P. Van Dyck, MD J. L. Gielen, MD, PhD
Department of Radiology, University Hospital Antwerp, Wilrijkstraat 10, 2650 Edegem, Belgium
F. M. Vanhoenacker, MD, PhD
Department of Radiology, AZ St-Maarten, Duffel/Mechelen, Belgium
and
Department of Radiology, University Hospital Antwerp, Wilrijkstraat 10, 2650 Edegem, Belgium
Imaging Techniques and Procedures in 2
Sports Injuries
PIETER VA N DYCK, JA N L . GIELEN, and FILIP M. VA N HOENACK ER
2.1
Introduction
Sports medicine is one of the most rapidly growing sub- specialties in orthopedics. It has been estimated that 25%
of patients seen by primary care physicians complain of
musculoskeletal problems, many of which are sports- or activity-related (Johnson 2000). Symptoms and clinical fi ndings in sports injuries are often non-specifi c and fur- ther imaging investigations may be required for accurate diagnosis and optimal treatment planning.
The choice of which imaging modality is used depends on the clinicians’ and radiologists’ comfort and experience with those modalities, the fi nancial costs, and availability and invasiveness of each tech- nique balanced against the diagnostic award. The
“optimal imaging pathway” that meets all these cri- teria probably does not exist and, in many cases, the imaging pathway to be followed should be tailored to individual cases. For a more in-depth discussion of the clinician’s point of view, we refer to Chap. 1.
This chapter reviews the imaging strategies that can be employed to diagnose and grade sports inju- ries. The role of each imaging technique, with its spe- cifi c advantages and limitations, will be highlighted.
The reader will fi nd some practical guidelines for the evaluation of sports injuries that, in our opinion, may be useful in daily clinical practice.
2.2
Imaging Modalities
2.2.1
Plain Radiography and Conventional Arthrography
Radiographs in two projections perpendicular to each other are general the fi rst and often the only diagnostic images needed for the evaluation of sports injuries, most commonly to detect or exclude fracture. The lack of soft tissue contrast-resolution is a well-recognized limitation of plain radiography, but when present, soft tissue changes can be used as indirect signs of osseous pathology. Furthermore, the presence of loose bodies or degenerative joint
C O N T E N T S
2.1 Introduction 7
2.2 Imaging Modalities 7 2.2.1 Plain Radiography and
Conventional Arthrography 7 2.2.2 Ultrasound 8
2.2.3 Multidetector Spiral CT Scan 9 2.2.3.1 Technique 9
2.2.3.2 CT Arthrography 9
2.2.4 Magnetic Resonance Imaging 9 2.2.4.1 Technique 9
2.2.4.2 Direct and Indirect Arthrography 11
2.3 General Principles and Indications 11
2.4 Optimal Moment of Investigation 12
2.5 Safety, Availability and Economic Aspects 12 2.6 Conclusion 13
Things to Remember 13 References 13
changes can easily be assessed with plain radiog- raphy.
Although oblique (¾) views may be helpful, e.g., to demonstrate fractures of the radial head or for detection of bone spurs in anterior ankle impinge- ment, they are not commonly used in daily clinical practice and have largely been replaced by cross-sec- tional imaging.
Stress views may provide indirect evidence of liga- mentous injury. However, recent studies have ques- tioned the value of stress radiographs. For example, in chronic ankle pain, it has been shown that there is signifi cant overlap between stable and unstable ankles, according to the guidelines of the American College of Radiology (2005).
Radiographs are mandatory to confi rm the results after internal or external fi xation with reduction of dislocations and alignment of displaced fracture fragments, for monitoring the progress of fracture healing with callus formation or detection of soft tissue calcifi cation after severe muscle trauma (e.g., myositis ossifi cans).
When complications of the healing process occur, such as infection or avascular necrosis, the role of plain radiography may be limited and other imaging techniques, such as bone scintigraphy and/or MRI, may be useful for confi rming the diagnosis.
For decades, conventional arthrography (after sterile preparation and injection of intra-articular contrast medium) was used for investigating intra- articular pathology. This imaging modality has now been largely replaced by cross-sectional imaging techniques and is only performed as part of CT- or MR-arthrography.
