Imaging Musculoskeletal Trauma E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Serie: Current Clinical Imaging
• Sprache: Englisch

Seitenzahl: 873

Veröffentlichungsjahr: 2012

Beschreibung

Offers a well-designed approach to imaging musculoskeletal trauma Medical imaging plays an important role in identifying fractures and helping the patient return to regular activities as soon as possible. But in order to identify the fracture, and describe all the relevant associated injuries, the radiologist first needs to understand normal anatomy and the mechanisms of fractures. Imaging Musculoskeletal Trauma reviews common fracture and dislocation mechanisms and provides up-to-date guidelines on the use and interpretation of imaging tests. Designed for use by professionals in radiology, orthopedics, emergency medicine, and sports medicine, this book offers a concise, systematic approach to imaging musculoskeletal trauma. Replete with easily accessible information, including well-designed tables and lists, the book features radiology report checklists for each anatomic site, numerous radiographs and CT and MRI images, simple illustrations for common fracture classification schemes, examples of common and serious injuries in the musculoskeletal system, and a chapter devoted to fracture complications--including complications relating to the use of hardware in treating injuries. This well-designed guide teaches professional and student users to: * Identify normal anatomy relevant to interpretation in musculoskeletal studies * Describe common fracture and dislocation mechanisms * Describe fractures using appropriate terminology * Recommend appropriate imaging studies for various clinical situations * Use a systematic approach to interpret imaging studies * Provide a clear and relevant radiology report * Recognize complications associated with fractures and fracture treatment Complete with on-call issues, common traumas, and specially highlighted "do-not-miss" fractures, this is an invaluable resource for everyone involved with the imaging of musculoskeletal trauma.

Leseprobe

Contents

Preface

List of Contributors

CHAPTER 1 Essential Concepts in Imaging Musculoskeletal Trauma

Introduction

Fracture mechanism and epidemiology

Appropriateness criteria for imaging musculoskeletal trauma

Approach to accurate fracture detection on radiographs

Description of fractures and joint injuries

Classification of fractures

Special types of fractures (stress, insufficiency, and pathologic)

Essential elements of the radiology report

CHAPTER 2 Pediatric Skeletal Trauma

Fracture principles in children

Appropriateness criteria for imaging musculoskeletal trauma in children

Approach to interpretation of pediatric radiographs in musculoskeletal trauma

Classification of fractures in pediatric patients

Little Leaguer’s shoulder

Elbow injury in children

Supracondylar fractures

Medial epicondyle fractures

Lateral condyle fractures

Avulsion fractures in the pelvis

Avulsion fractures of the tibial tubercle

Patellar sleeve avulsion fractures

Tillaux and Triplane fractures

Pediatric spine trauma

Musculoskeletal manifestations in non-accidental trauma (child abuse)

CHAPTER 3 Spine

Cervical spine anatomy

Appropriateness criteria for imaging cervical spine trauma

Approach to interpretation of cervical spine radiographs

Approach to interpretation of cervical spine CT

Craniocervical injuries

Occipital condyle fractures

Craniocervical junction dislocations and subluxations

Atlas (C1) fractures

Axis (C2) fractures

Subaxial cervical spine fractures

Hyperflexion injuries

Hyperextension injuries

Axial loading injuries

Thoracolumbar spine

Thoracolumbar spine injuries

Compression fractures

Burst fractures

Flexion distraction injuries

Hyperextension injuries

Fracture-dislocations

CHAPTER 4 Shoulder and Proximal Humerus

Anatomy

Appropriateness criteria for imaging shoulder trauma

Approach to interpretation of shoulder radiographs

Proximal humeral fractures

Humeral shaft fractures

Glenohumeral joint dislocations

Scapular fractures

Sternoclavicular joint dislocations

Clavicular Fractures

Acromioclavicular joint dislocations

CHAPTER 5 Elbow and Forearm

Anatomy

Appropriateness criteria for imaging elbow trauma

Approach to interpretation of elbow radiographs

Radial head and neck fractures

Olecranon fractures

Elbow dislocations

Fractures of ulna and radius shafts

CHAPTER 6 Wrist and Hand

Anatomy

Appropriateness criteria for imaging hand and wrist trauma

Approach to interpretation of hand and wrist radiographs

Distal radius and ulna fractures

Carpal bone fractures

Carpal dislocations

Metacarpal and phalangeal fractures

Dislocations at the hand

CHAPTER 7 Pelvis and Proximal Femur

Anatomy

Appropriateness criteria for imaging pelvis and proximal femur trauma

Approach to interpretation of pelvic radiographs

Pelvic ring fractures

Acetabular fractures

Hip dislocations

Femoral head fractures

Intracapsular femoral neck fractures

Extracapsular femoral neck fractures

Subtrochanteric and femoral shaft fractures

CHAPTER 8 Knee and Tibia and Fibula Shafts

Anatomy

Appropriateness criteria for imaging knee trauma

Approach to interpretation of knee radiographs

Distal femur fractures

Tibial plateau fractures

Tibiofemoral joint dislocations

Proximal tibiofibular joint dislocation and proximal fibula fractures

Patellar fractures

Patellar dislocations

Fractures of tibial and fibular shaft

CHAPTER 9 Ankle and Foot

Anatomy

Appropriateness criteria for imaging foot and ankle trauma

Approach to interpretation of ankle and foot radiographs

Pilon fractures

Malleolar fractures

Osteochondral lesions of the talus

Talar fractures and dislocations

Calcaneal fractures

Navicular fractures

Cuboid fractures

Lisfranc fracture-dislocations

Metatarsal and phalangeal fractures and dislocations

CHAPTER 10 Fracture Healing and Complications of Fractures

Fracture healing and healing problems

Imaging evaluation of fracture healing

Fracture complications

Articular disease

Osteonecrosis

Infection

Soft tissue complications

Treatment and hardware complications

Systemic complications

Other osseous abnormalities

Index

This edition first published 2012, © 2012 by John Wiley & Sons, Ltd.

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Library of Congress Cataloging-in-Publication Data

Imaging musculoskeletal trauma : interpretation and reporting / edited by Andrea Donovan, Mark Schweitzer. p. ; cm. Includes bibliographical references and index.

ISBN 978-1-118-15881-4 (hardback : alk. paper)I. Donovan, Andrea. II. Schweitzer, Mark E., MD.[DNLM: 1. Diagnostic Imaging–methods. 2. Musculoskeletal System–injuries. WE 141]616.7′075–dc23

2012017383

A catalogue record for this book is available from the British Library.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

Cover Design: Michael RutkowskiCover Illustration: © Sergey Galushko/iStockphoto

Preface

The idea for this book came from an expressed need by radiology residents for a “how to” resource on reporting musculoskeletal trauma. Recent changes in the structure of residency training, including duty hour restructuring and an increased clinical workload, has led to a decrease in not only “view-box” teaching but also in the total number of cases reviewed by the residents during their training. Residents have sought a resource for use on call as well as during emergency and musculoskeletal radiology rotations. Recent graduates have also felt a need for a ­succinct resource. The purpose of this book is to fill those gaps and provide the reader with an approach to acute trauma radiographs, CT and MR, and skills to identify and correctly interpret the findings.

