Traumatic Injuries: Imaging of Peripheral Muskuloskeletal Injuries 2.11
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Chapter Traumatic Injuries: Imaging of Peripheral Muskuloskeletal Injuries 2.11 M.A. Müller, S. Wildermuth, K. Bohndorf Contents In past years, computed tomography (CT) has gained an important place in the emergency evaluation of fractures 2.11.1 Introduction . 251 and in planning surgery of complex injuries. Magnetic res- 2.11.2 General Part: Imaging Modalities . 251 onance imaging (MRI) and ultrasound (US) are important 2.11.2.1 Conventional Radiography imaging modalities in the evaluation of soft tissues in addi- (Projection Radiography) . 251 tion to the clinical examination. 2.11.2.2 Computed Tomography . 252 2.11.2.3 Magnetic Resonance Imaging . 252 2.11.2.4 Ultrasound . 253 2.11.3 Soft Tissue Injuries in General . 253 2.11.2 General Part: Imaging Modalities 2.11.3.1 Muscle Injuries . 253 2.11.3.2 Tendinous and Ligamentous Injuries on US . 254 2.11.2.1 Conventional radiography (Projection radiography) 2.11.4 Upper Extremity . 254 2.11.4.1 The Clavicle and its Articulations . 254 2.11.4.2. Shoulder and Proximal Humerus . 256 Two projections perpendicular to each other preceded by 2.11.4.3 Elbow . 260 clinical examination are generally the first and often the 2.11.4.4 Distal Forearm and Wrist . 265 only necessary diagnostic approach in evaluation of ex- 2.11.4.5 Metacarpals and Fingers . 271 tremity trauma. Clinical prediction rules and cost-effec- 2.11.5 Lower Extremity . 273 tiveness analyses are valuable evidence-based tools for 2.11.5.1 Hip . 273 selecting optimal imaging approaches [1]. Conventional 2.11.5.2 Knee . 276 radiographs can almost always be obtained under difficult 2.11.5.3 Ankle . 282 circumstances, like in the acute setting of severe trauma 2.11.5.4 Foot . 285 and in unstable patients. Surgical planning is guided pri- References . 288 marily by clinical and conventional radiographic findings. General fracture signs are radiolucent fracture lines, corti- cal discontinuities or angulations, and periostal and tra- becular irregularities. Radiodense lines can represent impacted fractures. In general, conventional radiography 2.11.1 Introduction diagnoses fractures quickly and provides relevant infor- mation as to whether the adjacent joint is involved and Since the publication of the first peripheral musculoskele- about the position and number of fracture fragments. Due tal radiograph in Roentgen’s first description of X-rays in to the divergence of the X-ray beam, the region of interest 1895, demonstrating a hand, projection radiography has should be centered on the image to minimize contortion of remained the most important and, in many cases the only relevant structures, leading, for example, to widening of needed, imaging modality for fracture and other muscu- fracture lines in the film periphery. In the evaluation of the loskeletal injury diagnosis. The clinical importance of this shaft of a long bone, it is necessary to include both adjacent radiographic application is illustrated by the rapid diffu- joints in the examination. In skeletal regions with complex sion of X-ray knowledge in the first years after its discov- anatomy or superimposed soft tissues, additional special ery, as shown by the following example: One of the first views designed to eliminate superimposed structures can known clinical applications of radiology in soft tissue be used, but sometimes further imaging modalities are imaging and searching for foreign bodies for preoperative used to complete the assessment. Following treatment, assessment was performed 1897, not in a big city but in the conventional radiographs are mandatory to confirm treat- village of Poschiavo in a secluded valley in Switzerland [67]. ment results and clinical diagnosis of possible complica- 252 M.A.Müller,S.Wildermuth,K.Bohndorf tions such as infection, reflex osteodystrophy, or inade- of surfaces [4]. The possibility to visualize structures be- quate internal fixation. neath the surface while still seeing the surface, and espe- In evaluation of soft tissue injury, conventional radi- cially the display of minimal displaced fractures and dislo- ographs have limited value. In some joints, soft tissue cated fragments together with the fact that volume render- changes can be used as indirect fracture signs. If clinical ing is much less affected by hardware artifacts, favors the examination is not conclusive, further evaluation of soft use of VRT. tissue injuries is usually performed with US or MRI. The MDCT also is helpful in healing assessment follow- Digital techniques allow new features for acquisition, ing operative stabilization. In particular, the slice overlap post-processing, interpretation, reporting and storage of and pitch of <1 create a substantial flux, which allows for images.Advantages are obvious in the acute trauma setting imaging through orthopedic hardware [5]. High-mil- Becoming filmless is also an important progress in a con- liampere technique reduces metallic artifact (titanium pro- tinuous evaluation of the healing process, because there is duces the least artifacts, cobalt chrome the