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Letters to the Editor to:

Scientific Articles:
Domenick J. Sisto and Vineet K. Sarin
Custom Patellofemoral Arthroplasty of the Knee
J Bone Joint Surg Am 2006; 88: 1475-1480 [Abstract] [Full text] [PDF]
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Electronic letters published:

[Read Letter to the Editor] Custom Patellofemoral Replacement in thePresence Of Trochlear Dysplasia
Ronald P. Grelsamer   (9 August 2006)
[Read Letter to the Editor] Drs. Sisto and Sarin respond to Dr. Grelsamer
Domenick J Sisto, M.D., Vineet K Sarin PhD   (9 August 2006)

Custom Patellofemoral Replacement in thePresence Of Trochlear Dysplasia 9 August 2006
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Ronald P. Grelsamer,
Orthopaedic Surgeon
Mount Sinai Medical School, New York, NY

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Re: Custom Patellofemoral Replacement in thePresence Of Trochlear Dysplasia

Ronald.Grelsamer{at}mountsinai.org Ronald P. Grelsamer

To The Editor:

Young patients with isolated patellofemoral arthritis not uncommonly have a dysplastic trochlea. Instead of being concave, the trochlea is flat or even convex. In such a setting I have always worried that a custom implant that duplicates the articulating anatomy of the patient's patella (convex) will lead to an unstable construct. The authors do not appear to have encountered this problem. Could they comment on this?

As an aside, I would think that their patellofemoral replacement (or any other) would be equally indicated in the frail and elderly population where deterioration of the other compartments is not likely to take place in their lifetime.

The author(s) of this letter to the editor did not receive payment 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, educational institution, or other charitable or nonprofit organization with which the author(s) are affiliated or associated.
Drs. Sisto and Sarin respond to Dr. Grelsamer 9 August 2006
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Domenick J Sisto, M.D.,
Orthopaedic Surgeon
Los Angeles Orthopaedic Institute,
Vineet K Sarin PhD

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Re: Drs. Sisto and Sarin respond to Dr. Grelsamer

laortho1{at}yahoo.com Domenick J Sisto, M.D., et al.

We thank Dr. Grelsamer for his interest in our study and for the opportunity to discuss the custom approach to patellofemoral arthroplasty in more detail. Dr. Grelsamer correctly observes that our published series does not include patients with a flat or convex femoral trochlea. While we agree that treatment of patients with isolated patellofemoral arthritis and concomitant severe trochlear dysplasia can be a challenge, we believe that a custom approach to patellofemoral arthroplasty is a reasonable treatment option for this indication.

The posterior (articulating) surface of the custom patellar implant is designed to replicate the native surface and is defined by a pre-operative computed tomography scan. In contrast, the prosthetic femoral trochlea is designed to conform to the articular radius of the mating patella implant and is thickened laterally and medially along its borders to compensate for any lack of native medial-lateral stability. The thickness of the custom implant along the patellar tracking arc is designed to reestablish the anterior position of the femur.

Stability of the implant construct and extensor mechanism is fundamental to the successful outcome of any patellofemoral arthroplasty, including the custom approach. The presence of trochlear dysplasia, as Dr. Grelsamer points out, further underscores the importance of achieving a stable and balanced extensor mechanism intra-operatively. A convex trochlea may increase the tendency to overstuff the patellofemoral joint and this possibility must be addressed during design of the custom implant and during the implantation procedure.

Finally, we agree with Dr. Grelsamer that patellofemoral arthroplasty is indicated in the elderly patient with isolated patellofemoral arthritis whose medial/lateral compartments would not be expected to become symptomatic during their lifetime. The purpose of our study, though, was to report on the use of custom patellofemoral arthroplasty in a younger population.