Children's hip

Imaging of children’s hips

1D WILSON, MBBS, BSc, FRCP, FRCR and 2G ALLEN, BM DCH, MRCGP, MRCP, FRCR

1Nuffield Orthopaedic Centre, Oxford and 2Royal Orthopaedic Hospital, Birmingham, UK

Children may present with hip disease in avariety of ways. In the newborn it may be detectedby routine clinical examination. In the older childpain, stiffness and limping are the primarysymptoms. In the toddler ‘‘going of their feet’’may be the presenting event.

Most children who complain of pain in the hiphave genuine pathology. It is an unusual locationfor a child to make up or exaggerate complaints.Imaging has a pivotal role in the management ofthese patients who may have disease that requiresurgent medical or surgical treatment.

In most cases a child or infant complaining of apainful hip should be examined and investigatedas a matter or urgency. Hospitals should provideon-call imaging and general practitioners shouldbe fully aware of local facilities and managementprotocols.

Developmental dysplasia

Between 1 and 3 newborns per 1000 live birthswill be diagnosed as suffering from developmentaldysplasia of the hip (DDH), formerly known ascongenital dislocation of the hip, with a femalepreponderance of 9:1. This hides the much largerincidence of premature osteoarthritis that devel-ops in young adults who have a shallow andmechanically disadvantaged hip that is not badenough to have presented in infancy. Many whoundergo hip replacement in their middle years areundiagnosed cases of DDH. The true incidence ofDDH is therefore much higher, although there areno clear figures in the literature (Figures 1 and 2).

There is good evidence that early treatment ofDDH with splint therapy improves prognosis [1].This is only effective in the first 6 months oflife when remodelling is very active. Therefore ifdiagnosis is made early enough, overall popula-tion morbidity may be reduced. It was this rationalethat led to the now universal clinical screeningprotocols using Barlow and Ortolani manoeuvresto detect subtle subluxation and instability of thehip. Unfortunately clinical examination, even inthe best of hands, will overlook a substantialproportion of cases that would benefit from earlytreatment. Ultrasound introduces an additionalmethod of screening that considerably improvesdetection [2–7]. A number of methods have beendeveloped and each has strong and sometimes

vehement advocates. In reality, local outcome

measures must be the standard by which these

techniques are judged. The best method applied

badly or administered ineffectively will be of less

use than a less technically demanding method that

is used rigorously with top quality clerical and

management support.

Figure 1. Plain radiograph of a 28-year-old who hasearly osteoarthritis secondary to developmental dys-plasia that was asymptomatic as a child and youngadult.

Summary

N Ultrasound is an important tool in the detection

and management of developmental dysplasia

of the hip.

N Universal screening for developmental

dysplasia of the hip by ultrasound may be wise

but there is currently insufficient evidence to

clearly recommend this a national policy.

N A painful hip in childhood is a clinical

emergency.

N Ultrasound is the definitive method for

detecting joint effusion.

N Ultrasound cannot determine whether a joint

effusion is due to infection, haemorrhage or

transudate.

N Imaging has a role in determining the cause of

snapping hips.

Imaging, 14 (2002), 179–187 E 2002 The British Institute of Radiology

179Imaging, Volume 14 (2002) Number 3

Most techniques stem from that developed by

Professor Graf, an Austrian orthopaedic surgeon.

Graf uses coronal plane ultrasound to produce a

standard section equivalent in orientation to a

frontal radiograph of the hip. Lines drawn on the

image are used to measure the angular depth of

the acetabulum and the cover of the femoral head.

Strict adherence to the technique is essential as

small variations in measurement will alter classi-

fication and affect management protocols. Others

have introduced less demanding methods of mea-

surement, although still requiring discipline in

image acquisition (Figures 3–5). It has been

argued that a static image alone is less sensitive

than a morphological measure plus a dynamic

stress test, and there is evidence that this improves

detection [8]. In most practices a combination of

static and dynamic imaging is employed [9, 10].

More contentious is deciding upon the popula-

tion to be screened. Infants with family history of

hip dysplasia, those born by breech delivery and

those with other congenital anomalies are at much

higher risk of developing DDH. Screening of

those at high risk in addition to those who are

suspected as being abnormal on routine clinical

examination is the most common practice in the

UK. Others argue that this policy will fail to

provide the most accurate and sensitive detection

of all who might benefit from early treatment and

suggest universal screening [11]. In Austria and

Germany, child benefit entitlement is linked to

attending for screening. One counter to this

Figure 3. Ultrasound of a borderline depth acetabu-lum with measurement using the Morin method.

