A Guide to Patellofemoral Joint Replacement

Your knee joint has three compartments, namely the inner (medial) compartment, the outer (lateral) compartment, and the anterior (patellofemoral) compartment. Arthritis of the knee can affect any one of these areas alone, or in combination.

The symptoms which you have described, the findings on physical examination, the location of your pain, and the results of radiographic studies and prior arthroscopic findings, suggest that the arthritis in your knee is primarily located in the anterior or patellofemoral compartment.

Since a variety of non-surgical interventions like pain medicine, anti-inflammatory medications, cortisone shots, activity modification, physical therapy, and perhaps even arthroscopic surgery, have failed to adequately relieve your arthritic symptoms, isolated patellofemoral replacement may be an excellent option for you. This operation is reserved for patients with severe pain in the front or middle of the knee from cartilage degeneration. It is not used if you have maltracking of the patella.

The advantage of this particular procedure over a total knee replacement is that the surrounding cartilage, which may not be significantly degenerated, the meniscal cartilage, and the ligaments are left alone and not removed as they would have to be in a total knee replacement. However if more widespread arthritis is identified throughout the knee joint, a total knee replacement may be more appropriate. We will discuss before surgery the possibility that at the surgeon’s discretion a total knee replacement may be performed instead of a patellofemoral replacement.

What is a patellofemoral replacement?

This an open surgical procedure, not arthroscopic surgery, so a long surgical incision is made over the center of the knee unless other scars are present, in which case these previous surgical scars may be incorporated into the incision. With this procedure, the patella (knee cap) is cleared of its degenerated cartilage and capped with a plastic prosthetic button. The end of the femur (thigh bone) is also cleared of degenerated cartilage and is then capped with a metal prosthesis. Only the surfaces of the patellofemoral joint are replaced, after having shaved the arthritic ends of the bone. The implant is then "cemented" in place.

Hospital Stay

Patients are usually admitted to the hospital on the morning of surgery. Routine studies will be done prior to surgery on an outpatient basis, and include x-rays of the knee(s) and chest, EKG, urinalysis, and blood studies. It is rare that a blood transfusion is required for patellofemoral arthroplasty, but occasionally patients elect to pre-donate one unit of their own blood, particularly since a total knee replacement may be necessary.

If you experience any signs of infection or illness immediately prior to your admission, such as a cough, cold, sore throat, or urinary tract symptoms, you should call your physician for advice.

At the time of, or prior to, admission into the hospital, an anesthesiologist will discuss with you the preferred type of anesthesia. Although both regional and general anesthesia can be used, we generally advise the patient to respect the advice of the anesthesiologist.

The operation takes approximately 1 ½ to 2 hours. You are then taken to the recovery room where you will remain for approximately two hours or until it is felt that you can safely return to your room. The floor nurses are well trained in handling patients who have undergone knee replacement and special nursing is not generally required.

What to expect after surgery

You will be placed in a machine that moves your knee while you are hospitalized and you will begin physical therapy the morning after surgery. You will be instructed in walking with crutches or a walker initially, and after 6 weeks you will use a cane until your thigh muscles have recovered adequate strength. For some patients the recovery in strength and motion can be as short as six or eight weeks; for others, it may take as long as six months.

You will most likely be discharged from the hospital 3 days after surgery, either to a rehabilitation unit, where you will continue with therapy in an inpatient setting, or to home where you will continue therapy as an outpatient for several months. This varies with each patient depending upon age, health, home setting and location, or your own performance. At all times, your safety and best interests are considered in this decision.

The most apparent benefit of this procedure is pain relief. Most patients experience pain relief with improvement in function within six weeks to three months; however, continued pain reduction can be realized for over a year after surgery. Swelling and aching are common, particularly within the first several months after surgery. All patients will have a small area of numbness to the outer side of the surgical scar. This is inevitable with a vertical incision around the knee. You will be given a pain medication upon discharge.

If the surgery is being performed on your left knee, you may drive an automatic transmission car four weeks after surgery, provided you are not taking narcotic medications or other medications which may affect your ability to operate a motor vehicle. If the surgery is on your right knee, refrain from driving a car until six weeks after the surgery, once again provided you are off narcotic medications.

Remember, you have a knee prosthesis. If you do too much too soon you will find that the knee will swell and become uncomfortable. On the other hand, if you do not move your knee soon enough, you will find that motion is more difficult to achieve. You will be guided through this course of increasing activity and motion.

Staples will be removed approximately 2 weeks after surgery by a visiting nurse. You will return for follow up in the office four weeks after surgery, at which time x-rays will be reviewed.

What are some of the potential problems after patellofemoral replacement?

Like all prosthetic joint surgeries, the majority of complications can be largely avoided. Before surgery you will receive a complete medical examination and testing by a medical doctor. This will help to minimize the risk of medical complications during and after surgery. Additionally, it is mandatory to have a dental evaluation prior to surgery as this will help reduce the risk of infection. Infection is one of the most serious problems after joint replacement surgery and steps are taken to avoid it. Antibiotics are given before and after surgery and the surgical team works in a special laminar flow operating room, using "space suits"; these measures help to reduce the risk of contamination of the surgical wound. You will be given strict instructions after surgery regarding appropriate precautions to take during the life span of your prosthetic implant to help further reduce the risk of infection.

Other complications include the risk of a blood clot, or pulmonary embolism. These complications are rare and you will be placed on a blood thinning medication such as Coumadin, which may help to reduce this risk. Other long-term complications such as wear of the implant or loosening of the parts may occur and these are in part related to over activity. Because of this, I advise that you avoid kneeling, jogging, down hill skiing, or excessive athletic activity. But, you should be able to participate in non-impact activities, like walking several miles, swimming, golfing, dancing, or bowling.

On occasion, the prosthetic patellar component (knee cap) may have a tendency to sublux (slide sideways) because of muscular imbalance. Often times this will correct with time and adequate strengthening of the muscles, but on rare occasions secondary surgery may be necessary to re-align the prosthetic components or exchange the components. Additionally, because only a portion of your knee joint has been resurfaced, the remaining cartilage may degenerate over time. If this occurs and non-surgical intervention fails to relieve your arthritic symptoms, then eventual conversion to a total knee replacement may be necessary.

Other potential risks and complications of this surgery are common to all knee joint replacements and will be discussed with the surgeon and addressed further in the surgical consent form.

Conclusion

The results of patellofemoral replacement can be extremely gratifying. While the procedure may considerably reduce your pain and improve your function, it is important to remember that you have a prosthesis. Use common sense, expect occasional discomfort, and appropriately modify your activities.

Our commitment to you

We are committed to you, the patient. We understand that you may be anxious about your need for surgery.  If you have any questions regarding your treatment, please feel free to contact our staff by calling 215-829-2222.