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In Vivo Radiocarpal Kinematics and the Dart Thrower's Motion
Joseph J. Crisco, PhD1; James C. Coburn, MS1; Douglas C. Moore, MS1; Edward Akelman, MD2; Arnold-Peter C. Weiss, MD2; Scott W. Wolfe, MD3
1 Bioengineering Laboratory, Department of Orthopaedics, Brown Medical School/Rhode Island Hospital, 1 Hoppin Street, CORO West Suite 404, Providence, RI 02903. E-mail address for J.J. Crisco: joseph_crisco@brown.edu
2 Department of Orthopaedics, Brown Medical School/University Orthopaedics, 2 Dudley Street, Suite 200, Providence, RI 02905
3 The Alberto Vilar Center for Hand and Upper Extremity Research, Hospital for Special Surgery, Weill Medical College of Cornell University, 523 East 72nd Street, New York, NY 10021
View Disclosures and Other Information
In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from National Institutes of Health (AR44005). None of the authors 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, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at the Department of Orthopaedics, Brown Medical School/Rhode Island Hospital, Providence, Rhode Island

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2005 Dec 01;87(12):2729-2740. doi: 10.2106/JBJS.D.03058
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Background: Wrist motion is dependent on the complex articulations of the scaphoid and lunate at the radiocarpal joint. However, much of what is known about the radiocarpal joint is limited to the anatomically defined motions of flexion, extension, radial deviation, and ulnar deviation. The purpose of the present study was to determine the three-dimensional in vivo kinematics of the scaphoid and lunate throughout the entire range of wrist motion, with special focus on the dart thrower's wrist motion, from radial extension to ulnar flexion.

Methods: The three-dimensional kinematics of the capitate, scaphoid, and lunate were calculated from serial computed tomography scans of both wrists of fourteen healthy male subjects (average age, 25.6 years; range, twenty-two to thirty-four years) and fourteen healthy female subjects (average age, 23.6 years; range, twenty-one to twenty-eight years), which yielded data on a total of 504 distinct wrist positions.

Results: The scaphoid and lunate primarily flexed or extended in all directions of wrist motion, and their rotation varied linearly with the direction of wrist motion (R2 = 0.90 and 0.82, respectively). Scaphoid and lunate motion was significantly less along the path of the dart thrower's motion than in any other direction of wrist motion (p < 0.01 for both carpal bones). The scaphoid and lunate translated radially (2 to 4 mm) when extended, but they did not translate appreciably when flexed.

Conclusions: The dart thrower's path defined the transition between flexion and extension rotation of the scaphoid and lunate, and it identified wrist positions at which scaphoid and lunate motion approached zero. These findings indicate that this path of wrist motion confers a unique degree of radiocarpal stability and suggests that this direction, rather than the anatomical directions of wrist flexion-extension and radioulnar deviation, is the primary functional direction of the radiocarpal joint.

Clinical Relevance: The goal of reconstructive surgery for the treatment of injuries involving the scaphoid, the lunate, or their interosseous ligaments is to maximize healing, stability, and postoperative range of motion. Our in vivo findings suggest that specific rehabilitation protocols employing the dart thrower's motion could be designed to limit radiocarpal motion while providing the benefits of maintaining wrist motion.

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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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