Figure 4. Ultrasound of a shallow acetabulum thatwould be treated by a splint or harness.

Figure 5. Ultrasound of a dislocated hip that requiredsurgical reduction.

Figure 2. Plain radiograph of a pseudarthrosis result-ing from unrecognized dislocation of the hip.

D Wilson and G Allen

180 Imaging, Volume 14 (2002) Number 3

argument is that required resources are not costeffective, although this is a difficult line to take inwhat is an emotionally charged topic. Indeedthere is evidence that the overall saving inresources is conquerable in all screening strategies[12, 13]. More telling is the point that standards ofdetection are likely to drop in any universalscreening project and that there is currently noevidence that overall population outcome is betterin those centres where it is practiced. Furtherepidemiological research is required before firmrecommendations can be made, and currentadvice in the UK is to perform ultrasoundscreening in infants in the high risk category only.

In complex congenital hip disorders a combina-tion of ultrasound, plain radiography and MRIare indicated, especially for planning surgery [14,15]. For example, in deficiency of the proximalfemur either ultrasound or MRI may be used todetect whether there is a cartilage fragment in thegap and to determine the integrity of the hip joint[16].

Following surgery or splint therapy, MRI isuseful to assess the degree and efficacy of reduc-tion [17]. In managing pelvic and femoralosteotomies the information from cross-sectionalimaging is important [18, 19].

Irritable hip

Children between the ages of 3 years and 12years commonly suffer from acute episodes of hippain. The vast majority are suffering fromtransient synovitis, which is a benign and self-limiting condition. Unfortunately, a small butimportant minority have a more serious com-plaint such as septic arthritis and need urgentsurgical management to minimize long-termdisability [20]. The challenges are detecting andtreating this small subset whilst treating the painand discomfort of the majority in a timely andsafe manner.

Transient synovitis

The cause of transient synovitis is not known.There are postulates that it is traumatic orinfective in origin, but neither is proven. Thecondition presents with a short history of painand limping, which typically resolves within 3–4days. Although MRI, CT and ultrasound will alldetect effusions [21], ultrasound is the establishedmethod of choice as it is readily available, easy toperform and extremely accurate [22–24]. Ultrasoundexamination shows a joint effusion with capsulardistension and a varied amount of synovial thicken-ing. A difference of 2 mm or more between thehips is significant. Joint aspirate will be clear andstraw coloured and depressurizing the joint leads

to immediate pain relief [25, 26]. There are noorganisms present on Gram stain and culture willbe negative.

Pain may be treated with analgesia, however,this is not very effective. Some advocate skintraction and bed rest but this requires hospitaladmission. A diagnostic aspirate of the joint is amore effective method of analgesia as there isinstant pain relief and restoration of function.Local anaesthetic jelly and ultrasound guidanceallow a safe and rapid joint puncture and preventhospital admission in many cases.

Septic arthritis

Pyogenic organisms may infect the hip via ablood borne route. Staphylococcus aureus andhaemophylus influenzae are the most commonorganisms. If infection is untreated the joint willbe rapidly destroyed. Consequent septicaemiamay be life threatening. The only effective therapyis a combination of arthotomy with joint lavageand intravenous antibiotics. Clinical presentationis often indistinguishable from transient synovitis.Fever and serological signs of inflammation areoften absent. The degree of irritability does notpredict diagnosis and ultrasound appearances ofseptic arthritis are no different from transientsynovitis [27]. The only effective means of diag-nosis is aspiration, Gram stain and culture.Fortunately the condition is rare and those whorely on ineffective methods of diagnosis will onlyrarely cause permanent damage.

Perthes disease

Osteochondrosis of the hip, Legg–Calve–Perthes disease, is an uncommon disease ofunknown cause. The most convincing theory isthat it is the result of trauma in an immaturejoint. Again, presentation is with pain andlimitation of movement. The child may be older(7–14 years) and there is sometimes a history ofprevious episodes of pain. Plain radiography isdiagnostic showing fragmentation, roughening,flattening and distortion of the femoral capitalepiphysis (Figures 6–8). In the early phase theplain radiograph shows widening of the hip jointowing to cartilage overgrowth. Long-term dis-ability may result owing to alteration in shape andmechanical stress. Treatment is based aroundsurgery designed to confine the femoral headwithin the joint, and often includes pelvic andfemoral osteotomies. Ultrasound examination inthe early stages of the condition will show jointeffusion [5, 28–30] and the fragmented epiphysismay be visible, but this method should not berelied upon. For older children with an irritablehip a plain radiograph is mandatory to exclude



slipped epiphysis and Perthes disease [31]. Children

with recurrent irritable hip should be examined by

MRI as this technique may detect the condition

when plain radiograph changes have not yet

occurred [32–37] (Figure 3). Gadolinium (Gd)

DTPA enhancement may prove to be useful in

predicting osteonecrosis by assessing vascularsupply to the epiphysis [38]. MRI also hasimportant roles in surgical planning and indetecting occult disease in the opposite hip. It isalso valuable in assessing the late sequelae ofPerthes disease [39, 40].

