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Range of Impingement-Free Abduction and Adduction Deficit After Reverse Shoulder ArthroplastyHierarchy of Surgical and Implant-Design-Related Factors
Sergio Gutiérrez, MS1; Charles A. ComiskeyIV1; Zong-Ping Luo, PhD1; Derek R. Pupello, MBA1; Mark A. Frankle, MD1
1 Florida Orthopaedic Institute Research Foundation, 13020 North Telecom Parkway, Tampa, FL 33637. E-mail address for M.A. Frankle: frankle@pol.net
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Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants of less than $10,000 from Encore Medical. In addition, 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 a commercial entity (Encore Medical). Also, a commercial entity (Encore Medical) 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.
Investigation performed at the Phillip Spiegel Orthopaedic Research Laboratory at the Florida Orthopaedic Institute Research Foundation, Tampa, Florida

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Dec 01;90(12):2606-2615. doi: 10.2106/JBJS.H.00012
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Background: Evaluations of functional outcomes of reverse shoulder arthroplasty have revealed variable improvements in the range of motion and high rates of scapular notching. The purpose of this study was to systematically examine the impact of surgical factors (location of the glenosphere on the glenoid and tilt angle of the glenosphere on the glenoid) and implant-related factors (implant size, center-of-rotation offset, and humeral neck-shaft angle) on impingement-free abduction motion.

Methods: A computer model was developed to virtually simulate abduction/adduction motion and its dependence on five surgical and implant-related factors. Three conditions were tested for each factor, resulting in a total of 243 simulated combinations. The overall motion was determined from 0° of abduction until maximum abduction, which would be limited by impingement of the humerosocket on the scapula. In those combinations in which 0° of abduction could not be achieved, the adduction deficit was recorded.

Results: The largest average increase in the range of impingement-free abduction motion resulted from a more lateral center-of-rotation offset: the average increase was 31.9° with a change in the center-of-rotation offset from 0 to 10 mm, and this change resulted in an increase in abduction motion in eighty of the eighty-one combinations. The position of the glenosphere on the glenoid was associated with the second largest average increase in abduction motion (28.1° when the glenosphere position was changed from superior to inferior, with the change resulting in an increase in seventy-one of the eighty-one combinations). These factors were followed by glenosphere tilt, humeral neck-shaft angle, and prosthetic size in terms of their effects on abduction motion. The largest effect in terms of avoiding an adduction deficit was provided by a humeral neck-shaft angle of 130° (the deficit was avoided in forty-nine of the eighty-one combinations in which this angle was used), followed by an inferior glenosphere position on the glenoid (deficit avoided in forty-one combinations), a 10-mm lateral offset of the center of rotation, inferior tilt of the glenosphere, and a 42-mm-diameter prosthetic size.

Conclusions: An understanding of a hierarchy of prosthetic design and implantation factors may be important to maximize impingement-free abduction motion as well as to avoid inferior impingement.

Clinical Relevance: A better understanding of these factors may lead to a reduction in inferior scapular notching and improvements in impingement-free motion after reverse shoulder replacement.

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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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