Knee Replacements: Unicompartmental, Total, and Revision Arthroplasty

What are the three types of knee replacements?

Knee replacement surgery, or knee arthroplasty, primarily involves three distinct types: Unicompartmental (Partial) Knee Arthroplasty, Total Knee Arthroplasty, and Complex/Revision Knee Arthroplasty, each tailored to specific patient needs and the extent of knee joint damage.

Understanding Knee Arthroplasty: An Overview

Knee replacement surgery is a highly effective orthopedic procedure designed to relieve pain and restore function in a severely damaged knee joint. This damage is most commonly due to osteoarthritis, but can also result from rheumatoid arthritis, post-traumatic arthritis, or other degenerative conditions. When conservative treatments such as medication, physical therapy, and injections no longer provide adequate relief, surgery becomes a viable option. The goal of arthroplasty is to resurface the damaged parts of the knee, allowing for smooth, pain-free movement.

Unicompartmental Knee Arthroplasty (UKA) – Partial Knee Replacement

Unicompartmental Knee Arthroplasty, often referred to as partial knee replacement, is a procedure where only the diseased or damaged compartment of the knee is replaced, rather than the entire joint. The knee is divided into three main compartments:

• Medial compartment: The inside part of the knee.
• Lateral compartment: The outside part of the knee.
• Patellofemoral compartment: The front of the knee, behind the kneecap.

Description: In a UKA, the surgeon removes only the damaged cartilage and bone from one of these compartments and replaces it with metal and plastic components. The healthy cartilage and bone in the other two compartments, along with the major ligaments (cruciate and collateral), are preserved.

Indications: This procedure is suitable for patients whose arthritis is confined to a single compartment of the knee, typically the medial compartment. Ideal candidates usually have intact anterior and posterior cruciate ligaments, a good range of motion, and minimal deformity.

Advantages:

• Smaller Incision: Generally less invasive than a total knee replacement.
• Faster Recovery: Patients often experience a quicker return to normal activities.
• Preservation of Native Bone and Ligaments: Maintains more of the knee's natural anatomy, potentially leading to a more natural feel and better range of motion.
• Reduced Blood Loss and Shorter Hospital Stay: Often associated with less surgical trauma.

Disadvantages:

• Limited Applicability: Not suitable for widespread arthritis affecting multiple compartments.
• Potential for Progression: Arthritis can develop in the unreplaced compartments, potentially necessitating future surgery.
• Higher Revision Rate: While often revised to a total knee replacement, the long-term revision rate is slightly higher than for TKA.

Total Knee Arthroplasty (TKA) – Total Knee Replacement

Total Knee Arthroplasty is the most common type of knee replacement surgery. It involves replacing all three compartments of the knee joint.

Description: During a TKA, the damaged ends of the thigh bone (femur) and shin bone (tibia) are removed and replaced with precisely sized metal components. A medical-grade plastic spacer is inserted between these metal components to act as the new cartilage, allowing for smooth gliding motion. The back surface of the kneecap (patella) may also be resurfaced with a plastic component.

Indications: TKA is recommended for patients with widespread arthritis affecting multiple compartments of the knee, significant pain, stiffness, and functional limitations that have not responded to conservative treatments. It is particularly effective for severe osteoarthritis, rheumatoid arthritis, and significant post-traumatic arthritis.

Advantages:

• Highly Effective Pain Relief: Provides excellent and reliable pain reduction for severe arthritis.
• Restoration of Function: Significantly improves mobility and quality of life for most patients.
• Durable Long-Term Outcomes: Modern knee implants are designed to last 15-20 years or more in a majority of patients.
• Widely Practiced: It is a standard and highly successful procedure with well-established protocols.

Disadvantages:

• Larger Incision and More Invasive: Compared to UKA, it involves more extensive surgical intervention.
• Longer Recovery Period: Requires a more intensive and prolonged rehabilitation process.
• Less Natural Feel: Some patients report that a total knee replacement does not feel as "natural" as their original knee or a partial replacement.
• Potential for Complications: As with any major surgery, risks include infection, blood clots, nerve damage, and implant loosening.

