Keywords

1 Radiologic Perspective

Sports medicine is one of the most rapidly growing subspecialties 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 [1]. Sports injuries often generate nonspecific symptoms and clinical findings, demanding further imaging investigations for accurate diagnosis and optimal treatment planning.

Over the last 10 years, imaging techniques have become increasingly important as a diagnostic tool for sports injuries without replacing the traditional methods of management [2, 3].

The discipline of musculoskeletal radiology has evolved into a major imaging subspecialty in recent years since the first use of X-rays to diagnose fractures. Musculoskeletal radiology expertise has experienced enormous developments in diagnostic sensitivity and specificity and in image-guided treatment options, in addition to technologic advances far beyond X-rays. Advances in cross-sectional imaging such as CT and MR imaging and educational and research endeavors have contributed further to the growth of musculoskeletal radiology as a distinct subspecialty.

Diagnostic imaging plays an increasingly important role in the detection, management, and follow-up of sports disorders.

The use of a wide range of imaging modalities such as routine radiography and ultrasound, as well as advanced imaging modalities such magnetic resonance imaging (MRI) and computed tomography (CT), allows an accurate diagnosis of a broad range of osseous, articular, and soft tissue abnormalities.

However, over-imaging can cause problems in high-level athletes, who have easy access to imaging modalities.

The choice of the imaging modality depends on multiple factors inherent to the radiologist, athlete, and type of lesion, and the optimal imaging process may not exist and should be individually tailored.

While diagnostic imaging allows for accurate characterization of a lesion and local anatomy, it must be emphasized that clinical correlation is mandatory to avoid diagnostic discrepancies and promote optimal athlete management. Good communication between the radiologist and the sports physician is essential.

2 Role of Imaging

The athlete’s population differs from the normal population. In sports medicine, especially elite sports medicine, there is always the dichotomy between lesion severity and the pressure of time to resume to play.

Radiological imaging is often required to obtain accurate diagnosis in sports injuries. Even if symptoms and clinical findings in sports injuries are specific, sports medicine physicians often request additional and costly imaging more easily, as they often need a more rapid and accurate diagnosis for lesion severity grading and to optimize treatment planning [4]. Imaging techniques are also readily used to monitor ongoing pathology and to facilitate return-to-play decisions [5].

Imaging can play an important role allowing a fast and accurate diagnosis, helping in evidence-based decision for conservative versus surgical treatment, and also by demonstrating to the athlete the presence of the lesion and reinforcing his adherence to treatment. Imaging can also guide treatment interventions.

The sports medicine radiologist can provide confirmation of specific injury, monitoring of the healing process and the return to play, screening and evaluation before competition/signing, and technical assistance in invasive procedures.

The radiology department of sports medicine should provide different imaging techniques (X-ray, ultrasound, CT, MRI), radiologists with experience in sports medicine imaging, and availability 24 h/7 days with rapid response.

In an ideal setting, the radiologic exams should be available at the training center of the athlete. In recent years, there has been a crescent recognition of the importance of the imaging department within the medical departments of clubs, national and international federations, and Olympic committees. Top European clubs and Olympic Games have been establishing partnerships with imaging medical systems companies to provide radiologic equipment within their own medical and training centers and the Olympic village. It’s predictable the integration of radiologists in the medical department staff of top clubs, federations, and Olympic delegations.

3 Overview of Imaging Modalities

This chapter aims to review the role of imaging techniques available to the diagnosis and grading of injuries inherent to football practice, enlightening their specific advantages and limitations and delineating possible imaging strategies and pathways to evaluate most frequent problems and injuries in football, with additional practical guidelines that may be useful in daily clinical practice.

4 Conventional Radiology (CR)

Plain radiography is the initial screening examination for osseous disorders due to its ability to visualize osseous structures with high spatial resolution, low cost, and widespread availability [6].

The characterization of the cortical bone is excellent, but the trabecular bone is underdiagnosed. Bone lesions producing cortical disruption, namely, fractures, are relatively easily visualized. Bone loss limited to the trabecular bone from osteoporosis is more difficult to characterize.

The presence of metal is not a limiting factor for CR, allowing assessment of the postoperative bone lesions safely and without artifacts.

CR has important limitations in the evaluation of soft tissue lesions due to poor contrast resolution. It may play a role in the evaluation of the presence of calcifications within the lesion, for example, in myositis ossificans lesions.

Indications for radiography include trauma, pain, instability, impingement, infection, preoperative or postoperative evaluation and/or follow-up, and evaluation of soft tissues in an extremity (e.g., suspected foreign body) (ACR–SPR–SSR Practice Parameter for the Performance of Radiography of the Extremities [7]).

The minimum recommended views in routine circumstances most often include two orthogonal perpendicular projections. Views may be modified for any given clinical situation. Additional views (e.g., oblique views, stress views) may be warranted as part of the initial examination, or after review of the initial images, to clarify suspected pathology. In the evaluation of the shaft of a long bone, the X-ray should include both proximal and distal joints.

