406 THE JOURNAL OF BONE AND JOINT SURGERY

REAL-TIME ULTRASOUND IN THE DIAGNOSIS OF CONGENITAL

DISLOCATION AND DYSPLASIA OF THE HIP

N. M. P. CLARKE. H. THEODORE HARCKE, PETER McHUGH, MYUNG 500 LEE, PATRICIA F. BORNS,

G. DEAN MAcEWEN

From the Alfred I. duPont Institute, Wilmington, Delaware

A technique of examining the infant hip joint with real-time ulfrasound is described. Since the

cartilaginous femoral head is clearly imaged by ultrasound, anatomical structures and their relationships can

be accurately determined. Dislocated hips are easily detected and subluxations also can be visualised.

We report our experience with 131 examinations in 104 patients, comprising 259 single hip studies. Of

83 patients who were previously untreated, there were 178 hip studies with three false-negative and four false-

positive ulfrasound results. No dislocations were missed. Twenty-seven patients who were already being

treated were examined to assess hip location, comprising a total of 81 hip studies. In some cases the patients

were examined while in an abduction device, cast, or Pavlik harness. In one case a disloction was not detected.

The method of examination using real-time ultrasound is considered to be reliable, accurate, and a useful

adjunct to radiography. The advantages are that it is non-invasive, portable, and involves no exposure to

radiation.

The diagnosis of instability and dysplasia in the hip of

the newborn infant remains difficult. Although clinical

examination is recognised as an effective screening

method for dislocations, there remains a small popula-

tion of neonates in whom a confirmatory image is

desirable. Radiographs are, of course, helpful in the

assessment of unstable hips (Bertol, Macnicol and

Mitchell 1982) or frankly dislocated hips. However, the

exact indications for and limitations of radiographic

examination of the neonatal hip are still unclear. Un-

certainties arise in the interpretation of radiographs of

the immature pelvis, regardless of the intended position

of the hip; indeed, position may be an important cause of

simulated abnormality (Blank 1981).

Misinterpretation arises because the only structures

imaged by radiographs are the ossified portions of the

pelvis. It therefore becomes necessary to extrapolate the

image of the cartilaginous structures. Clearly this has

disadvantages, and a radiograph only contributes signifi-

cantly to the diagnosis and management ofthe hip ifit is

N. M. P. Clarke, FRCS. Senior RegistrarRoyal Orthopaedic Hospital, Woodlands, Northfield, BirminghamB3l 2AP, England.

H. T. Harcke. MD, Director, Department of Medical ImagingP. McHugh, Research StudentM. S. Lee, MD, Radiologist. Department of Medical Imagingp. F. Borns, MD, Radiologist, Department of Medical ImagingG. D. MacEwen, MD, Medical DirectorAlfred I. duPont Institute, P0 Box 269, Wilmington, Delaware19899, USA.

Requests for reprints should be sent to Mr N. M. P. Clarke.

�,i_�) 1985 British Editorial Society of Bone and Joint Surgery0301-620X/85/3051 $2.00

definitely abnormal. At present, clinical and radio-

graphic examinations are used to complement each

other. A single examination by itself may be unsatis-

factory, and invasive arthrography may, in some

patients, be the only means of obtaining a clear image

of the developing hip joint.

Since Kleinberg and Lieberman (1936) introduced

the acetabular index as a possible means of identifying

abnormal hips, confusion and controversy have existed

and many attempts to clarify the exact radiographic

indices for dysplasia have been made (Caffey et a!. 1956;

Laurenson 1959). In some methods of evaluation,

complicated calculations are required (Tonnis I 976;

Wientroub 1981).

In the context of this diagnostic dilemma, ultra-

sound has obvious potential for examining the infant

hip. It requires no exposure to radiation and clearly

images the cartilaginous structures that are so poorly

delineated by radiography.

Graf(1983) was the first to realise this potential. He

used a fixed-arm B-scanning unit to obtain sonographic

images ofinfant hipjoints. His technique was necessarily

complicated because of the equipment he used, and it

took considerable expertise and time to obtain a satis-

factory examination. Real-time ultrasound is much

simpler to operate and is portable, and the ultrasound

image changes rapidly enough to portray movement.

