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Two-Part Surgical Neck Fractures of the Proximal Part of the HumerusA Biomechanical Evaluation of Two Fixation Techniques
Sara L. Edwards, MD1; Nicole A. Wilson, MS2; Li-qun Zhang, PhD2; Steven Flores, MD1; Bradley R. Merk, MD1
1 Sara L. Edwards, MD Steven Flores, MD Bradley R. Merk, MD Department of Orthopaedic Surgery, Northwestern University, 645 North Michigan Avenue, Suite 910, Chicago, IL 60611
2 Nicole A. Wilson, MS Li-Qun Zhang, PhD Sensory Motor Performance Program, Rehabilitation Institute of Chicago, 345 East Superior Street, Room 1408, Chicago, IL 60611
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The authors did not receive grants or outside funding in support of their research for or preparation of this manuscript. They did not receive 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 Orthopaedic Surgery, Northwestern University, Chicago, Illinois

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2006 Oct 01;88(10):2258-2264. doi: 10.2106/JBJS.E.00757
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Background: Successful internal fixation of fractures of the surgical neck of the humerus can be difficult to achieve because of osteopenia of the proximal aspect of the humerus. The purpose of this study was to compare the biomechanical stability of a proximal humeral intramedullary nail and a locking plate for the treatment of a comminuted two-part fracture of the surgical neck in a human cadaver model.

Methods: Twenty-four cadaveric humeri were instrumented with use of either a titanium proximal humeral nail (PHN) or a 3.5-mm locking compression plate for the proximal part of the humerus (LCP-PH). The specimens were matched by bone mineral density and were separated into four experimental groups with six humeri in each: PHN bending, LCP-PH bending, PHN torsion, or LCP-PH torsion. Comminuted fractures of the surgical neck were simulated by excising a 10-mm wedge of bone. Bending specimens were cyclically loaded from 0 to 7.5 Nm of varus bending moment at the fracture site. Torsion specimens were cyclically loaded to ±2 Nm of axial torque. The mean and maximum displacement in bending, mean and maximum angular rotation in torsion, and stiffness of the bone-implant constructs were compared.

Results: In bending, the LCP-PH group demonstrated significantly less mean displacement of the distal fragment than did the PHN group over 5000 cycles (p = 0.002). In torsion, the LCP-PH group demonstrated significantly less mean angular rotation than did the PHN group over 5000 cycles (p = 0.04). A significant number of specimens in the PHN group failed prior to reaching 5000 cycles (p = 0.04). The LCP-PH implant created a significantly stiffer bone-implant construct than did the PHN implant (p = 0.007).

Conclusions: The LCP proximal humeral plate demonstrated superior biomechanical characteristics compared with the proximal humeral nail when tested cyclically in both cantilevered varus bending and torsion. The rate of early failure of the proximal humeral nail could reflect the high moment transmitted to the locking proximal screw-bone interface in this implant.

Clinical Relevance: The high failure rate in torsion of the proximal humeral nail-bone construct is concerning, and, with relatively osteoporotic bone and early motion, the results could be poor.

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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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