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398
11 Small Part and Hip Ultrasound
11.1 Hip US
11.1.1 General Remarks
Various methods on how to perform hip US. Two main queries with different
techniques:
• Assessment in neonates and infants: developmental hip dysplasia (DDH).
• Assessment throughout childhood: hip effusion, capsular thickening, other
pathology (e.g. irregularity of bony structures).
Indications
Hip US performed for:
• General or selective screening (e.g. familial risk, breach presentation, endemic
dysplasia and all girls and boys only with risk factors).
• Clinically suspicious scenario (typical hip instability, clicks, fetal malposition,
impaired mobility, neurological impairment, etc.).
• Incidentally (?).
• Examination of a painful hip.
Positioning for DDH Assessment
Different approaches depending on method, most commonly Graf’s technique
is used:
• Graf’s method- baby positioned in lateral decubitus position with slightly bent
hip and inward rotation:
– Specifi c devices for placing baby and stabilising transducer helpful (to reduce
angulation artefacts).
– Additional stress test for dynamic assessment performed in same standard
position and section, mandatory in all (but type I?) hips.
• Similar approach used for femoral head coverage assessment (French approach)
• Dynamic manoeuvre according to Harcke: part of most exams in North America.
– Transverse view in neutral position and with posterior stress.
• Assessment of joint pathology: supine position.
Transducers
• High-resolution linear arrays, 18–5 MHz (potentially “trapezoid/convex mode” –
phased linear).
• Assessment of effusions and pathology in older children: also curved arrays or
phased (“convex mode”) linear arrays, lower frequencies (10–3 MHz).
Device Presets
• Hard post-processing with strong contrast:
– Some prefer gray scale inversion or bicolor mode.
• Image orientation: typically cranially = right side of monitor image.
– Some turn monitor by 90° to have a somewhat anatomic presentation
(up – cranial).
• Rarely (not consistent with general recommendations) cranial position defi ned as
in abdominal US (left upper monitor corner – cranially), e.g. if hip scan performed after abdominal US.
11.1 H i p U S
a b
Fig. 11.1 Graf standard plane. ( a ) Schematic drawing of relevant structures, lines and angles for
hip US according to Graf. ( b ) Typical corresponding US image (standardised projection – upright
position, always projected as right sided)
11.1.2 Examination Technique
11.1.2.1 Hip US According to Graf
Access from lateral in coronal section
Acquire image in standard plane according to Graf (Fig. 11.1 ):
• Transducer placed over major trochanter in cranio-caudal coronal direction.
• Then carefully move to parallel sections and rotate on acetabular axis without
tilting for imaging the standard plane to be used for diagnosis and
measurements.
• Structures to identify on adequate view of acetabular mid portion: lower limb of
bony ilium in depth of acetabular fossa representing physis, middle of acetabular roof with straight iliac bone line and acetabular labrum (three obligatory
landmarks); additionally brief overview of entire joint space should be
performed.
Dynamic Assessment
Advisable (normal-appearing hips can be mobile due to laxity of joint capsule after
birth – elastic whipping in normal joint):
• Particularly if suspicious fi ndings on standard section – mandatory dynamic
assessment.
• Push and pull softly on leg for assessment of stability (femoral head stays well
positioned within joint).
• Instability – displacement of femoral head out of (dysplastic) joint fossa (e.g.
OEGUM/DEGUM recommendation – see: www.OEGUM.at/content/view/506/210
download “Standard dokumentation der Sonografi e der Neugeborenen- und
Säuglingshüfte”):
– In displaced or luxated hips: check for repositionability by respective manoeu-
vres under US surveillance.
399
400
11 Small Part and Hip Ultrasound
a b
Fig. 11.2 Relevant structures, one image without ( a ) and one with ( b ) angle measurements.
Patient identifi cation and side mandatory, (gestational) age helpful. ( a ) 1 transition zone of osseous
to cartilaginous part, 2 femoral head, 3 fold, 4 capsule, 5 cartilaginous labrum, 6 cartilaginous roof,
7 osseous contour of ilium bone, 8 bony rim. ( b ) 1 base line, 1a auxiliary line, 2 bony roof line, 3
cartilaginous coverage line, α (between line 1 and 2 ) 65°, β (between 1 and 3 ) 59°
Documentation
• Two individually acquired images per hip joint in standard plane:
– One of them must contain measurements (see below, Fig. 11.2 ).
• In instable hips, a series of images or video clip showing respective changes
during stress manoeuvres needs to be documented.
11.1.2.2 Modified Graf Classification (Rosendahl)
Objective : classify hip morphology and stability separately.