Images are obtained by placing a transducer on the skin

and scanning a specific sector of the anatomy. The sector

is varied by moving the transducer, allowing simulta-

neous images to be viewed on a screen. Novick, Ghelman

and Schneider (1983) examined a small number of infant

hips using real-time ultrasound and were encouraged by

Number of Repeatexaminations examinations

10 218 29 012 125 0

5 14 0

83 6

Totalnumberof hips

244018265012

8

I 78Total

Treated (27t patients)Pavlik harness�NilIn castIn braceIn traction

18 97 1l� 2I I0 2�

15

5416

542

Total 27 81

Exclusions (18 patients) 18 38

* Positive Barlow or Ortolani signst 6 patients originally examined before treatment were examined again

after treatment started, 4 once and 2 patients three times� Only 16 examinations in 10 patients were performed with the baby

actually in the harness§ Signifies only one hip examined

REAL-TIME ULTRASOUND IN DIAGNOSING CONGENITAL HIP DISLOCATION AND DYSPLASIA 407

VOL. 67-B, No. 3, MAY 1985

the views that they obtained. This led us to undertake a

prospective study of a group of infants referred for hip

evaluation.

The aims of this study were: to establish that real-

time ultrasound was a reliable method of identifying

anatomical structures and their relationships; to develop

a technique for routine examination; and to ascertain

whether ultrasound could differentiate between normal

and abnormal hips.

MATERIALS AND METHODS

A total of 122 patients referred to the Alfred I. duPont

Institute for evaluation of their hips have been studied.

All were examined clinically by an orthopaedic surgeon

for instability or dislocation of the hip. A conventional

anteroposterior radiograph was then obtained, followed

by real-time ultrasound examination of the hips. The

ultrasound studies were performed without knowledge

of the preceding clinical and radiographic findings. In

those instances where the infant was already being

treated, or had returned for a follow-up visit, it was

obvious that there was some clinical problem. However,

at the time of ultrasound examination, the examiner was

not aware of either the side or the type of involvement

which had been diagnosed.

Table I details the patient population. At review, 19

examinations in I 8 patients were excluded: one patient

(two examinations) had had multiple previous surgical

procedures; in I 5 there were no radiographs available for

comparison; in one patient there was a technical failure;

and in one osteogenesis imperfecta prohibited a satis-

factory examination. There remained I 31 examinations

in 104 patients (259 individual hip studies) which form

the basis of this report. Twenty-seven patients were

already being treated, most of them in a Pavlik harness.

Eighty-three patients were referred either for confirma-

tion of a diagnosis of hip dislocation or dysplasia, or for

initial assessment. The average age at examination was

22 weeks (range 4 days to 2 years 6 months). There were

37 boys and 67 girls. The ultrasound findings were

compared with the clinical examination and with the

radiographic appearance (which was reported indepen-

dently by a radiologist). A computer was employed to

analyse the information.

Patients being actively treated were assessed only

for hip location. In untreated patients, the sonogram was

studied for evidence of hip dislocation or subluxation

and for acetabular dysplasia. This was compared with

radiographic evidence of dislocation, subluxation, lateral

displacement and dysplasia. Clinical examination was

used to identify any limitation of abduction, and to

distinguish subluxatable, dislocatable and dislocated

hips.

Ulfrasound technique. The sonographic examinations

were performed using an Advanced Technology Labora-

tory M K I 00 sector scanner and were recorded on

videotape. Both 3 MHz and 5 MHz transducer frequen-

cies were tried, but most examinations were performed

with the 3 MHz scan head. The technique that was

developed has been reported elsewhere (Harcke et a!.

1984) but it is appropriate to describe it briefly here.

Studies were first performed on the hip joint of an

anaesthetised infant pig. Simultaneous fluoroscopic and

sonographic examinations allowed correlation of ana-

tomical landmarks. This was facilitated by the insertion

of a needle into key points within the joint, such as the

ossific nucleus. We established that the femoral head

appears as an area of few echoes while the bony ilium is a

bright echogenic structure except where the triradiate

cartilage is present and produces few echoes. The gap

created by the cartilage allows the transmission of sound

into the pelvis in the zone where bone has produced

acoustic shadowing.