My interest in musculoskeletal trauma and love for teaching, together with my current practice at the largest trauma center in Canada and support from my co-editor Dr. Mark Schweitzer, helped to develop a set of ideas into a book. I hope that our experience and dedication, together with that of our seventeen contributing authors, have led to a product that will satisfy the needs of radio­logy residents and practicing radiologists.

Unique features that were included in this book are the “key points” given at the beginning of each section and the interpretation “pearls” at the end. The frequent use of bulleted points helps to summarize relevant normal and abnormal measurements (angles, distance) for each anatomic site. Checklists are provided for radiograph and CT interpretation as a summary to ensure clear and clinically relevant reports. These lists also provide a quick future reference when reporting.

The chapters are organized to allow the reader to read the book cover to cover, or select specific chapters of interest. The first chapter provides the reader with basic ­fracture concepts, including biomechanics, fracture mechanism, and healing, followed by an approach to the description of fractures and dislocations. Subsequent chapters are based on anatomic sites, including spine and appendicular skeleton. Each chapter is similarly structured, beginning with an outline of key features, normal relevant anatomy, and a selection of appropriate imaging. For each type of traumatic injury, bulleted points and tables, in addition to the text, outline an approach to radiographs, classification schemes, and key pertinent descriptions that are necessary to be included in the report. Drawings and images facilitate the illustration of mechanisms of injury. The last chapter covers fracture complications and treatment complications.

This book is the collective effort of many individuals. First, I would like to thank my co-editor, Dr. Mark Schweitzer, for his ongoing mentorship and support as well as his supersonic energy and passion for musculoskeletal radiology. It is a tremendous privilege to work together! Second, many thanks to all of my seventeen radiology colleagues who contributed to the chapters in this book. Your hard work, excellent figures, illustrations, and text are greatly appreciated. This book would not have been possible without all of your efforts! Special thanks to Dr. Chris Granville for beautiful illustrations in the pelvic chapter, as well as Dr. Leon Rybak and Dr. Ritika Arorafor contributing images to the hand and wrist chapter, and Dr. Rita Putnins, Dr. Cicero Torres and Dr. Philip Hodnett for contributing images to the pediatrics ­chapter. Third, I am indebted to Wiley–Blackwell, my publisher, and the team that helped to bring this collective work into a final published text. My thanks to Ian Collins, Senior Editorial Assistant and Thom Moore, Senior Editor, Oncology & Radiology in Hoboken New Jersey, for their help with the initial book proposal and development. Thanks to Kate Newell, Senior Development Editor, Rob Bundell, Production Editor, and their team in the Oxford office in England, for their work in putting the finishing edits together! Last, but not least, I would like to thank my husband, Dr. Jeff Donovan, for his support, encouragement, and help to edit the book. I could not imagine completing this book without his selfless help, patience, and love.

I hope the reader finds this book to be a helpful aid to the interpretation of musculoskeletal trauma.

Andrea Donovan, MDSunnybrook Health Sciences CentreToronto, Ontario, Canada

List of Contributors

Emad Almusa, DODepartment of RadiologyUniversity of PittsburghPittsburgh, PAUSADeep Chatha, MDDepartment of Diagnostic ImagingCML HealthcareToronto, ONCanadaJorge Davila, MDDiagnostic Imaging DepartmentUniversity of OttawaChildren’s Hospital of Eastern OntarioOttawa, ONCanadaRafael Glikstein, MDDepartment of Medical ImagingThe Ottawa HospitalUniversity of OttawaOttawa, ONCanadaAndrew Haims, MDDepartment of Diagnostic RadiologyYale University School of MedicineNew Haven, CTUSAChris Heyn, MD, PhDDepartment of Medical ImagingUniversity of TorontoToronto, ONCanadaPhilip Hodnett, MDDepartment of RadiologyLimerick University HospitalIrelandStamatis N. Kantartzis, MDDepartment of RadiologyUniversity of PittsburghPittsburgh, PAUSAKhaldoun Koujok, MDDiagnostic Imaging DepartmentUniversity of OttawaChildren’s Hospital of Eastern OntarioOttawa, ONCanadaJoshua Leeman, MDDepartment of RadiologyUniversity of PittsburghPittsburgh, PAUSAAndrew Lischuk, MDDepartment of Diagnostic RadiologyYale University School of MedicineNew Haven, CTUSAMarcos Loreto Sampaio, MDDepartment of Musculoskeletal RadiologyThe Ottawa HospitalUniversity of OttawaOttawa, ONCanadaKristen Menn, MDDepartment of Diagnostic RadiologyYale University School of MedicineNew Haven, CTUSAElka Miller, MDDiagnostic Imaging DepartmentUniversity of OttawaChildren’s Hospital of Eastern OntarioOttawa, ONCanadaCarmen Rotaru, MDDiagnostic Imaging DepartmentUniversity of OttawaChildren’s Hospital of Eastern OntarioOttawa, ONCanadaAdnan Sheikh, MDDepartment of Medical ImagingThe Ottawa HospitalOttawa, ONCanadaEdward Smitaman, MDDepartment of Diagnostic RadiologyYale University School of MedicineNew Haven, CTUSA

CHAPTER 1

Essential Concepts in Imaging Musculoskeletal Trauma

Andrea Donovan

Department of Medical Imaging, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Canada

Introduction

Traumatic injuries to the musculoskeletal system are extremely common. These injuries are among the short list of medical disorders that may be completely resolved if recognized and appropriately treated. As radiologists, we have an important role in the diagnosis. In order to identify the abnormality and characterize it correctly, it is essential to be familiar with normal anatomy, protocols for imaging tests, patterns of injury, and implement an organized approach to image interpretation. The radiology report needs to be concise, yet include relevant information required for effective clinical management. It is important to be familiar with common fracture classification systems and understand how different grades of injury potentially affect treatment. Furthermore, it is important to be familiar with common treatment options for fracture and joint fixation, and be able to recognize potential complications on follow-up imaging.

Throughout this book, we emphasize the importance of an organized approach for the interpretation of imaging studies. This systematic approach includes assessment of the soft tissues, since an abnormality in the soft tissues can point to an abnormality in the adjacent joint or bone. In addition to a general approach, a checklist at specific anatomic sites is also needed to ensure that common sites of injury are evaluated for a fracture or dislocation. These specific sites of injury are discussed in the subsequent chapters, including the spine, pelvis, major joints, and long bones.

Fracture mechanism and epidemiology

Traumatic injury to the skeletal system is common at all ages. The location and appearance of the fracture depends on the mechanism of injury, age of the patient, and predisposing factors, such as an underlying osseous lesion [1]. The most common mechanism of fractures in the adolescent population is sports-related [2]. Adults are more likely to sustain an injury related to their occupation or related to a motor vehicle accident. There is a significant difference in fracture incidence between adult males and females. Fractures are more common in men before the age of 50, while after the age 50, women experience more fractures due to osteoporosis [3]. In the elderly, routine daily activities may result in a fracture, such as walking or using the stairs [4].

