What is a Partial Knee Replacement?
A partial knee replacement — also referred to as unicompartmental arthroplasty– is a replacement or resurfacing procedure to treat severe arthritis which is confined to mainly one part of the knee. The 3 compartments of the knee are:
- Patellofemoral compartment – front of the knee, between the patella (knee cap) and the groove in the femur (trochlea)
- Medial compartment – inner side of the knee between the femur and tibia
- Lateral compartment – outer side of the knee between the femur and tibia
Any compartment of the knee can be affected by osteoarthritis, or wear and tear arthritis, to varying degrees. When osteoarthritis is limited primarily to a single compartment, partial knee replacement may be a good option.
Compared to a complete knee replacement, there are several benefits to a partial knee replacement, including:
- Less invasive
- Less blood loss
- Less post-surgical pain
- Preservation of areas of the knee unaffected by arthritis
- Preservation of all your ligaments
- Shorter recovery time
- Greater range of motion of the knee
- A more natural feeling knee compared to total knee replacement
Dr. Cunningham is a knee surgeon at Vail Summit Orthopedics and Neurosurgery. He is an expert at diagnosing and treating arthritis and performing partial knee replacement for patients in Vail, Summit County, Aspen, and Denver, CO.
When is a Partial Knee Replacement Needed?
Patients suffering from knee osteoarthritis commonly report pain, swelling, warmth, and catching in the knee. Activities are often limited due to these ongoing symptoms. Non-surgical treatments for arthritis includes:
- Avoiding impact activities
- Weight loss
- Ice therapy for pain and swelling
- Eating an anti-inflammatory diet rich in plant foods
- Not smoking
- Fitness program or physical therapy to strengthen muscles around the knee
- Non-steroidal anti-inflammatory medications
- Injections to the knee (steroid, hyaluronic acid or lubricant injections)
- Platelet rich plasma (PRP) or stem cell injections
- Alternative treatments including acupuncture
If these non-surgical treatments fail to improve symptoms–or if the condition worsens–patients may be a candidate for a partial knee replacement. Following a thorough history and physical exam of the knee, xrays and an MRI are obtained to confirm that the arthritis is mainly confined to just one of the three compartments of the knee. If all damage is strictly confined to a single compartment of the knee, further criteria to be a candidate for partial knee replacement are:
- Intact ligaments in the knee
- Adequate knee range of motion
- Lack of severe knee malalignment
Partial knee replacement is a surgical treatment that is available to help patients young and old to regain the benefits of a healthy, arthritis free knee joint.
What is the Difference Between a Partial and Full Knee Replacement?
In a partial knee replacement, only one compartment of the knee is resurfaced using thin metal components cemented to the end of the femur and the top of the tibia, with a thin but durable plastic liner placed between these metal components. The other two compartments of the knee are not resurfaced; rather, the native cartilage is preserved. All of the ligaments of the knee are also preserved during partial knee replacement.
If the arthritis involves 2 or all 3 compartments of the knee, then total knee replacement is the best option as then all arthritic areas of the knee are resurfaced with metal components and a plastic liner. Furthermore, if there are torn ligaments in the knee in addition to there being arthritis throughout the knee, then total knee replacement is indicated as gets a mechanical substitute for any torn ligaments with a total knee replacement.
Both partial and total knee replacement can result in great pain relief and allow patients to return to sports and other activities.
How is an Unicompartment Knee Arthroplasty Performed?
Compared to a full knee replacement, a smaller incision is required, thus reducing pain, bleeding, and recovery time. An unicompartmental knee arthroplasty is performed under a general anesthesia as well with the addition of a femoral nerve block. The main steps of the surgery are:
- Exposing the involved portion of the knee
- Affixing mechanical cutting guides precisely on the bone
- Resecting a thin layer of bone and all the overlying worn cartilage
- Verifying correct fit and size of the replacement components with trial components
- Placing bone cement on the cleanly prepared bony surfaces
- Impacting a thin metal component onto the cut bony surfaces such that the component perfectly matches the normal contour of that portion of the knee joint.
- Placing a plastic liner between the metal surfaces and locking it into the metal component
- Ensuring proper positioning, movement, and stability of the knee
- Obtaining xrays in surgery to confirm good component positioning
- Closing the surgical wound in layers and applying dressings
What are Partial Knee Replacements Made Of?
Most knee replacement components are made of a metal alloy consisting primarily of cobalt and chrome, as this alloy allows for a low friction metallic surface that will minimally wear the plastic or polyethylene surface that it articulates against. In many cases, these durable medical devices can last up to 20 years.
What is the Recovery After a Partial Knee Replacement?
Recovery from a partial replacement is faster than the recovery from a full knee replacement. After surgery, patients will spend a few hours in surgical recovery before going home the same day. Patients can start to put weight on the leg right away with the assistance of crutches. Most patients can walk without crutches at 2 weeks from surgery. Physical therapy is begun immediately after surgery, with the initial focus being on reducing swelling and maximizing knee range of motion. By 3 months from surgery, pain is minimal and patients can be biking outdoors and doing modest activities. It could be 4 months from surgery until someone is doing cutting and pivoting activities such as skiing or tennis. Dr. Cunningham is a knee surgeon at Vail Summit Orthopedics and Neurosurgery. He is an expert at diagnosing and treating osteoarthritis and performing partial knee replacement for patients in Vail, Summit County, Aspen, and Denver, CO.