Clinical Ultrasound || Paediatric musculoskeletal imaging

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73CHAPTER

Paediatric musculoskeletal imaging

TECHNIQUE 1497

HIPS 1497Sonographic anatomy 1498Clinical examination of the infant hip 1498

Barlow test 1498Ortolani test 1498

Ultrasound examination of the infant hip 1498Graf technique 1498Modified Graf technique 1501The Harcke technique 1501Terjesen technique 1503

The irritable hip 1503Transient synovitis 1503Legg–Calvé–Perthes disease 1504Slipped femoral capital epiphysis 1504

PAEDIATRIC TRAUMA 1505Acute trauma 1505Non-accidental injury 1506Overuse injuries 1506Muscle injury 1506Muscle tears 1506Haematoma 1507Foreign bodies 1507Myositis ossificans 1508

INFECTION 1508Superficial soft tissues 1508Pyomyositis 1508Osteomyelitis 1508

MONITORING LEG LENGTHENING PROCEDURES 1509

MASSES 1509Normal anatomical variation 1509Cysts 1510Vascular/Lymphatic malformations 1510Sternocleidomastoid tumour 1511Lipoma 1511Sinister lesions 1512

Musculoskeletal imaging with ultrasound is now a well-recognised technique used by both radiologists and sonographers.

In the paediatric setting the absence of ionising radiation and the ability to visualise soft tissues and joints make this a useful tool in the assessment of a number of musculoskeletal pathologies.

TECHNIQUE

When scanning children it is often necessary to be opportunistic in order to acquire the best images. Children can be unpredictable and uncooperative and, although it is important to have a routine for scanning an area, it is also important to recognise areas of interest beyond the area in focus. This allows the assessment of pathology

Caren J. Landes

as early as possible during the scan before the infant or child becomes restless.

For superficial musculoskeletal imaging it is appropriate to use the highest frequency transducer available; usually this is in the form of a 17 MHz probe. A small footprint transducer, often known as a ‘hockey stick’ probe and usually with a frequency of 15 MHz, can be invaluable in paediatric imaging.

For older children and for the visualisation of deeper structures a lower-frequency transducer may be useful.

Other considerations during scanning should be the application of colour Doppler and in some instances pulsed wave. The use of extended field-of-view settings that allow the operator to visualise an area larger than the footprint of the transducer has uses in the limbs in particular.

There should also be the capacity to perform measurements, such as lengths, volumes and angles, including hip angles in the assess-ment of developmental dysplasia of the hip (DDH).

HIPS

Developmental dysplasia of the hip (previously congenital dyspla-sia of the hip) is a term applied to abnormal development of the hip joint.

In the normal hip the femoral head lies within the acetabulum as a ball in socket joint. In developmental dysplasia the acetabulum is poorly developed, resulting in a less secure joint. The femoral head becomes mobile within the joint and may be subluxed or com-pletely dislocated.

Infants with clicky hips at the neonatal assessment according to a Barlow or Ortolani test (Fig. 73.1) should be screened for DDH, as should other infants with risk factors for DDH (Table 73.1).

Girls are three times more likely to be affected than boys and the left hip is four times more likely to be affected than the right (prob-ably related to the left occiput anterior fetal lie in utero).1

Early detection and intervention has been shown to dramatically improve outcome and in 1969 a national UK screening programme was introduced to clinically assess at-risk infants.2–4

The femoral head is unossified in infants and starts to ossify between 6 and 12 months of age.

Plain radiography will demonstrate the ossified portion of the acetabulum, but will not show the unossified femoral head, and it is widely recognised that ultrasound is the best method for assess-ment of DDH.

Ultrasound will show the non-ossified cartilage of the femoral head and its relationship to both the ossified and unossified com-ponents of the acetabulum. It also allows multiplanar and dynamic assessment of stability (Fig. 73.2).

Unfortunately once the femoral head begins to ossify and causes acoustic shadowing, ultrasound becomes less useful.

There is, however, no universally agreed method for hip ultra-sound. At least two methods are available as described by Graf5 and Harcke.6

CHAPTER 73 • Paediatric musculoskeletal imaging

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Clinical examination of the infant hip (Fig. 73.1)

Barlow testThe hip is held in flexion with the leg abducted. In this position, posterior pressure (push) is applied to determine whether the hip moves posteriorly out of the acetabulum, thus indicating instability.

Ortolani testThe hip is held in flexion with the leg abduction. In this position anterior pressure (pull) is applied to the hip. Movement of the hip over the acetabulum indicates a dislocated hip and assesses reducibility.

Ultrasound examination of the infant hip

In infants under 6 months of age a high-frequency linear array transducer should be used. This is often a broadband frequency such as 12 MHz.

Graf techniqueThis requires a practised technique and is not to be undertaken sporadically by untrained operators.

Graf assessed acetabular morphology and devised a classification system based on the angles of inclination of the bony and

It is acknowledged that ultrasound is operator dependent and it is important that the operator involved in the screening programme, whether it be a radiologist or a sonographer, is performing hip scans on a frequent, regular basis.

Sonographic anatomy

In infants the hyaline cartilage of the femoral head is echo-poor with fine vascular echoes throughout. The ossification centre of the femoral head is visible on ultrasound several weeks before it can be demonstrated radiographically,6 although the age of ossification can vary widely.

In the normal hip, the femoral head should be seated within the bony acetabulum formed by the ossification centres of the ilium, ischium and pubis, which are separated by the triradiate cartilage (Fig. 73.2).

This cartilaginous roof is predominantly echo-poor hyaline car-tilage except for a small reflective fibrocartilaginous tip.7 The iliofemoral ligament and hip joint capsule cannot generally be sepa-rated on ultrasound and appear as a common reflective band lateral to the femoral head.

Sometimes curvilinear echoes can be seen outlining the capital femoral epiphysis during movement of the hip. This is thought to represent small bubbles of nitrogen within the joint space (the vacuum phenomenon).8

Figure 73.1 The position of the infant and examiner for the Barlow/Ortolani test.