2.2.2 Ultrasound
Since approximately 30% of sports injuries deal with muscle and tendon injuries, ultrasound (US) plays a major role in sports traumatology, helping the clini- cian to decide whether the athlete should or should not return to training and competition (Peterson and Renstrom 1986).
Due to the excellence of spatial resolution and defi nition of muscle structure, US keeps its leading edge when dealing with muscle pathology, both in the initial phase for recognition of a lesion, but also for follow-up of lesions and search for healing problems such as fi brosis, muscle cysts, hernias or myositis ossifi cans.
High-frequency (13.5 MHz) linear-array probes are used to perform musculoskeletal US examina- tions. Transverse and longitudinal slices are man- datory. US palpation is a very valuable tool, trying to fi nd the point of maximal tenderness, during the examination by a gentle but fi rm compression of the probe on the skin (Peetrons 2002). Dynamic US study may be very helpful to the correct diagnosis, e.g., to search for muscle hernia (during muscle con- traction) or to evaluate the snapping hip syndrome (during hip fl exion and lateral rotation). To avoid artefacts or pitfalls, comparison with the contralat- eral side is necessary.
Major advantages of US are its low cost, availabil- ity at short notice, ease of examination, short exami- nation times and lack of radiation exposure.
The recent addition of color-power Doppler imag- ing to US has allowed for the non-invasive study of blood fl ow and vascularity within anatomic structures and lesions. In patients with tendinosis, increased vascularity in the tendon may be corre- lated with clinical symptoms (Weinberg et al. 1998;
Zanetti et al. 2003).
Furthermore, US provides image guidance for interventional procedures such as drainage of fl uid collections and cysts (Peetrons 2002). Recently, US guided sclerosis of neovascularity in painful chronic tendinosis has been described as an effective treat- ment with signifi cant reduction of pain during activ- ity (Öhberg and Alfredson 2002).
The trade-off for high-frequency, linear, mus- culoskeletal transducers is their limited depth of penetration and the small, static scan fi eld. This is a disadvantage if the structure to be visualized is large (e.g., large intramuscular hematoma) or deeply local- ized (e.g., hip joint). Extended fi eld of view ultraso- nography (EFOVS) overcomes this disadvantage by generating a panoramic image. With this technique, sequential registration of images along a broad examination region and their subsequent combina- tion into an image of larger dimension and format is obtained (Weng et al. 1997). EFOVS does not add much in diagnosis but is, however, easily interpreta- ble by the novice and improves cross-specialty com- munication.
For better evaluating deeply localized structures, such as the hip joint in an obese patient, other (cross- sectional) imaging modalities are often required.
Other disadvantages of ultrasound include opera- tor dependency, selective and often incomprehen- sible documentation and the inability to penetrate osseous structures.
2.2.3
Multidetector Spiral CT Scan
2.2.3.1 Technique
CT imaging, by virtue of its excellent multiplanar capability and submillimeter spatial resolution due to the development of the spiral acquisition mode and current multidetector row technology, is a valuable imaging tool for the evaluation of all kinds of sports injuries (Berland and Smith 1998). Very fast image- acquisition times of large volumes with submillime- ter section thickness have become the norm.
It has proved to be an effective method of docu- menting injuries particularly in complex bony struc- tures such as the wrist and pelvis, and may often show post-traumatic changes not shown by radiography.
For most musculoskeletal studies, slice thickness is 0.75 mm, reconstructed to 1 mm images with incre- ment of 0.5 mm. The images should be assessed using both bone and soft tissue window settings.
From the three-dimensional data set, images can be reformatted in other planes (2-D technique) and be used for volume rendering (3-D technique).
The 2-D reformatting of sagittal and coronal images from axial images can highlight longitudinal fracture lines and can make it easier to evaluate hori- zontal interfaces, such as the acetabular roof.
The 3-D rendering allows different displays of the volume data. Surface rendering by thresholding, which, in contrast to volume rendering, incorpo- rates only a portion of the data into the 3-D image, is the most widely used technique. By adding a vir- tual light source, a shaded surface display (SSD) can be achieved, which enhances the 3-D understanding of the image. However, it may provide an inadequate display of undisplaced and intra-articular fragments and, in comparison to axial imaging, surface render- ing does not increase the detection rate of fractures and should only be supplementary to plain fi lms and axial CT scan in the evaluation of comminuted frac- tures. Volume rendering, incorporating all the data into the 3-D image, requires more computer manipu- lation.
