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Patients with arthritis are not excluded from athletic activities. Their daily activity may include biomechanical stresses on their bodies not unlike the demands of sports activities, albeit more subtle. Their physical therapy may be strenuous, and overuse syndromes can occur. Physical effort as simple as lifting groceries can result in focal osteoarticular trauma. Unguarded moments can result in occult stress fractures or unrecognized deep muscle contusions. This chapter can help rheumatologists become familiar with lesions of the musculoskeletal system that occur acutely or insidiously and that have all the earmarks of sports trauma. The expertise that the rheumatologist applies to visualizing joint diseases is the same knowledge of musculoskeletal ultrasound (MSKUS) employed by bone radiologists, orthopedic surgeons, sports medicine physicians, physiatrists, neurologists, podiatrists, sonographers, athletic trainers, physical therapists, emergency medicine physicians, and chiropractors in the evaluation of sports injuries. All these sonologists and sonographers have improved the well-being and performance of athletes.
Indications
In sports medicine, MSKUS is used to visualize the soft tissues and osteoarticular structures of the human body. It depicts the body parts in gray-scale imaging, which gives characteristic echo signatures to different organ structures in the locomotion apparatus. In an anatomic structural approach, MSKUS is applied to visualizing extra-articular and intra-articular structures. The former structures include tendons, ligaments or capsules, bursas, muscles, fasciae, fat pads, and the subcutaneous layer and skin. The latter structures encompass capsules or ligaments, joint fluids, synovia, cartilages, and the subchondral plate. Ligaments are the cordlike thickenings of the capsules, and they may have to be investigated as part of the intra-articular zone. Synovial proliferation can occur in recurrent athletic trauma, but it is more common in inflammatory disease. An advantage of ultrasound is that synovial disease can be detected and often characterized without the use of intravenous radiographic contrast necessary in computed tomography (CT) or magnetic resonance imaging (MRI). Occasionally, an acoustic window may be afforded through a fracture or permeative lesion, and the intramedullary portion of bone may be visualized.
The complete gray-scale representations of the different echo signatures of the musculoskeletal structures are covered thoroughly in earlier chapters of this textbook. The chapters describe how these normal structures appear on ultrasound (see Chapters XX and XX).
Equipment
Sports medicine ultrasound is practiced in medical centers and at the sports arena. In hospitals and clinics, the console-based and larger units are employed. These mobile units can scan patients in clinic rooms and alongside training tables. The handheld portability of the battery-powered laptop units has become a welcome addition to the sports medicine team. These portable units come close to the high resolution, fast processing power, and imaging software adjustments of their bigger console-based counterparts. Laptop units have become a part of sports team equipment as they travel to away games, and they frequently are used in the training room. More remote or distant sporting venues, such as skiing, require these units at the sidelines ( Fig. 21- 1 ).
The console-based and laptop ultrasound machines use the same types of transducers. The newer transducers have multirange frequencies, and they can be adjusted to a certain frequency to compensate for the depth and density of the structures or lesions being examined. The three most commonly used are the linear array, curved-linear array, and compact-linear array. MSKUS imaging revolves around the linear-array transducer with a frequency range of 6 to 12 MHz, centered at 7.5 MHz, usually with a contact surface of 4.0 cm (i.e., footprint of the transducer). This transducer can investigate most athletic lesions.
The curved-linear array transducer uses a lower frequency for the deeper structures of the musculoskeletal system (e.g., hip, popliteal fossa). The convex surface of this transducer fits snugly in the different fossae of the extremities. The compact-linear array transducer is desirable for superficial structures such as the tendon of the hands or retained foreign bodies. It dispenses with the use of stand-off pads. In sports medicine ultrasound, applying a thicker layer of gel on the skin while floating the transducer or using a water bath with the hand immersed in a basin can avoid the additional expenses of buying and storing stand-off pads or interrupting the flow of the examination to look for the seldom-used pads. Other shapes of compact linear transducers have been employed, such as the side-projecting transducer in the evaluation of the athlete’s groin. Chapter 4 describes available transducers and other ultrasound equipment.
Equipment
Sports medicine ultrasound is practiced in medical centers and at the sports arena. In hospitals and clinics, the console-based and larger units are employed. These mobile units can scan patients in clinic rooms and alongside training tables. The handheld portability of the battery-powered laptop units has become a welcome addition to the sports medicine team. These portable units come close to the high resolution, fast processing power, and imaging software adjustments of their bigger console-based counterparts. Laptop units have become a part of sports team equipment as they travel to away games, and they frequently are used in the training room. More remote or distant sporting venues, such as skiing, require these units at the sidelines ( Fig. 21- 1 ).