Figure 73.2 Ultrasound of the normal hip showing the femoral head within the joint and the landmarks for the measurement of the alpha angle.

Table 73.1 Risk factors for developmental dysplasia of the hip (DDH)

Breech presentationA family history of DDHOligohydramniosTalipesSpinal dysraphismArthrogryposisGeneralised ligamentous laxity

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Table 73.2 Ultrasound assessment of the infant hip

Technique Assessment Classification

Graf Static Bony/cartilaginous roofsModified Graf

Static Bony/cartilaginous roofsFemoral head is centred within the acetabulum

Harcke Dynamic Position and stability of femoral head

Terjesen Dynamic Femoral head coverage

cartilaginous roofs.5,9,10 Graf recommends that the baby is supported in a lateral decubitus position using a special cradle. The hip is positioned in approximately 20° of flexion and slight internal rota-tion: this represents the neutral position for an infant and brings the femoral head, neck, greater trochanter and acetabulum into the same plane (Fig. 73.3). The transducer is positioned over the greater trochanter and held parallel to the cradle and long axis of the body to obtain a coronal image of the acetabulum showing its maximum depth (Fig. 73.3).

Precise positioning is essential to acquire the standard image for interpretation.

The cardinal landmarks are:n the inferior edge of the iliumn the lateral margin of the ilium projected as a horizontal linen the acetabular labrum.

The chondro-osseous junction should also be visible as a linear echo below the femoral head (Fig. 73.4).

Figure 73.3 The Graf cradle used to support a baby in the lateral decubitus position for ultrasound of the hip.

Figure 73.4 A coronal neutral diagram of a developmentally mature hip (Graf type I) showing the cardinal landmarks that define the standard plane. Gmed, gluteus medius; Gmin, gluteus minimus; L, labrum; HC, hyaline cartilage; IL, ilium; TC, triangular cartilage; ISC, ischium; GT, greater trochanter; CFE, capital femoral epiphysis; COJ, chondro-osseous junction.

Gmed

GminHC

L

GT

CFE

IL

TC

ISC

COJ

Figure 73.5 Graf’s alpha and beta angles. Diagram showing lines drawn on a coronal neutral image of a developmentally mature hip to define Graf’s alpha and beta angles.

�

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The alpha angle (Fig. 73.5)This measures the depth of the acetabulum.

The baseline is drawn along the straight lateral margin of the ilium from the point where the perichondrium meets the ilium and a second line is drawn from the inferior point of the iliac bone tangential to the bony acetabulum (the bony roof line).

The alpha angle is the angle between these two lines. A small alpha angle indicates a shallow acetabulum.

Graf also describes a beta angle between the baseline and the cartilaginous roof line, to assess the degree of superior displace-ment of the femoral head, but this is not commonly measured or reported.

The beta angle cannot be measured in a dislocated hip.

Graf type I (Fig. 73.6)The hip is developmentally mature.

The acetabulum is deep with a steeply inclined bony acetabular roof.

The bony roof is well developed with a sharp ossific rim. The cartilage roof is long and narrow and extends over the femoral head.


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Figure 73.7 Graf type IIa/IIb. The alpha angle is 50–59°. The classification is determined by the age of the patient.

Figure 73.8 Graf type IIc. Deficient bony roof. The alpha angle is 43–49°.

The alpha angle is >60°.These patients have a described risk of developing dysplasia in

later infancy, but coexisting hip instability does not appear to be a predictive indicator.11

Graf type IIa (Fig. 73.7)A shallow acetabulum in an infant under 3 months of age may simply reflect physiological immaturity.

The bony roof is deficient due to delayed ossification and the ossific rim is rounded. The cartilage roof covers the femoral head.

The alpha angle is 50–59°.A recent meta-analysis revealed that between 84% and 95% of

these will develop normally without treatment11 within 3 months.

Graf type IIb

Appearances are equivalent to those in Graf IIa in a patient of greater than 3 months of age.

A shallow acetabulum in an infant over 3 months of age is con-sidered to be dysplastic, but stable.

The alpha angle is 50–59°.This requires referral to the orthopaedic surgeons for treatment.The appearance is equivalent to Graf type IIa and the age of the

patient differentiates the types.

Graf type IIc (Fig. 73.8)The bony roof is deficient with a rounded/flat ossific rim. The cartilage roof covers the femoral head.

A shallow acetabulum in an infant of any age where the alpha angle is 43–49° requires assessment of stability and immediate treatment.

Figure 73.6 Graf type I. The alpha angle is >60° and the hip is developmentally mature.

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Graf type D

The bony roof is severely deficient with a rounded/flat ossific rim. The cartilage roof is compressed and the hip is at risk of dislocation.

There is a shallow acetabulum with an alpha angle of between 43° and 49° that is inherently unstable.

Graf types IIIa, IIIb, IV (Fig. 73.9)The hip is dislocated.

The alpha angle is less than 43°.The bony roof is deficient with a flat ossific rim. The types are

differentiated by the position of the cartilaginous roof.

Figure 73.9 Graf type III. The hip is dislocated. The alpha angle is <43°. FH, femoral head.

Pitfalls

There are several technical pitfalls to be aware of:n Slight flexibility of the acetabular labrum occurs in normal

hips when the femoral head is manipulated and should not be mistaken for instability.12

n Anterior angulation of the transducer results in an apparent reduction in femoral head coverage.

n Posterior angulation of the transducer results in an apparent increase in femoral head coverage.

n Caudocranial angulation of the transducer can make a normal hip appear dysplastic.

n Dorsoventral angulation of the transducer results in a concave contour of the ilium representing the gluteal fossa.

n It is important to note that although it is possible to make a normal hip appear abnormal on ultrasound, it is not possible to make an abnormal hip appear sonographically normal.

Modified Graf techniqueRosendahl et al. described a technique where the femoral head is centred within the acetabulum on the ultrasound image.11

The Harcke techniqueThis is a dynamic assessment of the hip with application of stress manoeuvres similar to the techniques used during clinical examination.6,13

The hip is scanned in the coronal and transverse planes with the baby supine.

