Partial Knee Replacement - WordPress.com · knee and replaces it with prosthetic implants. Unlike a total knee replacement, which removes all of the cartilage, a partial knee replacement

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Partial Knee Replacement

A partial knee replacementremoves damaged cartilage fromthe knee and replaces it withprosthetic implants. Unlike a totalknee replacement, which removesall of the cartilage, a partial kneereplacement typically removes andreplaces cartilage from oneparticular region. The procedure isalso known as a unicompartmentalknee replacement, a uni, or partialknee resurfacing. A variation calleda bicompartmental replacementcan also be done to repair tworegions, but is less common. Thisanimation focuses on aunicompartmental partial kneereplacement.

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Dr. Brian Cole • 1611 W. Harrison Street • Suite 400 • Chicago, IL 60612 • 708.236.2701

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IntroductionA partial knee replacement removes damaged cartilage from theknee and replaces it with prosthetic implants. Unlike a total kneereplacement, which removes all of the cartilage, a partial kneereplacement typically removes and replaces cartilage from oneparticular region. The procedure is also known as aunicompartmental knee replacement, a uni, or partial kneeresurfacing. A variation called a bicompartmental replacement canalso be done to repair two regions, but is less common. Thisanimation focuses on a unicompartmental partial kneereplacement.

Doctor's Personal Note: A Message From Your DoctorThank you for visiting our website and viewing our 3D Animation Library. These animations should

assist you in better understanding your condition or procedure. We look forward to answering any

additional questions you may have at our next appointment.



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Knee AnatomyThree bones comprise the knee joint: the patella (knee cap), thefemur (thigh bone), and the tibia (shin bone). The patella is arounded triangle-shaped bone embedded within the quadricepstendon above it and the patellar tendon below. The two large,knob-like protuberances at the base of the femur, called thefemoral condyles, form the top of the knee. The back surface ofthe patella, weight bearing portions of the femoral condyles, andthe top of the tibia (tibial plateau) are lined with articular cartilage,which minimizes friction and helps prevent damage to the bonesduring movement. The knee’s side-to-side motion is stabilized bythe collateral ligaments (medial and lateral), and the cruciateligaments (anterior and posterior) prevent excessive back and forthmotion while allowing the knee to flex and extend.

The knee can be divided into three compartments: the medialcompartment is between the femoral condyle on the inside of yourknee and the tibial plateau; the lateral compartment exists betweenthe outer condyle and the tibial plateau; and the patellofemoralcompartment is the region between the patella and femoralcondyles. A partial knee replacement can be done in any of thesecompartments, but is most common in the medial compartmentwhere degenerative arthritis (osteoarthritis) tends to occur morefrequently.



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Patient CriteriaPartial knee replacements are reported to feel more natural thantotal knee replacements, but ideal candidates must fit selectioncriteria. For optimal results, unicompartmental knee replacementcandidates should have significant arthritic damage confined toone knee compartment; if arthritis is widespread, a total kneereplacement may be recommended. Partial knee replacements arerestricted to patients who are not obese and who have healthyknee ligaments, particularly an intact ACL. Also, the cartilagedamage should not be the result of anatomic knee alignmentproblems that may be better treated with different procedures.Other criteria used to determine whether a partial replacementprocedure is appropriate include age, range of knee motion, bonestructure, and the amount of exercise a person gets. Theseselection criteria help reduce the number of patients needingrevision surgery or a total knee replacement at a later date.



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Implant Materials & DesignA variety of partial knee replacement implant designs exist. Ingeneral they are made out of metal alloys and synthetics, such asdense polyethylene plastics or ceramics, that are well toleratedinside the body. The metal components typically move against thesynthetic components to minimize wear from abrasion. For medialor lateral compartment replacements, prosthetics will be cementedto bone to create a new moving surface between a femoralcondyle and the tibial plateau. The femoral component is usually acurved metal cap that emulates the shape of the condyle. Thetibial component is usually a metal plate topped with a syntheticbearing that may be either fixed or mobile. Fixed bearing implantsare secured to the tibial platform, whereas mobile bearing implantsmove on the base, allowing for a limited amount of joint rotation. Ifthe partial knee replacement is performed in the patellofemoralcompartment, the cartilage surface of the patella is removed andreplaced with polyethylene that articulates with a metal femoralcomponent.

PreparationDetailed X-rays will indicate the extent of knee damage and willhelp with preoperative measurements. You will be positioned onyour back for the procedure and may undergo general anesthesia,which may be administered by intravenous injection or as a gasthat puts you to sleep; regional anesthesia, in which a small tubecalled an epidural catheter delivers medication to the spinalcolumn, numbing you from the waist down; or a femoral nerveblock that numbs the surgical region. A tourniquet may be appliedto control bleeding, and your knee will be free to be placed in abent position to enable access to the joint surfaces. Once prepped,a partial knee replacement procedure generally takes one to twohours to complete.



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Procedure – Preparing the Joint SurfacesSurgical details vary by procedure and component design.Generally, a three to five inch incision is made above the damagedcompartment at the front of your knee. Muscle and fatty tissue arecarefully moved aside, and the patella is shifted to one side toprovide access to the femur and tibia in the affected compartment.The degenerative cartilage is removed, and some underlying boneis usually cut and sculpted to allow the implants to be cemented inplace. Some procedures involve computer-assisted 3D imagingand micro-robotic instruments to aid in removing damaged partsand cutting bone, while other procedures use manual instrumentswith precision guides.

If the patella needs resurfacing, a series of similar steps are usedto remove the damaged cartilage and prepare for the implant.

Procedure – Fitting the ImplantsOnce implant sites are prepared and tested, the prostheses arepositioned and cemented in place. Any excess cement is removed.For a medial or lateral compartment resurfacing, the bearingsurface is usually affixed to the tibial plate by press-locking orimpacting it into place to complete the repair. After proper motionand function are confirmed, the various layers of tissue that hadbeen separated are joined with resorbable (absorbable/dissolving)sutures and the skin incision is sealed with sutures or surgicalstaples. A bandage will be wrapped around your knee and you willbe taken to recovery



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Recovery and ResultsThe smaller incision used for a partial knee replacement makes fora quicker recovery than a total knee replacement. Some partialknee replacements are done as outpatient procedures, buttypically you will spend a night or two in the hospital. Range ofmotion exercises and bearing weight on the repaired knee areusually recommended immediately after surgery with physicaltherapy starting as soon as possible. Pain that can be managedwith medication and some discoloration following the procedureare normal and will subside with time. Non-absorbable sutures orstaples are typically removed within two weeks, and most peoplecan walk unassisted within a month after surgery. It generallytakes about six weeks for you to feel that your knee has recoveredand you can resume most normal activities. When performed onproperly selected patients, partial knee replacements exhibit goodlong-term results with a high degree of patient satisfaction.



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Partial Knee Replacement - WordPress.com · knee and replaces it with prosthetic implants. Unlike a total knee replacement, which removes all of the cartilage, a partial knee replacement