Table 1. Analysis of patients examined by ultrasound

Reason for evaluation

Untreated (83 patients)Hip clickSubluxationDislocation*Hip checkFoot disordersTorsional deformityMultiple

abnormalities

With children, several views of the infant hip were

obtained by placing the transducer in different positions.

A combination of two views was eventually selected as

being most reliable in the identification of the anatomical

structures. This involved a series of two-plane examina-

tions which, when considered together, yielded a three-

dimensional representation of the hip. Displacement of

the femoral head in any direction could therefore be

determined.

In both views, the images are obtained by placing

the transducer laterally in the region of the greater

trochanter. In the view designated as “transverse-

neutral” the infant is supine and the hip is in the neutral

position. The image is effectively a transverse section of

Fig. I

LAT.

Fig. 2

P0�1

Acetabulum Femoral Head

Fig. 4

LA T.

INF.

Fig. 6

Figures I to 6 are reproduced with permission from Harcke et al. J U/trasound Med 1984;3: 13 1-7.

ANT.

Figures 1 to 3

Figure I-The “transverse-neutral view.” Thesector scanned by the ultrasound is a transversesection of the hip joint which is in the neutralposition. Figures 2 and 3-The image obtainedfrom the “transverse-neutral” view of a left hipwith a corresponding diagram to identify the

anatomical landmarks.

Triradiate Cartilage

Pelvis

sup.

Fig. 3

Figures 4 to 6

Figure 4-The “coronal-flexion” view. Theultrasound sector effectively scans a coronalsection of the hip joint. The femur is in theflexed position and the transducer is rotatedthrough 90 when compared with the“transverse-neutral” view. Figures 5 and 6-The image obtained from the “coronal-flexion” view with a corresponding diagram to

identify the anatomical landmarks.

True Truenegative* positivet

False Falsenegative� positive� ConflictsL

REAL-TIME ULTRASOUND IN DIAGNOSING CONGENITAL HIP DISLOCATION AND DYSPLASIA 409

VOL. 67-B. No. 3. MAY 1985

the hip joint, femoral head and neck (Fig. 1). Figure 2

shows the actual image obtained, with a corresponding

diagram of the anatomical landmarks (Fig. 3). The

femoral head lies against the bony acetabular floor with

the triradiate cartilage clearly seen as a defect in the

bright echoes. The concentric relationship of the femoral

head to the triradiate cartilage in this view is crucial,

since failure to visualise it is indicative of displacement.

The femoral shaft serves as a reference point for the

examiner. By moving the transducer in a cephalad

direction, the femoral head is revealed. Lateral displace-

ment is seen as a gap between the femoral head and the

acetabular floor. Superior displacement will cause the

acetabulum to be obscured by echoes from the femoral

shaft and the triradiate cartilage will not be visualised.

In the second view, known as the “coronal-flexion”

view, the infant remains supine, the hip is flexed to 90#{176}

and the transducer is also rotated through 90#{176}.The area

scanned is effectively a coronal section of the flexed hip

joint (Fig. 4). Figure 5 shows the actual image obtained

and Figure 6 is the corresponding diagram. The position

view. In. a few cases infants who were being treated in

casts were examined after cutting a lateral window

through the plaster.

RESULTS

Of the 83 patients being evaluated for the first time, 89

examinations were performed comprising 178 individual

hip studies. These studies were evaluated by comparison

with both clinical and radiographic examinations (Table

II). There were I 36 true-negative and 22 true-positive

results.

Of the true positives there were eight subluxations,

10 dislocations, and four hips with acetabular dysplasia.

