DefinitionA partial knee replacement is surgery to replace either the inside (medial) or outside (lateral) parts of the knee. It is called a partial replacement because only one part of the damage knee is replaced.See also: Total knee replacementAlternative NamesUnicompartmental knee arthroplasty; Knee replacement - partial; Unicondylar knee replacement; Arthroplasty - unicompartmental knee; UKA; Minimally invasive partial knee replacementDescriptionPartial knee replacement surgery removes damaged tissue and bone in the knee joint and replaces the area with a man-made implant, called a prosthetic.Before surgery, you will be given anesthesia, which is medicine that blocks pain. You will have one of two types:General anesthesia makes you unalert and unable to feel pain.Regional ( spinal or epidural) anesthesia numbs you below your waist. You will also receive medicines to make you relax or feel sleepy.The surgeon will make a cut over your knee.This cut is about 3 to 5 inches long.Next, the doctor examines the entire knee joint. If there is damage to more than one part of your knee, you may need a total knee replacement. Most of the time, however, this is not needed.The damaged bone and tissue is removed.A man-made part made of plastic and metal is placed into the knee.Once it is in the proper place, it is secured with bone cement.The wound is closed with stitches.Why the Procedure Is PerformedThe most common reason to have a knee joint replaced is to relieve severe Arthritis pain. Your doctor may recommend knee joint replacement if you have:Symptoms of knee arthritis, including knee pain that keeps you up at night or prevents you from doing daily activitiesKnee pain that continues despite other treatmentsYou will need to understand what surgery and recovery will be like.Partial knee arthroplasty may be a good choice if you have arthritis on only one side of the knee, and you:Are older, thin, and not very activeDo not have very bad arthritis on the other side of the knee or under the kneecapHave only minor deformity of the kneeStill have good range of motion in the kneeHowever, most people with knee arthritis have a surgery called a total knee arthroplasty (TKA).Knee replacement is usually done in people age 60 and older.RisksRisks for anesthesia include:Problems breathingReactions to medicationsRisks for any surgery include:BleedingInfectionRisks for UKA include:Blood clotsFluid buildup in the knee jointImplant failureNerve and blood vessel damagePain with kneelingReflex sympathetic dystrophy (rare)Before the ProcedureAlways tell your doctor or nurse what drugs you are taking, including herbs, supplements, and medicines bought without a prescription.During the 2 weeks before your surgery:Ask your doctor which medicines you can still take on the day of your surgery.You may be asked to stop taking medicine that make it harder for your blood to clot. These include aspirin, ibuprofen (Advil, Motrin), naproxen (Naprosyn, Aleve), and other drugs.You may need to stop taking any medicines that weaken your immune system, including Enbrel and methotrexateIf you have diabetes, Heart disease, or other medical conditions, your surgeon will ask you to see the Doctor Who treats you for these conditions.Tell your doctor if you have been drinking a lot of alcohol (more than one or two drinks a day).If you smoke, you need to stop. Ask your doctor or nurse for help. Smoking slows healing and recovery.Let your doctor know if you get a cold, flu, fever, herpes breakout, or other illness before your surgery.You may want to visit a physical therapist before surgery to learn exercises that can help you recover.Practice using a cane, walker, crutches, or a wheelchair. You will need to learn how to: Get in and out of the showerGo up and down stairsSit down to use the toilet and stand up after using the toiletUse the shower chairOn the day of your surgery:You will usually be asked not to drink or eat anything for 6 - 12 hours before the procedure.Take the drugs your doctor told you to take with a sip of water.Your doctor or nurse will tell you when to arrive at the hospital.After the ProcedureMost patients go home the day after surgery.You can put your full weight on your knee right away.After surgery, you will be encouraged to do as much as you can for yourself. This includes going to the bathroom or taking walks in the hallways, always with someone helping you.Most patients recover quickly and have much less pain than they did before surgery. People who have a partial knee replacement recover faster than those who have a total knee replacement.Outlook (Prognosis)Many patients are able to walk without a cane or walker within 3-4 weeks after surgery. You will need physical therapy for 4 to 6 months.Most forms of exercise are okay after surgery, including walking, swimming, and biking. However, you should avoid high-impact activities such as jogging.ReferencesCrockarell JR, Guyton JL. Arthroplasty of the knee. In: Canale ST, Beatty JH, ed. Campbell's Operative Orthopaedics. 11th ed. Philadelphia, Pa: Mosby Elsevier;2007:chap 6.Berger RA, Meneghini RM, Jacobs JJ, et al. Results of unicompartmental knee arthroplasty at a minimum of ten years of follow-up. J Bone Joint Surg Am. 2005;87(5):999-1006.Patil S, Colwell CW Jr, Ezzet KA, et al. Can normal knee kinematics be restored with unicompartmental knee replacement? J Bone Joint Surg Am. 2005;87(2):332-338.Richmond J, Hunter D, Irrgang J, et al. American Academy of Orthopaedic Surgeons. Treatment of osteoarthritis of the knee (nonarthroplasty). J Am Acad Orthop Surg. 2009;17:591-600.Reviewed ByReview Date: 09/23/2011C. Benjamin Ma, MD, Assistant Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.