The console-based and laptop ultrasound machines use the same types of transducers. The newer transducers have multirange frequencies, and they can be adjusted to a certain frequency to compensate for the depth and density of the structures or lesions being examined. The three most commonly used are the linear array, curved-linear array, and compact-linear array. MSKUS imaging revolves around the linear-array transducer with a frequency range of 6 to 12 MHz, centered at 7.5 MHz, usually with a contact surface of 4.0 cm (i.e., footprint of the transducer). This transducer can investigate most athletic lesions.
The curved-linear array transducer uses a lower frequency for the deeper structures of the musculoskeletal system (e.g., hip, popliteal fossa). The convex surface of this transducer fits snugly in the different fossae of the extremities. The compact-linear array transducer is desirable for superficial structures such as the tendon of the hands or retained foreign bodies. It dispenses with the use of stand-off pads. In sports medicine ultrasound, applying a thicker layer of gel on the skin while floating the transducer or using a water bath with the hand immersed in a basin can avoid the additional expenses of buying and storing stand-off pads or interrupting the flow of the examination to look for the seldom-used pads. Other shapes of compact linear transducers have been employed, such as the side-projecting transducer in the evaluation of the athlete’s groin. Chapter 4 describes available transducers and other ultrasound equipment.
Archiving and Communicating
Images acquired by sports medicine ultrasound are ordinarily stored as static pictures in several electronic storage media, ranging from CD-ROMs to flash drives. The availability of information technology to many sports medicine caregivers has enabled the field of athletic medicine to archive video clips or cine loops for dynamic imaging in addition to the routine still pictures. A repository of athletes’ images is centrally stored in picture archiving and communicating systems (PACS). Web-enabled systems have facilitated faster and more efficient communication among imagers, clinicians, and patients.
The ability to archive and recall images from anywhere at a moment’s notice has fulfilled an important criterion for sports imaging. Immediate access to data has improved our efforts to have players “return to play” or resume their sports activities. All of the correlative images, such as baseline radiographs, MRI scans, CT scans, bone scans, arthrograms, or C-arm films from interventional procedures, help in the correct interpretation of MSKUS studies. Rheumatologists and other clinicians have physical and laboratory findings on which to base the ultrasound evaluation, but imagers and diagnosticians need other radiologic or laboratory studies from which they can best interpret the MSKUS examination. Radiographs provide essential information for diagnostic imagers.
The electronic nature of the ultrasound machine makes it possible to perform real-time imaging at the athlete’s side and to transmit the same images to another site for an expert to review. Many image-capturing devices coupled to ultrasound machines act as Internet servers. All imaging performed can be transmitted through the Internet or satellite phones and can be reviewed at a distant site as live video streaming by another expert ( Fig. 21-2 ). It should become a common practice for the sonographer to transmit live images to a consultant at a remote site while scanning an athlete, with the consultant directing the sonographer precisely where and how to scan.
Applications of Musculoskeletal Ultrasound
Several properties of MSKUS are important to the specialty of sports medicine. They include real-time imaging, which includes stress maneuvers, and for ultrasound guidance, Doppler angiography, split-screen presentation for right and left side comparisons, and extended fields of view ( Fig. 21-3 ). Other applications include three-dimensional, four-dimensional, and fusion imaging; elastrography; contrast-enhanced ultrasound; and ultrasound-guided percutaneous therapy such as direct tenotomy or platelet-rich plasma administration.
Real-time imaging is essential in sports medicine because the musculoskeletal structures are evaluated while going through their expected range of motion. The flexion and extension of muscles, tightening and relaxing of tendons, and mobility of joints, for example, can be observed and recorded. Included in real-time imaging is the capability to confirm visually lesions that are identified best with stress maneuvers. Examples of stress maneuvers are subacromial impingement, with the obstruction of shoulder elevation by a thickened subacromial-subdeltoid (SASD) bursa under the acromion during the active or passive abduction of the shoulder; a distracted medial elbow joint, with the widening of the humeroulnar joint attendant to a torn medial collateral ligament (MCL) during a valgus stress of the elbow; and subluxation of the peroneal tendons because of torn retinaculum while forcing the foot or ankle into dorsiflexion and external rotation.
