|Year : 2018 | Volume
| Issue : 5 | Page : 57-64
Pediatric musculoskeletal ultrasound
Department of Radiology, Chanan Devi Hospital, New Delhi, India
|Date of Web Publication||1-Aug-2018|
Dr. Nidhi Bhatnagar
Department of Radiology, Chanan Devi Hospital, New Delhi
Source of Support: None, Conflict of Interest: None
Musculoskeletal ultrasound (US) is rapidly becoming a very friendly and useful modality in the evaluation of musculoskeletal complaints. Whether it can compete with computed tomography/magnetic resonance imaging as a gold standard is entirely a different discussion; what needs attention is that, especially when dealing with pediatric population, how it transcends the fine line of disadvantages over other cross-sectional modalities to become a faithful, well-serving, bedside, outpatient, inpatient, point-of-care tool. Childhood trauma, inflammatory pathologies, congenital malformations, and infective foci are more amenable to US today, and our growing awareness about the applications of this modality is creating the possibilities of early detection, confirmation, and without delay in treatment as a one-stop shop.
Keywords: Bones, joints, musculoskeletal, pediatric, periosteum, soft tissues, ultrasound
|How to cite this article:|
Bhatnagar N. Pediatric musculoskeletal ultrasound. Indian J Rheumatol 2018;13, Suppl S1:57-64
Children should not be considered as smaller versions of adults. It cannot be more true for a sonologist while performing ultrasound (US) on children. One has to appreciate the essence of this since it holds more truth with regard to musculoskeletal system than any other field. A growing skeleton is a mine of dynamic activity unfolding at various stages, in a stepladder manner, be it long bones, muscles, or joints.
Its increasing popularity in pediatrics is due to the fact that it does not involve radiation, has the ability to visualize nonossified cartilaginous and vascular structures, and allows dynamic imaging and quick contralateral comparison. The common musculoskeletal complaints for which a child is brought to the emergency room (ER) are trauma, pain, swelling, and pseudoparalysis. In trauma and infections, US can often detect early and subtle soft-tissue abnormalities, and a comparison with the asymptomatic side can significantly aid in increasing the diagnostic confidence of subluxations, soft-tissue and ligamentous injuries, epiphyseal injuries, and fracture separations. In view of these advantages, it is considered the first step of assessment modality toady, even if a choice of other imaging modalities may be available.
| Technique|| |
Musculoskeletal US is generally performed with linear high-frequency, 7–15 MHz probe, which can be with large or small footprint, especially the latter in pediatric age group for obvious reasons. Since it is a dynamic, real-time, cross-sectional modality, the standard sections would be short axis (axial), long axis (sagittal/coronal), and oblique view as the circumstances may demand. One question which certainly helps to start on the right foot is “where does it hurt,” and a gentle probe placement, with liberal use of gel, gives a relatively quick diagnosis without much discomfort to the patient. The sonoanatomy of various musculoskeletal structures has been discussed in the following sections:
It comprises primarily of fat which is hypoechoic and shows thin horizontal interrupted striations of connective tissue. Fluid/increasing echogenicity is indicative of inflammatory pathology [Figure 1] and [Figure 2].
Fascia investing the muscle planes is reflective with smooth homogenous echogenic outlines. Absence of defect, nodularity, and thickening are mandatory criteria comprising normal fascia.
Bones are highly echogenic with smooth surface and contours without a step-off deformity which suggests a fracture, erosion, or cortical destruction. The smallest of cortical breach creates a window for imaging of medullary cavity and is highly useful in cases having infective pathologies [Figure 3] and [Figure 4]. Cortical discontinuity, only if less than a millimeter, can be missed on an US; for example, in buckle fractures. However, a cortical contour abnormality and the associated soft-tissue swelling with probe tenderness is a strong indicator of the underlying pathology. Long-axis scans parallel to the fracture site can sometimes lead to a false-negative diagnosis. A quick short-axis scan in craniocaudal direction should always be performed to visualize two separate fragments in the same sector for confirmation.
|Figure 3: Hyperechogenic bone with smooth surface. Normal periosteum not seen|
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Periosteum is a linear reflector and cannot be appreciated unless thickened or having subperiosteal fluid collection [Figure 5]. A focal thickening or lamellar configuration of the periosteum on long-axis scan should not be left underinvestigated even in the absence of a negative history.
