients may not regain full knee motion.
• Persistent Pain: While most experience significant pain relief, a small percentage may have ongoing discomfort.

Long-Term Outlook and Lifestyle Considerations

The vast majority of individuals undergoing total knee replacement experience significant pain relief, improved mobility, and enhanced quality of life. Modern knee implants are designed to last 15 to 20 years or more in 90-95% of patients.

• Improved Pain and Function: Most patients can resume normal daily activities without significant pain.
• Activity Modifications: While activities like walking, swimming, cycling, and golf are generally encouraged, high-impact activities such as running, jumping, and contact sports are typically discouraged to prolong the life of the implant.
• Regular Follow-Ups: Periodic check-ups with your orthopedic surgeon are recommended to monitor the implant and overall knee health.

Understanding the detailed process of a knee replacement, from pre-operative preparation to post-operative rehabilitation, empowers patients to make informed decisions and actively participate in their recovery journey for optimal long-term outcomes.