All reconstruction methods offer a more effective display of complex anatomic and pathologic struc- tures. It may be helpful for the assessment of com- minuted fractures, improving visualization of the fracture’s extent and location, shape and position of the fracture fragments and the condition of articular surfaces (Bohndorf et al. 2001).
2.2.3.2
CT Arthrography
Intra-articular injection of iodinated contrast mate- rial mixed with 1 ml of a 0.1% solution of epineph- rine is performed under fl uoroscopic observation ( Newberg et al. 1985). The volume of contrast medium injected depends on which joint is stud- ied: shoulder: 10–15 ml; wrist: 5 ml; hip: 10 ml; knee:
20 ml; ankle: 6–12 ml. After injection of contrast material, patients are asked to perform full-range mobilisation of the joint. Anteroposterior, lateral and oblique views are routinely obtained to image the entire articular cavity. Subsequently, multidetector CT is performed.
The major advantage of CTA for the assessment of the cartilage is the excellent conspicuity of focal morphologic cartilage lesions that results from the high spatial resolution and the high attenuation dif- ference between the cartilage substance and the joint contrast fi lling the lesion. Vande Berg et al. (2002) found, in a study with spiral CTA of cadaver knees, a better correlation for grading articular surfaces between macroscopic examination and spiral CTA than with MR imaging.
Other potential advantages of spiral CTA with respect to MR imaging are the short examination time, the availability at short notice (short waiting list) and the low sensitivity and limited degree of imaging artefacts related to the presence of micro- scopic metallic debris which may hinder MR imaging studies.
Limitations of CTA include its invasiveness, pos- sible allergic reaction, use of ionizing radiation and poor soft tissue contrast resolution. Another major limitation of CTA imaging of the cartilage is its com- plete insensitivity to alterations of the deep layers of the cartilage.
2.2.4
Magnetic Resonance Imaging
2.2.4.1 Technique
Equipment and techniques for MRI vary widely, and although it is generally accepted that high fi eld strength magnets provide the highest quality images, there has been considerable advancement in the tech- nology of low fi eld strength systems over the past few years, greatly improving their image quality.
Although appropriate selection of imaging planes will depend on the location and desired coverage of the anatomical region to be examined and the pathology to be expected, a complete MR examination requires that images be obtained in the axial, coronal and sag- ittal planes. Of utmost importance is to respect the anatomical orthogonal planes since, with excessive rotation of a limb, inappropriate positioning of imag- ing planes may result in images which are diffi cult to interpret. Oblique planes may also be useful, e.g. in the shoulder (paracoronal and parasagittal images).
The number of pulse sequences and combinations (‘hybrid techniques’) is almost infi nitive: in muscu- loskeletal MR, the most commonly used sequences include conventional spin echo (SE) for T1-weight- ing, turbo SE (TSE) sequences for T2- weighting and gradient echo (GRE) sequences.
SE T1-WI is used for anatomic detail, and as an adjunct in the evaluation of the osseous structures.
TSE sequence has replaced conventional SE for T2-weighting (due to its relatively long acquisition times). However, because of image blurring, TSE sequences are not recommended for proton density imaging. Blurring can be reduced by increasing TE, decreasing inter-echo time, echo train length (ETL), and by increasing matrix. TSE sequences are less sus- ceptible to fi eld inhomogeneity than SE sequences.
Therefore, when metallic artefacts are present, such as in post-surgical patients, TSE sequences are pre- ferred over SE and GRE.
GRE sequences are used for the evaluation of artic- ular cartilage and for dynamic contrast-enhanced imaging. They are also used in a limited number of T2*
protocols (glenoid labrum, meniscus of the knee).
When using short TE in T1-weighted or PD images, one should take the magic angle phenomenon into account, a source of false positive MR fi ndings.
Furthermore, a pulse sequence is always a com- promise between acquisition time, contrast, detail or signal-to-noise ratio (SNR). SNR is highest in TSE and decreases respectively in SE and GRE sequences.