Color or power Doppler imaging is useful in sports medicine to determine the activity or recurrence of disease. Severe or subacute tendinosis, for example, can have extensive and high-flow neovascularity, whereas ultrasound of healing tendinopathy can reveal involuting vessels. Recurrent and enlarging lesions demonstrate a flare-up of neovascularity, and chronic, thickened fibrosing disease contains minimal or no Doppler activity. The spectral display should be submitted for definitive confirmation that the colored structures inside the images are vascular (i.e., spectral display on the vessel). Localization of vessels and needle placement are other practical uses of Doppler imaging. To avoid hitting vital vessels and to avoid complications, a road map of vascular landmarks can be made. Along with mapping, the trajectory of the needle can be planned and the needle highlighted by the Doppler signal. Turning on the Doppler mode accentuates the reflectivity and motion of the metal shaft, tip, and bevel of the needle all the way to its target.
A focused and smaller field of view (FOV) gives MSKUS excellent spatial resolution (see Chapter 1 ). The monitor screen can be divided to render a split-screen or dual-screen view of the diseased side compared with the normal side or a right and left side comparison. The FOV, spatial resolution, and contralateral comparison give ultrasound machines matchless accuracy in measuring the sizes of lesions. Some ultrasound software programs, including extended field of view and three-dimensional reformatting, make it possible to measure the extent of the lesion and the distances between multifocal lesions.
Ultrasound Approaches and Strategies in Assessing Sports Injuries
Ultrasound can be directed to specific structures and focal lesions. The local disease may have corollary findings, such as Baker’s cyst with a torn medial meniscus and suprapatellar effusion. Exploration with ultrasound is localized to the athlete’s symptoms, and interrogation is aimed at the primary structure that is damaged. MSKUS can be applied in a modular approach to joint regions, from top to bottom, beginning with the shoulder and ending with the foot and ankle. The remainder of the extremities, such as the forearm and thigh, are examined according to their proximity to a joint. For example, the distal quadriceps tendon is part of a knee examination, and the rectus femoris tendon is considered in the examination of the hip and pelvis..
Shoulder
One of the most common musculoskeletal complaints of sports participants is a painful shoulder. Shoulder ultrasound makes up two thirds of the 8000 studies performed annually at our institution. Rotator cuff disease is the primary indication for assessing a painful shoulder. Other shoulder structures are examined to look for lesions such as effusions or lesions that may mimic rotator disease, as in the case of isolated acromioclavicular osteoarthrosis. Dynamic imaging completes shoulder exploration by showing the lesions that limit the athlete’s range of motion.
Rotator Cuff
Ultrasound is used to identify all four rotator cuff tendons: supraspinatus, infraspinatus, subscapularis, and teres minor. The normal rotator cuff tendon has a hyperechoic fibrillar pattern with a convex upward contour and the appearance of a bird or parrot’s beak ( Fig. 21-4 ). The most common cuff lesions are tendon tears. Full-thickness tears are detected accurately with ultrasound. The four criteria are nonvisualization of the cuff ( Fig. 21-5 ), atrophy of the tendon ( Fig. 21-6 ), a hypoechoic defect, and a focal hyperechoic lesion. The most common finding is a hypoechoic defect, and the least common finding is a high-level echo representing a tear.
A full-thickness tear penetrates through the entire body of the tendon, from the articular to the bursal surface, forming a communication between the glenohumeral joint and the SASD bursa ( Fig. 21-7 ). The full-thickness cuff tear has a hypoechoic pattern. A partial-thickness tear affects one or two of the arbitrary layers of the rotator cuff: the bursal surface ( Fig. 21-8 ), the intratendinous layer ( Fig. 21-9 ), and the articular undersurface. Effusions in partial-thickness tears do not flow between the glenohumeral joint and SASD bursa. Full-thickness tears caused by sports trauma usually have antecedent partial-thickness tears. Some avid and stoic sports participants compensate for full-thickness tears of their rotator cuffs with strengthening and alternative dynamics of the other shoulder muscles and mechanics to sustain an almost normal shoulder moment or motion.