While standard radiographs are a static form of imaging, stress radiography is employed to dynamic evaluation, allowing assessment of alignment and stability. These stressed views may demonstrate misalignment or signs of instability not visualized in neutral position.

CR plays an important role in assessing bone position following the treatment of a fracture or dislocation, in monitoring the progress of fracture healing with callus formation and in the diagnosis of fracture complications or complications arising from treatment. Two or more views are usually required to accurately assess bone position after any treatment procedure.

There are numerous normal anatomical variants which may mimic fractures. Correlation of X-ray findings with clinical features is often useful to eliminate significant injury. Some fracture mimics have characteristic features.

Conventional arthrography (X-ray joint evaluation after injection of intra-articular contrast medium) has evolved during the last century from crude techniques with postprocedural radiographic imaging to modern CT and MR arthrographic techniques. Arthrography saw its widest use in the 1960s and 1970s, but indications for its use in many joints decreased significantly after the introduction of cross-sectional imaging modalities such as CT and MR imaging. Arthrography nowadays is only performed as part of CT or magnetic ressonance arthrography (MRA) [8].

CR uses ionizing radiation. Medical ionizing radiation has great benefits and should not be feared, especially in urgent situations. Radiological dose and risk depends on good methodology and quality control, taking into account the possible risk from radiation exposure and the diagnostic image quality necessary to achieve the clinical objective (“as low as reasonably achievable”).

The prescribing physician must justify the examination and determine relevant clinical information before referring the patient to a radiologist. Indications and decisions should reflect the possibility of using nonionizing radiation examinations, such as MRI or ultrasonography. Repetition of examinations should be avoided at other institutions.

5 Ultrasound (US)

US technology is rapidly advancing and being refined, and is aimed at both increasing image quality and opening new fields of applications.

Acute skeletal muscle injury is one of the major causative factors for loss of playing time in all athletes and is the most common injury in professional football. A recent study on male professional footballers showed that injuries to muscle represent more than 30% of all injuries and are responsible for approximately one quarter of total injury absence. Over 90% of muscle injuries affect the four major muscle groups of the lower extremity: hamstrings, adductors, quadriceps, and gastrocnemius. Injury to the hamstring muscle group is reported to be the most common injury subtype [9].

Over the last 15 years, musculoskeletal ultrasonography has become an important imaging modality used in sports medicine, being considered the sports medicine stethoscope. This technique has become an indispensable tool in the clinical management of sports injuries and degenerative and traumatic lesions of the articulations and periarticular soft tissues. With the rapid development and sophistication of this modality, essential information for a better understanding of the pathophysiologic assessment of many disorders has been established, allowing crucial decisions regarding treatment planning and monitoring the effects of therapy.

Major advantages for the diagnostic accuracy of US in sports medicine practice are the ready availability, portability, affordability, speed, real-time and dynamic imaging, high spatial resolution, and absence of ionizing radiation. The possibility of using Doppler imaging is another advantage.

US main disadvantages are the inadequate characterization of bone and deep structures, operator dependency, and the short field of view. Despite the former, ultrasound is sensitive to rule out cortical fractures of superficially located bones and is more accurate to detect rib fractures compared to radiographs [10].

US is able to recognize the internal muscle architecture. Intramuscular vessels coursing within the hyperechoic septa are visible on color and power Doppler imaging. The outer muscle fascia (epimysium) appears as a well-delineated echogenic envelope circumscribing the hypoechoic muscle. Large hyperechoic septa (aponeuroses) directed within the muscle belly can be seen arising from it. In complex muscles, an individual hyperechoic fascial sheath surrounds each muscle belly thus helping the examiner to recognize the different heads. The interstice between juxtaposed fasciae of two adjacent muscles appears as a hypoechoic band and corresponds to loose connective tissue that allows some sliding of the muscles during contraction [11].

Dynamic US scanning performed during muscle contraction can show changes in size and relationship of fascicles and fibro-adipose septa.

High-frequency (7–18 MHz) linear-array probes are used to perform musculoskeletal US examinations. Broadband transducers use a spectrum of frequency distribution (i.e., 12–5 MHz) instead of a single fundamental frequency (i.e., 10 MHz): the high-frequency components tend to increase the intensity maximum in the focal zone but cause a prompt decrease in intensity with depth, whereas the low-frequency components extend the penetration depth [12]. Other systems use the total transducer bandwidth for the transmitted pulse and then adjust the receiver bandwidth to lower frequencies as deeper depths are sampled. These systems give increased flexibility to the US examination, enabling the same transducer to change the image acquisition parameters during scanning based on the desired clinical information. In musculoskeletal imaging, this is particularly important when the study focuses on both superficial (i.e., subcutaneous tissue planes) and deep (i.e., muscle tissue layers) tissues in the same study and body area to be explored.

