|Arthritis of the patella is one of the many causes of knee pain.
The knee can be likened to an apartment with 3 rooms. There are 3 "compartments". The "medial" compartment towards the inside of the knee, the "lateral" compartment towards the outside of the knee, and the "patello-femoral" joint, i.e. the kneecap and the underlying groove.
On rare occasions, arthritis affects just the kneecap and/or the underlying "trochlear" groove.
The treatment you are offered will depend in part on where you live. "Geography is destiny!" It will also depend on your age.
Generally speaking your (surgical) choices are the following:
- A "tibial tuberosity transfer" (a.k.a. tibia tuberosity osteotomy). The bump on which your patellar tendon attaches is moved. It is moved up, down, left or right depending on the surgeon's preference.
- These osteotomies go by the name "Roux", "Elmslie-Trillat", "Maquet", "Fulkerson", depending on which way the tuberosity is moved and what country you live in. The idea is to shift the load on the kneecap to a part of the kneecap that is still healthy - assuming there is such an area.
- A "patellectomy". The kneecap is removed outright. Sometimes this works. But removing the kneecap doesn't address any raw bone that might exist on the opposing trochlea. In some people the knee is weakened, and in some people it may hasten the onset of arthritis in the rest of the knee. Also there's no turning back. Once the kneecap has been removed, there's no putting it back. However, if your knee is infected in addition to being arthritic, the patellectomy moves up on the list of options.
Removing the hard bone under the worn out cartilage. There are two types of bone in the body: cortical and cancellous. Cortical is hard, wood-like. Cancellous bone is soft, spongy. The shell of the kneecap is cortical, the inside is cancellous. In a "spongialization" procedure (yes, that's the name!), the hard shell right under the (worn out) cartilage is removed leaving the spongy bone exposed.
Pain is transmitted through nerves. If you cut the nerves going to the kneecap, there shouldn't be any more pain. But of course it isn't possible to cut the myriad tiny pain fibers coming from the kneecap, and you can't get to the nerves coming from the trochlear groove at the end of the thigh bone.
Cartilage Culture / Transplant
Patients with a very localized area of cartilage wear in the knee, say from an accident, are potential candidates for having some form of cartilage transplant. Cartilage is harvested from the person's knee, grown in a lab, and placed into the area that is worn down. It is specifically contra-indicated in people with a gradual, arthritic process. Thus, by and large, people with kneecap arthritis are excluded. In time this may change.
Total Knee Replacement
This replaces every compartment in your knee. The advantage to this approach is that everything in the knee that could eventually break down is replaced. Also most orthopaedic surgeons are familiar with this procedure. The downsides include: a major surgical dissection, the need for blood pre-donation and/or transfusion, a lengthy recovery (bending and straightening of the knee requires major work for many weeks), and for many patients much less bending ability than they would really like.
It is officially called a "patello-femoral replacement" (PFR) because it replaces the patella (kneecap) and the trochlea, the groove at the end of the thigh bone (femur). Performing this procedure is one of our specialties.
The history behind such replacements is quite interesting. Surgeons first replaced just the kneecap, leaving the trochlea untouched. Over the last 25 years, surgeons have replaced both the kneecap and the trochlea. The replacement of the kneecap consists of a plastic button that is fixed to the undersurface of the kneecap. The replacement of the trochlea is a metallic piece that looks a bit like a shield that is shaped like a trochlea.
The PFR is a form of partial knee replacement, in contradistinction to the classic "total knee replacement" where 2 or 3 of the knee's compartments are replaced. The popularity of such devices is very geographical.
In the United States, there had been some initial interest. Failures were reported. These failures were unrelated to the basic concept of a kneecap replacement, but they were failures nonetheless. The baby was thrown out with the bathwater and the procedure fell into oblivion in the USA. However, the procedure retained a measure of popularity in Europe where techniques and implants were refined. The procedure is again available in the United States.
The major downside to this and any other partial replacement is that the other parts of the knee might eventually deteriorate, thus requiring conversion to a total knee replacement. Also very few surgeons have performed this procedure. The question then is "why not do the total replacement in the first place?" The answers are the following:
- A PFR requires much, much less surgical dissection.
- There is much, much less blood loss.
- The mobility is better (easier to bend the knee)
- The recovery is much quicker (the knee bends well within a few days of surgery and the bending requires minimal effort. This not the case for a total knee replacement).
- Some patients are clearly at minimal risk of having the rest of the knee deteriorate significantly in their lifetime (elderly patients).
- Certain patients are simply too young to have their entire knee replaced.
A number of options are available all of which have their pros and cons. No single solution fits all patients. Your place of residence will greatly influence the choice(s) you are offered and the preference of your surgeon.
*Adapted from What Your Doctor May NOT Tell You About Knee Pain and Surgery, R Grelsamer, MD, Warner Books 2004.