ORIGINAL ARTICLE Instability in Thoracolumbar Trauma Is a New Definition Warranted? Salman Abbasi Fard, MD, Jesse Skoch, MD, Mauricio J. Avila, MD, Apar S. Patel, MD, MPH, Kamran V. Sattarov, MD, Christina M. Walter, MS, and Ali A. Baaj, MD Study Design: Review of the articles. Objective: The objective of this study was to review all articles related to spinal instability to determine a consensus statement for a contemporary, practical definition applicable to thoracolumbar injuries. Summary of Background Data: Traumatic fractures of the thoracolumbar spine are common. These injuries can result in neurological deficits, disability, deformity, pain, and represent a great economic burden to society. The determination of spinal instability is an important task for spine surgeons, as treatment strategies rely heavily on this assessment. However, a clinically applicable definition of spinal stability remains elusive. Materials and Methods: A review of the Medline database between 1930 and 2014 was performed limited to papers in English. Spinal instability, thoracolumbar, and spinal stability were used as search terms. Case reports were excluded. We reviewed listed references from pertinent search results and located relevant manuscripts from these lists as well. Results: The search produced a total of 694 published articles. Twenty-five articles were eligible after abstract screening and underwent full review. A definition for spinal instability was described in only 4 of them. Definitions were primarily based on biomechanical and classification studies. No definitive parameters were outlined to define stability. Conclusions: Thirty-six years after White and Panjabi’s original definition of instability, and many classification schemes later, there remains no practical and meaningful definition for spinal instability in thoracolumbar trauma. Surgeon expertise and experience remains an important factor in stability determination. We propose that, at an initial assessment, a distinction should be made between immediate and delayed instability. This designation should better guide surgeons in decision making and patient counseling. Key Words: thoracolumbar, spinal instability, spinal stability, review articles (J Spinal Disord Tech 2015;00:000–000) Received for publication January 12, 2015; accepted July 16, 2015. From the Division of Neurosurgery, University of Arizona, Tucson, AZ. The authors declare no conflict of interest. Reprints: Ali A. Baaj, MD, Division of Neurosurgery, The University of Arizona, 1501 N Campbell Ave., Tucson 85724, AZ (e-mail: abaaj@surgery.arizona.edu). Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved. J Spinal Disord Tech Volume 00, Number 00, ’’ 2015 T raumatic thoracolumbar spine fractures are common, and these injuries can result in transient or permanent neurological deficits. Even in the absence of deficits, injuries to the thoracolumbar spine can be associated with long-term pain and disability and are a major economic burden to society.1,2 The thoracolumbar region (T10–L2) is the transition point between the more rigid thoracic spine and the more flexible lumbar spine and, as a result, is predisposed to unique fracture patterns and neurological deficits. The determination of spinal instability especially in this area, is important for spine surgeons, as treatment strategies rely heavily on this assessment. White and Panjabi3 have described spinal instability as “the loss of the ability of the spine under physiological loads to maintain relationships between vertebrae in such a way that there is neither damage nor subsequent irritation to the spinal cord or nerve roots, in addition, there is no development of incapacitating deformity or pain due to structural changes.” However, a clinically applicable method of determining spinal stability or instability remains elusive. Therefore, optimal management for some injuries remain controversial. For example, it is agreed that surgical treatment of most fracture dislocations with neurological compromise is warranted. However, predicting the stability of burst fractures in intact patients poses a much greater challenge. The objective of this study was to review all articles related to spinal instability to determine a consensus statement for a meaningful and practical definition of spinal instability applicable to thoracolumbar injuries. Furthermore, we propose that spinal instability should be redefined and viewed as either immediate or delayed. There are fractures that are immediately unstable, and others that potentially could lead to delayed instability. This identification could allow better decision making and patient counseling. MATERIALS AND METHODS A review of the literature using the Medline database (National Library of Medicine), between 1930 and September 2014 was performed. The following search strategy was used: “spinal” (All Fields) AND “instability” (All Fields) AND traumatic (All Fields) AND thoracolumbar (All Fields) AND “wounds and injuries” (MeSH Terms) OR “wounds” (All Fields) AND www.jspinaldisorders.com | 1 Copyright r 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. J Spinal Disord Tech Fard et al “injuries” (All Fields) OR “wounds and