A variety of linear-array transducers, including large (>40 mm), medium-sized (<40 mm) and small-FOV (hockey-stick-shaped) probes, are currently available in the frequency range used for musculoskeletal examinations. Selection of the adequate transducer primarily depends on the frequency. Hockey-stick probes are the best choice for imaging small superficial structures at sites in which the skin surface does not allow adequate contact with larger probes (i.e., soft tissues adjacent to bony prominences) or while performing dynamic maneuvers, but they are characterized by a restricted field of view. Compared with small transducers, high-frequency large-diameter transducers tend to have a large near-field beam width leading to a poor lateral resolution at shallow depths. Because they maintain beam shape to greater depths with less divergence of the US beam, they have the best potential for imaging deep-seated structures [11].

Recent technologic innovations in US have resulted in improved diagnostic performance for the evaluation of the musculoskeletal system, including wideband Doppler imaging, spatial compound imaging, extended field-of-view imaging, steering-based gray-scale imaging, elastography, and 3D imaging [11].

The ability of high-frequency color and power Doppler to detect low flow states in superficial structures and to correlate hyperemic changes with structural abnormalities has allowed for the noninvasive study of blood flow and vascularity within anatomic structures and lesions, opening new perspectives in the evaluation of a variety of musculoskeletal disorders.

The most studied example is the detection of intra-tendon neovascularization in tendinopathy, considered of diagnostic and prognostic value, related to clinical outcome, and the exclusive target of some therapeutic interventions [13–16], but with discrepant results, and recent studies have been questioning the value of neovascularization in tendinopathy [17–19].

Spatial compound imaging indicates an acquisition mode in which the information is obtained from several angles of insonation and is combined to obtain a single image [20, 21].

The advantages of compound mode are many, including reduction of image artifacts (e.g., speckle, clutter, noise, angle-generated artifacts), sharper delineation of tissue interfaces and better discrimination of lesions over the background, as well as improvement in detail resolution and image contrast. In the musculoskeletal system, compound imaging leads to an improved delineation of structures composed of specular echoes, such as tendons and muscles [21].

The extended field-of-view technique contributes to an improved presentation of the US information for the referring physician [22–25], displaying the full extent of an abnormality and showing its relationship with adjacent structures on a single image.

Three-dimensional acquisition can be achieved with US using either 2D conventional transducers equipped with a small electromagnetic positional sensor or dedicated “3D volume transducers,” which are larger than standard probes and more difficult to handle but have the advantage of providing more exact assessment of each scanning plane.

Ultrasound elastography (EUS) is a method to assess the mechanical properties of tissue, by applying stress and detecting tissue displacement using ultrasound. There are several EUS techniques used in clinical practice; strain (compression) EUS is the most common technique that allows real-time visualization of the elastographic map on the screen. There is increasing evidence that EUS can be used to measure the mechanical properties of musculoskeletal tissue in clinical practice, with the future potential for early diagnosis to both guide and monitor therapy [11].

Due to the excellent spatial resolution and definition of muscle structure, US has become an indispensable tool for evaluation of muscle pathology, not only for the diagnosis of the lesion, allowing an accurate characterization most of the times, especially in superficial muscles, but also for the follow-up of lesions during healing process, with detection of healing complications such as fibrosis, hematomas/seromas, hernias, or myositis ossificans.

The ideal time for the US examination of fresh traumatic muscle lesions is between 2 and 48 h after trauma. Before 2 h, the hematoma is still in formation. After 48 h, the hematoma can be spread outside of the muscle [26]. However, with some muscles it can stay for much longer. It is recommended 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 2 or 3 days, or even longer sometimes [27].

Dynamic US study may be very helpful to the correct diagnosis, e.g., to search for muscle hernia (during muscle contraction) or to evaluate the snapping hip syndrome (during hip flexion and lateral rotation). To avoid artifacts or pitfalls, comparison with the contralateral side may be necessary.

US has intrinsic limitations in the assessment of the bone. In some applications, however, it can be useful to assess selected bone disorders, especially if performed as a complement to standard radiographs [28]. With US, the interface between the soft tissue and cortical bone is highly echogenic because of an inherent high acoustic impedance mismatch [29]. The bone cortex appears as a regular continuous bright hyperechoic line with strong posterior acoustic shadowing and some reverberation artifact.

US can detect cortical outgrowths (exostoses, anatomic variants), defects (fracture, osseous tunnels, impact lesions), and erosions. Some authors have suggested that the process of fracture healing can be followed with color Doppler imaging and spectral analysis [30].

Bone abnormalities seen at US can easily be correlated with clinical findings and can suggest the requirement for additional radiographic views or other imaging studies if further evaluation is warranted.

The indications for joint US are rapidly expanding due to the refinement of high-resolution transducers and to the fact that both radiologists and clinicians are increasingly aware of the potential of US [31].

US allows visualization and characterization of superficial ligaments, intra-articular fat pads, and intra-articular fluid. Some ligaments located in the central portion of joints (i.e., the interosseous tarsal sinus ligaments and the cruciate ligaments of the knee) cannot be visualized with US because of the overlying osseous structures.

