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ECR 2019 / C-1429
Role of imaging in a limping child
Congress: ECR 2019
Poster No.: C-1429
Type: Educational Exhibit
Keywords: Congenital, Education, MR, Paediatric, Bones
Authors: S. A. M. Ibrahim1, T. Salem Alyafei1, N. M. Saloum2, M. Sabawi1; 1Doha/QA, 2Doha, Doha/QA
DOI:10.26044/ecr2019/C-1429

Findings and procedure details

Role of imaging:

Standard radiography is the initial imaging study of choice in the limping child. Orthogonal images of the hip should consist of AP and frog-leg lateral views of the hips. In very young children or those whose physical examination does not reveal a focal source of pain, radiographs of the entire lower extremity should be obtained. As many as 20% of children have unsuspected fractures. Radiographs can be helpful in the diagnosis of fracture, osteomyelitis, Legg-Calvé-Perthes disease, slipped capital femoral epiphysis, bone tumors (both benign and malignant), apophysitis,and congenital abnormalities.

The initial radiographs in children with stress fractures, toddlers fracture, Salter-Harris type I fractures, early osteomyelitis, and septic arthritis are often normal.

With the exception of radiographic evaluation of the hip, most experts recommend that radiographs of the normal limp not be taken routinely for comparison. Ultrasonography is effective in diagnosing a hip effusion; however, it is unable to differentiate a sterile from a purulent effusion.

CT is rarely needed in the evaluation of a limping child . It is useful in the diagnosis of appendicitis, deep soft tissue infections of the paraspinal and retroperitoneal regions, appendicitis osteoid osteoma and tarsal coalition.

MRI is the study of choice for soft-tissue pathology. MRI is also very useful in diagnosing stress fractures, osteomyelitis, malignancy, and early Legg-Calvé-Perthes disease. MRI is also indicated when spine pathology is suggested by physical examination or plain radiographs (discitis, herniated disc, spinal cord anomalies, or spinal tumors).

In addition, patients with evidence of bone tumors on plain radiograph should have further delineation of the extent of disease (including the presence of skip lesions) by MRI.

Bone scintigraphy is an alternative means of evaluation if MRI is unavailable, especially in children with prolonged limp and localized bone or back pain, fever, leukocytosis and/or elevated acute phase reactants (ESR and CRP). Bone scan is also an alternative to repeated plain radiographs over time in toddlers with suspected occult fractures.

 

Radiological findings in some of the DD:

Septic arthritis

S. aureus is the most commonly isolated organism. The knee is most commonly affected followed by the hip and ankle.

Bacterial entry into the joint can occur by two mechanisms:

direct inoculation from a penetrating injury and hematogenous

inoculation.

Septic arthritis causes rapid cartilage loss and joint destruction

and therefore is a medical and surgical emergency. Diagnosis

is based on clinical grounds and laboratory data.

Radiography is the first line of imaging to rule out an obvious alternative cause for symptoms, such as an underlying fracture. The initial findings may be nonspecific soft tissue swelling about a joint. In certain joints—such as the elbow, knee, and ankle—a joint effusion may be seen and is best delineated on a lateral radiograph.

The role of US is to identify the presence or absenceof joint effusion or to determine whether pathology is intraarticular or extraarticular, such as adjacent tenosynovitis. Synovial thickening maybe also seen.

Capsular distension with anechoic or hypoechoic fluid is usually seen. Debris and septations within the joint, as well as hyperemic flow in the

synovium, can be seen on power Doppler.

The MRI findings of isolated septic arthritis are also nonspecific.

Synovial thickening, enhancement, effusions,

and juxtasynovial soft tissue edema may be seen, but this is indistinguishable from transient synovitis and JIA. The role of MRI is not to diagnose septic arthritis but to identify the presence or absence of coexisting osteomyelitis, epiphyseal cartilage involvement , and juxtasynovial muscle inflammation or abscesses, because this will affect medical and surgical management.

 

Osteomyelitis

In children, the bacteria, most commonly Staphylococcus aureus, spread hematogenously and deposit in the bony metaphysis.

Early diagnosis and treatment can prevent long-term complications, such as bone necrosis and long-term deformity.

XRAY: With acute osteomyelitis, the earliest change on radiographs is soft tissue swelling; osseous changes are rarely present until the second week. The earliest bone changes are small radiolucencies in the metaphyseal region

With continuing appropriate antibiotic therapy, periostitis is visible after the second or third week.

The multiphase bone scan is very sensitive and is usually positive 24 to 48 hours after the onset of symptoms.