|Figure 5: Subperiosteal fluid collection with visualization of periosteum (between markers)|
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Pediatric joints are complex since the epiphysis of the participating bony components has not ossified. These unossified cartilages can be imaged very clearly on US and their specificity and sensitivity are equivocal to that of magnetic resonance imaging. Ossific nuclei when present are of added benefit in comparing the growth deficits when asymptomatic side is imaged. These unossified epiphysis are hypoechoic and should not be misinterpreted as fluid with internal echoes [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13].
|Figure 6: Effusion hip joint with distended capsule and convex ileofemoral ligament – long-axis scan (between cursor markers)|
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|Figure 7: Posterior short-axis scan elbow with effusion showing mid-level echoes – septic/hemorrhagic arthritis|
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|Figure 9: Hip joint. A – Capsule, B – ileum, C – bony acetabulum (roof), D – unossified proximal femoral epiphysis|
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|Figure 10: Lateral elbow long-axis scan. E – epiphysis, R – proximal metaphysis radius|
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|Figure 11: Short-axis scan wrist with ossified carpal bone and one ossific nucleus of capitate|
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|Figure 13: Distal ends of radius and ulna with distal diaphyseal, metaphyseal regions, unossified epiphysis, and ossific nucleus of radius (about 1 year)|
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Muscles with musculotendinous junction
Echo signature of the muscles is referred to as feathery pattern in long-axis scan and starry night appearance in short-axis imaging. They are hypoechoic with longitudinal striations of fibrofatty component. Aponeurosis, investing fascia, are echogenic. Musculotendinous junctions are the weak links and need special attention when evaluating for muscle tears. Other pathologies such as mass/cyst/hematomas/abscesses lead to disruption of the muscle pennation angle [Figure 14].
|Figure 14: Parasitic cyst in muscles with feathery pattern – echosignature|
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Tendons are echogenic linear structures with echosignature referred to as fibrillar pattern. The fibrils are linear echogenic lines arranged parallel to each other. The challenge is to overcome anisotropy by optimal scanning technique and keeping the angle of insonation perpendicular to the structure being scanned.
In children, since tendons are very thin and thread like, more susceptible to anisotropy than in adults, a time-saving technique especially when evaluating extremity tendons is to use passive movement and capture cine loops of the movement in real time for identification of these anatomical structures.
Unlike in adults, ligamentous attachments are difficult to visualize since they are attached to the unossified cartilaginous epiphysis.
Since the muscles are more hypoechoic than in adults due to lesser connective tissue, evaluation of vessels and nerves is easier. Color Doppler assists in clearer visualization of the vessels with probe compression, obliterating the thin-walled veins as a differentiating feature between the arteries and veins.
Differentiating between unossified epiphyseal cartilage and articular cartilage may pose difficulty sometimes. However, the even thickness and smooth hypoechoic band-like contour with absence of fraying of articular cartilage cannot be missed with the right depth settings, focus, and gain controls.
Osteochondral injuries lead to the formation of loose foreign bodies in the joint with diagnostic feature of visualizing donor site at the cartilage level. If the diagnosis is delayed, the osteochondral fragment can grow big and a discrepancy in the size of donor site may be found.
Bursae are not visualized unless inflamed, thickened, or show effusion. The most common bursa to show up in children is suprapatellar bursa secondary to synovitis.
Moreover, in children, the sono-anatomic descriptors need to be addressed every time we pick up probe for systematic evaluation of a pathology.
Normal synovium is undetectable on US. Effusion, thickening, or proliferation makes the synovium prominent and identifiable. The thickness can be measured and the associated capsular distention helps in grading the pathology on both gray scale and color Doppler. Synovial pathology may be present as thickened or distended bursae (Baker's cyst) or adventitious bursae/ganglions. Vascularity in hypertrophied proliferative synovium may be indicative of active inflammation.
Radiographs can give an indication of effusion by virtue of displacement of fat pads, especially at the elbow joint with fluid volume between 5 and 10 ml. However, US is sensitive enough to track <2cc of fluid and diagnose; for example, an early lipohemarthrosis.
Femoral capital epiphysis (FCE) between 3 and 6 months remains one of the most important landmark anatomical structures for identifying and eliciting developmental dysplasia of the hip (DDH) joint. Both gray scale static and dynamic scans are performed for differentiating between the subluxable, subluxed, dislocatable, and dislocated joints.