Motor vehicle accidents are currently the leading cause of death between the ages of 5 and 34 years [5]. Injury in these patients is usually more extensive and severe, with involvement of the pelvis, the spine, several joints and long bones. Falls are a common mechanism of injury at any age. Falls from a height are usually related to occupation, such as construction work, and often result in multiple fractures [6]. A fall on the outstretched hand is a common mechanism and results in different fractures depending on patient age. Supracondylar distal humerus or distal radius metaphyseal fractures are common in children. Colles’ type distal radius fractures predominate in adults and proximal humeral fractures are common in elderly females.

Fractures may result from either a direct force or an indirect force transmitted from a different site, away from the actual fracture. Radiographs are helpful to infer the mechanism of a fracture including the direction and magnitude of applied force [5–7].

Direct force

Direct forces on a bone include direct blow, crush injury, gunshot injury or sharp object laceration. Direct blows most commonly affect the forearm or leg. These may result in a transverse fracture to the ulna (nightstick fracture), or a transverse fracture to the tibia or the femur (Figure 1.1(a)). High-energy crush injury results in fragmentation of bone and there is usually a component of soft tissue injury (Figure 1.1(b)). Gunshot related fractures either result in severe comminution in cases of high-velocity bullet injury, or a divot in the cortex in cases of low-velocity ballistic injury (Figure 1.2). Saw injury is common in metal sheet workers and may result in a complete or incomplete traumatic amputations or lacerations, usually of the hand (Figure 1.3).

Figure 1.1 Direct force resulting in transverse fractures. (a) High-velocity injury with transverse distal femoral shaft fracture with one shaft-width lateral displacement and mild overlap. (b) High-energy crush injury to the arm with a large soft tissue defect in the proximal arm and predominantly transverse, fragmented, distracted proximal humerus shaft fracture.

Figure 1.2 Gunshot injuries and open fractures. (a) Pelvis radiograph shows radiodense bullet fragments projecting over the left lower quadrant with an associated comminuted iliac fracture. Mottled lucency represents soft tissue gas. (b) Hip radiograph in a different patient shows multiple metallic fragments in the soft tissues of the thigh and a comminuted proximal femoral shaft fracture. Soft tissue gas is seen about the fracture.

Figure 1.3 Crush injury with soft tissue amputation and associated fractures to the tufts of the index and long fingers.

Indirect force

Indirect forces on a bone include compression, tension, shear, rotation, and bending forces. Fractures may result from only one of these vectors, or more commonly, a combination of vectors. The resultant fracture orientation on radiographs can be used to infer the original dominant force vector.

Compression force compacts or pushes two objects together. It results in an oblique fracture of a long bone (Figure 1.4). Examples include fracture of the distal fibula with ankle inversion injury and resultant com­pression laterally. Compression is rarely the only force acting on a long bone. There is usually a combination of compression and angulation forces that lead to a shearing vector. Compression force is a frequent vector in spine injuries.

Shear force slides two parts of an object in opposite direction past one another. It results in an oblique fracture of a long bone. These fractures tend to be less stable than others. There is also often a compression vector involved that is present in addition to the shear vector (Figure 1.4(b)).

Tension force pulls or stretches two objects apart. It results in a transverse fracture. Examples include medial malleolar fracture following ankle eversion (Figure 1.5), olecranon fracture from pull of the triceps tendon or patella fracture related to pull of the quadriceps tendon.

Figure 1.4 Compression and shear forces resulting in oblique fractures. (a) Oblique distal fibular fracture related to a combination of compression and angulation. (b) Oblique midshaft femur fracture related to compression and shear vector.

Rotation force twists an object. It results in a spiral fracture, most commonly seen in the leg (Figure 1.5). Spiral fracture may be distinguished from an oblique fracture by the presence of two fracture planes.

Figure 1.5 Tension and rotation force resulting in transverse and spiral fractures. AP view of the ankle shows a transverse medial malleolar fracture related to avulsion by an intact deltoid ligament. Spiral fibular fracture shows two distinct fracture planes (arrows).

Bending or angulation force produces a curve on an object with resultant tension vector on the convex side and compression vector on the concave side. These ­fractures tend to produce a butterfly fragment along the concave, compression side (Figure 1.6).

Appropriateness criteria for imaging musculoskeletal trauma

The American College of Radiology (ACR) devised several guidelines for selecting the appropriate imaging test in a patient who sustained musculoskeletal trauma. These guidelines are published as ACR Appropriateness Criteria® for several clinical scenarios including ­suspected spine trauma, acute shoulder pain, acute trauma to the hand and wrist, to the knee, and to the foot and ankle. These guidelines are available on the ACR web site (www.acr.org/ac). In addition, there are several clinical ­guidelines that help clinicians select patients who do, or do not, require radiographs to evaluate their injury. These clinical guidelines include the Ottawa Ankle Rules [8], the Ottawa Knee Rule [9], and the Canadian Cervical Spine Rule [10].

Figure 1.6 Bending and angulation force resulting in a butterfly fragment. (a) Butterfly fragment along the mid-ulnar shaft (arrows). (b) Displaced butterfly fragment in a mid-femoral bending wedge fracture. Bending force results in a tension vector on the convex side and compression vector on the concave side. Butterfly fragment is seen on the concave, compression side.

Radiographs

Radiographs are the initial imaging test of choice ­following skeletal trauma. The decision to perform a radiograph usually depends on the clinical history and physical examination. There may be, however, additional influencing factors such as patient expectations and fear of litigation. It is therefore important to be familiar with the indications for imaging in order to limit unnecessary exams. Up to 75% of skeletal radiographs in the emergency room are normal, with the greatest ­proportion of these being cervical spine and knee ­radiographs [11].

Most fractures can be detected on standard trauma series radiographs. In situations where there is a high clinical suspicion for a fracture, but negative radiographs, the patient may be splinted and repeat radiographs ­performed in 6 to 10 days. This may help to identify a somewhat more overt, subacute fracture.

In the polytrauma patient, it may not be possible to obtain adequate views. In that setting, cross sectional imaging with computed tomography (CT) is recommended. CT is also recommended in complex fractures at a joint, pelvic fractures and spine injury. Magnetic Resonance (MR) imaging is occasionally helpful in cases of occult fractures, or when there is concern for associated ligament or articular cartilage injury. Ultrasound is used in the assessment of soft tissue injury, and most ­commonly in the setting of tendon tears such as the quadriceps or the Achilles. Most foreign bodies can also be well visualized on ultrasound.

Radiographs should be obtained in a minimum of two orthogonal projections. Additional oblique or axial views are often useful to accurately detect a fracture. For example, tibial plateau fractures and radial head fractures may only be seen on the oblique view (Figure 1.7), while the axillary view of the shoulder is often needed to evaluate for shoulder articular congruence. Special views are described in subsequent chapters for each anatomic site. Stress-views are obtained with application of manual stress, and help in detection of ligament injury at the ankle (Figure 1.8), wrist or the knee for example. These are rarely useful in the acute setting, because soft tissue swelling and muscle spasm may mask underlying ­ligament injury [12].

