Getting it Right by Analyzing Failures and Biomechanical Models   |    
Risk of Periprosthetic Femoral Neck Fracture After Hip Resurfacing Arthroplasty: Valgus Compared with Anatomic AlignmentA Biomechanical and Clinical Analysis
Corey J. Richards, MD, FRCSC1; Demetri Giannitsios, BSc2; Olga L. Huk, MD, MSc, FRCSC3; David J. Zukor, MD, FRCSC3; Thomas Steffen, MD, PhD, MBA2; John Antoniou, MD, PhD, FRCSC3
1 Department of Orthopaedics, Montreal General Hospital, 1650 Cedar Avenue, Montreal, QC H3G 1A4, Canada
2 Orthopaedic Research Laboratory, McGill University, 687 Pine Avenue Ouest, Room L4.60, Montreal, QC H3A 1A1, Canada
3 Division of Orthopaedic Surgery, McGill University and Lady Davis Institute for Medical Research, SMBD-Jewish General Hospital, 3755 Chemin de la Côte Ste-Catherine, Montreal, QC H3T 1E2, Canada. E-mail address for J. Antoniou: janton@orl.mcgill.ca
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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.

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Aug 01;90(Supplement 3):96-101. doi: 10.2106/JBJS.H.00444
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Background: Early clinical results of hip resurfacing arthroplasty have led to the recommendation to achieve a neck-shaft angle of 140° when inserting the femoral component. In addition, the idea of adhering to an absolute angle when inserting instrumentation in hips with excessive anatomic varus or valgus neck-shaft angles has raised concern. A biomechanical analysis was completed in order to determine if the achieved valgus orientation of the femoral component reduced the risk of periprosthetic fracture.

Methods: Twenty fresh-frozen cadaveric femora were blindly assigned to be implanted with a neutral or valgus-oriented hip-resurfacing femoral component. Bone mineral density scans were acquired for all femora. All specimens were loaded axially to failure at a rate of 0.21 mm per second. Radiographs of the specimens were measured in order to determine the relative valgus orientation of the femoral components and the change in offset.

Results: There was a significant increase in the ultimate failure load for the valgus-oriented components. While the bone density scans revealed that the bone mineral densities measured in the neutral and valgus-oriented femoral components were almost identical, the ultimate failure load was found to be significantly increased for the valgus-oriented components (6955 N) compared with the neutral-oriented components (5254 N). For the valgus-oriented femoral components, two had failure at the subcapital level, seven had vertical shear fractures, and one had an anterior shear fracture. For the neutral-oriented components, five subcapital fractures and five vertical shear failures were observed.

Conclusions: The study suggests that a valgus orientation decreases the risk of periprosthetic femoral neck fracture following hip resurfacing. It also brings into question the use of an absolute angle for all patients. Obtaining the maximum possible valgus angle, while avoiding notching, may in fact provide the optimum protection from periprosthetic femoral neck fractures.

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    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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