area of direct contact between endosteal bone and nail, which can help minimize undesirable interfragmentary shear and increase load sharing by the bone to decrease risk of fatigue failure.
3. Interlocking screws:
a. Static screws: Screws placed in tightly fitting holes allow very little relative movement and this provides axial and rotational stability for the construct.
b. Dynamic screw: A single screw placed in a short slot can allow axial shortening for use in intraoperative fracture compression or as postoperative intervention in cases of delayed union or nonunion (▶Fig. 4.6). In length-stable fractures, this allows compression with weight bearing and may stimulate healing.
c. Screw diameter: Larger-diameter screws have increased bending stiffness (flexural rigidity) and reduced risk of fatigue failure. Choosing a large diameter increases bending strength of screw and reduces construct failure especially in length unstable fractures.
d. Angularly stable screws: Some implant systems have design features that enable mechanical coupling between one or more screws and the nail body to increase the rigidity of the construct, particularly in torsion. Examples include threaded or partially threaded screw holes, polymer bushings in the screw holes or sleeves added to the screw prior to insertion, and locking or compression endcaps.
e. Number of screws: Addition of a third screw increases stiffness in the proximal tibia metaphysis. This benefit is not observed in the distal tibia.
f. Screw distance to fracture: Screws positioned closer to metaphyseal fractures afford greater rotational control, but do not increase axial stability.
g. Screw orientation: Oblique interlocking screws increase stability of proximal one-third tibia constructs but not distal one-third tibia constructs.
Summary
Bone fracture healing is a complex mechanoresponsive process that is biologically regulated by the mechanical conditions at the fracture site over the course of healing. In fracture management, surgeons may stabilize broken bones with plates, intramedullary devices, external fixators, or external splints, casts, or braces. These constructs allow the surgeon to tailor the mechanical environment to suit the individual needs of the patient by selecting the implant length, implant thickness or diameter, screw number, screw type, and screw configuration. Each decision alters the fracture’s biomechanical environment, which in turn determines if the fracture will attempt to heal with callus (relative stability leading to secondary healing) or without callus (absolute stability or interfragmentary compression leading to primary healing). A sound understanding of fracture fixation biomechanics is the foundation upon which a surgeon’s treatment will succeed or fail. This chapter introduced basic definitions and principles of biomechanics as they apply to trauma implants and describe techniques for altering the implant construct mechanics to achieve the desired mode of healing and minimize the risk of premature construct failure.
Suggested Readings
Bottlang M, Doornink J, Lujan TJ, et al. Effects of construct stiffness on healing of fractures stabilized with locking plates. J Bone Joint Surg Am 2010;92(Suppl 2):12–22
Perren SM. Evolution of the internal fixation of long bone fractures. The scientific basis of biological internal fixation: choosing a new balance between stability and biology. J Bone Joint Surg Br 2002;84(8):1093–1110
Stoffel K, Dieter U, Stachowiak G, Gächter A, Kuster MS. Biomechanical testing of the LCP: how can stability in locked internal fixators be controlled? Injury 2003;34(Suppl 2):B11–B19
Törnkvist H, Hearn TC, Schatzker J. The strength of plate fixation in relation to the number and spacing of bone screws. J Orthop Trauma 1996;10(3):204–208
5 How to Analyze a Journal Article?
Gregory J. Della Rocca
Introduction
This original chapter breaks down the basic components of a journal article. Common statistical methods are introduced and different types of scientific studies are defined. Insight is provided on how to critically analyze scientific literature.
Keywords: journal article, levels of evidence, statistics, scientific studies
I. Components of a Standard Article
A. Introduction
1. Sets the groundwork for the manuscript.
2. Provides background information detailing why the research question is being asked:
a. Typically acknowledges gaps in knowledge.
b. Reinforces the clinical relevance of the topic.
3. Clearly defines the research question(s).
B. Methods
1. Should be sufficiently complete to allow the reader to duplicate the study, if desired.
2. Description of the inclusion/exclusion criteria, intervention (i.e., study arms), how data was gathered and analyzed, and ethical approval (if applicable).
C. Results
1. Succinct and clear presentation of study findings. A well-written results section is organized and follows a logical progression. When applicable, data presentation should mimic the order in which research questions are posed in the last paragraph of the introduction.
2. Figures/tables should always be referenced in the text of the manuscript.
3. Interpretation of study findings should not be included in this section.
D. Discussion
1. Perhaps the least relevant part of the manuscript for the knowledgeable reader.
2. Perhaps the most important part of the manuscript for the reader with minimal knowledge.
3. Recognize that author opinions are often expressed in this section (these may be incorrect).
4. Pay close attention to a description of study weaknesses.
a. Study limitations should be appropriately identified.
b. The impact of limitations and weaknesses should be explained.
5. Allows study results to be placed into context of the recent literature.
6. Directions of future investigations outlined.
E. Abstract
1. Should provide concise summary of study.
2. Often the only part of the article that is read by the public.
3. If findings are interesting, care is required to verify if the abstract and the body of the manuscript are consistent with each other.
4. Do the authors draw conclusions based upon their data? (Answer: not always).
F. Title
1. Should grab attention without being flashy.
2. Is the title an accurate portrayal of the study report? (Answer: not always).
II. Types of Studies
A. Experimental (▶Fig. 5.1)
1. Prospective, randomized controlled trial:
a. One or more interventions with a “control” group.
b. Patient enters study at beginning of treatment via a randomization process and data is gathered moving forward.
c. Defined end