most). no further searching for lost films. With CT arthrography, also ligamentous injuries can be The role of conventional tomography and arthrography detected. The technique is particularly useful in patients has declined. Arthrography is presently mostly performed who require multiplanar imaging for preoperative plan- before a CT or MRI examination. ning and patients who cannot undergo MR arthrography. The CT arthrography can be a valuable imaging choice for the evaluation of the postoperative menisci [6].Advantages 2.11.2.2 Computed tomography of CT arthrography include higher spatial resolution and often minimal metallic artifacts. Display of complex fractures and assessment of fracture extension into joint surfaces are the main indications for CT imaging in the acute trauma setting. Most peripheral 2.11.2.3 Magnetic Resonance Imaging body parts can be positioned to prevent exposure of radia- tion-sensitive tissues. Multidetector CT (MDCT) has im- Magnetic resonance imaging has improved diagnostic proved the ability to image patients with skeletal trauma. imaging of traumatic ligamentous, muscle, and tendon Advantages of MDCT include extremely short scan times, lesions, and is the preferred method of investigation for the ability to produce very high-quality multiplanar refor- stress and insufficiency fractures. T2-weighted images are mations (MPR), and 3D reconstructions based on the highly sensitive to bone marrow edema. Presence of bone ability to acquire virtually isotropic images. Computed marrow edema and absence of a fracture line is suggestive tomography of bony structures requires high spatial reso- of trabecular microfracture. Computed tomography is an lution. The thinnest possible slice width and a bone-recon- alternative in imaging stress fractures, but is generally less struction algorithm will maximize image quality. Imaging sensitive particularly in absence of a fracture line. Magnet- of large joints, such as the shoulder, requires slightly thick- ic resonance arthrography can be performed as direct er slices to ensure reasonable image quality, particularly if technique with intraarticular contrast medium injection – surface rendering is to be performed [2]. The use of high in acute traumatized joints, joint effusion can have the kilovoltage levels increases the likelihood of penetrating same effects – or as indirect technique with intravenous the bone. The limiting factor becomes the level of noise in administration of contrast medium. Indications for direct the reconstructed image set. Submillimeter slices can be and indirect arthrography are sometimes controversial [7]. used to demonstrate minimally depressed fractures. The When imaging ligaments and tendons, it is important to be higher the kernel number,the sharper the image; therefore, aware of the magic-angle phenomenon. This artifact can detailed or sharp reconstruction algorithms are recom- lead to a signal increase in fibrous strictures which are mended for single slices. In contrast, for 3D imaging, there crossing the vector of the magnetic field at an angle of is the smoothest available kernel recommended for lower- about 55°. Sequences with a short echo time are most vul- ing the noise in the original slices; therefore, production of nerable to this phenomenon. two image sets from the raw data is required. Overlap of Recent studies have tried to assess the value of a short 20% for image reconstruction will give good image quality dedicated extremity MRI examination in different anatom- for most routine scans [3]. Besides transversal slices, MPR ic regions in the acute emergency setting for prediction of should be the first modality of assessment because 3D re- need for treatment. In the ankle, although there is high sen- constructions can obscure fine detail. A 3D shaded-surface sitivity in the detection of occult fractures, the sensitivity in display (SSD) and volume-rendering technique (VRT) can detection of avulsion fractures is low. The radiographic re- show articular surfaces. As volume rendering makes use of sult as a single predictor of the need for therapy appeared to the entire acquired volume data set and does not use inter- be of higher predictive value than the MRI result.An MRI in mediate geometrical representations, such as polygons in the initial evaluation of ankle trauma may be valuable in a SSD, it overcomes the problem of accurate representation setting where ruptured ankle ligaments are immediately re- Chapter 2.11 Traumatic Injuries: Imaging of Peripheral Muskuloskeletal Injuries 253 paired surgically [8], but actually this is not the case. In Sonography is especially helpful in detecting radio- acute knee trauma, neither abnormal nor normal MRI re- transparent foreign bodies. Foreign bodies that recently sults had significant added predictive value.A prediction of penetrated the skin can be difficult to see due to the artifact the need for treatment after acute knee trauma can be made from air. One should mark the position of the foreign body on the basis of age,trauma mechanism,and the radiograph- on the skin and note the depth. The first imaging modality ic results [9], and MRI not seems to be useful.