Frequently Asked Questions

Knee Surgery Specifics

How long will my knee incision be?

Total knee replacement usually requires an incision of 5-6 inches depending on the size of the patient. Partial knee replacement can be done through a 3 inch incision. In knees that are very large , or very stiff , or have severe deformity , a larger incision will be required.

Is the kneecap removed in a knee replacement?

No. Only the articular (joint side) surface is replaced with a new plastic surface in a total knee replacement (TKR). Typically this requires the removal of an 8mm thick slice of bone. The kneecap surface is usually not replaced in a partial knee replacement (unicompartmental knee replacement , UKR).

If my knee is bowed or knock-kneed, can you correct this?

Yes. In fact it is vital that we correct a deformity of your knee as much as possible in order to make the TKR last as long as possible. A TKR is required if significant deformity exists. A UKR cannot be performed in this situation.

Will my knee motion improve after TKR?

Pain relief is usually excellent with TKR , but range of motion usually increases only slightly after a TKR. This is because we are only replacing the painful surface of the knee. We are not replacing all the ligaments , muscles , and tendons around the knee joint.

What type of partial knee replacement do you use?

I use the Persona partial knee. Both components are fixed to the bone with cement. The bearing surface is metal against plastic.

Who can have a partial knee replacement versus a total knee replacement?

The knee is divided into three sections (compartments). If two or three of these compartments are worn out , a total knee replacement is required. However , if only one compartment is worn out , a much less invasive UKR can be performed to only replace the two surfaces of the single bad compartment. People who are severely obese (BMI greater than 35) or have a severe deformity of their knee , also require a TKR. Approximately 10% of people who need knee replacement are candidates for a UKR.

How durable are knee replacements?

This depends on age , weight and activity. In most older patients (greater than 65) a TKR will last 10-15 years. Partial knee replacements last approximately 8-10 years. However , UKRs are much less invasive. Less bone is removed , no ligaments are removed and the knee has a more stable and normal feeling than a TKR. I would recommend a UKR over a TKR whenever this is possible (only 10% of the time) , especially in a younger person.

What type of bearing surface does a knee replacement use?

Unlike hip replacement , ceramic on ceramic , crosslinked polyethylene , and metal-metal bearings are not possible in knee replacements. Most total knee replacements contain a cobalt chrome metal bearing against polyethylene.

What is a mobile bearing knee?

The plastic portion of a tibial component is usually fixed to the metal tibial base plate. In some knee designs , the plastic component is allowed to "float" on the metal tray. There is a hope that these types of implants may last longer before the plastic is worn out. However , despite heavy advertising there is currently no convincing evidence that these are more durable or allow greater range of motion than a fixed bearing total knee replacement. Despite the media hype as "new" implants , these implants have been around for many years. In fact , I was involved in a study of the Depuy LCS mobile bearing knee versus the Howmedica PCA fixed bearing knee while I was a resident at Johns Hopkins Hospital. We found no significant differences in the complications , performance , or durability of these two implants at four years follow up after surgery. However , I continue to be intrigued by the design concepts of a mobile bearing and hope to start a comparative study of fixed versus mobile bearings in the future.

What is a partial knee replacement?

Approximately 1/3 of the knee joint surface is replaced (compared to total knee replacement). The knee can be divided into three compartments. If only one of these three is worn out , a partial knee replacement can be performed. The chief advantages of this procedure are a quicker recovery with better range of motion and stability. The hospital stay is typically 1-2 days , physical therapy is usually only required for two weeks and a walker or cane is usually discontinued after two weeks.

How much bone is removed for a knee replacement?

The term total knee replacement sounds somewhat drastic. This operation would be better named a surface replacement of the knee. The remaining cartilage and approximately 5-10 mm of bone is removed from the ends of all of the bones: femur , tibia , and patella. Three artificial component surfaces are then fixed to the ends of these bones. The anterior cruciate ligament and sometimes the posterior cruciate ligament are removed when this surgery is performed. Much less bone is removed in a partial knee replacement (unicompartmental knee replacement , UKR).

What type of knee replacement do you use?

I currently use the Persona partial knee system. Whenever the bone quality is good , I use an uncemented femoral component. The tibial and patellar components are currently always cemented.

Phone Consultation

If you are interested in determining if you are a candidate for surgery, please mail your completed new patient forms to the office and include a digital x-ray. Dr. Gross will call you back to discuss your options.

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