Figure 1.7 Importance of oblique views for fracture detection. (a) AP view does not show a definite radial head fracture. (b) Oblique view clearly demonstrates a fracture lucency (open arrow) and extension to the articular surface (closed arrow).

Figure 1.8 Stress view to evaluate ligament insufficiency at the ankle. Telos ankle apparatus is shown with varus stress applied to the ankle. There is abnormal widening of the lateral ankle gutter, which was absent on the nonstress views.

Computed Tomography (CT)

CT is commonly used in the trauma patient to identify and characterize the injury. The advantage of CT over radiography is the ability to identify subtle fractures, visualize articular fracture extension and assess for the presence of articular step-off or gap. Small intra-articular bodies that may prevent adequate reduction can also be visualized (Figure 1.9). Avulsion fractures on CT infer the presence of associated ligament or tendon injury. CT is also used to characterize fractures at complex anatomic sites such as the spine, pelvis, shoulder, elbow, sternoclavicular joint, and foot and ankle. At these locations, the overlap of osseous structures limits the ability of radiographs to accurately detect and characterize fractures [13].

Reformatted images in coronal and sagittal planes offer enhanced fracture detection. For example, axially oriented sacral fractures may only be detected on ­reformatted sagittal or coronal images, and not the axial images. Orthopedic surgeons find 3D reconstructed CT images helpful to visualize the position of fracture ­fragments and to plan the surgical approach (Figure 1.10). Most surgeons have a preference for ­translucent bone rendered images (Figure 1.10(a)) to show fracture ­relationships rather than surface rendered images (Figure 1.10(b)) that may partly obscure osseous detail. The addition of intravenous contrast facilitates evaluation for vascular injury including vasospasm, vessel transection, intimal injury and active extravasation (Figure 1.11). In many patients, CT angio­graphy precludes the need for conventional angiography. Following reduction of a dislocation, CT is helpful to assess the adequacy of joint alignment and the congruency of articular surfaces. This congruence is especially important to prevent future osteoarthrosis. In patients with suspected delayed union or nonunion, CT can assess fracture ­healing, which is evident by osseous bridging.

Figure 1.9 CT for detection of intra-articular bodies. Sagittal reformatted image through the olecranon shows an intra-articular ossific body (arrow) within the joint in a patient who sustained an elbow fracture-dislocation.

Figure 1.10 Bone CT 3D reconstructed images. (a) Translucent bone 3D volume-rendered CT of AP pelvis and (b) bone 3D surface rendered images through the pelvis. Many orthopedic surgeons find these images helpful in planning surgery. This patient has a vertical shear injury with a distracted right sacral fracture, offset at the symphysis and left iliac wing distracted fracture. Translucent bone rendering in image (a) more clearly shows the fracture extent and relationships between fragments. Surface rendering in image (b) partly obscures the fracture by the overlying bone.

Magnetic Resonance (MR) imaging

MR imaging is the modality of choice in the assessment of internal derangement of joints. This includes evaluation of the articular cartilage, ligaments, tendons, menisci, and fibrocartilagenous labrum. Occult fractures are also well visualized because of sensitivity of MR for marrow edema. Fracture lines are usually best depicted on T1-weighted sequences as linear low signal intensity. Surrounding marrow edema on T2-weighted sequences also helps to identify the fracture site. Subtle tibial plateau fractures, proximal or distal femur fractures may be radiographically occult, yet readily identified on MR (Figure 1.12) [14]. Bone bruises appear as an area of T2 hyperintense signal, with no discrete low signal intensity fracture line. Stress fractures in the long bone are ­characterized by a low signal intensity line on T1-weighted images with surrounding marrow edema on T2-weighted images. In the midfoot, diffuse marrow edema, even in the absence of a discrete fracture line, may represent a fracture. Proton density sequence is reserved for imaging the menisci, articular cartilage, ligaments, and tendons (Figure 1.13(a)).

Figure 1.11 CT angiogram in a patient with distal femoral displaced fracture. (a) Maximum intensity projection (MIP) image shows transection of the right popliteal artery (arrow). (b) Axial image shows a severely displaced right distal femoral shaft fracture with both the proximal and distal shaft visualized on the same image.

Figure 1.12 Occult tibial plateau fracture on MR. (a) Coronal T1- and (b) T2-weighted, fat-suppressed images through the knee show a minimally depressed lateral tibial plateau fracture, with a low signal intensity fracture line paralleling the articular surface (arrow) and adjacent marrow edema. The fracture was not detected radiographically.

MR imaging of osteochondral injury is helpful to characterize the fragment size and potential stability [15–17]. Osteochondral fractures may be described as either ­displaced (fragment is at least partly displaced into the joint) or impacted (subchondral bone and overlying ­cartilage are impacted into the adjacent medullary cavity with no major displaced osteochondral fragment) [15]. Typical displaced fractures include those of the patella ­following a dislocation, while typical impacted fractures include femoral condyle subchondral fractures (Figure 1.13(b)). MR is sensitive in the detection of displaced fragments into the joint. Impacted fractures are associated with extensive marrow edema on T2-weighted images. The typical appearance of a femoral condyle osteochondral impacted fracture is marrow edema extending all the way to the intercondylar notch and a low signal intensity line at the impaction site, paralleling the articular surface.

Figure 1.13 Anterior cruciate ligament injury and femoral condyle osteochondral impaction injury. (a) Sagittal proton density image shows a discontinuity in the mid ACL fibers (arrow). (b) Sagittal T2-weighted fat-suppressed image shows an impacted fracture at the level of the lateral sulcus (arrow).

Figure 1.14 Bone scan in an insufficiency fracture. (a) Static image from the bone scan shows focal increased activity in the left distal fibula. (b) Radiograph confirms the fracture evident by linear sclerosis in the distal fibular shaft (arrow).

Bone scintigraphy

The most common use of bone scintigraphy in the setting of trauma is to facilitate detection of radiographically occult fractures, stress fractures and insufficiency fractures [18]. Bone scans are also used in situations where ­cross-sectional imaging is not available or is contraindicated. Specific clinical situations where bone scintigraphy is ­useful are fractures at the hip, scaphoid and some types of stress fractures [19]. The scintigraphic pattern varies with the age of the fracture, as well as the age of the patient. Approximately 80% of scans are positive within 24 hours of injury and 95% of scans are positive within 72 hours [20]. There are however, false negative scans, especially when evaluating acute injuries in elderly patients [21].

There are three characteristic scintigraphic patterns that reflect different stages of fracture healing [20]. The acute fracture appears as a diffuse area of increased activity at the fracture site, and this appearance will persist for 2 to 4 weeks after injury (Figure 1.14). The subacute fracture is characterized by a linear area of increased activity, and persists for 8 to 12 weeks. With further healing, the area of increased activity on bone scintigraphy gradually diminishes, but can persist for 5 to 7 months. In the vast majority of patients (90%), the bone scan returns to ­normal within 2 years following injury [20]. In general, bone scans return to normal faster in younger patients.