Concerning the different fat suppression (FS) techniques, in our institution, we prefer the spectral FS technique because of its better SNR and spatial resolution compared to the inversion recovery fat suppression techniques (Fleckenstein et al. 1991).
Both T2-WI with (spectral) FS and STIR images are most sensitive to bone marrow and soft tissue edema or joint effusion. This item is discussed more in detail in Chap. 6. For good detection of fl uid with preser- vation of anatomical detail and good differentiation between joint fl uid and hyaline cartilage, we include
an FS TSE intermediate weighted sequence (TR/
TE=75/30–35 msec) in at least one imaging plane in our standard protocols.
Cartilage specifi c sequences have been developed, and are discussed more in detail in Chap. 4 (Disler et al. 2000).
The musculoskeletal system, especially in the extrem- ities, is not infl uenced by motion, and, as a consequence, motion artefacts are rare. Infolding artefacts can be avoided by selecting an appropriate imaging matrix, saturating anatomical areas outside the region of inter- est, and off-center imaging. Artefacts due to distortions of the local magnetic fi eld are attributable to ferromag- netic and, to a lesser degree, nonferromagnetic ortho- paedic devices. The use of surface coils will improve the SNR; smaller slice thickness and larger matrices are essential for soft tissue imaging. The choice of small
“fi eld-of-view” (FOV) without changing the matrix size will increase the spatial resolution. Sometimes, imag- ing of the contra-lateral side may be useful, requiring a larger FOV and the use of a body coil.
Contrast-enhanced MR studies lead to a prolonged examination time and high costs, and therefore, the use of intravenous contrast agents is not indicated when evaluating a sports lesion. It should be reserved for cases in which the results would infl uence patient care (Kransdorf and Murphey 2000). Applica- tion of intravenous gadolinium is indicated when dealing with a tumoral or pseudotumoral mass (see also Chap. 8) to detect neovascularization and intra- lesional necrosis (which is a major parameter for malignancy), in cases of infl ammation or as part of indirect arthrography. For detection of subtle areas of contrast enhancement, we use subtraction images (SE T1-WI with FS after minus SE T1-WI with FS before gadolinium) (static MR imaging). After i.v. adminis- tration of gadolinium, STIR type sequences should not be used, since not only fat but also enhancing tissue will be shown with a reduced signal intensity.
Recently, diffusion tensor imaging (DTI) has been used to study muscle architecture and structure. In future, DTI may become a useful tool for monitor- ing subtle changes in skeletal muscle, which may be a consequence of age, atrophy or disease (Galban et al. 2004). Furthemore, important information about muscle biomechanics, muscle energetics, and joint function may be obtained with unique MRI contrast such as T2-mapping, spectroscopy, blood-oxygen- ation-level-dependent (BOLD) imaging, and molecu- lar imaging. These new techniques hold the promise for a more complete and functional examination of the musculoskeletal system (Gold 2003).
The clinical MR imaging protocol will be greatly infl uenced by local preferences, time constraints and MR system available (fi eld strength, local coil). For an in-depth discussion of the different MR imaging pro- tocols, the reader is referred to subsequent chapters.
MRI has the disadvantage of not always being well accepted by patients, of being incompatible with dynamic manoeuvres and of not always being possible in emergency conditions. Furthermore, it provides the evaluation of an entire anatomical area – bone structures included – but is only good for the study of a limited part of the skeleton. This is in con- trast to scintigraphy, with which the whole skeleton can be evaluated at once. Otherwise, MRI helps to elucidate the true nature of highly nonspecifi c hot- spots on scintigraphy. For a discussion of the value of nuclear medicine techniques used in sports lesions, we refer to the following chapters.
2.2.4.2
Direct and Indirect Arthrography
MR arthrography is a technique which is mainly used in the shoulder, wrist, ankle, knee and hip joint. Two different techniques are described – direct and indi- rect MR arthrography.
Direct Technique
The contrast medium is a 2 mmol/l solution of Gd- DTPA in 0.9% NaCl. Eventually add 1–5 ml 1% Lido- caine. Fluoroscopy is used to bring the needle-tip into a correct intra-articular position. To assure the correct position, 1–2 ml of 60% non-ionic contrast medium is injected. The amount of the MR-contrast medium injected depends on the selected joint. MR imaging (with FS SE T1-WI) is initiated within 30 min after injection to minimize the absorption of contrast solution and the loss of capsular distension.