In most joints, small amounts of normal intra-articular fluid can be detected in the articular cavity by means of high-resolution US.

Many joints contain fibrocartilaginous structures, including the meniscus in the knee, the labrum in the hip and the shoulder, the triangular fibrocartilage in the wrist, and the volar and plantar plates in the hand and foot. Because of their deep location and close contact with the bone, these structures can be evaluated with US only in part and not reliably. However, some conditions involving the superficial part of these structures, such as an extruded meniscus, a meniscocapsular detachment with fluid intervening between the capsule and the fibrocartilage or a meniscal ossicle can be inferred on US.

In contrast to the results of fibrocartilage evaluation, US has proved to be an effective modality for diagnosing parameniscal and paralabral cysts [32–34].

Ligament tears can be demonstrated with US at different sites, including the ankle and foot [35, 36], the wrist and hand [31, 37–39], the knee [40–42], and the elbow [43]. The US features of a torn ligament vary depending on whether the lesion is acute or has healed. In acute phases, a partially torn ligament appears swollen and hypoechoic but continuous; an anechoic band over the superficial aspect of the ligament may be observed representing reactive soft tissue edema [35]. In complex ligaments, US can distinguish the abnormal hypoechoic portion of the ligament from the unaffected one retaining a normal appearance. In acute complete ruptures, a hypoechoic cleft reflecting the hematoma can be detected through the ligament substance, and the free ends of the severed ligament may appear retracted and wavy. In doubtful cases, the ability to assess the ligament dynamically is a definite advantage of US: under stress, a normal ligament tightens preventing excessive widening of the joint space; if the ligament is torn, a paradoxical movement is obtained reflecting joint instability [44, 45]. In chronic partial tears, the ligament always appears thicker than normal on US images. Calcifications within the ligament substance in old tears and irregularities of the bony insertions in avulsion injuries may be observed [45]. A typical example is the Pellegrini-Stieda syndrome (calcification of the proximal end of the medial collateral ligament of the knee).

One of the major limitations of US in evaluating osteoarthritis is the incomplete evaluation of the cartilage surface, which is, for the most part, masked by the ends of opposing bones. This is true for both tight and large joints. In the knee, for instance, articular cartilages that are vulnerable to tears and ulcerations are mainly located at the posteroinferior aspect of the femoral condyle and on the lateral facet of the patella: both surfaces are barely evaluated with US. Similarly, geodes (subchondral cysts) are not visible at US because they are completely surrounded by the bone. On the other hand, osteophytes can be readily appreciated as beak-like bone projections covered by hypoechoic cartilage adjacent to the joint line. They increase the surface area of the articular cartilage, thus lessening the stress and loading forces that are experienced by the joint and, at the same time, increasing its stability: typical locations of osteophytes are the posterior humeral head, the internal femorotibial, and the anterior tibiotalar joints [46].

Finally, US can be useful in assessing para-articular soft tissue abnormalities that can be responsible for pain in osteoarthritis and may help to guide intra-articular drug injection.

Detection and localization of postoperative infection and complications may be a challenging task and underdiagnosed with US.

6 Multidetector Spiral CT (MDCT) Scan

CT is a frequently and an increasingly used imaging modality with multiple musculoskeletal applications. Technological improvements and innovations have refined and broadened the utility of CT for clinical imaging.

CT has distinct advantages and inherent limitations in the assessment of bones, joints, and soft tissues, both need to be considered when choosing CT for a specific imaging task.

CT technology has evolved since the first scanner was introduced in 1972. The past four decades have witnessed major improvements. These include development of spiral CT, rapid acquisition and processing of raw data, and improvements in spatial resolution. These have resulted in the ability to generate isotropic volume data sets and multiplanar reformations (MPRs). There have been multiple generations of CT scanners, but most of the current clinical scanners use a third-generation geometry in which the X-ray tube or tubes and detector arrays are opposed and mounted to a rotating gantry. Advances in tube, detector and software design continue to refine and redefine clinical applications.

Multislice CT has brought about major advances in bone and joint imaging. A volumetric image set with isotropic properties can be obtained in a single acquisition with a 0.5-mm slice width. Multislice CT allows extended anatomic coverage with thin slices; large patients and patients with metal hardware in their bodies now can be scanned without sacrificing diagnostic quality. To take full advantage of these capabilities, production of multiplanar reformatted images has become an integral part of the examination. Different three-dimensional rendering techniques can be applied to reduce the large image sets into clear pictures for the referring physician and the patient.

Most musculoskeletal applications demand high spatial resolution. The progressive increase in the number of detector elements in each row and decrease of detector width have improved spatial resolution. A typical 64 multidetector computed tomography (MDCT) scan can achieve a spatial resolution of 0.33–0.47 mm.

Reconstruction algorithms can be applied to image data in order to enhance detail or contrast resolution depending on the purpose of the study. High spatial resolution filters can enhance image detail and sharpness to better evaluation of bone trabecular structure. Lower space resolution filters can generate a smoother image, better for evaluation of soft tissues and low contrast structures.