Slipped epiphysis

Older children (8–14 years) may suffer fromslipped upper femoral capital epiphysis (SUFE).This typically occurs in boys heavier than averageand is thought to be the result of mechanicalstress on the immature growth plate. Presentationis also with pain and limping of short duration.The only effective treatment is surgical fixation,most commonly achieved by inserting pins intothe epiphyses via the femoral neck. If treatment isdelayed the slip will worsen with considerablyincreased risk of osteonecrosis in the displacedepiphysis and severe long-term consequences [41,42]. Detection and treatment are therefore urgent.Whilst ultrasound will show an effusion in 75% ofcases, and may show the step in the contour of thefemoral head [43–45], it is not as safe andeffective as plain radiograph examination using afrog lateral projection. SUFE represents a Salter–Harris 1 type lesion of the proximal femoralepiphysis. The slip most often occurs in a postero-medial direction and may be difficult to see onanteroposterior (AP) radiography [46]. A froglateral is mandatory. It is reasonable to omit theconventional AP film to reduce radiation dose tothe patient. MRI is useful to asses direction andseverity of the slip, especially in planning surgery[47]. It is particularly useful in detecting occult orsubtle slip in the opposite asymptomatic hip,which may occur in up to 60% of cases. Thisexamination should be performed prior to surgeryon the affected hip as prophylactic pinning underthe same anaesthetic is possible [48] (Figures 9–11).

Investigation of irritable hip

From the above it should be apparent that achild with an irritable hip should be seen as anemergency. The clinician should take a historyand confirm the hip as the origin of pain byclinical examination. Ultrasound examinationshould be arranged as an emergency [49, 50]. Ifthere is no joint effusion plain radiography shouldbe undertaken [44, 45]. If this is normal then othercauses of pain should be considered, e.g. retro-caecal appendicitis, muscle strain and referredback pain.

If ultrasound examination shows fluid, atherapeutic and diagnostic aspiration should beperformed. Fluid should be sent for urgent Gramstain and culture (Figures 12 and 13).

Figure 7. The same child as in Figure 6, 1 monthlater, showing contour changes and sclerosis ofPerthes disease.

Figure 8. Established Perthes disease with frag-mentation and flattening of the right femoral capitalepiphysis.

Figure 6. A frog lateral view of a child with sus-pected slipped upper femoral capital epiphysis;appearances are normal.



In older children (over 8 years) plain radiog-raphy in a frog lateral should be performed.

In complex or recurrent cases, MRI should beconsidered as an additional investigation [51, 52].If MRI is not available there is a role for isotopebone scintigraphy to detect occult bone lesions[53].

Osteomyelitis

Bone infection may be primary due to bloodborne organisms or secondary due to implantation,surgery or other forms of trauma. Occasionallyinfection spreads to bone from septic arthritis.

Presentation varies greatly from an acutely

painful region, immobility and systemic toxicity

through to a completely occult disease with minimal

local symptoms and just s general sense of ill

health.Acute infection is typified by bone oedema and

subperiosteal reaction. The latter may be seen on

plain radiography but both are readily apparent

on MRI. The oedema extends beyond the area

that is histologically identifiable as active inflam-

matory response but it is difficult, if not impossible,

to distinguish this margin using imaging. It has

been suggested that areas of true infection would

enhance with intravenous Gd DTPA injection on

Figure 10. 6 weeks after the image in Figure 9, theslip was recognized. There is now significant change,the epiphysis being rendered avascular with a pooroutcome.

Figure 11. MRI of advanced slipped epiphysis.

Figure 12. Ultrasound of a normal hip without aneffusion.

Figure 9. Early slipped epiphysis missed as the subtlechanges were not noticed and a lateral view was notperformed.