Indirect Technique
Intravenous administration of 10–20 ml 0.1 mmol Gd-DTPA/kg body-weight. Synovial excretion of con- trast medium occurs in the minutes after injection to shorten the relaxation time of the synovial fl uid, and is heightened by rigorous exercise (joint movements) for about 10 min. MR imaging (with FS SE T1-WI) is initiated within 30 min after injection, when maximal enhancement is reached blanc line.
The clinical and radiological importance of the direct technique for the assessment of chondral and
ligamentous lesions is well established. A major disad- vantage of the direct technique is its invasiveness. An additional drawback of the direct technique is that in many European countries, intra-articular injection of gadolinium is not permitted. The indirect technique has the advantage of not requiring direct access to the joint but lacks the advantages of joint distension.
2.3
General Principles and Indications
As a general rule, MRI and US are most accurate for grading soft tissue injuries while bone injury can be assessed with conventional radiography and MRI.
For internal derangements of joints, we prefer MRI because of its non-invasive character. In our institu- tion, CT is used for better evaluation of fracture or fracture healing or for biometric views (e.g., ante- version femoral neck, Q-angle). We recommend that conventional radiography should always be the fi rst diagnostic modality performed to depict (associ- ated) skeletal or joint abnormalities.
Radiographic assessment of a stress fracture, an entity frequently encountered in sportsmen, can be insensitive, especially in the early stage of the con- dition and follow-up fi lms may demonstrate abnor- malities in only 50% (Spitz and Newberg 2002).
Bone scintigraphy has a high sensitivity but low specifi city and lacks spatial resolution and has been largely superseded by MRI, providing excellent sen- sitivity and specifi city, as it can also identify alter- native sources of pain, such as muscle tears or joint degeneration (Anderson and Greenspan 1996).
Moreover, MRI is useful for follow up of stress injury, with a return of normal bone marrow signal on T2- WI at three months compared to scintigraphy, which may show abnormal uptake for up to ten months (Slocum et al. 1997).
Conventional arthrography has now been replaced by cross-sectional imaging techniques and is only performed as part of CT- or MR-arthrography.
For the diagnosis of muscle and tendon lesions, US is considered the best imaging modality, both in the initial phase for recognition of a lesion, but also for the assessment of the various changes it undergoes until complete healing has been achieved. In most cases, MRI adds no additional diagnostic informa- tion. Well-established indications for US are summa- rized in Table 2.1.
If plain radiographs and/or US are negative or reveal unequivocal fi ndings and clinical symptoms persist, MR imaging must be performed.
MR examinations most frequently requested are of the knee and shoulder. Well-established indica- tions for MRI are summarized in Table 2.2.
Due to the recent developments in CT technology, multidetector CTA has become a valuable alternative to MR imaging for the assessment of internal derangement of joints and has proved to be an accurate technique to detect articular cartilage lesions. A major drawback of spiral CTA, however, is its invasive character.
The choice between multidetector CTA and MR imaging for assessment of internal joint derange- ment is offered to the referring clinician, depend- ing on the clinical situation. In general, children and young patients, patients with allergy to iodinated con- trast, patients with suspicion of ligamentous lesions and patients with recent trauma (and hemarthrosis) are imaged with MR imaging. Multidetector CTA is favored in patients with chronic symptoms, suspected cartilage lesions, or in patients with recurrent symp- toms after surgery (e.g., post-operative meniscus).
2.4
Optimal Moment of Investigation
The ideal time for the US examination of fresh trau- matic muscle lesions is between 2 and 48 h after trauma. Before 2 h, the hematoma is still in forma- tion. After 48 h, the hematoma can be spread out- side of the muscle (Peetrons 2002). However, with some muscles it can stay for much longer. It is rec- ommended that for lesions in the hamstrings the US examination be done as soon as possible after the 2-h delay. For rectus femoris and gastrocnemius lesions, the examination can be postponed for as long as two or three days, or even longer sometimes (Brandser et al. 1995).