Isotropic data sets also improved the quality of three-dimensional (3D) rendering techniques, like volume rendering, shaded surface display, and maximum intensity projection (MIP). The generated 3D overview provides good visualization of structure spatial relationship, helpful in presurgical planning.

Recent advances in technology and software development also allowed improvements in some disadvantages of CT. The most observable changes are the availability of radiation dose reduction and metal artifact reduction.

The optimal CT protocol for musculoskeletal imaging contemplates several parameters with the objective of achieving the best diagnostic image quality for the specific clinical scenario.

Major musculoskeletal clinical applications of CT are trauma; nontraumatic osseous, soft tissue, and periarticular lesions; and imaging around metal hardware.

Possibly the most obvious ideal application for spiral CT is in the evaluation of musculoskeletal trauma. Once a volumetric data set is generated, the images can be used for multiplanar and three-dimensional reconstruction. The value of rapid acquisition is particularly apparent in trauma patients when the trauma involves areas where patients may have difficulty remaining still such as the shoulder, sternoclavicular joint, elbow, or wrist.

More common CT applications in musculoskeletal trauma include the pelvis and acetabulum, the knee including the tibial plateau, the ankle joint, the wrist, and the spine. Transaxial CT supplemented by multiplanar reconstruction and 3D imaging could have a major impact on both diagnosis and patient management. The use of MPR and 3D imaging can alter the patient management versus the use of transaxial CT alone. These changes in management are predominantly two types: tentative surgery scheduled due to a situation worse than anticipated and acute surgery deferred in favor later definitive arthrodesis or arthroplasty, again usually when the images revealed a clinical picture worse than anticipated.

In acetabular and pelvic trauma, spiral CT data sets coupled with a real-time 3D volume-rendering program allow visualization of the entire pelvis through any plane or perspective [47]. By scanning and creating 3D maps of the entire pelvis, we can easily detect any associated sacral or sacroiliac injuries.

CT is especially useful in lower extremity trauma involving either the knee joint or the ankle. In the patient with a tibial plateau fracture, spiral CT with sagittal and coronal reformatting of data is an important study in defining whether or not a patient needs surgical intervention. The use of these displays coupled with 3D images is ideal for defining plateau depression and quantifying it. In cases of proximal tibiofibular dislocation, the 3D images are especially valuable. Severe ankle trauma also illustrates the role of multiplanar and 3D imaging in finalizing assessment and surgical planning [48]. Pilon fractures, with severe impaction and destruction of the articular plafond, may be triaged into those patients needing immediate surgery and those who will be treated later with arthroplasty. Injuries to the talus, calcaneus, or tarsal bones are well imaged with spiral CT protocols.

Spiral CT with direct coronal reconstructions is an excellent approach to the traumatized wrist [49], allowing successful evaluation of occult or complex fractures.

Trauma to the spine can be routinely visualized successfully with a combination of transaxial CT, MPR images, and 3D studies.

One limitation of CT in acute trauma is the poor depiction of bone marrow edema and soft tissue injuries compared with magnetic resonance imaging (MRI), which is more accurate for detecting non-displaced fractures, bone contusions, ligament and tendon tears, and other soft tissue lesions.

In addition to acute trauma, CT can be used in the setting of chronic trauma. Fractures require serial follow-up to assess healing and to look for potential complications. Although radiographs alone are sufficient in most cases, certain situations may warrant additional cross-sectional evaluation. CT is used commonly to assess fracture complications like malunion, nonunion, hardware failure, and infection. CT allows more precise determination of the relative volume of osseous to fibrous union and cortical bone bridging. The cortical bone destruction of infection is easier to visualize at CT than MRI, particularly in cases with adjacent metal hardware.

CT can provide advantages over radiography for characterization of nontraumatic osseous, soft tissue, and periarticular lesions. CT can improve the detection of focal lesions if they are small or located in anatomic complex regions, like the pelvis, and characterization of the lesion, like the matrix mineralization or presence of cortical shell, nidus, or sequestrum.

The evaluation of soft tissue or muscle infection and/or tumor is another clinical application for spiral CT. With the use of iodinated contrast material, the scan can evaluate an area of suspected musculoskeletal abnormality during peak levels of contrast enhancement. It has been previously documented that contrast enhancement allows for better detection of intramuscular pathology whether it is inflammatory or neoplastic [50, 51]. CT is also useful in distinguishing vascular masses from hematoma, abscess, or tumor.

Artifacts from metal hardware traditionally have been a major limitation to diagnostic imaging, including CT.

Recently metal artifacts have become less problematic in CT imaging by using optimal scanning technique in conjunction with advances in scanner hardware and software. These artifacts can be reduced by adapting the acquisition protocol and scanning technique to the clinical question and type of the hardware.