For the purposes of this study, a false-negative ultra-

sound result was deemed to have occurred when ultra-

sound missed an abnormal hip detected by both clinical

examination and radiography. Similarly, a false-positive

ultrasound result occurred when ultrasound was inter-

preted as showing an abnormal hip when clinical and

radiographic examinations were both normal. There

were three false-negative and four false-positive results

Table II. Hip evaluations in previously untreated patients

Reason for evaluation

Hipclick 19 2 1 1 1

Subluxation 26 6 1 1 6

Dislocation 7 8 0 1 2

Hipcheck 18 3 1 1 3

Foot disorder 48 2 0 . 0 0

Torsional deformity 12 0 0 0 0

Multiple abnormalities 6 1 0 0 1

Total 136 22 3 4 13

* Normal clinical, radiographic, and ultrasound examinations

t Abnormal clinical, radiographic, and ultrasound examinations� Abnormal clinical and radiographic examinations; normal ultrasound examination§ Normal clinical and radiographic examinations; abnormal ultrasound examinationU Inconsistent clinical and radiographic results

of the bright echoes of the ilium superiorly reflect

acetabular depth and, therefore, coverage of the femoral

head. The greater the cover, the less the radiographic

acetabular index, thus enabling an assessment to be

made ofacetabular dysplasia. Again, the femoral shaft is

a reference point. It lies anteriorly because of the flexed

position ofthe hip. By moving the transducer posteriorly,

the femoral head and acetabulum will come into view.

Femoral head displacement will again cause the acet-

abulum to be obscured by the echogenic femoral shaft.

Most ultrasound examinations in this series were

performed using a combination of the two views de-

scribed. Evaluation of infants in the Pavlik harness,

however, was based only upon the “coronal-flexion”

(Table III). No frank dislocations were missed. Ultra-

sound missed a unilateral dysplastic hip in one patient; in

two other patients, each with bilateral subluxation,

ultrasound diagnosed only unilateral subluxation. No

dislocations were falsely diagnosed. In three of the false-

positive results, clinical or radiographic examinations

had suggested unilateral abnormality, but ultrasound

demonstrated bilateral involvement.

Table II also details the 13 hip studies in which the

clinical and radiographic examinations did not agree;

these are categorised as “conflicts” . In seven hips, the

radiographic and ultrasound examinations were ab-

normal but clinical examination was normal; in five the

radiographic results were abnormal but both clinical and

Radiograph

Bilateral hip clicksPossible subluxation

Bilateral lateraldisplacement

99 Subluxation Bilateralpositive Barlow test

Normal Bilateral subluxation

410 N. M. P. CLARKE, H. T. HARCKE, P.McHUGH, M. S. LEE, P. F. BORNS, G. D. MACEWEN

THE JOURNAL OF BONE AND JOINT SURGERY

Table III. False-negative and false-positive evaluations in untreated patients (178 hips examined)

Patient Reason fornumber evaluation Clinical examination

False negatives5 Hip click

83 Hip check Left adduction Left dysplasiacontracture

False positivesI 3 Dislocation Left positive Barlow test

Bilateral lateral displace-ment with abnormalacetabula

39 Subluxation Normal Right lateral displace-ment

89 Hip check Normal Normal

1 18 Hip click Normal Left dysplasia

Classification

Ultrasound Left hip Right hip

Left-not concentrically True positive False negativereducedRight-normal

Normal bilaterally False negative True negative

Left-subluxated True positive False negativeRight-normal

Conflict False positive

Bilateral dysplasia False positive Conflict

Left not concentrically False positive True negativereduced

Left-subluxated Conflict False positiveRight-not concentricallyreduced

ultrasound examinations were normal; and in one, clini-

cal and ultrasound examinations were abnormal although

radiographs were normal. Excluding these “conflicts”,

the specificity* for ultrasound in the untreated

group was 97% and the sensitivity* was 88%.

In the group of 27 patients already receiving

treatment at the time of initial ultrasound examination,

42 examinations were made, comprising 81 individual

hip studies. There were 75 true-negative studies (showing

that the hip was normally located), and four true-

positives. Three of these true-positives were hip disloca-

tions (one in an abduction brace and two in the Pavlik

harness) and one was a severely dysplastic hip being

treated in a Pavlik harness. There were no false-positives

in the treated group, but one false-negative result and

one “conflict” did occur. The “conflict” was in a patient

being followed for unilateral hip dysplasia in whom

ultrasound was interpreted as normal but the radio-

graphic appearances were equivocal. The only false-

negative study was in a patient in an abduction brace

with a dislocation that was missed by ultrasound. In this

patient, initial radiographs had been reported as normal,

but suspicion led to confirmation of the diagnosis by

computerised tomography.