MRI, however, this is not a reliable test and in

practice it is rare for contrast enhancement to

assist in management. Subperiosteal reaction may

be detected using ultrasound. A positive finding

on ultrasound is very specific but a negative study

does not exclude acute osteomyelitis.Chronic infection and acute infection after

antibiotic therapy are best studied by a combina-

tion of plain radiographs to detect bony destruc-

tion and sclerosis, with MRI to show the extent of

diseased bone, abscess within and outside bone

and the extent and nature of soft tissue involve-

ment [54]. Ultrasound is useful in excluding or

defining soft tissue abscesses [55]. CT is sometimes

useful in defining the shape and extent of sclerotic

sequestered fragments. The response to drug

treatment and planning of surgical debridement

depends very much on follow up studies. Serial

MRI studies are invaluable in deciding timing and

extent of surgery. Again, contrast enhancement

rarely alters clinical decisions.Tumours may mimic infection and vice versa.

In most cases biopsy is indicated and MRI will be

important in deciding where to biopsy and via

which route. Infection in bone is notorious for the

difficulty in identifying the organisms. Even in

proven and definite osteomyelitis only 30% of

biopsy specimens will grow organisms. For this

reason it is important to send biopsy material for

histological examination as this is more often the

means by which infection is established. Image

guided needle biopsy is valuable. However, in

children an open biopsy under general anaesthesia

is not only kinder but may also treat symptoms

as the marrow oedema may be depressurized,

relieving some of the pain.

Juvenile arthritis

Juvenile arthropathy may present in the hip,although other joints such as the wrist or kneesare more common presenting locations. It shouldbe considered as a possible diagnosis in recurrentor complicated cases where diagnosis of transientsynovitis is in doubt. Synovial reaction will bevisible on ultrasound as thickening and irregular-ity of the capsule. MRI may be more difficult tointerpret as the high signal from fluid in the jointseen on T2 weighted or short tau inversion recovery(STIR) images will be the same signal as exhibitedby thickened and oedematous synovium [56](Figure 14). Intravenous Gd DTPA enhancementwould resolve this issue but ultrasound is cheaper,faster and more acceptable to the patient. Ultrasoundis the imaging method of choice for detectingeffusion and pannus [57] and it has a very usefulrole in follow-up studies [58].

Trauma

Fractures and dislocations around the hipare rare in children [59, 60]. They tend to beassociated with high energy injuries. Fracturesshould be apparent on plain radiography butminimally displaced fractures and stress lesionsmay not. MRI is the definitive test and will showall fractures as low signal lines on T1 weightedimages surrounded by high signal material on T2

weighted or STIR sequences. MRI also has a rolein complex fractures of the acetabulum when CT isnot conclusive [61]. Non-accidental injury should

Figure 14. T2 weighted coronal MRI of a joint effu-sion and synovitis in juvenile arthritis.

Figure 13. Ultrasound of a hip with a substantialeffusion. Aspirate was sterile. The appearances ofseptic arthritis may be identical.



always be considered in younger age groups.Ultrasound can also pick up fractures in theyounger patient.

Acute chondral injuries due to sheering forcesmay cause an acute arthropathy. If there is aresulting defect in the articular surface, symptomsmay persist and fail to resolve. Conventional MRImay show the lesion especially on T2 weighted fastspin echo images, although it may be necessary toperform MR arthrography to be sure. CT arthrog-raphy is also effective but is less suitable inchildren as the radiation burden is large.

Muscle strains and tears may mimic irritablehip. They may be invisible on all imaging butsignificant tears will be well seen on ultrasound asdefect in the myofibrillar structure, oedema andscar tissue. Dynamic stress ultrasound will showmuscle tears by the retraction of muscle andbulging of the margins of the tear. In the acutephase, MRI of the affected area may be the mostsensitive test.

Growth plate injuries are a particular problemin children. Their management depends on theextent and the skeletal age of the child. MRI isthe best method of studying the nature of theinjury [62].

Snapping hip

A variety of clicks and snaps may occur aroundthe hip. These are most common in teenage girls.They include iliopsoas snaps, iliotibial tractsnapping, greater trochanteric bursitis and glenoidlabral injuries. Static ultrasound will demonstrateinflamed bursae and thickening whilst dynamicultrasound is much more useful as it will show theclicking or snapping tendon [63–65]. Local anaes-thetic blocks of the snapping tendon guided byimaging are useful in confirming diagnosis whenmore invasive forms of treatment are beingconsidered. Labral tears will only be visible onMRI or CT arthrography [66–69]. They are morecommon anteriorly than superiorly and imagingshould include axial sections following the jointinjection.

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Children's hip