Copyright © 2006 by The Journal of Bone and Joint Surgery, Inc.
Commentary & Perspective
Commentary & Perspective by
Ronald P. Grelsamer, MD*,
Department of Orthopaedic Surgery, Mount Sinai Medical Center, New York, NY
Posted November 2006
The conversion of tibiofemoral unicompartmental knee replacements
has already been discussed in the literature1, but the article by
Lonner et al. is the first article, to my knowledge, to investigate patellofemoral unicompartmental knee replacement
surgery.
To those of us with an interest in patellofemoral
replacement surgery, the results reported by Lonner et al. are not surprising.
A patellofemoral replacement should lend itself to a relatively easy conversion
to a total knee replacement, in comparison with other knee revision procedures.
Very often the patellar component can be retained.
Patellofemoral replacements, however, are available in an ever-increasing
variety of models, not all of which may present the same ease of conversion.
Some models are of the resurfacing type, whereby minimal bone is resected from
the femoral trochlea. The DePuy LCS (Low Contact Stress; DePuy, Warsaw,
Indiana) and the Smith and Nephew Richards
III (Smith and Nephew Richards, Memphis, Tennessee)
are representatives of such implants. Conversely, the Stryker Avon (Stryker
Orthopaedics, Limerick, Ireland) and the Ceraver Hermès (Ceraver Osteal, Paris, France)
require resection of the anterior aspect of the femoral condyles. In these systems, the
femoral-trochlear component resembles the anterior aspect of a total knee
replacement. On the patellar side, the component may be dome-shaped, but, in
the case of the LCS, it is shaped "anatomically" and rotates on a metallic base.
Converting a trochlear resurfacing implant to a total knee replacement
should be straightforward. However, if placement of the trochlear component has
already required the anterior cut that is also required for a total knee
replacement, then the angle of that cut, if suboptimal (e.g., insufficient
external rotation), will need to be addressed at the time of the conversion.
The article by Lonner et al. also highlights the
complications that are well known to every experienced patellofemoral
replacement surgeon. These include subsequent tibiofemoral deterioration. When
patellofemoral arthritis is of indeterminate cause, the patellofemoral
involvement can be just a prelude to global knee arthritis, and an isolated
patellofemoral replacement may be only the first of at least two arthroplasties.
Patients with the best results after isolated patellofemoral arthroplasty tend
to be those in whom patellofemoral arthritis is the result of malalignment,
dysplasia, or trauma2. In the absence of such a specific cause, isolated
patellofemoral replacement surgery is best reserved for the patient who is deemed
too young to undergo total knee replacement, as mentioned by Lonner et al. In
my opinion, the older, frail patient with isolated patellofemoral arthritis is
also a candidate for patellofemoral replacement surgery regardless of the cause
of osteoarthritis, since tibiofemoral degeneration of any clinical consequence
is not likely to occur in his or her lifetime.
A second point brought out by Lonner et al. is that patients
with isolated patellofemoral arthritis often demonstrate malalignment of the
extensor mechanism. This malalignment can be severe, which accounts for its occasional
persistence following patellofemoral replacement surgery. Some patellofemoral
replacements, such as the DePuy LCS and the Smith and Nephew Richards III,
feature a particularly deep, retentive trochlear groove, but even this can be
insufficient. Consideration can be given to resurfacing the patella first, and
then aligning the prosthetic trochlea under it, rather than the other way
around3.
On a minor note, because the LCS patella is not a dome, I must
assume that, contrary to the authors' assertion, at least one patellar
component had to be removed and converted to a domed patella. Also, I was
surprised that a patient would require plica excision despite two knee
replacement procedures. I am not aware of a "retained plica" as a source of
pain following total knee replacement surgery, but this is certainly food for
thought. Finally, two manipulations in a series of twelve operations strikes me
as being high, but perhaps the authors are more liberal than I am with regard
to the indications for manipulation.
All in all, this paper represents an important addition to
the orthopaedic literature.
*The author did not receive any outside funding or grants in
support of his research for or preparation of this work. Neither he nor a
member of his immediate family received payments or other benefits or a
commitment or agreement to provide such benefits from a commercial entity. No
commercial entity paid or directed, or agreed to pay or direct, any benefits to
any research fund, foundation, division, center, clinical practice, or other
charitable or nonprofit organization with which the author, or a member of his
immediate family, is affiliated or associated.
References
1. Padgett DE, Stern SH, Insall JN. Revision total knee arthroplasty for failed unicompartmental replacement. J Bone Joint Surg Am. 1991;73:186-90.
2. Grelsamer RP, Stein DA. Patellofemoral arthritis. J Bone Joint Surg Am. 2006;88:1849-60.
3. Cartier P, Sanouiller JL, Khefacha A. Long-term results with the first patellofemoral prosthesis. Clin Orthop Relat Res. 2005;436:47-54.
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