The underlying morphological disturbance of the acetabular cavity can also be assessed through Rosenthal and Graf's technique of assessing the stability of the femoro-acetabular joint.
Alpha angle of >56° remains the diagnostic gold standard US parameter of a normal configuration.
Unossified epiphysis should be aligned with the diaphyseal surface with well-defined interface between the metaphysis and growth plate.
Since the bones are more plastic than in adults, pediatric population is more prone to Salter–Harris injuries. Disruption of metaphyseal-epiphyseal complex, involving the growth plate if left unattended due a false-negative radiograph, as may the case in the peripheral regions of our country, can lead to growth discrepancy. US has stepped in as a major tool in its evaluation. Type I is not conducive to US diagnosis. However, a gap of >1 mm at the growth plate can be an indication of Salter–Harris injury. Type II is more reliably diagnosed where a metaphyseal corner separation can be made with confidence. In case of uncertainty, a contralateral limb comparison helps.
The common complaints for which a child is brought to the ER are:
- Swelling and
| Relevance of Musculoskeletal Ultrasound Features in Rheumatology Practice|| |
The most frequently selected features were the ability to improve the immediate diagnosis of joint/tissue disease, guidance for joint/tendon sheath injections (70.3%), assessment of synovitis (64.2%), assessment of tendons/tendon sheaths (63.6%), and high patient acceptability (63.4%). The specific joints that were judged of foremost importance as targets for US assessment were the hip, ankle, midfoot, and wrist. The shoulder and the small joints of the hands and feet were assigned slightly lower scores. Thus, the precise quantification of synovitis activity in joints like the hip or wrist was felt to be most important. Notably, given the high frequency and wide variability of tenosynovitis in children with juvenile idiopathic arthritis, assessment of tendons, particularly in the wrist and ankle, deserves particular consideration.
| Ultrasound-Guided Interventions|| |
One of the important applications in pediatric pathologies is when patient presents with suspect joint effusion of inflammatory (transient synovitis), infective (septic arthritis), or posttraumatic (hemorrhagic). The gold standard is aspiration of the fluid for diagnostic purpose. An accurate needle placement is the need of the hour which US provides in shortest possible time. Two millimeters is the upper limit of measurement (depth) to differentiate between pathological and physiological fluid collection in a pediatric joint. In case of uncertainty, a comparative study with asymptomatic joint helps raise the level of diagnostic confidence. Color Doppler imaging with increased vascularity in the soft tissues is an indirect evidence of pathology despite the fluid volume being inconclusive. Anisotropy sometimes plays a spoiler and can mimic fluid. Relatively large unossified cartilagenous epiphysis with small ossific nucleus of proximal FCE is another structural pitfall confused with effusion sometimes. A probe compression strong enough to displace the fluid should be a confirmatory maneuver.
Some common developmental pediatric pathologies are as follows.
Vascular malformations: Hemangioma
Infantile hemangiomas are predominantly superficial soft-tissue hypoechoic-to-relatively echogenic lesions and can be easily assessed with US. They present as well-defined masses that may exhibit prominent high-flow vascularity on color Doppler [Figure 15]a and [Figure 15]b.
|Figure 15: (a) Gray scale image of hypoechoic mass showing suspected hemangioma. (b): Colour Doppler of the same confirming hemangioma at the tragus|
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Epidermal inclusion cyst
The synonyms of epidermal inclusion cyst include “epidermoid cyst” and “epidermoid inclusion cyst.” These are occasionally termed “sebaceous cyst,” although technically, this is a different entity. The term sebaceous cyst implies that the lesion originates in the sebaceous glands, which is not correct, and as such the term epidermal inclusion cyst is preferred. On US, if small, it can mimic a typical anechoic cyst. Larger lesions can be a little heterogeneous. Usually, there is no associated vascularity. They, however, can have a variable appearance if ruptured with occasional associated vascularity and lobulated contours [Figure 16].