Figure 1.15 Ultrasound-detected fracture. (a) Sagittal image through the distal thigh shows a fracture (arrow) involving the distal demur, proximal to the patellofemoral joint. (b) AP radiograph confirms the fracture evident by cortical buckling (arrow). (c) Coronal fat-suppressed proton density image shows the bright fracture line and adjacent periosteal edema (arrow).

Stress fractures can usually be identified on scintigraphy within 1 to 3 days of occurrence, while radiographs may remain negative for 2 to 3 weeks [22]. There are several mimickers of fractures on bone scintigraphy including metastatic disease, infection and traumatic synovitis [19].

Ultrasound

The primary role of ultrasound in the setting of trauma is the assessment of soft tissues. Ultrasound is useful in the characterization of focal tendon tears. The most common requests from the emergency department for musculoskeletal ultrasound include evaluation of the Achilles tendon, quadriceps tendon, distal insertion of the long head of biceps tendon and assessment of the rotator cuff [23, 24]. The presence of a complex joint effusion in the setting of trauma is compatible with a hemarthrosis and implies either a ligament injury or an intra-articular fracture. In patients who have sustained trauma, and have focal tenderness, it is important to evaluate the underlying cortex for a fracture. It is not infrequent that a fracture is detected on ultrasound when soft tissue injury is suspected clinically (Figure 1.15). Ultrasound can detect callus at an early stage of bone healing, and may have some role in fracture detection in infants [25].

Approach to accurate fracture detection on radiographs

Potential fracture mimickers

There are several potential mimickers of a fracture on radiographs. It is important to be familiar with the typical location and appearance of these mimickers to avoid ­mistaking them for a fracture. These potential mimickers include vascular channels, physeal fusion lines, and accessory ossicles. Visual misperception can also lead to the false positive interpretation of radiographs.

Vascular channels

Vascular channels for nutrient arteries are differentiated from fractures by sclerotic margins and their typical location and course. Vascular channels begin, and are more often seen, at the mid aspect of a long bone. A general rule is that vascular channels course diagonally so that they point toward the knee (Figure 1.16(a)), away from the elbow and toward the distal aspect of the phalanges [5]. Vascular channels should not extend into the medullary canal or involve any portion of the cortex that is not ­projected in profile.

Junctional lines

The junctional lines of fusion between the epiphysis and diaphysis, or the physeal scar, are most prominent in the lower extremities. These appear as a transverse sclerotic line in the metaphysis (Figure 1.16(b)). The location of junctional lines is predictable and should not be mistaken for an insufficiency or stress fracture. In the distal radius, the healed physis may mimic an intra-articular fracture.

Accessory ossicles

There are many accessory ossicles, some of which may be mistaken for a fracture, especially around the foot. These include an accessory navicular (Figure 1.16(c)) and the os peroneum. Accessory ossicles should be ­distinguished from a fracture based on sclerotic margins, rounded morphology, and typical locations. It is helpful to refer to the atlas of normal variants in cases of uncommon ossicles to verify that they indeed represent a ­normal variant.

Figure 1.16 Radiographic mimickers of fractures. (a) Vascular channel is shown in the distal femoral shaft (arrows). The margins are smooth and lucency is limited to the cortex. (b) Junctional line or physeal scar in the distal tibia (arrow) as well as a healing, lucent and sclerotic distal fibular fracture (open arrow). (c) Accessory navicular ossicles are well corticated (arrow). (d) Mach bands may simulate a fracture. They appear as lucent lines in the cortex of the tibia and fibula (arrows).

Mach bands

Mach bands represent an optical illusion and should not be mistaken for a fracture. They appear at sites of cortex overlap between two bones, or skin fold overlap of the cortex [26]. This phenomenon is related in part to edge enhancement that the eye creates at the border between two superimposed objects. The mach bands appear as a lucent line and may be mistaken for a fracture. The most common site for this phenomenon is on ankle radiographs, where the tibia overlaps the fibula (Figure 1.16(d)).

Pattern search approach to radiographs in musculoskeletal trauma

1. Collect clinical information

In the trauma patient, it is important to collect information about the site and mechanism of injury prior to radiographic assessment. For multi-trauma patients, it is useful to know the most significant injury by reviewing additional imaging and reports. This information will help to guide search pattern for additional injuries that may occur with similar mechanisms. For example, a patient with a known calcaneal fracture should be carefully assessed for thoracolumbar spine burst ­fractures.

2. Compare to prior imaging

Prior imaging is sometimes available from an outside institution, and it is important to retrieve and review such imaging, if at all possible. A joint that appears reduced on the current study may have been dislocated on the prior study. This information is useful to guide the radiologist to inspect for fractures commonly associated with dislocations. If possible, the radiologist should obtain clinical history regarding the site of pain or the technologist can be advised to place markers at the site of tenderness [27]. This practice can improve fracture detection, especially in small bones.

3. Evaluate for radiographic signs of a fracture

Lucent fracture line

Most fractures appear as a radiolucent line. In nondisplaced fractures, the lucent line is thin and may be difficult to appreciate. In displaced fractures, with separation of fracture fragments, the fracture line is more overt (Figure 1.17). Visualization of the fracture on radiographs depends on the angle the X-ray beam makes with the ­fra­cture. Therefore, two orthogonal projections facilitate fracture detection. In 5% of fractures, the fracture line is only visualized on one of the two orthogonal projections. In another 5% of fractures, they are only visualized on an oblique (non-AP or lateral) projection. This is more common with fractures that occur at the end of the bone rather than involve the shaft (Figure 1.18). The vast majority of fractures however, are visualized in both AP and lateral projection.

Sclerotic fracture line

Compression fractures may appear as a sclerotic, rather than lucent line. The most common locations for traumatic compression are the vertebral bodies and distal radius related to axial loading (Figure 1.19(a)). A tibial plateau depression fracture also often results in a ­sclerotic, rather than lucent fracture line.

Figure 1.17 Separation of fracture fragments. (a) AP view shows a faint lucent line in the distal tibia (arrow). (b) Oblique view shows separation of the fracture fragments and intra-articular extension (arrows).

Figure 1.18 Fibular fracture visible on lateral view only. (a) Lateral view of the ankle shows an oblique distal fibular fracture (arrow). (b) AP view shows lateral soft tissue swelling, but the fracture is not well visualized.

Double line

Impaction fractures of a round end of the bone may appear as a sclerotic linear density or as a double line. Examples include a humeral head impacted fracture following a shoulder dislocation or a femoral head fracture following a hip dislocation (Figure 1.19(b)). The fracture is a result of impaction of a round articular surface against a firm edge of the adjacent bone. The result is a trough-like depression in the humeral or femoral head.

Cortical buckling

Commonly missed fractures are those that appear as cortical buckling in the absence of a fracture line traversing the bone. These can be seen in the distal radius and involving the radial neck region (Figure 1.20). Cortical buckling may only be seen on one view, so it is important to carefully inspect all projections.