CT arthrography (CTA) consists of intra-articular injection of iodinated contrast solution performed under fluoroscopic observation [52]. The volume of contrast medium injected depends on which joint is studied: shoulder, 10–15 ml; wrist, 5 ml; hip, 10 ml; knee, 20 ml; and ankle, 6–12 ml. After injection of contrast material, patients are asked to perform full-range mobilization of the joint. Anteroposterior, lateral, and oblique views are routinely obtained to image the entire articular cavity. Subsequently, multidetector CT is performed.

CTA can be an acceptable alternative to MRI and MRA for evaluation of internal derangements of joints in several situations; in some cases it can be the study of choice. Technical advances in CT have improved the usefulness of CTA.

The main advantages of CTA over MR and MRA include faster acquisition speed, higher spatial resolution, and fewer artifacts near metal hardware. MR has some contraindications, like cardiac pacemakers, and CTA can replace MR in these cases.

The advantage of CTA for the assessment of the cartilage is the excellent conspicuity of focal morphologic cartilage lesions that result from the high spatial resolution and the high attenuation difference between the cartilage substance and the joint contrast filling the lesion [53]. A limitation of CTA imaging of the cartilage is its complete insensitivity to alterations of the deep layers of the cartilage.

The faster acquisition speed may constitute an important strength of CTA in patients with claustrophobia, pain, and other constraints that would limit MR scan.

Metal artifacts are less problematic in CT than MRI, and CTA is a useful technique in many postoperative scenarios.

Other limitations of CTA include its invasiveness, possible allergic reaction, use of ionizing radiation, and poor soft tissue contrast resolution.

Radiation dose from CT has received considerable attention from the imaging community and from the public. Adapting protocols to the particular patient body region and clinical scenario is critical to optimization of the radiation dose. Efforts to lower the dose begin by determining the appropriateness of CT as an imaging technique for the specific clinical problem; alternative nonionizing or low-dose imaging techniques must be considered.

Radiologist and technologist should anticipate cases where dose is wasted and should be eliminated, excessive and can be reduced, or inadequate and should be increased.

It is therefore important to understand the clinical questions to be answered prior to performing the spiral CT examination. There are a variety of current CT techniques available for imaging musculoskeletal problem, and radiologists must decide judiciously to when and where they should be applied.

7 Magnetic Resonance Imaging (MRI)

Since its introduction in the 1970s, magnetic resonance imaging (MRI) has revolutionized the diagnosis and treatment of musculoskeletal disorders. Excellent soft tissue contrast, spatial resolution, and multiplanar imaging are among the major advantages of MRI. The majority of applications for musculoskeletal MRI fall into one of three major categories of disease: (i) derangement within and about joints, (ii) infectious processes, and (iii) tumors and tumorlike conditions. MRI for sports medicine includes high spatial resolution multiplanar depiction of anatomy and abnormalities in almost every joint in the body, as a result of its ability to assess a wide variety of anatomy and pathology ranging from ligament injuries to articular cartilage lesions [54–56]. The field of musculoskeletal radiology is constantly advancing as MRI applications in the musculoskeletal field continue to grow enormously. Remarkable advances have taken place in both hardware and software technology that allow for improved visualization of anatomy and pathology.

Specialized non-contrast sequences enable the direct quantitative assessment of articular cartilage and other joint structures, thereby providing indirect assessment of tissue health and biochemistry. T2 mapping displays local water content and collagen fibril orientation, and the method of T1 rho mapping displays the local proteoglycan content of the tissue. Ultrashort echo imaging improves the contrast of joint structures with high tissue isotropy or low water content, such as ligament, tendon, and meniscus.

Traditionally, most MRI of the musculoskeletal system is done at intermediate field strengths of 1.5 T or lower. However, imaging at 3.0 T has become increasingly more common for clinical evaluation, while other higher field systems are being evaluated in the research field. Despite initially being used for neurological imaging, availability of specialized coils and numerous studies have confirmed the benefits and abilities of higher field systems in musculoskeletal imaging [57–59]. The most valuable benefit includes an improved signal to noise (SNR) which can result in increased image resolution and decreased exam time. However, with the increase to a 3.0 T or higher field strength comes numerous issues that must be considered in order to optimize its intrinsically superior imaging capabilities.

The gain in SNR that is afforded by 3 T MR imaging systems has tremendous clinical applications in the musculoskeletal system. The potential for demonstrating and enhancing the visibility of normal osseous, tendinous, cartilaginous, and ligamentous structures is exciting. Radiologists have enjoyed great success in assessing joint disease with current MRI field strengths; however, many intrinsic joint structures remain difficult to evaluate, which leads to a golden opportunity for 3 T MRI. The articular cartilage of the knee, the glenoid labrum of the shoulder, the intrinsic ligaments and TFC of the wrist, the collateral ligaments of the elbow, the labrum and articular cartilage of the hip, and the collateral ligaments of the ankle have been evaluated suboptimally on 1.5 T systems using routine non-arthrographic MRI. Because of the enhanced SNR, the higher spatial resolution, and the greater CNR of intrinsic joint structures at higher field strengths, 3 T MRI has the potential to improve diagnostic abilities in the musculoskeletal system vastly, which translates into better patient care and management. As coil technology advances and as the use of parallel imaging becomes more available in the extremities, it’s expected to see even more dramatic improvements in image quality.