MSKUS can detect incipient tendon dehiscence leading to rotator cuff tears. Most occur in the critical zone of the rotator cuff. These early and minute tears are the rim rent, footprint tear, and the cuff-interval tear. A rim rent ( Fig. 21-10 ) manifests as a bull’s-eye lesion, with a hyperechoic center ringed by a hypoechoic halo, representing central high-level debris or a fibrillar strand surrounded by the echolucent tear or edema, respectively. It characteristically sits in the reflection of the cuff with a tiny, subjacent bony defect in the anatomic neck of the humerus. The footprint tear appears as a tendon defect of mixed echogenicity in the tendon enthesis or ledge of the greater tuberosity, and it does not violate the bursal or articular surface of the cuff. Tears of the rotator cuff interval involve the inside margins of the supraspinatus or subscapularis lining the space between these two tendons where the long head of the biceps tendon passes through. This type of tear involves the rotator cuff pulleys or coracohumeral ligaments, and it often results in subluxation of the long bicipital tendon. The interval tear also exhibits irregularity of the bone surface of the greater or lesser tuberosities and humeral convexity.
Most full- or partial-thickness tendon tears delaminate from the original site and tunnel into the rest of the rotator cuff in no predictable direction. The delaminating defects are seen as linear, hypoechoic rays arising from the primary tear. The extensions can radiate outward from the tear and can lead to intratendinous or extratendinous ganglia.
Fractures
The teres minor is the least traumatized tendon in the rotator cuff, although isolated tears usually occur in adolescents or as a result of fractures to the proximal humerus. Fractures of the greater tuberosity detected by ultrasound are those initially radiographically occult; the athlete seeks medical help because of persistent shoulder pain centered on the supraspinatus or infraspinatus. The tendon may be hypoechoic because of edema or contusion. The fracture appears as an interruption or step-off deformity of the hyperechoic bone surface that is outlined in at least two sites, often from the anatomic neck and to the lateral deltoid shelf ( Fig. 21-11 ).
Tendinosis
Tendinosis, which usually appears as a focal, ill-defined, hypoechoic intrasubstance defect with no subjacent bone surface irregularities, must be differentiated from the artifact of anisotropy. Proper transducer technique, such as the heel-toe maneuver, or Doppler imaging can help to avoid this pitfall. Tendinosis may exhibit minimal neovascularity and may show some discernable fibers crossing the hypoechoic area. Diffuse tendinosis is less common and may be encountered after more severe or sustained sports activity. Underlying inflammatory arthritides should be suspected when the rotator cuff is diffusely hypoechoic. A focal nodular enlargement of the hypoechoic tendon may harbor an evolving full-thickness or deep partial-thickness cuff tear.
Calcifications
Focal or diffuse heterogeneity of the rotator cuff may be interpreted as tendinosis, but it can result from widespread dissemination of dystrophic calcification throughout the rotator cuff. Easier to identify are calcifications of increasing density, with consistencies ranging from “milk of calcium” to solid concretions. Sports participants are not exempt from calcific tendinosis, but its relationship with athletic activity is not clear.
Subscapularis Tendon
Interest in the detection of lesions of the subscapularis has been tweaked as isolated tears have been steadily identified. The sensitivities of ultrasound and MRI have recently improved, and attention to this tendon has revealed that bony avulsion may accompany tears and that tears can occur at any level from the cranial to the caudal margin, usually in the tendon footprint. Like the other cuff tendons, a subscapularis tear may have concomitant bone surface irregularities of the lesser tuberosity.
Shoulder Impingement
In the athlete, dynamic imaging is routinely performed to detect three types of impingement: subacromial, internal, and coracohumeral. The quadrilateral triangle is seldom reviewed. Subacromial impingement is the most common finding in overhead athletes. Many recreational and professional sports, from tennis to water polo, involve overhead motions. On abduction of the shoulder, the normal transit of the lateral part of the rotator cuff, the SASD bursa directly above it, and the subjacent greater tuberosity passes effortlessly and frictionless under the subacromion. Lesions such as SASD bursitis or calcific tendinosis or mechanical causes such as the lateral type of subacromial spur can obstruct the expected smooth translation. Elevation of the arm and shoulder should be in the plane of the observed abnormality. The SASD bursa bunches up, or the intratendinous calcification may block further upward motion. There may be a visible or audible snapping motion as the offending lesion clears the subacromial margin.
Overhead athletes, including weightlifters performing bench presses, show three tandem defects on ultrasound: fraying or blunting of tearing of the posterosuperior glenoid labrum, undersurface tearing of the infraspinatus, and a deepened or widened bare area of the posterior humerus. Dynamic imaging shows the glenoid labrum impaling the bare area, and the superjacent infraspinatus appears frayed and hypoechoic. A markedly deformed or cleaved bare area can mimic a Hill-Sach deformity. If this type of deformity is uncovered, quick investigation for the corollary Bankart lesion is carried out by looking at the anteroinferior glenoid labrum, especially if there is a glenohumeral effusion or hemarthrosis. The patient places his hand behind his head, and the transducer is placed in the axillary fossa to locate the shortened Bankart arc.
