When the knee develops arthritis in just one joint compartment, it’s known as a unicompartmental disease state. Unicompartmental arthritis causes swelling, inflammation, pain, and stiffness in the knee joint. 

Osteoarthritis is the most common form of arthritis affecting the knee, and it causes the joint cartilage to wear away. Your joint cartilage is there to help cushion the knee and keep it moving smoothly. When it declines you can experience the “bone on bone” sensation that is quite painful and debilitating. 

The knee is made up of three compartments:

1. Lateral compartment (outer part of the joint)
2. Medial compartment (inner part of the joint)
3. Patellofemoral compartment (kneecap area of the joint)

When it comes to osteoarthritis, the medial compartment is most commonly affected (90%), followed by the lateral compartment. Osteoarthritis that only flares up in the patellofemoral compartment is rare.

For patients with unicompartmental osteoarthritis, normal activities can grow increasingly hard. Stiffness and pain cause limping and this rolling gait can affect your balance and cause hip and spine pain. In the past, surgeons have completed total knee replacements on patients with unicompartmental osteoarthritis. 

However, today, knee replacement surgery is much more precise, and can even be completed as an outpatient procedure, where you can go home the same day. Instead of replacing the entire knee joint, there is an alternative called the uni-knee replacement.

The unicompartmental knee replacement is also known as a uni-knee replacement, partial knee replacement, or unicompartmental knee arthroplasty. No matter the name, a uni-knee replacement surgery seeks to replace the arthritic section of the knee with prosthetic parts while sparing the remaining compartments of the knee. 

Your surgeon will carefully remove just the section that is affected by arthritis, replacing and cleaning these parts with resurfacing and implants, while the healthy tissue and bone of the knee will remain in place.

During a unicompartmental or partial knee replacement, your surgeon will make a small incision to gain access to the affected knee compartment and carefully remove the diseased portion of the knee joint. The surrounding surfaces will be prepared to accept the prosthesis and then the surgeon will precisely cement the replacement parts onto these sections. Finally, all of the surrounding tissues and structures will be restored to their original locations and the incision will be sutured. 

This procedure is typically performed in an outpatient setting, meaning you’ll be walking within a few hours of the procedure and on your way home in the afternoon. As you recover at home, you will undergo physical therapy to recover your mobility and help the knee heal as quickly as possible.

In a total knee replacement, your surgeon will remove the entire joint and replace it with a fully prosthetic or artificial joint. However, in many cases, you may just have wear and tear in one section of the knee, which may make uni-knee replacement a better option. The uni-knee simply replaces the section of the knee that is affected by arthritis and leaves the unaffected areas. The procedure is, therefore, less invasive, leading to less postoperative pain and a faster recovery. Because only one section of the knee is replaced and the rest is left intact, patients report that their knee feels much more natural.

There are many benefits to having a unicompartmental knee replacement over a total knee replacement. The benefits of a uni-knee procedure include:

• Quicker recovery period
• Less postoperative pain
• Better range of motion after surgery
• More natural feeling knee
• Fewer complications when compared to a total knee replacement
• Less blood loss
• Less bone and soft tissue disruption

A Uni-Knee replacement in the properly selected patient can last just as long as a total knee replacement. Approximately 75-80% of uni-knees last 20 years or more. If ever the uni-knee wears out, the subsequent procedure would simply be conversion to a total knee replacement.

The first question your surgeon will ask when considering the type of knee replacement is where the arthritis and pain are located in your knee. You will undergo a variety of diagnostic tests to understand what parts of the knee or knees are affected by the arthritis. The ideal person undergoing a uni-knee replacement is:

• At least 50 years old or older
• Pain localized to one-sided of the knee
• Does not have rheumatoid arthritis
• Has good range of motion before the surgery
• Has intact ligaments, particularly the ACL
• Has severe knee osteoarthritis limited to just one section of the joint
• Has tried several more conservative treatments that failed
• Lacks significant knee deformities 
• BMI under 40

Every patient is different. That’s why your surgeon will carefully evaluate the condition of the knee as well as your overall health before deciding whether uni-knee replacement surgery is right for you.