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Scientific Articles   |    
The Mechanical Axes of the Wrist Are Oriented Obliquely to the Anatomical Axes
Joseph J. Crisco, PhD1; Wendell M.R. Heard, MD2; Ryan R. Rich2; David J. Paller, MS2; Scott W. Wolfe, MD3
1 Bioengineering Laboratory, Department of Orthopaedics, The Warren Alpert Medical School of Brown University and Rhode Island Hospital, 1 Hoppin Street, CORO West Suite 404, Providence, RI 02903. E-mail address: joseph_crisco@brown.edu
2 Department of Orthopaedics, The Warren Alpert Medical School of Brown University and University Orthopedics, 2 Dudley Street, Suite 200, Providence, RI 02905
3 The Hand and Upper Extremity Center, Hospital for Special Surgery and Weill Medical College of Cornell University, 523 East 72nd Street, 4th Floor, New York, NY 10021
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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 in excess of $10,000 from the National Institutes of Health (HD052127) and Extremity Medical, LLC. 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 (Extremity Medical, LLC).

Investigation performed at the Warren Alpert Medical School of Brown University and Rhode Island Hospital, Providence, Rhode Island

Copyright © 2011 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2011 Jan 19;93(2):169-177. doi: 10.2106/JBJS.I.01222
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Abstract

Background: 

The complex motions of the wrist are described in terms of four anatomical directions that are accomplished through the multiple articulations of the carpus. With minimal tendinous insertions, the carpus is primarily a passive structure. This emphasizes the importance of its mechanical properties, which few studies have examined to date. The purpose of the present study was to determine the mechanical properties of the wrist in twenty-four different directions of wrist motion.

Methods: 

The moment-rotation mechanical behavior of six fresh-frozen cadaver wrists was determined in four directions: flexion, extension, ulnar deviation, and radial deviation. Twenty other directions that were a combination of these anatomical directions were also studied. A custom-designed jig was interfaced with a standard materials testing system to apply unconstrained moments. Moments of ±2 Nm were applied, and the moment-rotation data were recorded and analyzed to determine the neutral zone, range of motion, and stiffness values as well as the orientation of the envelope of these values.

Results: 

The envelope of wrist range-of-motion values was ellipsoidal in shape and was oriented obliquely (p < 0.001) to the direction of pure flexion-extension by a mean (and standard deviation) of 26.6° ± 4.4°. The largest wrist range of motion was a mean of 111.5° ± 10.2°, in the direction of ulnar flexion, 30° from pure flexion. The largest stiffness (mean, 0.4 Nm/deg) was in the direction of radial flexion, while the smallest stiffness (mean, 0.15 Nm/deg) was in the direction of ulnar flexion.

Conclusions: 

The mechanical axes of the wrist are oriented obliquely to the anatomical axes. The primary mechanical direction is one of radial extension and ulnar flexion, a direction along a path of the dart thrower's wrist motion.

Clinical Relevance: 

Understanding the mechanical function of the wrist can aid clinical treatment decisions, arthroplasty, and implant designs. The findings of this study provide new evidence that the mechanical axes of the wrist are not collinear with the anatomical axes.

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    References

    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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