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Letters to the Editor to:

Surgical Techniques:
Matthew J. Kelly, Mustasim N. Rumi, Milind Kothari, Michael A. Parentis, Katrina J. Bailey, William M. Parrish, and Vincent D. Pellegrini, Jr.
Comparison of the Vastus-Splitting and Median Parapatellar Approaches for Primary Total Knee Arthroplasty: A Prospective, Randomized Study. Surgical Technique
J Bone Joint Surg Am 2007; 89: 80-92 [Abstract] [Full text] [PDF]
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Electronic letters published:

[Read Letter to the Editor] Patellofemoral Joint Radiographs
Alan C. Merchant, M.D.   (7 May 2007)
[Read Letter to the Editor] Dr. Pellegrini et al. respond to Dr. Merchant
Vincent D. Pellegrini, Jr., M.D., Matthew J. Kelly, M.D., Mustasim N. Rumi, M.D., Milind Kothari, DO, Katrina J. Bailey, PT, William M. Parrish, M.D., Michael A. Parentis, M.D.   (7 May 2007)

Patellofemoral Joint Radiographs 7 May 2007
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Alan C. Merchant, M.D.,
Research Consultant
Clinical Professor, Stanford University, Stanford, CA

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Re: Patellofemoral Joint Radiographs

kneemd{at}sbcglobal.net Alan C. Merchant, M.D.

To The Editor:

The otherwise excellent article, "Comparison of the Vastus-Splitting and Median Parapatellar Approaches for Primary Total Knee Arthroplasty: A Prospective, Randomized Study. Surgical Technique" by Matthew J. Kelly, et al. was marred by an error in the legend of Figure 1. The axial view radiograph of the knee was mislabeled as "a Merchant radiograph of the patella".

The shape and appearance of the distal femur on the film demonstrates that it is really a Settegast view. This technique requires the knee to be acutely flexed well beyond 90° drawing the patella, which might otherwise be severely subluxed laterally at the trochlear level, into the intercondylar space to articulate with the distal, or weight bearing surface, of the femoral condyles.

Conversely, the "Merchant" axial view radiograph is exposed with both knees flexed no more than 45°, showing the patella's true relationship to the trochlea.(1,2)

This may seem to be a minor point, but if the surgeon is not aware that the patella is subluxed laterally prior to surgery, he or she may not take sufficient measures to correct that subluxation during surgery. Many postoperative patellofemoral complications can be avoided if the surgeon is aware of this problem before surgery.

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. Merchant AC, Mercer RL, Jacobsen RH, Cool CR: Roentgenographic analysis of patellofemoral congruence. J Bone Joint Surg 56A:1391–1396, 1974.

2. Merchant AC: Patellofemoral imaging. Clin Orthop 389:15–21, 2001.
Dr. Pellegrini et al. respond to Dr. Merchant 7 May 2007
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Vincent D. Pellegrini, Jr., M.D.
Dept. of Orthopaedics, University of Maryland School of Medicine, Baltiimore, MD 21201,
Matthew J. Kelly, M.D., Mustasim N. Rumi, M.D., Milind Kothari, DO, Katrina J. Bailey, PT, William M. Parrish, M.D., Michael A. Parentis, M.D.

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Re: Dr. Pellegrini et al. respond to Dr. Merchant

vpellegrini{at}umoa.umm.edu Vincent D. Pellegrini, Jr., M.D., et al.

We thank Dr. Merchant for correctly identifying our error as it relates to patellofemoral imaging of the knee. We concur with his comments and, indeed, customarily perform patellofemoral imaging with the knee in 30 degrees of flexion to more sensitively identify lateral subluxation of the patella. The patellar view presented in our paper does not reflect our usual practice.

We appreciate Dr Merchant's efforts in bringing this inadvertent misrepresentation to our attention as well as that of the readership of The Journal.