Complex/Revision Knee Arthroplasty

Complex or Revision Knee Arthroplasty is performed when a previously implanted knee replacement fails or when the initial condition of the knee is unusually severe, requiring specialized techniques and implants.

Description: This procedure involves removing some or all of the components from a previous knee replacement and implanting new ones. Revision surgery is often more complex and lengthy than primary knee replacement, frequently requiring specialized tools, larger implants, bone grafting, or customized components to address significant bone loss or severe deformity.

Indications:

• Implant Loosening or Wear: The most common reason, where the original components become unstable or worn out over time.
• Infection: A serious complication that may require multiple surgeries to clear the infection and replace the components.
• Periprosthetic Fracture: A fracture that occurs around the knee replacement components.
• Instability: When the knee feels unstable or gives way after the initial surgery.
• Persistent Pain or Stiffness: If the primary replacement does not adequately relieve symptoms.
• Severe Bone Loss or Deformity: In certain primary cases where standard total knee components are insufficient.

Complexity and Outcomes:

• Technically Challenging: Revision surgery is more demanding due to altered anatomy, scar tissue, and potential bone deficits.
• Longer Recovery: The recovery period is typically longer and more challenging than for a primary knee replacement.
• Higher Risk Profile: Generally carries a higher risk of complications compared to primary TKA.
• Variable Outcomes: While often successful in relieving pain and improving function, the outcomes of revision surgery may not be as favorable as those of a primary TKA.

Factors Influencing Surgical Choice

The decision regarding which type of knee replacement is most appropriate is highly individualized and is made in consultation with an orthopedic surgeon. Key factors considered include:

• Extent and Location of Arthritis: Whether the damage is confined to one compartment or is widespread.
• Ligamentous Integrity: The health and stability of the knee's natural ligaments.
• Patient Age and Activity Level: Younger, more active patients might be candidates for partial replacement if their arthritis is isolated.
• Overall Health and Medical History: Comorbidities can influence surgical risk and recovery.
• Bone Quality and Alignment: The structural integrity of the bones and any existing deformities.
• Surgeon's Experience and Expertise: Surgeons often have preferences and specialties based on their training and experience.

Recovery and Rehabilitation: A Kinesiological Perspective

Regardless of the type of knee replacement, comprehensive rehabilitation is crucial for optimal outcomes. From a kinesiological standpoint, the focus is on restoring strength, mobility, and function.

• Pre-habilitation: Engaging in physical therapy before surgery can significantly improve post-operative recovery by strengthening muscles and improving range of motion.
• Early Mobilization: Post-surgery, early weight-bearing and movement are encouraged to prevent stiffness and reduce the risk of blood clots.
• Physical Therapy Program: A structured program focuses on:
  • Pain Management: To allow for effective participation in exercises.
  • Range of Motion Exercises: To regain knee flexion and extension.
  • Strengthening: Targeting the quadriceps, hamstrings, glutes, and calf muscles to support the new joint.
  • Gait Training: Re-educating proper walking patterns.
  • Balance and Proprioception: Essential for stability and fall prevention.
• Progressive Loading: Exercises are gradually advanced to challenge the knee and surrounding musculature, preparing the patient for daily activities and, eventually, a return to recreational pursuits. Adherence to the physical therapy regimen is paramount for achieving the best possible functional outcome.

Conclusion

Knee replacement surgery is a transformative procedure for individuals suffering from debilitating knee pain and dysfunction. Understanding the three primary types—Unicompartmental, Total, and Complex/Revision Knee Arthroplasty—is essential for grasping the breadth of treatment options available. Each type is meticulously designed to address specific anatomical and pathological considerations. The choice among them is a critical decision, made collaboratively between the patient and an experienced orthopedic surgeon, taking into account the extent of disease, individual patient factors, and functional goals. With meticulous surgical technique and dedicated post-operative rehabilitation, these procedures offer profound improvements in quality of life, enabling individuals to return to active, pain-reduced lives.