There are four steps.

Step 1: coronal neutral

This view is equal to the coronal view advocated by Graf but Harcke and colleagues advocate a visual subjective assessment without the use of specific measurements.6

Step 2: coronal flexion (Figs 73.10 and 73.11)This view is similar to the coronal neutral view except that the hip is flexed to 90°.

The transducer is moved anteriorly and posteriorly relative to the standard mid-acetabular plane in order to evaluate the entire hip.

An image is obtained over the posterior lip of the triradiate car-tilage in which a normally located femoral head is not visible; visu-alisation of the femoral head implies posterior dislocation.

Table 73.3 Graf classification of hip dysplasia

Graf type Acetabulum Alpha angle Patient age Stability Other

Ia Deep >60° Any Stable Developmentally matureIIa Shallow 50–59° <3 months Stable Physiological immaturityIIb Shallow 50–59° >3 months Stable DysplasticIIc Shallow 43–49° Any May be unstableD Shallow 43–49° Any Unstable

TYPES IIIA, IIIB AND IV ARE DISTINGUISHED BY THE APPEARANCE OF THE CARTILAGE ROOF

Graf type Acetabulum Alpha angle Patient age Stability Cartilage roof

IIIa Shallow <43° Any Dislocated Displaced upEcho-poor

IIIb Shallow <43° Any Dislocated Displaced upMore reflective than femoral head

IV Shallow <43° Any Dislocated Interposed


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Figure 73.12 Normal hip, transverse flexion view. ‘U’ configuration of normal transverse flexion view of a neonatal hip. FM, femoral metaphysis; CFE, capital femoral epiphysis; P, pubis; ISC, ischium.

P

CFEFM

ISC

Figure 73.13 Normal hip, transverse flexion view. A: Transverse flexion view of a normal hip showing ‘U’ configuration. B: Similar view in an older baby with visible ossification centre of the capital femoral epiphysis.

A B

With the infant relaxed and the transducer held over the posterior lip of the triradiate cartilage, firm but gentle pressure is applied to the knee in both an anterior and posterior direction, i.e. a push–pull movement.

In an unstable hip the femoral head will appear over the posterior lip of the triradiate cartilage with the application of posterior pres-sure (push).

Step 3: transverse flexion (Figs 73.12 and 73.13)The baby is moved into a supine oblique position with the hip flexed to 90°.

The transducer is held in a transverse plane posterolaterally over the hip.

The normal appearance is a ‘U’ configuration with the femoral capital epiphysis central to the femoral metaphysis and the ischium.

When dislocated the femoral capital epiphysis cannot be seen within the ‘U’.

Figure 73.10 Normal hip. Normal image obtained over the posterior lip of the triradiate cartilage in a coronal flexion view of a neonatal hip. The femoral head should not be visible. IL, ilium; TC, triangular cartilage; ISC, ischium.

TC

ISC

IL

Figure 73.11 Normal hip, coronal flexion view. Normal image obtained over the posterior lip of the triradiate cartilage in a coronal flexion view.

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The image acquired is of the acetabulum at the centre of the triradiate cartilage.

The bony acetabulum consists of the larger ischial portion poste-riorly and the anterior pubic portion, with the two portions con-nected by the echo-poor triradiate cartilage. The femoral head is normally positioned centrally within the acetabulum with its mid-point approximately over the triradiate cartilage. There should be no echoes between the femoral head and the bony acetabulum.

As with the Graf method, this technique requires skilled, prac-tised operators.

Terjesen techniqueTerjesen describes a dynamic technique that assesses femoral head coverage.

The infant lies supine with the leg in the neutral position and the hip slightly flexed.

The transducer is positioned over the lateral aspect of the hip and images are acquired in the longitudinal and transverse planes.

As with the Graf technique, a baseline is drawn. Further lines are drawn tangential to the medial junction of the femoral head with the acetabular fossa and through the lateral margin of the acetabu-lum parallel to the long axis of the transducer. Femoral head cover-age is defined as the distance between the baseline and the medial line divided by the distance between the medial and lateral lines multiplied by 100.

The lower limits of normal are defined as 46% in boys and 44% in girls.11

The irritable hip

The commonest cause of an irritable hip is transient synovitis, but the differential diagnosis includes septic arthritis, Perthes disease and slipped capital femoral epiphysis.

Ultrasound is a useful first-line investigation in the assessment of a limping child.

If a joint effusion is identified it is the clinician’s role to narrow the differential diagnosis. Transient synovitis can be treated con-servatively, whereas septic arthritis requires prompt intervention and treatment.

The patient lies supine with both legs straight and in the neutral position. The transducer is placed anteriorly in a parasagittal oblique orientation along the femoral neck.14,15 It is important to ensure that the proximal femoral shaft is visible in the scan plane, to avoid a false negative scan (Fig. 73.16).

Both hips should be scanned during the same examination.Dual imaging is useful in demonstrating both hips side by side

for comparison.

Transient synovitisIn transient synovitis there is inflammation of the synovial lining of the hip joint, often with a joint effusion.

Transient synovitis typically affects children of between 2 and 10 years of age. The aetiology is unknown but there is sometimes a history of recent upper respiratory tract infection. The pain is decreased at rest and usually resolves within a few days, but the effusion may persist, generally resolving within 4–11 days.16

Ultrasound is extremely sensitive for the detection of a hip joint effusion, and relies on visible displacement of the hip joint capsule (Fig. 73.17). The normal hip joint capsule is seen as a continuous concave reflective line paralleling the anterior aspect of the femoral neck and capital femoral epiphysis. Synovial thickening or an effu-sion causes the joint capsule to become convex and bulge anteriorly. Synovial thickening is often seen both anterior to the fluid collection and in the synovial reflection along the femoral neck.

The anteroposterior diameter (anterior capsular distance) of the effusion can be measured and provides a reproducible objective assessment.

Posterior stress on the adducted hip during examination can cause an increase in the gap between the femoral head and acetabu-lum, indicating instability/subluxation.

