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Effect of a Variable Prosthetic Neck-Shaft Angle and the Surgical Technique on Replication of Normal Humeral Anatomy
Jinyoung Jeong, MD, PhD1; Jason Bryan, MS2; Joseph P. Iannotti, MD, PhD1
1 Department of Orthopaedic Surgery, The Cleveland Clinic, 9500 Euclid Avenue, A-41, Cleveland, OH 44195. E-mail address for J. Jeong: osjeong@hotmail.com. E-mail address for J.P. Iannotti: iannotj@ccf.org
2 Department of Biomedical Engineering, The Cleveland Clinic, 9500 Euclid Avenue, ND-20, Cleveland, OH 44195. E-mail address: bryanj2@ccf.org
View Disclosures and Other Information
Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. One or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from commercial entities (DePuy, a Johnson and Johnson Company, and Tornier). Also, a commercial entity (DePuy, a Johnson and Johnson Company) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immediate family, is affiliated or associated.
A video supplement to this article will be available from the Video Journal of Orthopaedics. A video clip will be available at the JBJS web site, www.jbjs.org. The Video Journal of Orthopaedics can be contacted at (805) 962-3410, web site: www.vjortho.com.
Investigation performed at The Cleveland Clinic, Cleveland, Ohio

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2009 Aug 01;91(8):1932-1941. doi: 10.2106/JBJS.H.00729
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Abstract

Background: Replicating the normal anatomy of the shoulder is an important principle in the design of prosthetic devices and the development of surgical techniques. In this study, we used a three-dimensional surgical simulation to compare the abilities of an adjustable neck-shaft angle prosthesis and a fixed neck-shaft angle prosthesis to restore the normal geometry of the proximal part of the humerus.

Methods: A total of 2058 cadaveric humeri were measured to define the normal distribution of neck-shaft angles. Thirty-six humeri were selected to represent a wide variation in neck-shaft angles, and computed tomographic scans with three-dimensional reconstruction were made of these specimens. With use of a three-dimensional computer surgical simulator, the humeral head was then cut at the anatomic neck to replicate a normal neck-shaft angle and version or it was cut at a fixed 135° angle with anatomic version. The anatomy of an adjustable-angle prosthesis and that of a fixed-angle prosthesis of the same design were both compared with native humeral anatomy in three dimensions.

Results: The average neck-shaft angle of the 2058 humeri was 134.7° (range, 115° to 148°), and the angle was between 130° and 140° in 77.84% of the humeri. In the setting of a high varus or valgus neck-shaft angle, an adjustable-angle prosthesis allowed optimal reconstruction when the humeral head was cut along the anatomic neck and allowed a standard and consistent surgical technique with use of anatomic landmarks. A fixed-angle prosthesis also replicated the anatomic center of rotation, tuberosity-head height, and head volume if the surgical procedure was altered to adapt to variations in humeral anatomy. There was no significant difference in anatomic parameters between the two types of prostheses, except that in all cases the head thickness was decreased when a fixed-135°-angle prosthesis was used in a humerus with a high valgus or high varus neck-shaft angle, resulting in a smaller articular arc and percent articular surface match.

Conclusions: This study demonstrates the ability of both an adjustable and a fixed neck-shaft angle prosthesis to replicate humeral anatomy. However, the fixed-angle device requires specific modifications of the surgical technique to accommodate the specific prosthetic design and optimize the surgeon's ability to replicate normal anatomic parameters in humeri with an extreme neck-shaft angle.

Clinical Relevance: This information can be used to optimize humeral component placement intraoperatively.

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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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