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Technical Briefs

The Biomechanical Effect of Torsion on Humeral Shaft Repair Techniques for Completed Pathological Fractures

[+] Author and Article Information
Ahmed Al-Jahwari

  Martin Orthopaedic Biomechanics Lab,St. Michael’s Hospital, Toronto, ON, Canada, M5B-1W8

Emil H. Schemitsch

 Division of Orthopaedic Surgery,St. Michael’s Hospital, Toronto, ON, Canada, M5B-1W8

Jay S. Wunder, Peter C. Ferguson

 University Musculoskeletal Oncology Unit and the Division of Orthopaedic Surgery,Department of Surgery, Mount Sinai Hospital, Toronto, ON, Canada, M5G-1X5

Rad Zdero1

 Martin Orthopaedic Biomechanics Lab,St. Michael’s Hospital, Toronto, ON, Canada, M5B-1W8;  Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, ON, Canada, M5B-2K3zderor@smh.ca

1

Corresponding author.

J Biomech Eng 134(2), 024501 (Feb 15, 2012) (7 pages) doi:10.1115/1.4005696 History: Received December 12, 2011; Revised December 12, 2011; Posted January 24, 2012; Published February 14, 2012; Online February 15, 2012

In the presence of a tumor defect, completed humeral shaft fractures continue to be a major surgical challenge since there is no “gold standard” treatment. This is due, in part, to the fact that only one prior biomechanical study exists on the matter, but which only compared 2 repair methods. The current authors measured the humeral torsional performance of 5 fixation constructs for completed pathological fractures. In 40 artificial humeri, a 2-cm hemi-cylindrical cortical defect with a transverse fracture was created in the lateral cortex. Specimens were divided into 5 different constructs and tested in torsion. Construct A was a broad 10-hole 4.5-mm dynamic compression plate (DCP). Construct B was the same as A except that the screw holes and the tumor defect were filled with bone cement and the screws were inserted into soft cement. Construct C was the same as A except that the canal and tumor defect were filled with bone cement and the screws were inserted into dry cement. Construct D was a locked intramedullary nail inserted in the antegrade direction. Construct E was the same as D except that bone cement filled the defect. For torsional stiffness, construct C (4.45 ± 0.20 Nm/deg) was not different than B or E (p > 0.16), but was higher than A and D (p < 0.001). For failure torque, construct C achieved a higher failure torque (69.65 ± 5.35 Nm) than other groups (p < 0.001). For the failure angle, there were no differences between plating constructs A to C (p ≥ 0.11), except for B versus C (p < 0.05), or between nailing groups D versus E (p = 0.97), however, all plating groups had smaller failure angles than both nailing groups (p < 0.05). For failure energy, construct C (17.97 ± 3.59 J) had a higher value than other groups (p < 0.005), except for A (p = 0.057). Torsional failure always occurred in the bone in the classic “spiral” pattern. Construct C provided the highest torsional stability for a completed pathological humeral shaft fracture.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Radiographs of humeral fixation methods, namely, Constructs A, B, C, D, and E

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Figure 2

Experimental test setup for torsion testing. The proximal humerus was placed into a solid steel cup simulating the shoulder joint and secured with 3 pins on either side, while the distal square chamber was mounted into an industrial vice.

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Figure 3

Torsional stiffness results. All pairwise comparisons showed statistically significant differences (p < 0.001), except for those indicated otherwise. Error bars are one standard deviation.

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Figure 4

Failure torque results. All pairwise comparisons showed statistically significant differences (p < 0.001), except for those indicated otherwise. Error bars are one standard deviation.

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Figure 5

Failure angle results. All pairwise comparisons showed statistically significant differences (p < 0.05), except for those indicated otherwise. Error bars are one standard deviation.

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Figure 6

Failure energy results. All pairwise comparisons showed no statistically significant differences (p > 0.236), except for those indicated between Construct C and each of B, D, and E. Error bars are one standard deviation.

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