Anterior stress on the abducted hip, as in the Ortolani test, allows visualisation of relocation of the hip.

Step 4: transverse neutral (Figs 73.14 and 73.15)The hip is in the neutral position and the hip is scanned transversely.

Figure 73.14 Normal hip, transverse neutral view. Normal transverse neutral view of a neonatal hip. CFE, capital femoral epiphysis; P, pubis; TC, triangular cartilage; ISC, ischium.

CFE

P ISC

TC

Figure 73.15 Normal hip, transverse neutral view.


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Joint effusion fluid is usually anechoic, but may contain fine echoes depending on the cellular content of the fluid. The appear-ance of the fluid is not a reliable indicator for distinguishing between transient synovitis and septic arthritis. If there are clinical concerns the joint fluid should be aspirated for culture.

Legg–Calvé–Perthes diseaseThis condition usually affects children between 3 and 12 years of age with a peak incidence of 5–8 years and a slight male preponder-ance. Around 15% of cases are bilateral.17

Although ultrasound has a theoretical role in the diagnosis and follow-up of Legg–Calvé–Perthes disease, in practice plain radiog-raphy, magnetic resonance imaging (MRI) and nuclear medicine studies are more sensitive and specific.

The initial diagnosis is made clinically and with plain X-rays, but ultrasound may be the initial investigation of a child with hip pain or a limp. It is therefore imperative that the hip is examined in its entirety, including the femoral capital epiphysis (Fig. 73.19).

The earliest sonographic sign is that of a joint effusion.The features that help to differentiate Legg–Calvé–Perthes disease

from transient synovitis are:

1. thickening of the joint capsule2. mild contralateral capsular distension3. a joint effusion that persists for more than 2 weeks.

On ultrasound the unossified cartilage of the femoral head is hypoechoic, whereas the ossification centre is seen as a band of high echogenicity with posterior acoustic shadowing.

The margin of the femoral ossification centre can be defined with ultrasound and ultrasound can be used to identify irregularity, flat-tening or fragmentation. In the more chronic phases of the disease ultrasound can identify new bone formation earlier than the plain radiograph and may also identify recalcification.

In this instance the strong echoes of the necrotic bone disappear and are replaced by less reflective material that extends over the epiphysis and shows gradual increase in ossification.

In the more acute stage of the condition the articular cartilage becomes thickened and this increases with progressive collapse of the femoral head.

Slipped femoral capital epiphysisConventional radiography remains the first-line investigation for suspected slipped upper femoral epiphysis (SUFE) and any child

A difference of greater than or equal to 2 mm between the left and right hips can also indicate a joint effusion, but it should be considered that joint effusions can be bilateral.

The interface sign is where an additional line is seen anterior to the echo-poor cartilage of the femoral head, corresponding to the junction between the cartilage of ossification and the articular car-tilage (Fig. 73.18). The interface sign is absent in the presence of a joint effusion.

Figure 73.17 In the presence of a joint effusion at the hip the joint capsule is distended and the capsule is lifted away from the proximal femoral shaft.

Figure 73.18 Joint fluid. Image showing the interface sign representing the extra interface (arrow) between articular cartilage and joint fluid.

Table 73.4 Anterior capsular distance (ACD)

Age ACD: upper limit of normal

<4 years 5 mm4–7 years 6 mm8 years 7 mm

Source: Graf and Wilson.12

Figure 73.16 Ultrasound of the normal hip including the proximal femoral shaft.

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Figure 73.19 Legg–Calvé–Perthes disease. A: Image showing irregular, flattened and fragmented capital femoral epiphysis compared to B: the normal contralateral side.

A B

Figure 73.20 Slipped capital femoral epiphysis. On the left the epiphysis is normally aligned with the femoral metaphysis. On the right the epiphysis is stepped posteriorly in relation to the metaphysis.

Hip ultrasound

Use a linear probe

CDH: Graf technique: Position the hip in flexion and internal rotation

Align the transducer parallel to the body

Identify the landmarks

Measure the depth of the acetabulum with the alpha angle

Hip effusion Align the probe with the femoral neck

Include the proximal femoral shaft in the field of view

Examine both hips

Perthes The femoral head becomes irregular/flattened/fragmented

The joint capsule becomes thickened

SUFE Malalignment of the proximal femoral epiphysis with the proximal femoral metaphysis

over 8 years of age presenting with hip pain should have antero-posterior and frog lateral views of the pelvis in the first instance.

SUFE can occur in younger children who present with hip pain and have ultrasound as the initial investigation. It is therefore important to assess the alignment of the femoral capital epiphysis relative to the femoral metaphysis during routine ultrasound exam-ination of the hip18 (Fig. 73.20).

If there is suspicion on ultrasound, anteroposterior and frog lateral X-rays should be acquired. Prompt diagnosis is essential to allow prompt orthopaedic intervention and avoid long-term com-plications such as avascular necrosis.

PAEDIATRIC TRAUMA

Conventional radiography remains the best initial investigation for suspected bony injury. Ultrasound should, however, be the initial investigation for most suspected soft tissue injuries in children. This may be subsequently supplemented by MRI.

Ultrasound is also useful in instances where there may be trauma to non-ossified cartilage.

Acute trauma

Conventional radiographs may not demonstrate physeal fractures in young children with non-ossified epiphyses or apophyses.

Ultrasound can show extension of the fracture line through the epiphysis or show epiphyseal displacement with transphyseal fractures.

The apophysis is a focal area of ossification at the periphery of the bone. It ossifies in cartilage and has a cartilaginous connection to the adjacent bone. In the immature skeleton the apophyseal growth plate is a point of particular weakness. Apophyseal avul-sion injuries typically occur at a bony prominence that serves as a tendon or ligament attachment site, for example at the anterior inferior iliac crest, with a peak incidence for injury between 10 and 20 years of age, i.e. when the apophyseal growth plate is just closing or just after radiographic closure.

In these cases the radiograph may be normal and ultrasound may be helpful in identifying apophyseal displacement or associated intramuscular injury.

