2. Biologic factors can be modifiable or nonmodifiable. Effort should be made, where appropriate, to optimize modifiable factors in favor of the physiology of fracture healing. See ▶Table 1.1 for a list of purported biologic factors at play in the physiology of fracture healing. Aberrations in these higher-level physiologic systems manifest as alterations in the “microscopic” processes.
Table 1.1 List of purported biologic factors at play in the physiology of fracture healing. While some risk factors are modifiable, others are not
| Biologic risk factors for non-union | |
| Nonmodifiable | Potentially modifiable |
| Polytrauma/multiple injury patient | Various medications (e.g., chemotherapy, steroids, anticonvulsants, anticoagulants) |
| Bone | NSAID use |
| Location within bone | Smoking |
| Fracture pattern | Malnutrition |
| Open fracture | Alcohol abuse |
| High-energy injury | Diabetes |
| Age | Vitamin D deficiency |
| Sex | Endocrine disorder (e.g., hyperthyroid/hyperparathyroid) |
| Prior irradiation | Time to weight bearing |
| Arthritis | Renal diseaseb |
| HIV | Liver diseaseb |
| Osteoporosisa | |
| Obesitya | |
| Abbreviations: HIV, human immunodeficiency virus; NSAID, nonsteroidal anti-inflammatory drugs.aNot likely sufficiently alterable during the course of normal healing. bMay not be modifiable depending on specific diagnosis and stage of disease. |
3. Mechanical factors: Improper surgical technique and mechanical stabilization can be detrimental to fracture healing physiology and increase nonunion rates. A multitude of chapters in this book are devoted to optimal nonoperative and operative procedures in fracture care. Two governing mechanical principles for fracture healing physiology are Perren’s strain theory and Wolff’s law.
a. Perren’s strain theory (▶Fig. 1.4): The strain (change in length with load/initial length) seen at the fracture site determines the type of tissue that forms.
b. Wolff’s law (▶Fig. 1.5): Bone will remodel in adaptation to the stress environment it experiences.
4. Orthopaedic fracture care interventions (nonoperative splints/casts/slings, percutaneous pinning, plating, intramedullary nailing, external fixation, arthroplasty, arthrodesis, and amputation) are limited in number. Understanding the physiology of fracture healing allows the surgeon to apply these methods to a given injury to promote a biologically favorable environment for bony union.
Fig. 1.4 Perren’s strain theory. The strain experienced at the fracture site determines the type of tissue formed. Strain is the ratio of elongation to initial length. Bone forms in low-strain environments.
Fig. 1.5 Wolff’s law. Bone models/remodels itself according to the mechanical environment it experiences. The image shows idealized stress distribution in the proximal femur subject to axial loading. The adjacent image is a computed tomography cut showing how trabecular bone is laid down in a strikingly similar pattern.
Summary
A. Physiology of fracture healing is an orchestrated set of events from the organ system level to the cellular level, down to and including complex intracellular processes.
B. Multiple organ systems are involved including bone, endocrine, vascular, gastrointestinal (e.g., overall nutrition and vitamin D), kidneys, immune, and respiratory systems.
C. At the local bone level there are two types of fracture healing, primary/intramembranous and secondary/endochondral.
D. Formation of new bone at a fracture site is the ultimate macroscopic outcome of cellular and intracellular events.
E. The goal of fracture surgery is to create a mechanical environment that optimizes the biology of fracture physiology to promote bony union.
Suggested Readings
Brinker MR, O’Connor DP, Monla YT, Earthman TP. Metabolic and endocrine abnormalities in patients with nonunions. J Orthop Trauma 2007;21(8):557–570
O’Keefe RJ, Jacobs JJ, Chu CR, Einhorn TA (2013). Orthopaedic Basic Science, Foundations of Clinical Practice, Fourth Edition. Rosemont, IL: American Academy of Orthopaedic Surgeons.
Schenker ML, Wigner NA, Lopas L, Hankenson KD, Ahn J (2014). Fracture Repair and Bone Grafting. In L.K. Cannada (Ed.), Orthopaedic Knowledge Update 11. Rosemont, IL: American Academy of Orthopaedic Surgeons.
Schottel PC, O’Connor DP, Brinker MR. Time trade-off as a measure of health-related quality of life: long bone nonunions have a devastating impact. J Bone Joint Surg Am 2015;97(17):1406–1410
Yang L, Tsang KY, Tang HC, Chan D, Cheah KS. Hypertrophic chondrocytes can become osteoblasts and osteocytes in endochondral bone formation. Proc Natl Acad Sci U S A 2014;111(33):12097–12102
Zura R, Mehta S, Della Rocca GJ, Steen RG. Biological risk factors for nonunion of bone fracture. JBJS Rev 2016;4(1): 01874474-201601000-00005
Zura R, Xiong Z, Einhorn T, et al. Epidemiology of fracture nonunion in 18 human bones. JAMA Surg 2016;151(11):e162775
2 Open Fractures and Principles of Soft Tissue Management
Mark J. Gage and Robert V. O’Toole
Introduction
Open fractures are fractures with an associated breach in the surrounding soft-tissue envelope. This results in a communication between the fracture and the outside environment, and increased risk of surgical site infection compared to closed injuries. These injuries typically represent a higher-energy injuries with more significant associated soft tissue and blood supply disruption. As a result, goals of treatment for this unique scenario are focused on reducing risk of infection and avoiding complications.
Keywords: open fracture, compound fracture, limb salvage, soft tissue injury, soft tissue reconstruction, wound infection, debridement
I. Mechanism of Injury
A. Blunt injuries
1. These are the results of a direct blow leading to a focal area of injury (▶Fig. 2.1).
2. This is the most common mechanism for open fractures.
B. Ballistic injuries
1. Determine between low- (i.e., handguns) and high- (i.e., military and hunting rifles) velocity injuries and high-mass injuries (close-range shotgun).
a. Low-velocity ballistic fractures often can be treated as closed fractures. Weak