Partial Knee Replacement

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What is a partial knee replacement?

A partial knee replacement—also called unicompartmental knee replacement or partial knee arthroplasty—is a surgical procedure in which damaged bone or cartilage involving only one surface of the knee joint is removed and replaced with metal or plastic parts. Partial knee replacement has several advantages over total knee replacement, including shorter recovery time and more range of motion preserved after surgery. But partial knee replacement is only an option for people with knee damage in just one place, either the inside, outside or kneecap.

Why is partial knee replacement performed?

The most common reason for partial knee replacement is single-compartmental knee damage from advanced osteoarthritis—significant wear and tear on the knee joint. People with knee osteoarthritis have damaged cartilage, which is the shock absorber in joints. When the cartilage begins to wear out, the joint movements aren’t as smooth, and the bones begin to rub against each other causing pain and stiffness. Knee replacement is a treatment option for most people after a course of nonsurgical treatments aren’t successful at relieving the pain and discomfort or your symptoms are interfering with your daily activities. The goal of knee replacement is to make knee movement pain-free, smooth and stable.

Although total knee replacement is a common procedure, people who have arthritic damage in only a single part, or compartment of the knee may be good candidates for partial knee replacement surgery. The medical terms for the different compartments are medial (inner side of the knee), lateral (outer side of the knee), and patellofemoral (where the thigh bone faces the kneecap).

One of the main benefits of partial knee replacement (unicompartmental knee replacement, or arthroplasty) is the preservation of healthy cartilage, bone and ligaments in the unaffected parts of the knee. It is usually a minimally invasive operation with smaller incision instead of one larger one for open knee replacement. With a half-knee replacement—often the medial side—there is a possibility of further wear and tear on the other half. This would require replacing the entire knee joint in another surgery.

If your doctor recommends partial knee replacement, ask your doctor to outline the risks and benefits of partial knee replacement compared to total knee replacement for your particular situation.

Who performs partial knee replacement?

An orthopedic surgeon performs partial knee replacement. This type of doctor specializes in treating injuries and diseases in the musculoskeletal system, which includes all your bones, joints, ligaments, and other body parts that help you move. An orthopedic surgeon can treat your knee problems from diagnosis to treatment to rehabilitation. On top of their regular orthopedic training and expertise, some orthopedic surgeons choose to specialize in one area of the musculoskeletal system, such as the arms, spine, hips or knees.

While all orthopedic surgeons will be able to help you determine whether you need a knee replacement, you should choose a surgeon who specializes in knee replacement and partial knee replacement surgery. If you are considering partial knee replacement, work with a surgeon who has a lot of experience performing the surgery with good results—meaning a very low risk of complications and successful outcomes for patients.

How is partial knee replacement performed?

You will have surgery in a hospital or orthopedic specialty surgery center. Before your surgery date, discuss your anesthesia options with your surgeon. You may have a choice of regional anesthesia, which is when you are awake but numb from the waist down. The surgical team will most likely give you a sedative to make you groggy and relaxed during the procedure. The other option is to be completely asleep using general anesthesia.

The orthopedic surgeon will make a cut in your knee about three to five inches long to ensure the damage is confined to just one part of your knee. Typically, knee imaging beforehand will determine the extent of damage, but if there is more damage to the knee than expected, you may need a total knee replacement instead. Your surgeon should discuss this possibility with you in advance.

Partial knee replacement surgery is less invasive than total knee replacement, and the recovery is much quicker and easier. You’ll be able to start moving again right away. Depending on your overall health and how you fare after surgery, you may have a hospital stay of only one to two days.

What to expect the day of your partial knee replacement

In general, this is what happens the day of the surgery, which typically takes one to two hours:

  • A preoperative nurse will help you prepare for surgery, start an intravenous (IV) line for medications and fluid, and take you to the operating room.

  • You will receive either a general or regional anesthetic.

  • The orthopedic surgeon will make a cut and inspect the knee joint.

  • The surgeon removes the damaged cartilage and bone and prepare the surface for the knee implant (knee prosthesis)—metal components and surfaces—and cements the implant into your joint. A plastic spacer between the metal pieces ensures they slide smoothly when you move your knee.