Sonography may also be useful in diagnosing fracture com-plications. An avulsed ischial tuberosity may lead to long-term


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Sinding-Larsen and Johansson independently described the disease of apophysitis at the inferior pole of the patella with abnor-mality within the proximal third of the patellar tendon. This usually occurs in children aged 10–14 years who are involved with jumping sports.

Ultrasound shows fragmentation of the inferior pole of the patella and focal thickening and heterogeneity within the proximal patellar tendon.20 Small focal echoes may be seen consistent with calcifica-tion within the tendon.

A sleeve fracture can occur with avulsion of the extension mecha-nism at the inferior pole of the patella. This is usually visible on a plain radiograph, but can also be detected sonographically.

Ultrasound is particularly useful in assessing overuse injuries to the soft tissues.

The unfused growth plate is a particular weak point in the skel-eton and will often fracture before the soft tissues are damaged.

Children and young adults involved in sports can, however, present with superficial tendon pathology. The tendon at the point of insertion is most commonly affected. Sonographic findings include fluid around the tendon/within the tendon sheath, thicken-ing of the tendon and loss of the normal homogeneous signal (Fig. 73.21).

In young people involved in running or jumping activities the tendons around the ankle joint are commonly affected, whilst the Achilles and popliteal tendons are less often involved.

Throwing sports such as cricket or racquet sports can cause injury to the tendons and soft tissues of the glenohumeral joint. Rotator cuff tears are uncommon in paediatrics, and when present are often associated with os acromiale or joint instability.

Muscle injury

Ultrasound is particularly useful in assessing muscle injuries in children. Unlike MRI, ultrasound is readily available, can be used in the acute setting and does not require sedation or anaesthesia.

Young children may present with a soft tissue lump without a history of specific trauma. Ultrasound is not only useful for the diagnosis of haematomas or muscle tears but also in identifying the subsequent complications, including infection and myositis ossificans.

Muscle tears

In the presence of a tear the normal architecture of the muscle is disrupted by an area of increased echogenicity. This is seen as a

morbidity due to sciatic nerve entrapment and in these circum-stances ultrasound may show the precise relationship of the fracture callus to the sciatic nerve. Infection of fracture haematomas is a recognised complication following muscle and tendon avulsion injuries and can be diagnosed with ultrasound.

Accessory ossification centres can cause confusion on a radio-graph. Ultrasound can be used to differentiate them from fractures. An accessory ossification centre will be seen as a small, highly reflective focus within the cartilage of the adjacent bone, without disruption of this cartilage.

A fracture will be associated with disruption of the cartilage and in the acute phase is also associated with soft tissue swelling or a haematoma.

Non-accidental injury

The Standards for Radiological Investigations of Suspected Non-accidental Injury issued jointly by the Royal College of Radiologists and the Royal College of Paediatrics and Child Health in March 2008 state that there are case reports of the use of ultrasound in the identification of subperiosteal haematomas in occult rib fractures and around fractures prior to any radiographically visible signs of healing.

The guidance also states that the use of ultrasound in the inves-tigation of bony injury has not been validated in suspected non-accidental injury and cannot be advocated as a primary tool for the investigation of bone injury.19

Overuse injuries

Repetitive microtrauma in children can lead to conditions affecting bone, cartilage and soft tissues that are specific to the immature skeleton, but affect children of different ages differently. Repetitive trauma that causes apophysitis at a tendon insertion site in a young child will often cause tendinitis in an older child.

Osgood–Schlatter disease is a clinical diagnosis, based on anterior knee pain localised to the tibial tuberosity, assumed to occur fol-lowing repetitive traction trauma. Affected children are typically very active and aged between 10 and 15 years, with a peak inci-dence at 13–14 years.

Ultrasound can be useful in atypical cases, where it can identify fragmentation of the tibial tuberosity apophysis, swelling of the overlying cartilage and focal thickening and heterogeneity of the patellar tendon. In some cases there may be a fluid collection deep to the inferior aspect of the patellar tendon representing pretibial bursitis.20

The cartilage changes usually occur first and are followed by tendon or bursal abnormalities, and if detected, changes in the latter structures are an indication of more severe or well-established disease.

The tibial apophysitis and associated swelling has a compressive effect on the distal tendon, elevating it towards the anterior tibial plateau. The pretibial bursa acts as a shock absorber and the repeated injury with movement causes inflammation of the tendon and bursa. Rarely, a true avulsion of the tibial tuberosity epiphysis can be demonstrated with ultrasound.

Figure 73.21 An anechoic fluid collection adjacent to the tendon fibres, with associated synovial thickening.

Trauma

Muscle tear Disruption of the normal alignment of the muscle fibres with a focal area of echogenicity

Haematoma Mixed echogenicity lesion with disruption of the muscle fibres

No abnormal vascularity within the lesion

Foreign bodies Highly reflective focus with posterior acoustic shadowing

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diffuse area of abnormality without mass effect, with or without associated soft tissue swelling (Figs 73.22 and 73.23).

Interval scanning reveals gradual resolution of the changes.If there is concern, cross-sectional imaging with MRI is helpful

but biopsy of the abnormal area may be the only definitive way of excluding a malignancy.

Haematoma (Figs 73.24 and 73.25)

A haematoma will appear as a mixed echogenicity mass within the muscle, causing distortion of the muscle fibres. The adjacent tissues may be oedematous or show signs of reactive inflammation.

There should be no evidence of increased vascularity within a haematoma on colour Doppler imaging. This helps to distinguish it from other more sinister soft tissue lesions, but is not conclusive. The mass may show central anechoic areas consistent with areas of fluid as well as more echogenic foci consistent with localised haemorrhage.

The lesion will change in appearance and morphology over time, but should not progress unless there has been repeated trauma or there is an underlying bleeding disorder. Large, unresolving lesions

Figure 73.22 Muscle tear. The normal muscle architecture on the left and disruption of the fibres on the right due to a muscle tear.

Figure 73.23 Extended field-of-view technique to demonstrate the tear.