Soft-tissue calcification: Myositis ossificans/calcinosis cutis
Calcinosis cutis is an uncommon disorder characterized by the progressive deposition of crystals of calcium phosphate (hydroxyapatite) in the skin in various areas of the body. It is classified into four types according to etiology: as dystrophic if calcium and phosphorus levels are normal and tissue damage is present, as idiopathic if calcium and phosphorus levels are normal and no tissue damage is present, or as metastatic if there is hypercalcemia or hyperphosphatemia. On US, these lesions show focal echogenic amorphous deposits with distal shadowing and are seen in the dermis/epidermis [Figure 17].
|Figure 17: Calcinosis (dystrophic) dorsum of wrist in premature infant secondary to repeated needle punctures|
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It is defined as a benign proliferation of fibrous tissue infiltrating the lower third of the sternocleidomastoid (SCM) and is the most common cause of neonatal torticollis. It is also called as sternomastoid tumor of infancy. US is the imaging modality of choice. The SCM muscle is diffusely enlarged to assume a fusiform shape with resultant shortening; therefore, the head is turned away from the affected side (the mastoid process is drawn inferiorly toward the ipsilateral head of clavicle). Echogenicity may vary. Spectral Doppler interrogation may reveal high-resistive waveforms. The enlarged area often moves synchronously with the rest of the SCM on real-time sonography. It is a self-limiting condition and usually resolves within 4–8 months and requires no more than physiotherapy [Figure 18]. Its differential diagnosis comes with inflammatory lymphadenitis in which the neck is drawn toward the affected side, the most common etiology being viral afflictions leading to enlarged cervical chain of lymphnodes.
Congenital developmental pathologies
- Genu recurvatum: Congenital dislocation of the knee is commonly referred with a variety of names, mainly genu recurvatum of knee, backward bending of the knee, hyperextension of the knee, dislocation of the knee, and recently as developmental dysplasia and dislocation of the knees. The US consultation is to assess the patella and the associated DDH. It is important to recognize that, if seen as an isolated finding, patients improve within days to months of starting the treatment. The mainstay of treatment is conservative, with physical therapy, splinting, and serial casting, which can be started as early hours after birth, but no later than a month of life. If these measures fail, corrective surgery may be done as well [Figure 19] and [Figure 20]
- Soft-tissue masses: Benign lipomas are circumscribed soft masses, usually encapsulated, and composed almost entirely of fat. A small amount of nonadipose component is often present, representing fibrous septations, areas of fat necrosis, blood vessels, and interposed muscle fibers. Any nonadipose component must be carefully assessed to exclude a more aggressive component. Histology demonstrates mature adipocytes with no cellular atypia or pleomorphism. US is the modality of choice with high sensitivity and specificity
A minority of lipomas are found in deeper locations and include intramuscular, intermuscular, intrathoracic, and retroperitoneal lipomas [Figure 21]. In the figure, lipoma is noted in the flexor hallucis longus deep to triceps surah
- Congenital mallet thumb: The etiology is unknown. Tendon of flexor pollicis longus shows fibrous thickening with nota nodule at the base, leading to hyperflexion at the interphalangeal joint. It needs to be differentiated from congenital trigger fingers and amniotic constriction ring syndromes. US is helpful in the evaluation by virtue of the real-time dynamic scanning [Figure 22].
Very nervous parents feel secure with the child and vice-a-versa during US examination, which remains one of the biggest advantages of US in pediatric age group.
| Conclusion|| |
Paediatric musculoskeletal is not entirely similar to adult version of it. Some helpful tips while performing MSK US examination in this age group has been listed out in [Box 1].
| Suggested Reading|| |
- Aurell Y, Johansson A, Hansson G, et al. Ultrasound anatomy in the normal neonatal and infant foot: An anatomic introduction to ultrasound assessment of foot deformities. Eur Radiol 2002; 12:2306-12.
- Aurell Y, Johansson A, Hansson G, Jonsson. Ultrasound anatomy in the neonatal clubfoot. Eur Radiol 2002;12:2509-17.
- Aurell Y, Adlercreutz C, Andriesse H, et al. Repeatability of sonographic measurements in clubfeet. Acta Radiol 2004; 45:622-7.
- Bar-on E, Maschiach R, Inbar O, et al. Prenatal ultrasound diagnosis of clubfoot: Outcome and recommendations for counselling and follow-up. J Bone Joint Surg Br 2005;87:990-3.
- Rohrschneider WK, Fuchs G, Tröger J. Ultrasonographic evaluation of the anterior recess in the normal hip: A prospective study on 166 asymptomatic children. Pediatr Radiol 1996;26:629-34.
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There are no conflicts of interest.
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