The quality of MRI depends on the lack of motion, signal and resolution, and tissue contrast.

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 sagittal planes. Oblique planes may also be useful, e.g., in the shoulder (paracoronal and parasagittal images). A typical musculoskeletal examination includes three to six sequences obtained in various anatomic planes.

The number of pulse sequences and combinations is almost infinitive. Conventional spin echo (SE) include T1-weighted (T1 W), T2-weighted (T2 W), and proton density weighted (PDW). Fast spin echo (FSE) allows for much more rapid acquisition than the conventional spin echo method. Decreased overall acquisition time lessens the potential for patient motion. FSE sequences are commonly used in musculoskeletal imaging. This technique has some drawbacks; the signal intensity of fat remains intensely bright on FSE-T2 W images and consequently can obscure pathology in subcutaneous fat and bone marrow. FSE can result in blurring tissue margins, making some pathology difficult to detect, like meniscal tears.

Short tau inversion recovery (STIR) is a fat saturation technique that results in markedly decreased signal of fat and strikingly increased signal from fluid and edema. As a result, STIR sequences are a very sensitive tool to detection of soft tissue and bone marrow pathology. FSE-STIR sequences are widely used in musculoskeletal protocols.

Gradient echo (GRE) sequences were originally developed to generate T2 images more rapid than SE sequences. Ligaments, cartilage, and fibrocartilaginous structures like knee menisci and glenoid labrum are well shown in GRE sequences. GRE imaging can be performed using a two-dimensional technique or a three-dimensional (3D) volumetric technique.

One feature of GRE sequences is a heightened sensitivity to susceptibility artifacts. This refers to artifactual signal loss at the interface between tissues of widely different magnetic properties. This can be advantageous to detect subtle areas of hemorrhage, loose bodies, and soft tissue gas. Susceptibility effects can be problematic when imaging patients with metallic hardware.

Fat signal suppression can be achieved with two main techniques: frequency-selective (chemical) fat saturation and STIR imaging.

The frequency-selective technique can be used with T1 W imaging, like in MR arthrography and after intravenous injection gadolinium contrast material, and FSE-T2 W imaging to highlight areas of soft tissue and bone marrow pathology. A major problem with frequency-selective technique is the potential for inhomogeneous suppression of fat signal.

STIR technique tends to produce more homogeneous suppression of fat signal but cannot be used with IV or intra-articular injection of gadolinium because its signal would be saturated along with fat in STIR sequences.

Most useful sequences to evaluate the bone are STIR, FSE-T2, and T1 and GRE T2*, articular cartilage are STIR or fat-saturated FSE-T2 and 3D–T1 W gradient echo with fat saturation, fibrocartilage are SE PD and GRE T2* and T1, tendons and ligaments are STIR or FSE-T2 with or without fat saturation and GRE T2* and T1, muscle are T1 and STIR, and synovium is T1 W fat-saturated images after IV administration of Gd-DTPA.

Because each anatomic site contains multiple different structures being imaged, it is necessary to use protocols that adequately characterize these structures. Pulse sequences and imaging planes must be carefully selected to optimal characterization in the shortest time achievable in order to clarify the clinical indication for the imaging study.

MRI allows characterization of multiple clinical scenarios at different body regions by adapting MRI protocols and is an excellent diagnostic tool for evaluation of the bone marrow, tendons and muscles, peripheral nerves, arthritis and cartilage, osseous trauma, musculoskeletal infections, tumors, and internal derangements of the different joints.

Recently, diffusion tensor imaging (DTI) has been used to study muscle architecture and structure. In the future, DTI may become a useful tool for monitoring subtle changes in skeletal muscle, which may be a consequence of age, atrophy, or disease [60]. Furthermore, important information about muscle biomechanics, muscle energetics, and joint function may be obtained with unique MRI contrast such as T2-mapping, spectroscopy, blood-oxygenation-level-dependent (BOLD) imaging, and molecular imaging.

The contrast medium injected for MRA separates the articular capsule from other structures and, due to considerable T1 shortening, outlines intra-articular structures on T1-weighted images. Direct MRA has been successfully used in many joints of the body for a variety of conditions. MRA is a technique which is mainly used in the shoulder, wrist, ankle, knee, and hip joint. Compared with standard MRI, MRA improves the detection of intra-articular bodies and osteochondral lesions in any of the peripheral joints. Moreover, direct MRA improves the assessment of internal joint derangements, such as the detection of labral and ligamentous abnormalities in the shoulder and hip. In the wrist, MRA improves confidence in the diagnosis of interosseous ligament tears and tears of the triangular fibrocartilage complex (TFCC).