Figure 73.24 A large haematoma in the triceps muscle.

Figure 73.25 Colour flow imaging is useful in identifying vascularity within the lesion. This helps to distinguish between haematoma and tumour, but is not definitive.

should be carefully examined to exclude an underlying vascular malformation.

Foreign bodies

Imaging in trauma is a large part of paediatric radiology and iden-tification and location of foreign bodies is a frequently requested investigation.

Large, radio-opaque foreign bodies are easily detected on plain radiographs.

Ultrasound is particularly useful in locating small, non radio-opaque foreign bodies, such as wood, thorns and other vegetable matter and even in visualising small fragments of glass.21 Wooden foreign bodies as small as 2 mm in the soft tissues of the hand or foot can be located with a sensitivity of 90–100% and a specificity of 97–100%.22–24

Ultrasound can be used to more specifically locate large radio-opaque foreign bodies and position them in relation to adjacent structures, such as blood vessels. Sonography can also provide intra-operative guidance to surgeons, but caution should be applied not to mistake air within the soft tissues for a removable foreign body.


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injury, but clinical concern regarding an evolving soft tissue mass makes exclusion of a sinister lesion at an early stage very valuable. Ultrasound can identify calcification as early as 7 days post injury and can provide the necessary reassurance.

INFECTION

Superficial soft tissues

Infection of the superficial soft tissues causes disruption of the normal planes between the skin and the subcutaneous fat. In cel-lulitis the subcutaneous fat becomes thickened and echogenic (Fig. 73.28).

Ultrasound can be used to identify focal fluid collections within the soft tissues. These are typically anechoic or hypoechoic and may have poorly defined margins. The collection may extend across the planes between fat, skin and muscle.

Pyomyositis

Pyomyositis may develop following trauma or as a result of hae-matogenous spread of infection and should be considered in immu-nocompromised patients with unexplained pyrexia and limb pain.

Differentiation between haematoma and intramuscular infection can be difficult as the appearances are similar and range from focal thickening with disruption of the normal muscle architecture to a discrete anechoic or hypoechoic collection. Once identified, the true extent of the infection is best assessed by MRI, but sonographic follow-up is useful where MRI availability is limited.

Osteomyelitis

A subperiosteal collection may be the first indicator of osteomyelitis in a child (Fig. 73.29) and can precede radiographic features of osteomyelitis by several days.24 This appears as a thin margin of fluid below the dark periosteal layer overlying the bone, and is not usually seen in older patients or adults where the periosteum is more strongly adherent to the bone. The typical sites affected are proximal femur, distal tibia, proximal humerus and distal radius/ulna.17

Foreign bodies appear on ultrasound as highly reflective foci. They typically demonstrate posterior acoustic shadowing, most notable when the foreign body is orientated perpendicular to the ultrasound beam (Figs 73.26 and 73.27).

Oedema or granulation tissue may develop around the foreign object, particularly around vegetable matter and chronic foreign bodies, and can cause a reflective halo that increases the visibility of the foreign body. These appearances will change over time and the foreign body will become less reflective as the inflammatory mass increases.

Myositis ossificans

The commonest site for myositis ossificans is the quadriceps femoris muscle. The radiographic appearances become definitive at 3–4 weeks after an injury when a characteristic cleavage plane can be seen between the area of calcification or ossification and the adja-cent bone.

The typical centrifugal calcification or circumscripta pattern can be seen on computed tomography at about 2–3 weeks following

Figure 73.26 With foreign bodies it is important to assess the whole area. There are two foreign bodies within the soft tissues of the knee on this scan.

Figure 73.27 A wooden splinter within the soft tissues, seen as a linear area of focal echogenicity with posterior acoustic shadowing.

Figure 73.28 Diffuse thickening of the subcutaneous fat with multiple small areas of low echogenicity throughout the tissue consistent with oedema.

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Intervening bone within the distraction gap is visible on plain radiographs at approximately 8 weeks, whereas on ultrasound reflective foci appear by approximately 2 weeks. These foci are initially disorganised within the developing matrix, but start to align longitudinally by 4 weeks, developing into reflective bone continuous with the cortex at the bone ends and with a character-istic concave contour by 8 weeks.25 This intervening new bone progresses to form a dense cortical line with posterior acoustic shadowing. Cystic spaces may develop within the distraction gap and interrupt new bone formation. These can be identified and even aspirated under ultrasound guidance.26

During the early stages of distraction when the edges are still well defined, ultrasound can provide accurate measurement of the dis-traction gap without the magnification created by conventional radiographs. Subsequently, new bone formation obscures the margins of the osteotomy.27 Unfortunately, because of its limited field of view, ultrasound is less sensitive than radiography for the assessment of alignment.28 Ultrasound can thus reduce the need for conventional radiographs in lower limb lengthening patients but cannot replace radiography entirely.

MASSES

Children frequently present with soft tissue ‘lumps’ that are not associated with trauma or other signs or symptoms.

Assessment of these with ultrasound is quick, simple and can be very reassuring. Equally ultrasound can be used to differentiate between those that need further imaging and those that do not.

Prior to examination with ultrasound it is pertinent to ask the patient or parent to localise the area of pathology. If appropriate, clinical examination prior to sonographic evaluation can be invaluable.

Normal anatomical variation

Chest wall asymmetry or intermittent soft tissue swelling of a periphery can easily be assessed with ultrasound.

Prominent or bifid ribs can be defined and compared with the contralateral side and reassurances given regarding the absence of a soft tissue mass or sinister lesion. In these cases it is important to ensure that the echogenic cortex of the rib is intact and that the overlying soft tissues are not swollen or distorted (Figs 73.30 and 73.31).

In more established infection ultrasound may show cortical breech or an associated pyomyositis or septic arthritis.

Doppler ultrasound can be used to assess disease progression. It has been reported that persistently increased vascularity around the periosteum, despite antibiotic therapy, is an indication for surgical intervention.

MONITORING LEG LENGTHENING PROCEDURES

Leg lengthening involves surgical resection of a portion of the dia-physis with progressive distraction of the opposing ends until a satisfactory length has been achieved.

