Patellofemoral Arthroplasty
Authors: Odgaard Anders , Eldridge Jonathan , Madsen Frank 
Published: April 2019

Update
This article was updated on June 19, 2020, because of a previous error. On page 5, Figure 4 has been rotated 180° in order to clarify the view for the reader. In addition, the legend that had previously read “View of a left knee from above (the surgeon's view). The trochlear wear is mainly in the medial part. Similarly, the patellar changes were also mainly medial. This wear pattern is unusual” now reads “Intraoperative view of the trochlear portion of the distal part of a left femur (with the medial side of the femur on the left side of the photograph and the lateral side on the right). The trochlear wear is mainly on the medial side. Similarly, the patellar changes were also mainly medial. This wear pattern is unusual.”
An erratum has been published: JBJS Essent Surg Tech. 2020 July 9;10(3):e0094ER.

Background:
The first report of patellofemoral arthroplasty (PFA) was published in 1979
1
. Reviews in 2005 and 2007
2,3
called for studies comparing PFA with total knee arthroplasty (TKA) for isolated patellofemoral osteoarthritis. A blinded randomized controlled trial (RCT) was initiated in 2007 for this purpose, and the first report with 2-year results was awarded the Mark Coventry Award of the Knee Society in 2017
4
. It was found that (1) patients recover more quickly from PFA than from TKA; (2) during the first 2 years after surgery, PFA-treated patients have better average knee function than TKA-treated patients; and (3) PFA-treated patients regain their preoperative range of movement within the first postoperative year whereas TKA-treated patients do not regain it within the first 2 years
4
.

Description:
There are general principles that are common to all brands of PFA implants. These include (1) an indication based on bone-on-bone contact in the patellofemoral joint with a preserved tibiofemoral joint; (2) replacing all surfaces of the patellofemoral joint, with metal on the femoral side and polyethylene on the patellar side; (3) ensuring a smooth transition from normal articular cartilage to the trochlear component; and (4) creating normal patellofemoral tracking.

Alternatives:
The primary treatment of any degenerative condition should be nonoperative, but when such measures are insufficient surgical treatment may be indicated. Many procedures have been suggested for relieving patellofemoral pain, but if there is bone-on-bone contact in the patellofemoral joint, the only current surgical option (except for experimental treatments) is joint replacement—i.e., either PFA or TKA.

Rationale:
Our general principle for joint replacement of the knee is to replace only the affected compartment if unicompartmental changes are found. If ≥2 compartments are affected, we perform TKA. This principle is challenged both by proponents of performing TKA in all cases of knee osteoarthritis and by proponents of bicompartmental knee replacement for 2-compartment disease. The 2-year results of our blinded RCT comparing PFA and TKA
4
support our current practice of PFA. In our practice, we have found PFA to be a rewarding procedure when the correct indications are used. PFA is likely to remain a fairly rare procedure, but any knee arthroplasty center should be able to offer it.