Knee Replacement: Understanding Unicompartmental, Total, Patellofemoral, and Revision Options

How many types of knee replacement are there?

There are primarily three main types of knee replacement surgery: Unicompartmental Knee Arthroplasty (UKA), Total Knee Arthroplasty (TKA), and Patellofemoral Arthroplasty (PFA), with Revision Knee Arthroplasty serving as a distinct category for re-operations.

Understanding Knee Replacement Surgery

Knee replacement, medically known as knee arthroplasty, is a surgical procedure designed to alleviate 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. The procedure involves removing damaged bone and cartilage from the thighbone (femur), shinbone (tibia), and sometimes the kneecap (patella), and replacing them with prosthetic components made of metal alloys, high-grade plastics, and sometimes ceramics. The specific type of knee replacement chosen depends on the extent of the joint damage, the patient's age, activity level, and overall health.

Primary Types of Knee Replacement

The knee joint is complex, typically divided into three compartments: the medial (inner) compartment, the lateral (outer) compartment, and the patellofemoral (front, under the kneecap) compartment. The type of knee replacement performed depends on which of these compartments are affected.

Unicompartmental Knee Arthroplasty (UKA) / Partial Knee Replacement

Description: This procedure replaces only one compartment of the knee, most commonly the medial compartment. If only a specific area of the knee is damaged, a partial replacement preserves the healthy bone, cartilage, and ligaments in the unaffected parts of the knee. Indications:

• Arthritis confined to a single compartment of the knee.
• Intact knee ligaments (specifically the anterior cruciate ligament, ACL).
• Minimal deformity and good range of motion.
• Often preferred for younger, more active patients with isolated damage. Advantages: Less invasive surgery, smaller incision, faster recovery time, more natural knee motion, and preservation of healthy bone and tissue. Disadvantages: Not suitable for widespread arthritis, potential for arthritis to develop in other compartments later, potentially less durable than TKA in some cases.

Total Knee Arthroplasty (TKA) / Total Knee Replacement

Description: This is the most common type of knee replacement. It involves resurfacing all three compartments of the knee joint: the end of the femur, the top of the tibia, and the back of the patella. The damaged cartilage and bone are removed and replaced with metal and plastic components. Indications:

• Severe arthritis affecting multiple compartments of the knee.
• Significant pain and functional limitations that are not relieved by conservative treatments.
• Significant knee deformity or instability. Advantages: Highly effective in relieving pain and restoring function for severe, widespread arthritis. It is a well-established procedure with long-term success rates. Disadvantages: More invasive surgery, longer recovery period compared to UKA, and removal of more natural bone and tissue.

Patellofemoral Arthroplasty (PFA) / Kneecap Replacement

Description: This specific type of partial knee replacement addresses arthritis that is isolated to the patellofemoral compartment (the joint between the kneecap and the thighbone). The damaged surface of the kneecap and the corresponding groove on the femur are replaced. Indications:

• Arthritis strictly confined to the patellofemoral compartment.
• Healthy medial and lateral compartments. Advantages: Preserves the majority of the natural knee joint, less invasive than TKA, potentially faster recovery. Disadvantages: Limited applicability, as isolated patellofemoral arthritis is less common than multi-compartment arthritis.

Revision Knee Arthroplasty (RKA)

Description: This is a second, or subsequent, knee replacement surgery performed when a previous knee replacement has failed. Failure can occur due to various reasons, including implant loosening, infection, wear of the components, instability, or fracture around the implant. Revision surgery is often more complex than primary knee replacement. Indications:

• Pain, instability, or loss of function following a primary knee replacement.
• Evidence of implant loosening, infection, or component wear.
• Periprosthetic fracture (fracture around the implant). Considerations: Revision surgery typically involves more extensive bone removal, specialized implants, and a longer, more challenging recovery process.

Factors Influencing Surgical Choice

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

• Extent and Location of Arthritis: Is the damage localized to one area or widespread across multiple compartments?
• Ligament Integrity: The condition of the knee's ligaments (especially the ACL) is crucial for the stability of partial knee replacements.
• Patient Age and Activity Level: Younger, more active individuals with isolated damage might be candidates for partial replacements, aiming for greater natural knee kinematics.
• Bone Quality: Adequate bone stock is necessary to support the prosthetic implants.
• Overall Health and Co-morbidities: Underlying health conditions can influence surgical risk and recovery.
• Surgeon's Expertise: Experience with specific techniques and implants also plays a role.

Understanding the Implants

Regardless of the type of knee replacement, the implants are designed to mimic the natural function of the knee joint. They typically consist of:

• Femoral Component: A metal cap that fits over the end of the thighbone.
• Tibial Component: A flat metal plate with a polyethylene (medical-grade plastic) insert that fits onto the top of the shinbone.
• Patellar Component: A polyethylene button that replaces the back surface of the kneecap (used in TKA and PFA).

These components are typically fixed to the bone using bone cement, although some designs allow for "press-fit" where the bone grows onto the implant surface.

The Role of Rehabilitation

For all types of knee replacement, the success of the surgery is significantly dependent on a diligent and structured rehabilitation program. Post-operative physical therapy is crucial for:

• Restoring Range of Motion: Regaining the ability to bend and straighten the knee.
• Strengthening Muscles: Rebuilding strength in the quadriceps, hamstrings, and calf muscles to support the new joint.
• Improving Balance and Gait: Re-learning how to walk and perform daily activities safely and efficiently.
• Pain Management: Managing post-surgical pain to facilitate participation in therapy.

Conclusion

While the term "knee replacement" is often used broadly, it encompasses several distinct surgical procedures, each tailored to the specific needs and extent of damage in a patient's knee. From the targeted approach of a partial knee replacement to the comprehensive resurfacing of a total knee replacement, and the specialized patellofemoral option, these interventions offer significant relief from pain and improved quality of life for individuals suffering from debilitating knee arthritis. A thorough evaluation by an orthopedic surgeon is essential to determine the most appropriate type of knee replacement for individual circumstances.