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Scientific Articles   |    
Far Cortical Locking Can Improve Healing of Fractures Stabilized with Locking Plates
Michael Bottlang, PhD1; Maren Lesser, DVM2; Julia Koerber, MS3; Josef Doornink, MS1; Brigitte von Rechenberg, DVM, ECVS2; Peter Augat, PhD3; Daniel C. Fitzpatrick, MD1; Steven M. Madey, MD1; J. Lawrence Marsh, MD4
1 Legacy Biomechanics Laboratory, 1225 N.E. 2nd Avenue, Portland, OR 97232. E-mail address for M. Bottlang: mbottlan@lhs.org
2 Equine Department, Musculoskeletal Research Unit, Vetsuisse Faculty, University of Zürich, Winterthurerstrasse 260, CH 8057, Zürich, Switzerland
3 Institute of Biomechanics, Prof. Kuentscher Strasse 8, 82418 Murnau, Germany
4 University of Iowa Hospitals and Clinics, 200 Hawkins Drive, Iowa City, IA 52242
View Disclosures and Other Information
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 (National Institute of Arthritis and Musculoskeletal and Skin Diseases R21 AR053611) and Zimmer. 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 (Zimmer) and less than $10,000 (Stryker) or a commitment or agreement to provide such benefits from these commercial entities.

Investigation performed at the Legacy Biomechanics Laboratory, Portland, Oregon; the University of Zürich, Zürich, Switzerland; and the Institute of Biomechanics, Murnau, Germany

Copyright ©2010 American Society for Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2010 Jul 07;92(7):1652-1660. doi: 10.2106/JBJS.I.01111
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Abstract

Background: 

Locked bridge plating relies on secondary bone healing, which requires interfragmentary motion for callus formation. This study evaluated healing of fractures stabilized with a locked plating construct and a far cortical locking construct, which is a modified locked plating approach that promotes interfragmentary motion. The study tested whether far cortical locking constructs can improve fracture-healing compared with standard locked plating constructs.

Methods: 

In an established ovine tibial osteotomy model with a 3-mm gap size, twelve osteotomies were randomly stabilized with locked plating or far cortical locking constructs applied medially. The far cortical locking constructs were designed to provide 84% lower stiffness than the locked plating constructs and permitted nearly parallel gap motion. Fracture-healing was monitored on weekly radiographs. After the animals were killed at week 9, healed tibiae were analyzed by computed tomography, mechanical testing in torsion, and histological examination.

Results: 

Callus on weekly radiographs was greater in the far cortical locking constructs than in the locked plating constructs. At week 9, the far cortical locking group had a 36% greater callus volume (p = 0.03) and a 44% higher bone mineral content (p = 0.013) than the locked plating group. Callus in the locked plating specimens was asymmetric, having 49% less bone mineral content in the medial callus than in the lateral callus (p = 0.003). In far cortical locking specimens, medial and lateral callus had similar bone mineral content (p = 0.91). The far cortical locking specimens healed to be 54% stronger in torsion (p = 0.023) and sustained 156% greater energy to failure in torsion (p < 0.001) than locked plating specimens. Histologically, three of six locked plating specimens had deficient bridging across the medial cortex, while all remaining cortices had bridged.

Conclusions: 

Inconsistent and asymmetric callus formation with locked plating constructs is likely due to their high stiffness and asymmetric gap closure. By providing flexible fixation and nearly parallel interfragmentary motion, far cortical locking constructs form more callus and heal to be stronger in torsion than locked plating constructs.

Clinical Relevance: 

Far cortical locking fixation may be advisable for stiffness reduction of locked bridge plating constructs to improve fracture-healing.

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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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    Michael Bottlang, PhD
    Posted on December 15, 2010
    Dr. Bottlang responds to Dr. Chisena and Dr. Rastegar
    Director, Legacy Biomechanics Laboratory, Portland, Oregon

    We thank Dr. Chisena and colleagues for their comments and request for clarification. We agree that applying a splint over a soft padding layer may induce some soft tissue compression. We further agree that soft tissue pressure, along with interfragmentary motion and strain are interrelated mechanical factors that affect the fracture healing cascade.

    However, both study groups had the identical post-operative treatment, including splint application, with the only difference between groups being the controlled and parallel interfragmentary motion provided by FCL constructs.

    Therefore, the pronounced improvement in fracture healing seen in the FCL group can only be explained by the defined interfragmentary motion provided by FCL screws. This conclusion is furthermore supported by the results of the standard locked plating group, whereby rigid fixation suppressed callus formation, particularly at the near cortex adjacent to the plate where interfragmentary motion is minimal.

    Ernest C. Chisena, MD, MS
    Posted on December 15, 2010
    Micro-motion Versus Soft Tissue Pressure
    Orthopedic Surgeon, Huntington Hospital, St. Catherine of Siena, New York

    To the Editor:

    The article, "Far Cortical Locking Can Improve Healing of Fractures Stabilized with Locking Plates" (2010;92:1652-60) by Bottlang et al. was read with great interest. It is a very intriguing mechanical analysis of a complex topic which attempts to isolate the effects of micro-motion on fracture healing. However, the study does not account for the effects of the local soft tissue compression around the fracture and the pressure applied to the fracture when the limb was immobilized in a cast applied over a soft padding. The sheep remained in a protective harness for three weeks after surgery. Photographs of the harness suspending the animal, referenced in the paper (1) demonstrate the contact made with the fractured limb (Figure 1). Some pressure must have been applied to the extremity with this padding, casting and harness.


    Fig 1. Picture from Auer et al. (1) demonstrating the animal suspended with the harness contacting the casted lower extremity after osteotomy. Reproduced from: Auer JA, Goodship A, Arnoczky S, Pearce S, Price J, Claes L, von Rechenberg B, Hofmann-Amtenbrinck M, Schneider E, Müller-Terpitz R, Thiele F, Rippe KP, Grainger DW. Refining animal models in fracture research: seeking consensus in optimising both animal welfare and scientific validity for appropriate biomedical use. BMC Musculoskelet Disord. 2007;8:72. Reproduced with permission.

    Furthermore, it is unclear from their description of the post-operative treatment whether both groups of animals had the same immobilization.

    In a recent study (2), it was shown that local soft tissue compression enhanced the fracture healing in a rabbit fibula. These results provide evidence that make inter-fragmentary micro-motion unlikely to be key contributor to fracture healing. While the referenced experiment was a pilot study, the data that was collected clearly demonstrates that the variable of pressure must be controlled for when studying fracture healing.

    There are then two reasons why the conclusion that the callus formation and fracture healing is dependent on the inter-fragmentary motion can be questioned. First, the pressure applied to the osteotomy site cannot be assumed to be zero (and should have been measured and controlled) with the padding, casting and suspension in a harness as described. Second, it is unclear from the article whether the postoperative treatment was the same for both groups.

    References

    1. Auer JA, Goodship A, Arnoczky S, Pearce S, Price J, Claes L, von Rechenberg B, Hofmann-Amtenbrinck M, Schneider E, Müller-Terpitz R, Thiele F, Rippe KP, Grainger DW. Refining animal models in fracture research: seeking consensus in optimising both animal welfare and scientific validity for appropriate biomedical use. BMC Musculoskelet Disord. 2007;8:72.

    2. Morr S, Chisena EC, Tomin E, Mangino M, Lane JM. Local soft tissue compression enhances fracture healing in a rabbit fibula. HSS J. 2009 Nov 13. [Epub ahead of print]

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