Figure 1.19 Sclerotic fracture lines related to impaction. (a) Distal radius impacted fracture shows a sclerotic line related to impacted trabeculae (arrow). (b) AP view of the shoulder shows a vertical sclerotic line (arrow) related to anteromedial humeral head impaction fracture in a patient with posterior dislocation.

Figure 1.20 Cortical buckling. Radial neck fracture shows focal cortical buckling (arrow). This finding may only be seen on one view and represents a fracture.

Angulation

Abnormal angulation may be the only manifestation of some fractures. For example, distal radial fractures may appear as loss of the normal minimal volar inclination of the distal radial articular surface (Figure 1.21) and distal humeral fractures may appear as loss of normal anterior angulation of the distal humeral metaphysis with respect to the shaft.

Trabecular malalignment

Proximal femur fractures can be subtle and appear as ­misalignment of trabeculae across the femoral neck (Figure 1.22). It is important to have an organized pattern approach to assess the cortical lines about the pelvis. Cortical disruption or an abrupt step-off along the ­ilioischial or ilipectineal line is a sign of a fracture of the pubic rami or the acetabular columns. Disruption of the sacral arcuate lines is a sign of a sacral fracture. These pelvic lines are described in greater detail in Chapter 7.

4. Assess the soft tissues

Soft tissues should be assessed on all musculoskeletal radiographs for swelling, gas, joint effusion and radio­dense foreign bodies. Soft tissue swelling at some sites helps identify an underlying fracture. This is especially helpful when assessing trauma to the phalanges.

Tendons

One of the areas frequently overlooked on radiographs is the very anterior and very posterior soft tissues on lateral radiographs. Specifically, the quadriceps and the patellar tendon on the lateral knee radiograph, and the Achilles tendon on the lateral ankle radiograph. Injury to these superficial ­tendons is often visible radiographically, but only if one specifically and carefully evaluates these ­structures [28].

Fat pads

Displacement, obliteration or blurring of certain fat planes is also a helpful sign of an adjacent osseous injury. For example, the supinator fat pad may be obscured with radial head and neck fractures, the pronator fat pad with distal radial fractures, and the scaphoid fat pad with scaphoid fractures.

Joint effusions

The presence of a joint effusion in the acute setting in a patient with no underlying arthritis is a presumptive sign of a hemarthrosis. This blood may be the result of an intra-articular injury to either the soft tissues or adjacent bone. Radiographs are accurate in the detection of a joint effusion at the knee and the elbow. However, the accuracy of radiographs to detect joint effusion at other joints is limited. A cross-table lateral radiograph should be obtained in all patients with knee trauma to evaluate for the presence of fat within the joint, termed a lipohemarthrosis. This fat is displaced from the marrow into the joint in cases of an intra-articular fracture (Figure 1.23). The cross table radiograph will show a fat-fluid level in patients with a lipohemarthrosis.

Figure 1.21 Loss of normal angulation. (a) Lateral view shows loss of the normal volar angulation of the distal radial articular surface (line along the distal radial shaft and line along the distal radial articular surface show neutral alignment of the distal radial articular surface) compatible with a distal radial fracture. (b) Oblique view shows subtle sclerosis in the metaphysis related to impaction (arrow) at the fracture site.

Figure 1.22 Malalignment of the trabeculae across a subcapital fracture. (a) AP view shows valgus impaction across subcapital fracture evident by abrupt change in angulation of compressive trabeculae along the femoral neck (closed arrow) and femoral head (open arrow). (b) Frog-leg lateral view shows cortical disruption along the femoral neck (arrow).

Open fractures

Complex fractures, as well as fractures related to high-velocity energy, are more likely to be associated with an open wound. These fractures can also be referred to as compound or open fractures. It is important to assess for the presence of soft tissue gas on trauma radiographs (Figure 1.1(b)). The finding of gas directly impacts patient management, as these compound fractures require urgent open fixation. Other findings of an open fracture include a soft tissue defect, fracture fragment protruding beyond the expected soft tissues and radiodense foreign body material under the skin (Figure 1.24) [29]. The most common open fractures occur in the tibia (46%), followed by the femur (13%) and forearm (11%) [30]. It is therefore important to carefully inspect radiographs in patients with tibial fractures for evidence of an open fracture.

Figure 1.23 Lipohemarthrosis. Cross-table lateral radiograph shows a fat-fluid level (arrow) in the suprapatellar pouch. Sclerosis in the proximal tibia is related to a depressed tibial plateau fracture.

Figure 1.24 Open fracture. (a) AP view shows soft tissue gas (arrow) and laterally displaced tibial and fibular fractures with overlap of fragments. (b) Lateral radiograph shows anteriorly displaced tibial fracture that protrudes through the skin (arrow).

Foreign bodies

It is important to assess trauma radiographs for the presence of a radiodense foreign body (Figure 1.25). Foreign bodies may require surgical removal. The radiology technologist may place a marker at the skin to demarcate the site of the puncture. This facilitates detection of smaller radiodense foreign bodies.

5. Look for additional fractures and dislocations

It is important to remember that there may be several mechanisms of injury associated with a given traumatic event and this may result in more than one fracture. For example, a fall on an outstretched hand in the elderly may lead to concomitant humeral and radius fractures. It is important to assess adjacent joints for associated fractures. In the pelvis, and the foot, fractures are often multiple and the radiologist should not be satisfied after detecting one, or even several fractures. It is important to have an organized approach to assess all areas for a fracture. Checklists for each anatomic site are included in the chapters that follow.

Figure 1.25 Foreign body. A linear radiodense foreign body is shown adjacent to the fifth MTP joint (arrow). The technologist placed a paper clip adjacent to the foreign body entry site.

6. Assess for intra-articular fracture extension and joint alignment

Fractures that occur near a joint should be carefully assessed for the presence of articular fracture extension, articular step-off or gap (Figure 1.17). Joint alignment should be assessed on all views. Some joints, including the shoulder and the patellofemoral joint, often require special axial views to adequately assess alignment. Commonly missed joint dislocations on frontal radiographs include posterior shoulder dislocations, posterior hip dislocations, carpometacarpal dislocations, and tarsometatarsal (Lisfranc) dislocations. It is important to specifically assess for these dislocations and accompanying fractures.

Description of fractures and joint injuries

A complete description of a fracture should specify the precise anatomic location of the fracture, appearance of the fracture line, whether the fracture is open or closed, and fracture alignment and angulation. If the fracture involves a joint, congruence of the articular surface and alignment at that joint should be described. Accurate description of a fracture necessitates knowledge of appropriate terminology used to describe fractures and joint injuries. This terminology represents specific medical vocabulary that should be used correctly in order to facilitate effective communication between the radiologist and the clinician. The goal is to describe a fracture with enough accuracy that someone else could draw the fracture, without seeing the image itself.

Figure 1.26 Osteochondral fracture. Axial view of the patella shows an osteochondral fracture along the medial patellar facet (arrow) in a patient with a prior transient lateral patellar dislocation.