Technique : hip morphology ( α -angle) assessed in standard coronal view (Graf) with
centred femoral head:
• If hip decentering, eccentric or dislocated hips (Graf 2c, D, 3, 4): femoral head
relocated by mild traction, then thereafter reassess hip morphology.
• Irreducible hip – morphology assessed with dislocated femoral head.
NOTE : Always additional Barlow manoeuvre to assess for coexisting instability
even in morphologically normal hips.
• Stability classifi cation as above.
11.1.2.3 Hip US According to Harcke
Objective : classify hip stability.
Technique : infant lying supine, transducer positioned over lateral aspect of hip.
• Coronal images with hip neutral and in fl exion, plus posterior lip view.
• Transverse images with hip fl exed with passive abduction and adduction,
followed by transverse images with stress to evaluate hip stability.
• Images must document fi ndings and need to be labeled appropriately (Fig. 11.3a ).
11.1 H i p U S
401
ab
cd
Fig. 11.3 Harcke hip US (image and image with labels). ( a , b ) Normal hip: normal posi-
tion of femoral head on this transverse view. Notice cup-like appearance formed by
metaphysis and ischium. No change with stress manoeuvre. ( c , d ) Abnormal hip: trans-
verse view of hip with stress showing subluxation of femoral head from its normal position and disruption of cup-like configuration. This hip was reducible. Abbreviations: F
femoral head, M femoral metaphysic, I ischium, T triradiate cartilage, Arrow cartilaginous
labrum
11.1.2.4 Femoral Head Coverage According to Morin (and Modified
Morin – Terjesen)
Assesses degree of lateralisation of femoral head based on Harcke’s coronal fl exion
view.
Two lines drawn paralleling Graf’s baseline:
• One tangent to lateral part of femoral head.
• One tangent to medial junction of head and acetabular fossa.
• Measure distance between medial and iliac lines and between medial and lateral
lines.
• Calculate ratio multiplied by 100 = % of femoral head covered by bony
acetabulum.
• Modifi ed Morin (Terjesen): instead of iliac line, use line through lateral bony rim
of acetabulum parallel to long axis of transducer measuring “bony rim percentage”, later named “femoral head coverage”.
402
11 Small Part and Hip Ultrasound
11.1.2.5 Assessment of Joint Effusion, Capsular Thickening,
Perthes, Arthritis and Others
US performed in supine position leaving leg in spontaneous position:
• Support of knees helpful to relax – less painful.
Transducer positioned anteriorly along femoral neck; usually slightly lateral to
course of femoral vessels sagittal and parasagittal sections acquired – cross sections
rarely helpful but can be acquired.
11.1.3 Normal Anatomy
Typically femoral head is roundish, in neonates cartilaginous – later central echogenic ossifi cation centre appears, varying size depending on age.
Additionally: ossifi ed femoral neck, border zone between cartilaginous and ossi-
fi ed parts, joint capsule – tracking from femoral neck to acetabulum.
11.1.3.1 US Criteria in Graf
• Good defi nition of bony rim.
• Undisplaced cartilaginous roof triangle.
• Normal position of well-covered femoral head in acetabular fossa.
• Iliac bone seen as straight line with clear border to cartilaginous acetabular
labrum – good osseous defi nition.
• Bony angle ( α ) >60°, cartilaginous angle ( β ) <55° (defi ned below):
– Values can be present at birth but must be reached by 3 months.
NOTE : Correct section through joint with suffi cient depiction of all three land-
marks mandatory for judging hip maturity and for performing angle measurements
– if section taken angulated or too ventral or dorsal (usually recognised by bent
shape of iliac line or incorrect/missing identifi cation of bony fossa defi nition), measurements always wrong and diagnostically useless.
11.1.3.2 Rosendahl Modification
No essential difference from Graf technique with addition of compulsory stress test
(similar to Graf’s “dynamic examination”).
Angle Measurements – Measured Between three Lines.
1. First line (baseline) from osseous rim of iliac bone in straight line paralleling
osseous iliac contour (Fig. 11.4a ).
2. Second line (“bony roof line – acetabular roof line”) from inferior rim of iliac
bone as pivot point tangential to bony roof (Fig. 11.4b ).
3. Third line (“cartilage roof line”) from centre of labrum to bony rim, defi ned as
point where convexity changes into concavity of acetabulum (Fig. 11.4c ).
Bony angle α : defi ned between fi r s t and second line, shows osseous coverage:
• If normal = good (e.g. more than 50 %) (Fig. 11.4d ).
Cartilaginous angle β : measured between fi r s t and third line, defi nes site and con-
fi guration of cartilaginous roof:
• If roof fl at = high β angle – risk of instability (Fig. 11.4e ).
NOTE : Angle measurements only valid in correctly performed exams.