  • A member of the surgical team will move you to a recovery room immediately after the procedure and monitor you until the anesthesia wears off.

  • A team member will move you to a regular hospital room until your doctor confirms you are stable enough to go home.

What are the risks and potential complications of partial knee replacement?

As with any surgical procedure, a partial knee replacement comes with some risks.

Risks of partial knee replacement surgery

General risks of knee replacement surgery include:

  • Blood clots, which are common in the legs or pelvis and could cause a heart attack or stroke if they travel to your heart or brain

  • Buildup of fluid in the knee joint

  • Infection, which can happen at the surface of your skin or deeper within the surgical site

  • Damage to nearby nerves or blood vessels, although this is uncommon

  • Reaction to the anesthetic

Partial knee replacement complications

Most partial knee replacements are successful, but potential complications include:  

  • Failure of the prosthesis—the replaced joint parts do not remain attached to the knee

  • Dislocation or loosening, which may require additional surgery to secure the new joint

  • Continued pain and stiffness

  • Wear and tear of the new joint, especially if you continue doing high-impact activities such as running. This wear can eventually lead to a total knee replacement surgery.

Reducing your risk of complications from surgery

You can reduce your risk of some surgical complications by:

  • Resuming light activity and possibly physical therapy right away

  • Using a walking aid, such as a cane or crutches, if necessary

  • Taking blood thinners (temporarily) to prevent blood clots from forming

  • Taking a prescription antibiotic to prevent infection

  • Taking pain relievers if your doctor recommends them

  • Notifying your doctor immediately of any concerns, such as bleeding, fever, or increase in pain

  • Telling your surgical team if you have allergies

How do I prepare for partial knee replacement?

To prepare for a partial knee replacement, you can:

  • Prepare your home so you will be able to get around with as little trouble as possible

  • Possibly stop taking certain medicines that could increase your chance of blood clots—as your doctor recommends

  • Possibly stop taking medicines that weaken your immune system—as your doctor recommends

  • Stop smoking

Questions to ask your doctor

Ask your doctor questions well ahead of your partial knee replacement so you will be prepared for the procedure. Some possible questions include:

  • Which medicines can I take the day of my surgery?

  • What medicines will I need after surgery?

  • What exercises are best for my recovery?

What can I expect after partial knee replacement?

Being prepared for what’s next can help you have a smooth recovery from partial knee replacement surgery.

Partial knee replacement recovery

The procedure itself should take one to two hours, and then you’ll begin your recovery. Most people go home the day after partial knee replacement, although sometimes the surgery will mean two days in the hospital. You should be able to walk right away. Most people recover quickly if they have no complications. Partial knee replacement recovery time is typically six to eight weeks. Then you can resume all your normal activities as cleared by your surgeon. Physical therapy for several months will help you continue improving your range of motion.

Will I feel pain?

You may have some pain after the surgery, but pain relievers will help you manage the symptoms. Either over-the-counter or prescription medicines should relieve your pain. People who have a partial knee replacement usually have less pain after surgery than people who have a total knee replacement because the surgery involves less cutting and preserves more of the soft tissue, including muscles.

When should I call my doctor?

Talk with your doctor about follow-up care and appointments after your surgery. Other reasons you may need to call your doctor include:

  • Pain that won’t go away with medication

  • Bleeding

  • Signs of infection, such as pus; a bad smell coming from the incision site; or fever

How might partial knee replacement affect my everyday life?

You should feel less pain after your complete recovery (six to eight weeks) than you felt before your partial knee replacement. Your doctor may recommend you choose more low-impact sports and exercise, such as biking, walking or swimming, rather than high-impact activities, such as jogging, to prevent excessive wear on the new joint.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2017 Nov 10
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  2. Partial Knee Replacement. MedlinePlus, U.S. National Library of Medicine. https://medlineplus.gov/ency/article/007256.htm
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  8. Surgical Wound Infection – Treatment. MedlinePlus, U.S. National Library of Medicine. https://medlineplus.gov/ency/article/007645.htm
  9. Arthritis of the Knee. American Academy of Orthopaedic Surgeons. http://orthoinfo.aaos.org/topic.cfm?topic=a00212
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