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Patellofemoral Evaluation After Total Knee ArthroplastyValidation of a New Weight-Bearing Axial Radiographic View
Andrea Baldini, MD1; John A. Anderson, MD2; Pierpaolo Cerulli-Mariani, MD1; James Kalyvas, BA1; Helene Pavlov, MD2; Thomas P. Sculco, MD2
1 Santa Chiara Clinic, Piazza Indipendenza 11, 50129 Florence, Italy. E-mail address for A. Baldini: drbaldiniandrea@yahoo.it
2 Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021
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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families 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 authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at the Hospital for Special Surgery, New York, NY

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2007 Aug 01;89(8):1810-1817. doi: 10.2106/JBJS.E.00432
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Background: Radiographic assessment of the patella after total knee arthroplasty is typically performed with use of static, unloaded views that may not reproduce the in vivo patellofemoral kinematics. The purpose of the present study was to evaluate and validate the reliability and reproducibility of a weight-bearing radiographic assessment of the patellofemoral joint in patients who have undergone total knee arthroplasty.

Methods: Radiographs were made for 100 knees in sixty-nine patients who had undergone total knee arthroplasty. Radiographic assessment of the patellofemoral joint was performed with use of both the standard Merchant axial view and a modification of that view. The Merchant axial view was modified by positioning the standing patient in the semi-squatted position with the knees in 45° of flexion. The relationship between the x-ray source, the angle of incidence on the joint, and the cassette position was kept unchanged from the original view. The standing position and consequent muscle involvement were the only differences.

Results: Compared with the standard Merchant axial view, the weight-bearing axial view showed a number of patellofemoral tracking changes. Specifically, lateral tilt and subluxation of the patella were significantly reduced; the rate of exposed, uncovered patellar bone contact with the femoral trochlea was significantly increased; and radiographic evidence of maltracking was more closely correlated with clinical symptoms.

Conclusions: An axial weight-bearing radiographic view with the patient in the semi-squatting position was developed to reproduce patellofemoral joint loading. This view demonstrates that the position of the patella, as seen on the standard unloaded Merchant view, changes during squatting. Utilization of this axial weight-bearing view to evaluate total knee arthroplasty may provide additional information over standard radiographic views.

Level of Evidence: Prognostic Level I. See Instructions to Authors for a complete description of levels of evidence.

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    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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