Open versus closed

Use of the term closed or simple fracture is reserved for injuries with intact skin, while an open or compound fracture implies that the skin is disrupted (Figure 1.24). By definition, fractures caused by a laceration or a gunshot wound, as well as amputations are open fractures.

Location

Fracture location is described in terms of position in the bone. For long bones, the location is divided into proximal, mid and distal shaft. It should be specified whether the fracture extends to the joint surface, in which case it is intra-articular in location. Whenever possible, fracture location should be specified by including an anatomic point of reference such as the surgical neck of the humerus, the tibial plateau, or the metacarpal neck. For flat or irregular bones, examples of specific anatomic descriptors include the scaphoid waist or the scapular spine. These are discussed in chapters dedicated to specific anatomic sites.

Intra-articular extension

Intra-articular fractures may involve the articular cartilage only (chondral fracture), involve the bone and traverse the articular cartilage (transchondral fracture) or result in a fracture fragment that contains both the bone and articular cartilage (osteochondral fracture). Chondral and osteochondral fractures usually result from shearing or rotational impaction forces at a joint [31]. The fracture line is typically parallel to the joint, and it may be visible radiographically only if it contains a reasonable sized fragment of bone. This osteochondral fragment is often subtle radiographically (Figure 1.26). A pure chondral fracture may only be visualized on MR. Osteochondral injuries may accompany joint dislocations. Some examples of chondral and osteochondral injury following a joint dislocation include shoulder dislocation with resultant glenoid fracture, elbow dislocation with posterior capitellar fracture, hip dislocation with femoral head fracture, and patellar dislocation with medial patellar facet fracture.

Figure 1.27 Segmental fracture with angulation, displacement and overriding of fracture fragments. (a) AP and (b) lateral tibia–fibula radiographs show a segmental tibial fracture with valgus angulation at the distal fracture site. Companion distal fibular shaft fracture shows one shaft width anteromedial displacement and mild overriding of fracture fragments.

Morphology of fracture lines

Fracture lines are often described in terms of their orientation as transverse (Figure 1.1), oblique (Figure 1.4), or spiral (Figure 1.5). Spiral fracture lines are by far the least common. In children (see Chapter 2), there are several unique fractures including bowing, torus, and greenstick fractures. A comminuted fracture contains more than two fracture fragments. Severity of comminution may be graded as minimal (small fracture fragments adjacent to dominant fracture line), moderate or severe (several large fracture fragments). If there is a dominant fracture ­fragment, it should be described in terms of size and ­displacement. A butterfly fracture is a subtype of a comminuted fracture with a wedge-shaped fracture fragment along the shaft of the bone (Figure 1.6). The location and any displacement of the fracture fragments should be described.

It is important to recognize a segmental fracture. This fracture type consists of two anatomically separate fracture lines along the shaft of the bone that isolate a middle segment of the bone (Figure 1.27). These fractures may be missed both clinically and radiographically, since the two fracture sites may be at a distance from one another. When describing segmental fractures, it may be helpful to describe fracture appearance at the proximal and distal fracture site separately, especially in cases of displacement and angulation. Some segmental fractures may be located on the opposite sides of a joint, and result in a “floating joint.” Examples include a “floating elbow” with distal humeral and proximal ulna and radius fractures and a “floating knee” with distal femoral and proximal tibia and fibula fractures. Recognition of floating joint type segmental fracture facilitates appropriate treatment of these unstable injuries [32].

Alignment

The position of fracture fragments is described in terms of alignment and angulation. If these are all normal, the ­fracture is said to be nondisplaced, or in near anatomic alignment. Alignment is described in terms of position of the longitudinal axis of the distal fracture fragment with respect to the proximal fracture fragment. Loss of normal anatomic position is described as displacement. Additional descriptors include fracture apposition and rotation. Displacement should be graded in terms of shaft width (one quarter, one half, one shaft, or greater than one shaft width) (Figure 1.27(b)). The direction of displacement is described using two orthogonal views. The AP view is used to describe medial to lateral displacement and the lateral view to describe anterior to posterior displacement. Additional terminology is used at the wrist (volar, dorsal) and at the foot (plantar, dorsal).

Apposition

Apposition at the fracture site describes the extent of cortical contact between the fracture fragments. In cases of complete apposition, the fracture is nondisplaced. Fractures with two fracture fragments situated alongside of one another are described as overriding (Figure 1.27). Some fractures may be separated by a gap with no overlap, and are described as distracted. Distraction is common with transverse fractures that result from a tension force (patella, olecranon) or avulsion fracture related to a tendon pull (Figure 1.28). If there is overlap of the fracture fragments or distraction at the fracture site, these should be measured in millimeters or centimeters. Fractures can be impacted as well. Distracted or impacted fractures occurring in the lower extremity may lead to a leg length discrepancy if uncorrected.

Figure 1.28 Distracted patellar fracture. Lateral radiograph shows significant separation of inferior pole and the remainder of the patella (arrows). The quadriceps tendon retracts the superior fracture fragment, and the patellar tendon retracts the inferior fracture fragment, with resultant patella alta.

Rotation

Rotation at the fracture site can only be assessed if both the joint proximal and distal to the fracture site are imaged on the same radiograph (Figure 1.29). In cases where one joint is seen in AP projection and the other joint in lateral projection, rotation is described as 90 degrees. Another clue to rotation is significant disparity between the diameter of the proximal and distal fracture shaft, suggesting that they are profiled at a different angle on the radiograph [33].

Angulation

It is important to appreciate that description of fracture alignment is separate from description of angulation. A fracture may be severely displaced, with no angulation, or conversely, it may be severely angulated with no displacement or loss of contact at the fracture site. By convention, angulation is described in terms of position of the distal fragment with respect to the proximal fragment (rather than the position of the apex of angulation). It is important to use two orthogonal views to describe fracture angulation (Figure 1.27). The AP view provides information regarding angulation in the coronal plane including medial and lateral at most fracture sites and radial and ulnar at the forearm. The terms varus and valgus are often used in lieu of medial and lateral. Varus refers to angulation of the distal fragment towards the midline of the body and valgus away from the midline (Figure 1.30). The lateral view provides information regarding angulation in the sagittal plane including anterior and posterior at the humerus, femur, tibia and fibula, volar and dorsal at the wrist, and plantar and dorsal at the feet. Measurements in terms of degrees of angulation are helpful for the clinician to guide management. The fracture may be angulated in two planes, for example anteromedial or posterolateral. Angulation in the plane of motion of a joint is less debilitating than angulation outside the plane of motion of joint. Therefore varus or valgus is usually the worst type of angulation for future limb function.

Impaction

Some fractures may be impacted and it is important to grade the severity of impaction by providing a measurement. It may be difficult to directly measure impaction of a distal radial fracture. In those cases, indirect measurement with respect to ulnar shaft length is used to infer the severity of impaction. This measurement is provided in terms of ulna variance; positive ulna variance indicates impaction at the radial fracture site. Ulnar variance is ­further discussed in Chapter 6.