Imaging is required to evaluate the intervening new bone forma-tion and to help determine the rate of distraction. If distraction is too slow premature fusion may occur, whereas if distraction is too rapid new bone formation may be inadequate.

In order to avoid significant radiation doses ultrasound can be used in place of serial radiographs to assess new bone formation in leg lengthening procedures.

The external fixation device often makes radiography technically difficult and can obscure the area of interest; this is less of a problem for sonography, especially if a small footprint probe is used.

Figure 73.29 In osteomyelitis a subperiosteal collection may be the first radiological sign.

Figure 73.30 Bifid rib. A transverse section through an area of chest asymmetry due to a bifid rib on the left. Note the visualised structures are intact and undistorted.

Infection

Superficial infection Disruption of the distinct planes between the tissues

Pyomyositis Mixed echogenicity mass within the muscle with a focal area of low echogenicity

Osteomyelitis Subperiosteal collection below the anechoic periosteum layer

Septic arthritis Fluid within the joint

Distension of the joint capsule


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bruit, but may present as an unexplained mass without specific clinical features.

Ultrasound, with Doppler imaging, is particularly useful in assessing these lesions.

These lesions may be predominantly vascular or lymphatic, but may be mixed. The vascular lesions appear as serpiginous, com-pressible, low-echogenicity masses with variable colour flow seen within the low-echogenicity areas (Figs 73.34 and 73.35). The lym-phatic portions of the mass will not show colour flow, but will appear as anechoic cysts. Sometimes the loculi may be reflective or show fluid or debris levels due to haemorrhage or infection.

Vascular/lymphatic malformations may be superficial, but may be deep within the soft tissues. Usually their extent can be defined with ultrasound, particularly with the use of panoramic imaging, but occasionally these are extensive malformations requiring MRI to determine their complexity.

Figure 73.31 A longitudinal view of the left-sided bifid rib. There is no evidence of a soft tissue mass.

Figure 73.32 A thin-walled multiloculated synovial cyst (ganglion) arising from the midcarpal joint.

Figure 73.33 Baker’s cyst. A thin-walled unilocular cyst in the popliteal fossa with no visible communication with the joint on this scan.

Doppler assessment of the area is useful in excluding a vascular malformation.

Intermittent swelling can be difficult to assess if the child presents for ultrasound during a quiescent episode. At this point it is helpful to exclude an underlying mass or vascular lesion and to ensure normal architecture of the tissues at the site of the swelling.

Colour Doppler should be applied to the area to exclude abnor-mal vascularity or signs of inflammation.

If further reassurance is required a repeat scan at the time of swelling is indicated.

Ultrasound is relatively non-invasive and requires no radiation exposure. It is almost always appropriate to examine the contralat-eral limb or adjacent structures for comparison, but it should be noted that pathology can be bilateral and that both sides may be abnormal.

Cysts

These can often be defined by their size and location.Ganglions are small, well-defined synovial cysts that are most

commonly associated with the small joints of the wrist and hand. They are usually less than 2 cm in diameter and are seen as well-demarcated anechoic cysts with posterior acoustic enhancement. The cyst may be unilocular or septated, but does not typically contain debris or echogenic material (Fig. 73.32).

Ganglions are very common in adults, but as many as 15% are seen in patients under 21 years of age.

Baker’s cysts are synovial cysts arising from the posteromedial aspect of the knee joint, that typically present as a painless swelling in the popliteal fossa. They can occur in isolation or following trauma, but may be associated with inflammatory arthropathy in the knee joint. As with ganglions of the hand, popliteal cysts are typically thin-walled, anechoic and may be uni- or multilocular (Fig. 73.33). They arise between the semitendinosus and medial head of gastrocnemius and there may be a visible communication with the joint.

Baker’s cysts can rupture and present with acute pain behind the knee. Ultrasound may show a fluid collection tracking between the muscle bundles, with associated diffuse soft tissue swelling and loss of definition of the muscle planes on the symptomatic side.

Vascular/Lymphatic malformations

Vascular lesions may have the classical clinical appearance of a superficial soft tissue swelling with a bluish hue and an audible

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Sternocleidomastoid tumour29

This is a lesion of uncertain aetiology also known as fibromatosis colli. It may be related to birth trauma and typically presents in infants at about 2–3 weeks of age as a firm swelling in the neck, with or without torticollis.

On ultrasound a localised swelling of the sternocleidomastoid muscle can be seen at the site of the palpable mass. There is distor-tion of the alignment of the muscle fibres but the structure of the muscle is usually maintained. These appearances represent fibrosis of the muscle (Fig. 73.36). This is usually unilateral and comparison with the normal, contralateral side can be useful.

These lesions typically regress spontaneously within a few months.

Lipoma

Lipomas are uncommon in children, but do occur and show the same appearances as in adulthood.

The mass is of relatively high echogenicity with posterior acoustic shadowing, it is well defined and located within the subcutaneous fat. There is absence of abnormal colour flow and the adjacent structures are normal (Figs 73.37 and 73.38).

Figure 73.34 A relatively low-echogenicity lesion within the subcutaneous tissues of the abdominal wall.

Figure 73.35 Colour Doppler scan of a soft tissue lump. The marked vascularity is characteristic of a vascular malformation.

Figure 73.36 Diffuse swelling and increased echogenicity within the sternocleidomastoid tumour, without loss of the normal fibrous architecture.

Figure 73.37 A well-defined chest wall lipoma.

Figure 73.38 A more diffuse lipoma within the fibres of the gastrocnemius muscle.


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REFERENCES1. Wynne-Davies R. Acetabular dysplasia and familial joint laxity: 2

etiological factors in congenital dislocation of the hip. A review of 589 patients and their families. J Bone Joint Surg Br 1970;52B:704–716.

2. Cooperman DR, Wallensten R, Stulberg SD. Acetabular dysplasia in the adult. Clin Orthop 1983;175:79–85.

3. Place MJ, Parkin DM, Fitton JM. Effectiveness of neonatal screening for congenital dislocation of the hip. Lancet 1978;ii:249–251.