MRI findings of osteomyelitis may have a tumefactive

appearance and may be paradoxically hypointense on fluidsensitive sequences. Over time, the lesion may remain masslike and demonstrates the expected, more homogeneous hyperintense signal on fluid-sensitive sequences. Eventually, periostitis and adjacent soft tissue involvement may be seen in the early phase of osteomyelitis. Subperiosteal abscess formation may be seen by preceding radiographic bony changes. A salt-and-pepper appearance to the marrow may be seen in the late acute phase and is presumedto represent small areas of noncoalescent microabscess

formation and early bone destruction.

 

Transient Synovitis

Transient synovitis is the most common cause of childhood hip pain and limping.

It is an acute, self-limiting disorder of unknown origin.

Ultrasound is the gold standard imaging modality. It is aimed at identifying effusion in the hip joint anterior recess.

It may be useful to compare the image with that of the

contralateral normal hip.

The anterior joint capsule can be seen as a tissue band between

the anterior surface of the femoral neck and the fascial

layer of the iliopsoas muscle. Thickness difference >2 mm between asymptomatic and symptomatic hips is considered valid for the presence

of effusion. In the absence of joint effusion, a linear reflection can be observed in the center; it is the interface between the two layers indicating the absence of effusion (“stripe sign”).

 

Toddlers’ fractures 

They happen in children between 9 and 36 months and to involve the distal one-third of the tibia; the mechanism of injury usually is trivial (eg, falling from a low height, tripping, or twisting the ankle)

X-RAY: a faint lucent oblique line crossing the distal tibia, also is subtle. It is seen with an internal oblique view, although it may be seen on the AP view. Initial radiographs may be normal.

 

Slipped upper femoral epiphysis (SUFE/ SCFE)

It is the most common hip disorder affecting the adolescent population. SCFE is essentially a Salter-Harris I fracture of the

proximal femoral physis. Approximately 25% of patients will have bilateral SCFEs.

Epiphyseal slips may occur in the medial

direction, posterior direction, or both. The frogleg lateral view is helpful, since most epiphyseal slips occur in the posteriordirection, which can be subtle on the anteroposterior view. Klein’s line is drawn parallel to the lateral margin of the femoral neck on the anteroposterior view. Normally, a small portion of the femoral head extends lateral to Klein’s line. When the femoral head does not extend lateral to Klein’s line, medial displacement should be suspected. CT and MRI may also be used to make the diagnosis of SCFE; however, usually radiographs are enough.

 

Developmental Dysplasia of the Hip

DDH represents abnormal relationship of the femoral head to the acetabulum. It is a result of a combination of both structural and ligamentous laxity leading to an abnormal incongruent hip.

Ultrasound is the modality of choice prior to ossification of the proximal femoral epiphysis. Once there is a significant ossification then x-ray examination is required. 

Radiograph: Several lines may be drawn to assist in the assessment of hips, but attention should be made to the overall configuration.

The Hilgenreiner line passes horizontally through the superior

aspect of the triradiate cartilages. The Perkin line is the

vertical line extending from the lateral margin of the acetabulum.

The expected location of the femoral head is in the

medial, inferior quadrant of the intersection of the Hilgenreiner

and Perkin lines. The Shenton line

curves along the lesser trochanter, femoral neck, and inferior

margin of the pubis or obturator foramen and should be

smooth.

The acetabular index is the angle between the acetabulum

(from the superolateral margin of the acetabulum and the

superolateral margin of the triradiate cartilage) and the Hilgenreiner

line. The acetabular index changes with age: 28 degrees in newborns, 23.5 degrees at age 6 months, 22 degrees at age 1 year, and 20 degrees at age 2 years. Themaximal normal measurement for the acetabular index is 30 degrees up to age 4 months and 25 degrees up to age 2 years.

 

Legg-Calvé-Perthes (LCP) disease

It  is one of the most common forms of epiphyseal osteonecrosis.

The best initial test for the diagnosis of Perthes is a pelvic radiograph.

The changes to the femoral epiphyses depend on the severity of osteonecrosis and the amount of time that there has been alteration of blood supply:

·       early: there may be no appreciable change

·       established: reduction in epiphysis size, lucency

·       late: fragmentation, destruction

Early signs

·       joint effusion: widening of the medial joint space

·       asymmetrical femoral epiphyseal size (smaller on the affected side)

·       apparent increased density of the femoral head epiphysis

·       blurring of the physeal plate

·       radiolucency of the proximal metaphysis 

Late signs

Eventually, the femoral head begins to fragment with subchondral lucency (crescent sign) and redistribution of weight-bearing stresses leading to thickening of some trabeculae which become more prominent.

The typical findings of advanced burnt out Perthes disease are:

·       femoral head deformity with widening and flattening (coxa plana)

·       proximal femoral neck deformity: coxa magna

·       "sagging rope sign" (thin sclerotic line running across the femoral neck)

 

 

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