injuries” (All Fields) OR “injury” (All Fields). We reviewed listed references from pertinent search results and located relevant manuscripts from these lists as well. Abstracts were reviewed and articles related to definitions of spinal instability and stability in the thoracolumbar area were included. Only articles written in the English language were included. Case reports were excluded. Volume 00, Number 00, ’’ 2015 proposed mechanisms of injury (5 articles),4,8,9,13,15 or based on biomechanical data (1 article).20 The majority of these classification systems were introduced in an attempt to aid treatment decision making (11 articles). One classification system introduced was based on radiologic criteria and neurological presentation (TLICS).19 Explicit definitions of instability were introduced in 5 articles.3,10–12,16 These results are summarized in Table 1. RESULTS DISCUSSION The review produced a total of 694 published articles. Twenty-five articles were eligible after abstract screening and underwent full review (Table 1). The oldest article was from 1930, and the most recently published from 2014. In 12 of the 25 articles, the authors designed a new classification system. These systems are typically based on either anatomic structures (5 articles),5,7,14,21 Defining instability after traumatic thoracolumbar fractures is one of the most challenging and controversial areas in spine surgery. It is often difficult to determine whether an injury is stable or unstable. Current concepts of instability are primarily a product of biomechanical studies that are not easily applicable to available clinical data.23 The crux of the matter is that utilizing these TABLE 1. Summary of Articles Related to the Definition of Thoracolumbar Spinal Instability References Definition Bohler4 Watson-Jones5 Nicholl6 Holdsworth7 Panjabi22 Denis8 Ferguson et al9 Louis10 AAOS11 Stokes et al12 Benson13 McCormack14 Magerl et al15 Benzel16 Sharma et al17 Iencean18 Vaccaro et al19 Wang et al20 Baaj et al21 Comment Introduced a classification system based on mechanism of injury—5 groups (compression, flexion-distraction, extension, shear, and rotational injuries)—without definition of stability Seven types of fractures listed and emphasized 3 prominent injury categories: simple wedge compression fracture, comminuted fracture, and fracture dislocation The major determinant of stability was integrity of interspinous ligament Introduced the 2 column concept of stability—the integrity of the posterior bony elements and the posterior ligaments and ligamentum flavum, are the major determinant of stability Defined spinal instability as the inability of the spine under physiologic loads to maintain relationships between vertebrae such that there is neither acute nor subsequent neurological injury, deformity, or pain Introduced the 3 column concept for spinal instability–4 groups (compression, burst, seat belt, and fracture dislocation)—based on mechanisms of injury Thoracolumbar spinal injuries are classified on the basis of the mechanical mode of failure of the vertebral bodies. The fractures are presented in 7 categories Defined spinal stability based on the 3 column model The American Academy of Orthopedic Surgeons defined segmental instability as an abnormal response to applied loads, characterized by activity in the motion segment beyond normal constraints Segmental definition of instability—authors introduced segmental instability according radiologic landmarks in only lumbar degenerative diseases The fractures are divided into compression injuries, seat belt injuries, fracture dislocations, and burst fractures Introduced classification of fractures graded according to the degree of comminution of the body, apposition of the fracture fragments, and deformity Introduced classification based on mechanistic and morphologic criteria—3 groups (A compression, B distraction, C axial torque)—based on mechanisms and morphology of fractures—ligamentous injury not considered Anatomic definition of stability. Instability is defined as the inability to limit excessive spinal displacement. General definition for whole spine based on displacement Defines the efficacy of posterior ligaments on lumbar stability Spinal instability occurs because of lesion of the central axial spinal pillar TLICS classification system based on morphology, neurological involvement, and PLC Load sharing classification—no definition of stability or instability Radiographic classification for thoracolumbar fractures anatomically based on axial zones 2 | www.jspinaldisorders.com Copyright r Classification (mechanism) Anatomic and radiologic classification No definition Anatomic and clinical classification Biomechanical definition Clinical classification and definition (mechanism) Mechanistic classification Definition in lumbar spine Definition Biomechanical definition Clinical classification (mechanism) Clinical classification (anatomic) AO (Arbeitsgemeinschaft fur Osteosynthesefragen) Clinical Classification (mechanism) Definition Biomechanical definition—lumbar Clinical classification (anatomic) Clinical classification In vitro biomechanical classification Anatomic, clinical classification 2015 Wolters Kluwer