What is a patellofemoral replacement?

Patellofemoral replacement is done when you have arthritis that is isolated to the patellofemoral joint.  The patellofemoral joint is the joint surface underneath the patella and the trochlea, which is the groove where the kneecap resides while the knee bends.  This joint is very prone to wear and tear, especially in people who do lots of squatting.
The patellofemoral replacement fixes arthritis if it is only located under the kneecap, as seen in the picture.

How do I know if it is my patellofemoral joint?

X-Ray and clinical exam must be performed to determine if there is arthritis in the patellofemoral joint.  Typical complaints are usually severe pain going up and down stairs, isolated swelling to the front of the knee, grinding under the knee cap and pain with deep bending.
The procedure is rare due to the fact that this pattern of arthritis is not very common.  Most of the time, patients present with arthritis and have degenerative issues elsewhere in the knee, therefore, they are not candidates for the patellofemoral replacement.

Illustration showing severe wear and tear arthritis of the patellofemoral joint.

Treatment

As is the case in most orthopedic surgery, the mainstay of treatment is physical therapy and cortisone shots.  If these fail, an MRI may be ordered to further look at your knee and understand exactly where the arthritis is located. 
Surgery is indicated for those who fail conservative management.  The surgeon must evaluate multiple factors to see if you are a candidate for a patellofemoral replacement.

X-Ray showing a partial knee replacement in excellent position.

Rehabilitation

Like other joint replacement procedures, the recovery is very difficult.  Immediate weight bearing and therapy are started post operative day 1.  The procedure is routinely done as an outpatient.  Usually it takes around 3-4 months before patients feel significantly better.  Full range of motion should be attained within the first 2-3 weeks of surgery.  Swelling is very common for the first few months after surgery as well.