. . True negatives* Specificity = ___________________________

True negatives + false positives

. . . True positivesSensitivity = .

True positives + false negatives

DISCUSSION

We have established that real-time ultrasound can, in

fact, be used to image the infant hip. Anatomical

structures and their relationships are clearly visualised,

and the capacity for imaging the cartilaginous femoral

head offers an important advantage over conventional

radiography. The technique for ultrasound examination

that we have described is reliable for hips in infants up to

the age of about one year.

Our experience has shown that one limiting factor

for accurate interpretation of the image is the size of the

ossific nucleus of the femoral head. When the bony

nucleus is present, a zone of acoustic shadowing appears

medially and may be mistaken for the triradiate car-

tilage. The crucial sector in the transverse-neutral view is

one which demonstrates concentric reduction of the

femoral head against the acetabular floor while at the

same time imaging for the triradiate cartilage. It is clearly

important that any artefactual triradiate cartilage is not

mistaken for the actual triradiate cartilage. When the

ossific nucleus is less than 10 mm in its transverse

diameter, the ultrasound beam can be directed at an

angle that bypasses this nucleus and enables the triradi-

ate cartilage to be viewed. However, larger bony nuclei

will obscure medial structures by virtue of the diminished

cartilaginous space between the nucleus and the femoral

metaphysis (Fig. 7).

The combination of two views-the transverse-

neutral and the coronal-flexion--was chosen because

easily identifiable landmarks were consistently visible.

These landmarks could not be misrepresented by a

change in projection, hence normality was always quickly

and reliably established. These two views allow dis-

placement in any direction to be detected, and acetabular

Fig. 7

Transverse-neutral view of a right hip illustrating how a large ossificnucleus may obscure medial structures by virtue ofacoustic shadowing

(arrow).

Fig. 8

REAL-TIME ULTRASOUND IN DIAGNOSING CONGENITAL HIP DISLOCATION AND DYSPLASIA 411

VOL. 67 B. No. 3. MAY 1985

dysplasia can be diagnosed by studying the coronal

section. The flexed posture of the hip in the coronal-

flexion view reflects the position used during the clinical

examination; this view also permits infants to be

examined while retained in a Pavlik harness or abduction

brace, when proper location of the hip is of prime

interest.

We have found that an adduction contracture of the

hip makes the examination easier, in that the ultrasound

“aperture” is effectively enlarged; an abduction contrac-

ture closes the “aperture” and makes the examination

more difficult.

Several aspects of our results merit further dis-

cussion. First, the standards by which we judged the

accuracy of ultrasound-clinical and radiographic

examination-are themselves open to question. The

subtleties of the lax or clicking hip on physical examina-

tion have long been recognised as complicating the

definitive diagnosis of hip dislocation. Likewise, radio-

graphic studies do not always reveal mild degrees of

dislocation, subluxation or, even more obscure, sub-

luxatability. Hence the ultrasound “false-positive” re-

suits may conceivably reflect true pathology, particularly

when consideration is given to the fact that three patients

with false-positive ultrasound studies each had a con-

tralateral hip in which the clinical and radiographic

results were in conflict (Table III).

Those examinations classified as “conflicts”, in

which the clinical and radiographic assessments differed,

are a testimony to the difficulties that may be encoun-

tered in diagnosing hip dislocation and dysplasia. We

have not included these results in our final calculations

because we cannot, except in extreme cases, objectively

determine whether the clinical or radiographic results are

actually correct.