Health, Inc. All rights reserved. Copyright r 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. J Spinal Disord Tech Volume 00, Number 00, ’’ 2015 definitions would require the application of loads that would be unsafe if indeed the spine was unstable. We are therefore left with classification systems that attempt to predict instability indirectly. There have been multiple descriptive and mechanistic classification systems for thoracolumbar injuries.4–41 These systems have evolved with an increased understanding of spinal biomechanics and advances in clinical imaging. Various classification systems have been developed that more or less incorporate the concept of stability. To be of clinical utility, the information conveyed in a classification system should aid the physician in guiding treatment. Despite numerous new classification systems for spinal injuries, a clinically applicable and meaningful definition for spinal instability in thoracolumbar trauma remains elusive. In addition to the definition posited by White and Panjabi in 1978,5 Denis,8 previously introduced the 3 column concept of the spine in 1983. According to Denis, radiographic failure of the middle column was key in defining the spinal instability. The American Academy of Orthopedic Surgeons defined segmental instability in 1985, as an abnormal response to applied loads, characterized by activity in the motion segment beyond normal constraints.11 Vaccaro et al19 in 2005, introduced the thoracolumbar injury classification and severity score system (TLICS) as a practical algorithm for the description and treatment of traumatic thoracolumbar fractures. This classification system provided a simple and reproducible severity scoring system that can be used as a guideline to orient the clinical decision making between conservative and surgical management. It takes into account the mechanism of injury (as inferred by radiographic characteristics), neurological status, and the integrity of the posterior ligamentous complex. Use of this system will still result in many scenarios where patients will be placed in an indeterminate category that calls upon a surgeon’s judgment.19,24 It is these types of cases in particular where we believe a better working definition of spinal instability can aid in both treatment decision making and communication to the patient. These are typically patients who have a burst fracture with minimal or no posterior element disruption and are neurologically intact. Patients with comminuted burst fractures deserve special attention, even if initially classified as nonoperative according to the TLICS algorithm. Patients with bony Chance fractures without misalignment and patients with progressive kyphotic deformity after conservative management of compression fracture are the other aspects related to instability that are not addressed in the TLICS classification. This review has highlighted the following facts: (1) there are several thoracolumbar classification systems that suggest instability and surgical criteria, but (2) there remains no practical, contemporary definition of spinal instability. Furthermore, instability does not always equate with need for surgery and vice versa. We propose that traumatic fractures should not be viewed simply as Copyright r 2015 Wolters Kluwer Health, Inc. All rights reserved. Instability in Thoracolumbar Trauma TABLE 2. Examples of Common Fractures Causing Immediate or Potentially Delayed Instability Immediately instability Fracture dislocation Burst with complete disruption of posterior elements and kyphosis Ligamentous Chance-type fracture with malalignment Delayed instability Compression fracture Burst fracture with minimal or no posterior element disruption or malalignment Bony Chance-type fracture without malalignment Delayed instability present in the form of prolonged pain, pseudoarthrosis, or deformity progression. “stable” or “unstable”; rather they should be viewed as having the potential for “immediate” or “delayed” instability. For example, a fracture dislocation with neurological compromise should be viewed as an immediately unstable injury. Whereas a mild burst fracture in an intact patient should be regarded as not immediately unstable but rather having the potential for delayed instability. Similarly, a compression fracture typically is not immediately unstable but rather could cause delayed instability. Delayed instability, in these instances, could mean delayed healing, prolonged pain, or progression to deformity for example. Adopting these concepts and this language could better guide both surgical decision making and patient counseling (Table 2). CONCLUSIONS More than 3 decades after White and Punjabi’s original definition of instability, and many classification schemes later, there remains no clinically practical definition for spinal instability in thoracolumbar trauma. As a result, surgeon expertise and experience remains the most important factor in stability determination in many cases. To better make surgical decisions, and counsel patients, we propose making a distinction between fractures that lead to “immediate” versus “delayed” instability. 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