In the direct arthrography technique, the contrast medium is a 2 mmol/l solution of Gd-DTPA in 0.9% NaCl. Eventually add 1–5 ml 1% lidocaine. Fluoroscopy is used to bring the needle tip into a correct intra-articular position. To assure the correct position, 1–2 ml of 60% nonionic contrast medium is injected. The amount of the MR contrast medium injected depends on the selected joint. MRI (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. In the indirect arthrography technique, there is intravenous administration of 10–20 ml 0.1 mmol Gd-DTPA/kg body weight. Synovial excretion of contrast medium occurs in minutes after injection to shorten the relaxation time of the synovial fluid 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.

Gadolinium contrast agents, however, have not been approved for intra-articular injection by the Food and Drug Administration (FDA). Intra-articular administration of gadolinium contrast agents, therefore, represents an unapproved use of an approved drug. Intra-articular administration of gadolinium contrast agents is currently considered safe, and FDA approval is not required for use on an individual patient. Future contrast agents for MRA may incorporate paramagnetic contrast agents entrapped in liposomes to prevent diffusion into articular cartilage.

A major disadvantage of the direct technique is its invasiveness. The indirect technique has the advantage of not requiring direct access to the joint but lacks the advantages of joint distension.

MRI has become the dominant imaging modality in the assessment of sports-related injury, because sports medicine and high-quality imaging are inextricably linked. There are, however, many findings on MRI that may not represent clinically significant disorders. Therefore, optimization of image acquisition and interpretation requires correlation with clinical findings.

8 General Principles and Indications

There is no doubt that radiography is the first-line imaging modality for assessment of bone disorders: it allows a panoramic, low-cost, and reproducible evaluation of the bone. Conventional radiography should always be the first diagnostic modality performed to depict associated skeletal or joint abnormalities. More accurate analysis can be obtained by means of CT, especially if complex anatomic areas must be examined. CT can be used for better evaluation of fracture, for assessment of fracture healing process and complications, or for biometric views. While CT allows an optimal assessment of the bone cortex, MRI is the technique of choice to evaluate the bone marrow. US has intrinsic limitations in the assessment of the bone. In some applications, however, it can be useful to assess selected bone disorders, especially if performed as a complement to standard radiographs [28].

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. Bone scintigraphy has a high sensitivity but low specificity and lacks spatial resolution and has been largely superseded by MRI, providing excellent sensitivity and specificity, as it can also identify alternative sources of pain [61].

For the diagnosis of muscle and tendon lesions, US is considered the best imaging modality (sports medicine stethoscope), both in the initial phase for recognition of a lesion and also for the assessment of the various changes it undergoes until complete healing has been achieved. Complementary characterization and detection of associated abnormalities and complications can be obtained by MRI.

For internal derangements of joints, MRI is the preferred technique because of its noninvasive character and soft tissue contrast, allowing detailed characterization of the different intra- and periarticular structures.

Concomitant knee multiaxial laxity quantification and ligaments structure and functional assessment is useful for clinical management in the ACL-ruptured individual. Thus, the availability of laximeters, which are safe and compatible with MRI environment (e.g. Porto Knee Testing Device), may embody an opportunity for further understanding of specific patterns of tissue damage and knee arthrokinematics changes [62, 63].

If plain radiographs and/or US are negative or reveal unequivocal findings and clinical symptoms are suspicious for musculoskeletal lesion, MRI must be performed.

Due to the recent developments in CT technology, multidetector CTA has become a valuable alternative to MRI 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 and use of ionizing radiation.

MRA is considered the reference standard of arthrographic techniques for joint imaging. The choice between multidetector CTA and MRI for assessment of internal joint derangement depends on the clinical situation. Multidetector CTA constitutes a valid alternative when MRA is contraindicated or the acquisition time is a major concern. CTA may be preferred if osseous lesions can be present and constitute a decisional element in the surgical strategy.

Familiarity with mechanisms of injury, position of the player, and the need for rapid diagnosis and reporting will help radiologists with imaging of football players. Although plain radiographs are typically the first imaging modality used, magnetic resonance imaging has become the cornerstone on which diagnoses and treatment decisions are based. As football athletes become stronger, faster, and more skilled, the ability to accurately assess their injuries becomes even more important, and understanding the challenges that these patients present becomes critical.

Medical imaging has attained a preeminent role in the treatment of these athletes. Although history and physical examinations remain the primary means of diagnosis, and plain radiographs are often the first line of imaging for these players, MRI has become the definitive imaging examination, particularly as the level of player becomes more elite. MR imaging is relied on by players, coaches, and team physicians because of its ability to confirm suspected diagnoses, add additional unknown information, and provide a roadmap for surgical or conservative treatment planning. When dealing with professional football players, time is always a pressure, and rapid diagnosis of an injury can be critical. This is where imaging, and, namely, advanced imaging, can play an important role for both the sports physician and the athlete, by helping in making an accurate diagnosis as well as guiding therapy and monitoring response to treatment and return to play.