The ability of ultrasound to image the cartilaginous

femoral head-rather than the ossified femoral

metaphysis-in relation to the acetabulum makes it a

very attractive imaging tool. However, its sensitivity

must be viewed with caution. Barlow (1962) has stated

that more than 60% of unstable hips recover sponta-

neously in the first week of life. We have seen several

instances in which ultrasound images of neonatal hips

have displayed slight subluxation of the femoral head

(Fig. 8) which shows as a gap between the head and the

acetabular floor. We have performed an insufficient

number of hip studies in such patients to establish

whether this appearance resolves spontaneously at the

same time as the clinical laxity, or whether it is a true

pathological entity. Clearly, before ultrasound can be

used with certainty as a screening tool for congenital hip

dislocation or dyspiasia, the natural history of this type

of appearance will have to be defined.

In our series, 27 infants were examined while

retained in either a brace or a cast. Those in casts were

examined through a lateral window, using the landmarks

of the coronal-flexion view to assess hip location. Hips

retained in a brace were subject to the difficulties of

examination caused by abduction. The one missed

dislocation was such a case: the femoral head was very

small, the acetabulum very shallow, and the posterior

dislocation was only clearly seen with the aid of com-

puterised tomography.

Transverse-neutral view ofa right hip in a neonate. The femoral head isnot concentrically seated, as evidenced by a gap between the head andacetabular floor medially (arrow). There is also slight posterior

displacement of the femoral head.

No mention has yet been made of the potential for

dynamic examination offered by real-time ultra-

sonography. One dislocatable hip was examined in such

a way that the hip could be viewed in both the located

and the dislocated positions. While this case effectively

demonstrated the possibility of dynamic study, the real

value of such an examination lies in its ability to image

412 N. M. P. CLARKE, H. T. HARCKE, P.McHUGH, M. S. LEE, P. F. BORNS, G. D. MAcEWEN

THE JOURNAL OF BONE AND JOINT SURGERY

hips with less distinct abnormalities. Ultrasound offers

great advantages over conventional radiographs in the

detection of hip abnormalities, certainly as an adjunct to

radiographic evaluation (both diagnostic and follow-up

studies), and possibly even as a screening tool. Ultra-

sound could also eventually replace some of the multiple

radiographs required to assess relocation during treat-

ment, thus reducing exposure to radiation. Ultrasound

may be a non-invasive alternative to the measurement of

angles or distances on a radiograph, since the relation-

ships of the cartilaginous femoral head are defined in

three dimensions. As such, sonographic imaging may

contribute significantly to the understanding of the

natural history and pathological anatomy of the spec-

trum ofjoint abnormality encompassing congenital hip

dislocation and dysplasia.

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Bertol P, Macnicol MF, Mitchell GP. Radiographic features ofneonatal congenital dislocation of the hip. J Bone Joint Surg [Brl1982;64-B: 176-9.

Blank E. Some effects of position on the roentgenographic diagnosis ofdislocation at the infant hip. Skeletal Radiol 198 1 ;7(l): 59-61.

Caffey J, Ames R, Silverman WA, Ryder Cl’, Houaji G. Contradictionof the congenital dysplasia-predislocation hypothesis of con-genital dislocation of the hip through a study of the normalvariation in acetabular angles at successive periods in infancy.Pediatrics 1956; 17:632-40.

Graf R. New possibilities for the diagnosis of congenital hip jointdislocation by ultrasonography. J Pediatr Orthop l983;3:354-9.

Harcke HT, Clarke NMP, Lee MS, Bores PF, NiacEwen GD.Examination of the infant hip with real-time ultrasound. JUltrasound Med 1984:3: 13 1-7.

Kleinberg S, Lieberman HS. The acetabular index in infants in relationto congenital dislocation of the hip. Arch Surg l936;32: 1049-54.

Laurenson RD. The acetabular index: a critical review. J Bone JointSurg [Br] 1959;4l-B:702-lO.

Novick G, Ghelman B, Schneider M. Sonography of the neonatal andinfant hip. AJR l983;141(4):639-45.

T#{212}nniSD. Normal values ofthe hipjoint for the evaluation ofx-rays inchildren and adults. C/in Orthop 1976; 1 19: 39-47.

Wientroub S, Tardiman R, Green 1, Salama R, Weissman SL Thedevelopment of the normal infantile hip as expressed by radio-logical measurements. mt Orthop 1981 ;4(4):239-41.