X-ray of a patellar replacement

Patello-Femoral Arthroplasty

The joint between the underside of the knee cap (patella) and the end of the femur is covered with articular (hyaline) cartilage that can wear out over time.  When this happens, the condition is referred to as patello-femoral osteoarthritis. Degeneration of this joint usually occurs concomitantly with the rest of the knee joint so it is unusual for patients to develop isolated patello-femoral arthritis absent arthritis in other parts of the knee.  The most common reason for this presentation is previous fracture or trauma to the patella or trochelar groove (the shallow trough that the knee cap slides in). In most instances, patello-femoral arthritis is troublesome with a creaking sensation in the knee and pain with moderate activity, especially walking downhill). In a few cases, the pain and mechanical symptoms can be disabling.  For patients with severe pain and mechanical symptoms, patello-femoral arthroplasty may provide good long term pain relief.  Patient selection is critical to achieve a good outcome and the use of this surgery remains somewhat controversial within the field of orthopaedics.  I offer patello-femoral arthroplasty on patients over age 40 with severe osteoarthritis of the patello-femoral joint, a BMI (body mass index) of 30 or less and failure to achieve good pain relief with other treatments including arthroscopic debridement, visco polymer injection such as synvisc or supartz and oral medication.  I have included a link to a recent publication addressing the selection criteria for patients who may be candidates for patello-femoral arthroplasty.

Patello-femoral Selection Criteria, JBJS, 2007

Diagram showing patello-femoral osteo-arthritis

The prosthesis that I currently use for this procedure is manufactured by a company called Stryker, the prosthesis name is Avon.  I have been using this implant for about 5 years and I have been very happy with the clinical results. 

Link to:  Avon Prosthesis

The surgery takes roughly 1 hour and I admit patients overnight for pain control.  I prefer to do the procedure under a spinal anesthetic because pain control after surgery is much easier if patients have a spinal anesthetic.  In addition, many patients receive an additional femoral nerve block after the surgery.  This numbs the area over the front of the thigh and knee for about 18-24 hours after surgery. I have patients begin physical therapy by standing the night of surgery and more vigorous therapy begins on the second hospital day. Most patients use a continuous passive motion machine (CPM) the day after surgery and continuing after discharge from the hospital.  I allow patients to put their full weight on the leg right after surgery, albeit with some help from the physical therapists. Most patients go home on the second day after surgery

Knee CPM Machine

Most total knee implants are designed to last somewhere between 15-25 years.  The factors that influence the rate of wear of the polyethylene liner (the plastic portion of the total knee that wears out over time) include activity level (running and impact activities are discouraged as they increase wear), weight (obesity is one of the primary risk factors for total knee arthroplasty mechanical failure) and manufacturing characteristics of the polyethylene. I do not offer total knee arthroplasty in patients with a BMI (Body Mass Index) of greater than 40 ( this is the objective definition of morbidly obese). The reasoning is that the relative risk of complications including infection, wound problems, soft tissue balancing problems, patellar tracking problems and component malpositioning are 2-3 times higher in morbidly obese patients.  I would recommend patients seek help to get their BMI down to a safe level before proceeding with a total knee replacement under less than ideal circumstances.  I would suggest the article link below helpful in understanding the scientific basis for my decision.

 Obesity and Knee Replacement Surgery, JBJS-2004

After surgery all patients are started on a medication called low molecular weight heparin to prevent blood clots in the veins of the pelvis and leg, which is the single most common complication after surgery. The medication that I use currently is called Lovenox and I have included a link below:

 Lovenox

I have included a link to my post-op total knee instruction sheet which covers a number of questions about what to expect in the hospital, what types of exercises to do, how long you will be in the hospital and what to expect after surgery.  This should answer most of the questions you will have.

Patello-Femoral Arthroplasty  Post Op Instructions