Avulsion

Avulsion fractures are caused by abnormal tensile stress on ligaments or tendons [34]. These fractures occur at ­typical locations in the hands (dorsal distal phalanx with extensor tendon avulsion), feet (base of fifth metatarsal with peroneus brevis avulsion), and pelvis (ischial ­tuberosity with hamstring tendon avulsion). The avulsed fracture fragment may be purely cartilaginous, osteocartilagenous, or most commonly, just osseous. The latter two avulsion fractures are visible radiographically. The size of the fragment varies, and the degree of displacement also varies. Some avulsion fractures may be subtle, with displacement of a tiny ossific fragment. It is important to look for associated soft tissue swelling, especially at the digits, and joint alignment to infer ligament or tendon injury (ACL avulsion and anterior translocation of the tibia with respect to the femur). MR is more sensitive than radiographs to identify and characterize these injuries. Some avulsion fractures should be presumed pathologic until proven otherwise. These include lesser trochanter avulsion or avulsion at an atypical site such as the distal humeral epicondyle (Figure 1.31) in adults.

Figure 1.29 External rotation across a fracture. (a) AP view of the proximal and (b) distal femur shows an oblique distal femoral shaft fracture with one half shaft width medal displacement and external rotation (curved arrow). (c) AP view of the ankle shows the ankle in lateral projection related to external rotation at the distal femoral fracture site. Traction device is in place across the fracture.

Joint alignment

Abnormal alignment at a synovial joint is described either as subluxation if there is partial contact between the articular surfaces, or dislocation, if there is no contact between the opposing articular surfaces (Figure 1.32). The severity of subluxation may be described in terms of percentage of articular congruity. A common error in description terminology is to describe a joint as displaced, a term which should be used only for a fracture. The convention of naming the dislocation depends on the size of the bones involved at a joint. For example, if the major bones at a joint are involved, such as with tibiofemoral dislocation, the injury is called a knee dislocation. If a smaller bone is involved at a joint with several bones, the injury is called according to the bone that is in an abnormal position (ex. patellar dislocation, lunate dislocation). It is important to recognize soft tissue gas about a dislocation. An open dislocation is a surgical emergency that requires urgent closure to prevent septic arthritis and potential devastating joint destruction [35].

Abnormal alignment at a synarthrodial or parti­ally mobile joint is termed diastasis. Commonly involved joints include the symphysis pubis and the sacroiliac joint. There are often associated fractures either adjacent to the joint or extending into the joint (Figure 1.33).

Spine alignment

Alignment on spine radiographs should be described in both the coronal and sagittal plane. Kyphosis and acute lordosis should be described on the lateral radiograph, and dextro- or levoscoliosis on frontal radiographs. Rotatory abnormality may be present on both the lateral and frontal radiographs. Listhesis is defined as abnormal slippage of one vertebral body with respect to the other, and is usually described in terms of the body above with respect to the body below.

Figure 1.30 Varus and valgus angulation. (a) Varus angulation across bending wedge distal humeral fracture. (b) Valgus angulation across oblique mid-humeral shaft fracture.

Figure 1.31 Pathologic avulsion fracture. AP radiograph of the elbow shows an avulsion fracture at the lateral epicondyle of the distal humerus (arrow) with an underlying lytic lesion.

Retrolisthesis represents posterior displacement of the body above with respect to the body below. For example, “retrolisthesis of L2” refers to an abnormality occurring at L2-3. Anterolisthesis is usually described as “anterolisthesis at L2-3” if the abnormality occurs at L2-3.

Lateral listhesis should be described by reviewing frontal radiographs in terms of the position of the body above with respect to the body below. For example “left lateral listhesis of L2 with respect to L3”. Description of alignment in the spine is discussed in greater detail in Chapter 3.

Classification of fractures

Accurate fracture description is usually sufficient to guide patient management. Classification systems have been developed to stratify patients into different treatment categories, grade the severity of the injury and predict outcomes. There are specific classification systems for each fracture site and these are described in subsequent chapters.

Figure 1.32 Dislocation at the distal interphalangeal joint. (a) Lateral and (b) PA radiographs show a dorsal dislocation and the DIP joint to the long finger (arrows).

Figure 1.33 Diastasis of the left sacroiliac joint and the symphysis pubis.

The most common classification system used by orthopedic surgeons is the Mueller AO Classification system [36]. This classification system was developed to provide consistency in long bone fracture classification, with the goal to standardize research across institutions. This classification system is detailed, and it can be applied to most fracture sites (Figure 1.34). It is arranged in order of increasing severity according to fracture complexity, ­difficulty of treatment and worsening prognosis. Note that the classification system differs for end-of-bone versus middle segment fractures. Middle diaphysis segment fractures can be either simple (one fracture line with >90% cortical contact after reduction), wedge (three or more fragments, main fragments have contact after reduction) or complex (three or more fragments, main fragments have no contact after reduction). End-of-bone fractures can be either extra-articular, partial articular (part of the articular component involved, while the other part is attached to metadiaphysis) or complete articular (metaphyseal fracture component completely separates the articular component from the diaphysis).

Special types of fractures (stress, insufficiency, and pathologic)

There are special types of fractures other than the typical injury to normal bone from acute trauma. These special fractures are termed stress, insufficiency, and pathologic fractures. Incorrect use of terminology with respect to these fractures is unfortunately common.

Stress fractures

Definition: A stress fracture is a fracture through bone as a result of abnormal, repetitive and persistent stress. If the bone is normal, this is termed a fatigue fracture; if the bone is systemically abnormal, it is termed an insufficiency ­fracture.

Figure 1.34 AO classification of long bone fractures. The classification system is based on fracture location (proximal, distal or diaphyseal), articular involvement and severity of fracture fragmentation. Modified from www.aofoundation.org with permission.

Epidemiology

The triad associated with most stress fractures includes: 1) activity is new or different for the individual, 2) strenuous, and 3) repeated with a frequency that ­ultimately produces symptoms [37]. Examples of ­activities include new exercise routine or occupational work (Table 1.1) [38, 39]. The amount of increased load on the bone may vary between patients. A sedentary individual may sustain a stress fracture after commencing a new training program of daily walking, or a ­competitive marathon runner may sustain a stress fracture by doubling the running distance during daily running regimen. Patients typically present with pain that occurs during activity and resolves after the ­activity stops.

Location

The likelihood of a stress fracture is dependent on the quality of the bone, the magnitude of stress, and the frequency and time period during which the stress is applied [39]. The location of stress fractures is quite typical with certain activities. For example, running is associated with stress fractures of the second and third distal metatarsal shaft, posterior calcaneus, distal tibia or fibula shaft, ­femoral neck and pubic ramus. Midfoot stress fractures are also common in runners and dancers, especially the navicular and cuneiforms [40, 41].

Table 1.1 Location and causes of common stress fractures

Modified from Daffner and Pavlov [42] with permission from American Roentgen Ray Society.

Location of stress fracture

Inciting activity

Metatarsal shaft

Running, marching, hallux valgus surgery, ballet dancing