2.5
Safety, Availability and Economic Aspects
Because all ionizing radiation is harmful and there is no safe lower threshold of radiation, consideration must be given to the radiation dose to the patient when plain radiography or a CT examination is requested. Examinations on children require an even higher level of justifi cation since they are at greater risk from radiation than are adults. Therefore, when clinically appropriate, the alternative use of safer non- ionizing techniques (such as ultrasound and MRI) or of low dose radiography/CT techniques must always be considered (see also Chap. 26).
The number of sport participants, both amateur and professional athletes, has increased dramati- cally over recent decades. The benefi ts to health are debated but are generally accepted. However, more participation has led to more sports-related injuries.
The increase has been in both acute and, even more, in overuse injuries (Garrick and Requa 2003).
Although some researchers and policy makers have expressed concern about the lack of high quality evidence regarding the cost-effectiveness and effi - ciency of MRI, it was demonstrated that, in most diagnostic categories, MRI fi ndings may have a sig- nifi cant impact on diagnosis and treatment plan- ning ( Hollingworth et al. 2000). For example, several studies have documented that MR imaging can be an accurate, cost-effective means of assess- ing injuries in the knee, preventing patients from undergoing unnecessary arthroscopy. Appropri-
Table 2.1. Well-established indications for US
Foot/ankle Achilles tendinosis, plantar fasciitis, ligamen- tous injury
Shoulder Rotator cuff disease, biceps tendon (dynamic evaluation), spinoglenoid cyst
Elbow Common extensor, fl exor and triceps brachii tendinosis
Wrist/hand Tenosynovitis, synovial cyst
Hip/pelvis Inguinal hernia, snapping hip, bursitis, avul- sion injury
Knee Collateral ligaments, patellar and quadriceps tendon, bursitis, meniscal cyst
Table 2.2. Well-established indications for MRI
Foot/ankle Osteochondral lesion
Shoulder Labral abnormalities, suprascapular nerve entrapment, quadrilateral space syndrome, Parsonage-Turner
Elbow Osteochondral lesion, ligamentous injury, instability
Wrist/hand TFCC, AVN, distal radioulnar joint (DRUJ) Hip/pelvis Osteitis pubis, adductor strain, labral abnor-
malities, AVN
Knee Meniscus, osteochondral lesion, cruciate ligaments, posterolateral corner
ate selection of patients will probably yield similar results in other anatomic locations. The advance- ments in MRI technology may expand the range of usefulness of this modality, leading to even greater utilization of MR imaging in patients with sports injuries, and, eventually, to reduced costs and greater availability.
2.6
Conclusion
The diagnosis of sports injuries can be diffi cult owing to the degree of overlap of symptoms between different injuries, necessitating further imaging evaluation. Different imaging techniques, with their specifi c advantages and limitations, can be used to diagnose and grade such injuries. The correct use of these imaging modalities will lead to an early and accurate diagnosis preventing the development of chronic pain or other complications and thus, avoid- ing waste of limited fi nancial resources. The specifi c merit of each imaging modality in the evaluation of sports related lesions will be further high-lighted in the next chapters and summarized in schematic boxes.
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Things to Remember
1. The imaging requirements for sports medi- cine physicians should begin with conven- tional radiography.
2. Ultrasound is considered the imaging tech- nique of fi rst choice for the diagnosis of muscle lesions. The examination must be performed between 2 and 48 h after the muscle trauma to assess the extension of the hematoma and hence predict a grading of muscle lesions.
3. MR imaging has become the dominant imag- ing modality in the assessment of sports- related injury, because sports medicine and high-quality imaging are inextricably linked.
There are, however, many fi ndings on MRI that may not represent clinically signifi cant disorders. Therefore, optimization of image acquisition and interpretation requires cor- relation with clinical fi ndings.
4. Multidetector CT arthrography is a valuable alternative to MR imaging for the assessment of internal derangement of joints. In daily, clinical practice, the choice between the two imaging modalities is offered to the referring clinician, depending on the clinical situation.
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Zanetti M, Metzdorf A, Kundert H-P et al.(2003) Achilles ten- dons: clinical relevance of neovascularization diagnosed on power doppler US. Radiology 227:556–60