Coracohumeral impingement on ultrasound often looks like an old-fashioned washing machine wringer, because the defective subscapularis or its overlying SASD bursa plops underneath the coracoid process. It is intuitive that the long bicipital tendon can be impinged by the acromion, because it lies directly underneath this bony overhang, bit no studies have been performed to determine if this tendon sustains an insult from the acromion.
Subacromial Subdeltoid Bursa
The SASD bursa is notorious for causing focal or diffuse subacromial impingement. Focal impingement is a sign for a bursal-surface partial-thickness tear. Athletes have uniformly distended and sharply defined SASD bursae. Near-perfect symmetry of these bursae between the two shoulders is the rule in these athletes. Hemobursitis in acute trauma can be evaluated throughout its entire extent; it often forms a fluid-blood level, and a positive teardrop sign can be seen over the lateral deltoid shelf. Synovial proliferation can develop in recurrent sports injuries, but is usually seen in inflammatory diseases.
Long and Short Bicipital Tendons
Tears of these tendons occur when a sudden eccentric force is applied to an abducted shoulder. Usually, only one of the two tendon heads rupture, but both produce the same Popeye sign, in which the muscle belly of the biceps descends toward the elbow. However, the cartoon character Popeye is featured with a hypertrophied forearm, not his biceps. An empty bicipital groove points to a tear of the long bicipital tendon. A torn short bicipital tendon leaves behind a measurable hematoma under the coracoid process down to the level of the pectoralis major insertion into the humerus while preserving the long bicipital tendon within the intertubercular groove. Care should be exercised in determining whether the tendon substance is discontinuous or the tear is at the myotendinous junction or intramuscular. Tenodesis is the standard treatment, but long-term dysfunction has not been studied. Partial-thickness tears appear as longitudinal splits in the tendon or as boutonnière defects when draped over the lesser tuberosity.
Fluid that appears as a hypoechoic halo around the long bicipital tendon can occur after exercise or a sports competition. When inordinately voluminous or asymmetric, it should serve as a harbinger of inherent tendinopathy, including of the rotator cuff. When fluid pools eccentrically along the medial aspect of the distended bicipital tendon sheath and is coupled with thickening of the rotator cuff pulleys, adhesive capsulitis is the probable diagnosis. Ganglions can form along the long bicipital tendon and initially may be interpreted as focal, eccentric effusion. No dire consequences are associated with the ganglion.
Posterior Shoulder
The most specific, albeit minor, criteria for full-thickness rotator tears are an effusive glenohumeral joint and SASD bursa. Effusion appears as a hypoechoic tract of fluid distracting the posterior glenohumeral joint, splaying the glenohumeral capsule upward, and deflecting the infraspinatus tendon. Only the posterosuperior arc of the glenoid labrum can be evaluated with ultrasound. This is sufficient to detect degeneration or tears of this ring of fibrocartilage. The latter defect, known as a superior labrum anteroposterior (SLAP) tear, can give rise to paralabral cysts or the larger suprascapular ganglion ( Fig. 21-12 ), with both fulfilling the ultrasound characteristics of a cyst: anechoic pattern, imperceptible wall, and enhanced through-transmission.
Acromioclavicular Joint
Osteoarthrosis is the most common diagnosis of the acromioclavicular joint. This may be predictable in the older athletes, but it also is associated with the more acute disorders of the acromioclavicular joint. Hemarthrosis is seen as minimally inhomogeneous fluid because of blood particulates distending the acromioclavicular capsule. Only a history of trauma or aspiration of bloody fluid can differentiate it from other acromioclavicular effusions. The asymmetrically widened, posttraumatic joint is readily diagnosed and the joint instability further evaluated with the ipsilateral hand doing cross-chest maneuver. Abnormal translation, distraction, or subluxation shows the offset between the acromion and distal clavicle. A chronic form of acromioclavicular subluxation occurs in posttraumatic osteolysis, in which there is joint effusion and subarticular resorption of the distal clavicle. Ultrasound can depict the subchondral defects eccentric to the distal clavicle and sparing the acromion ( Fig. 21-13 ).