4. Standing Medical Advisory Committee. Screening for the detection of congenital dislocation of the hip in infants. London: Department of Health and Social Services; 1969.

5. Graf R. The diagnosis of congenital hip-joint dislocation by the ultrasonic-Combound treatment. Arch Orthop Trauma Surg 1980;97:117–133.

6. Harcke HT, Grissom LE. Performing dynamic sonography of the infant hip. AJR Am J Roentgenol 1990;155:837–844.

7. Yousefzadeh DH, Ramillo JL. Normal hip in children: correlation of ultrasound with anatomic and cryomicrotome sections. Radiology 1987;165:647–655.

8. Harcke HT. Hip in infants and children. Clin Diagn Ultrasound 1995;30:179–199.

9. Graf R. Classification of hip joint dysplasia by means of sonography. Arch Orthop Trauma Surg 1984;102:248–255.

10. Graf R. Hip sonography. Diagnosis and management of infant hip dysplasia. 2nd ed. Berlin: Springer; 2006.

11. Rosendahl R, Toma P. Ultrasound in the diagnosis of developmental dysplasia of the hip in newborns. The European approach. A review of methods, accuracy and clinical validity. Eur Radiol 2007;17:1960–1967.

12. Graf R, Wilson B. Sonography of the infant hip and its therapeutic implications. Weinheim: Chapman and Hall; 1995.

13. Harcke HT, Clark NMP, Lee MS, et al. Examination of the hip with real time ultrasound. J Ultrasound Med 1984;3:131–139.

14. Boal DKB, Schwentker EP. Assessment of congenital hip dislocation with real time ultrasound. A pictorial essay. Clin Imaging 1991;15:77–90.

15. Terjesen T, Osthus P. Ultrasound in the diagnosis of and follow up of transient synovitis of the hip. J Paediatr Orthop 1991;11:608–613.

16. Marchal GJ, Van Holsbeeck MT, Raes M, et al. Transient synovitis of the hip in children: role of ultrasound screening. Radiology 1987;162:825–828.

17. Bryn R. Paediatric ultrasound. How, why and when. London: Elsevier; 2005. p. 301–319.

18. Bellah R. Ultrasound in pediatric musculoskeletal disease. Techniques and applications. Radiol Clin North Am 2001;39(4):597–618.

19. Standards for imaging in suspected non accidental injury. Royal College of Radiologists/Royal College of Paediatrics and Child Health; March 2008.

Figure 73.39 There is disruption of the superficial fat at the site of a recent immunisation in keeping with localised fat necrosis.

Figure 73.40 Soft tissue mass. Normal appearances on the right, with a large soft tissue mass disrupting the soft tissue planes on the left.

Masses

Normal anatomical variants Normal echogenicity of the soft tissues with no focal pathology

Synovial cyst Well-defined, anechoic structures associated with a joint

Vascular malformation Multiloculated, serpiginous anechoic structure with increased vascularity

Lipoma Focal area of increased echogenicity within the subcutaneous fat or muscles

Sarcoma Mixed echogenicity mass with irregular margins that extends across the tissue planes

Abnormal vascularity within the lesion

Fat necrosis can be seen following immunisation and may present with a palpable lump or with a focal indentation of the skin.

On ultrasound the area will appear as a superficial area of irregu-lar low echogenicity within the subcutaneous fat. There should be no abnormal colour flow and no extension into the deeper tissues (Fig. 73.39).

Any superficial mass that extends into the muscle layer should be diagnosed with caution. Follow-up ultrasound is certainly warranted to assess any change and if there are concerns MRI is justified.

Sinister lesions

Soft tissue sarcomas or even bony sarcomas may present as a pal-pable lump and ultrasound may be the primary investigation.

Any lesion that has ill-defined margins, extends across the differ-ent tissue planes and has abnormal vascularity should raise con-cerns and be investigated further and without delay (Fig. 73.40).

The presence or absence of calcification should be noted and the adjacent bony cortex should be examined to define any cortical breech or associated periosteal reaction.

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References

20. De Flavius L, Nessi R, Scaglione P, et al. Ultrasonic diagnosis of Osgood-Schlatter and Sinding-Larsen-Johansson diseases of the knee. Skeletal Radiol 1989;18:193–197.

21. Banerjee B, Das RK. Sonographic detection of foreign bodies of the extremeties. Br J Radiol 1991;64:107–112.

22. Bray PW, Mahoney JL, Campbell JP. Sensitivity and specificity of ultrasound in the diagnosis of foreign body in the hand. J Hand Surg (Am) 1995;20A:661–666.

23. Rockett MS, Gentile SC, Gudas CJ, et al. The use of ultrasonography for the detection of retained wood foreign bodies of the foot. J Foot Ankle Surg 1995;34:478–484.

24. Riebel E, Nash R, Nazarenko O. The value of sonography in the detection of osteomyelitis. Paediatr Radiol 1996;26:291–297.

25. Young JWR, Kovelman H, Resnik CS, Paley D. Radiological assessment of bones after Ilizarov procedures. Radiology 1990;177:89–93.

26. Young JWR, Kostrubiak IS, Resnik CS, Paley D. Sonographic assessment of bone production in the distraction site for Ilizarov limb lengthening procedures. AJR Am J Roentgenol 1990;154:125–128.

27. Eyres KS, Hughes T, Fixsen JA. Methods for assessing new bone formation during limb lengthening – ultrasonography, dual energy X-ray absorptiometry and radiography compared. J Bone Joint Surg Br 1993;75B:358–364.

28. Maffulli. N, Hughes T, Fixsen JA. Ultrasonographic monitoring of limb lengthening. J Bone Joint Surg Br 1992;74B:130–132.

29. Dahnert W. Radiology review manual. 5th edn. Philadelphia: Lippincott Williams and Wilkins; 2003. p. 379.

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Clinical Ultrasound || Paediatric musculoskeletal imaging