11.1 H i p U S
403
ab
cd
Fig. 11.4 Hip angle measurements and lines ( a – d ). ( a ) How the baseline is defi ned. ( b ) Defi nition
of acetabular roof line . ( c ) Cartilaginous roof line added, with normal angle α and β – not an
upright standardised view, increasingly used for practicability and device restrictions; left hand
image is cranial. ( d ) Hip US with integrated sonometer software: the software automatically indi-
cates angles ( α 54°, β 78°) and thus hip type ( full line ) after manual defi nition of respective lines
(immature type II hip, suboptimal coverage, dynamic assessment shows elastic whipping) not an
upright standardised view, increasingly used for practicability and device restrictions; left hand
side on image is cranial
Small α angle always indicates dysplasia and poor coverage and at least immaturity.
11.1.3.3 Normal Findings During Harcke Investigation
• Cartilaginous femoral head positioned in acetabulum as defi ned by triradiate cartilage centrally and posterior ischium, with femoral metaphysis seen anteriorly.
• No displacement seen with stress – image remains the same, with head centred
in fossa (see Fig. 11.3a ) .
11.1.3.4 Anatomic Landmarks and Normal Limits for Measuring
Femoral Coverage
• Lateral part of femoral head, medial junction of head, acetabular fossa.
• Lower normal limits: boys – 47 %, girls – 44 %.
11.1.3.5 Hip US in Older Children
Applications and queries: Perthes disease, infection, proximal femoral defi ciency,
slipped capital femoral epiphysis, trauma, joint effusion.
404
11 Small Part and Hip Ultrasound
a
c
b
Fig. 11.5 Normal hip ( a ) in older children – as opposed to hip effusion ( b ) and septic hip ( c ). ( a )
Normal longitudinal hip US in an older child; normal joint capsule (synovium) appears prominent,
as both layers are collapsed. ( b ) Simple hip effusion (transient synovitis, extended fi eld of view):
echo-free fl uid in widened joint space, thickened capsule. ( c ) Power Doppler in septic arthritis:
note impressive hypervascularity of thickened synovium, complex fl uid (*) in widened joint space
Normal US fi ndings:
• Typically longitudinal section, frontal sagittal view.
• Ossifi ed head, neck connected by non-ossifi ed physis – anechoic line.
• Minimal fl uid within joint space.
• Capsule small, sometimes diffi cult to delineate.
• Visible contours of acetabulum and femoral head and neck – continuous, without
disruption, smooth and clearly defi ned surface (Fig. 11.5a ).
11.1.4 Pathologic Findings
11.1.4.1 Developmental Dysplasia of the Hip (DDH)
Criteria vary depending on method applied (Graf, Harcke, adapted Graf, femoral
head coverage, femoral distance).
Remark / Comment : early detection and treatment = only way for non-invasive man-
agement – important to early recognise DDH to avoid long-term sequelae, immense
healthcare costs, individual morbidity, e.g. by repeated surgery. The debate of role
of screening ongoing in Anglo-American literature; in most of middle Europe some
screening established.
NOTE : Hip US for dysplasia – “fi nal” investigation (if you miss an endangered hip,
the patient will only come back after years or decades when symptomatic) – strict
and consistent adherence to all quality criteria is essential. As with mammography,
clinical investigation and anamnestic data are mandatory part of every
examination.
DDH According to Graf
Strict classifi cation that differentiates between immaturity, dysplasia, instability and
luxation (Table 11.1 ).
Normal Hip – Type I (described above – “normal fi ndings”, Figs. 11.1 , 11.2 , and 11.4 ).
11.1 H i p U S
Table 11.1
405
Immaturity – Type II
Consider age: depending on subtype, defi ned by suffi cient to poor ossifi cation, with
some rounding of bony rim:
• Cartilaginous acetabulum usually still covering hip but much wider than osseous
acetabulum:
– Due to ossifi cation defi cit – covering > half of femoral head.
• Potentially delayed ossifi cation.
Subtypes :
• II A +: physiological immaturity.
• II A–: maturation defi cit during fi rst 3 months.
• II B: after third month of life, α ≤ 60°.
• II C: developmentally dysplastic hip – defi nitely endangered, needs treatment:
– Dynamic stress manoeuvres are mandatory.
• (II) D – usually unstable hip with beginning decentering:
– Dynamic stress manoeuvres mandatory.
– Very rounded bony rim.
– Initially displaced cartilaginous acetabulum.
– α = 43°–49°, β > 77°.
– Only treatment option – fi xation.
Decentered Hip – Type III (Fig.
11.6 )
US Criteria:
Femoral head has pushed cartilaginous acetabular roof cranially:
• Insuffi cient osseous containment with fl at bony rim.
• Insuffi cient bony as well as cartilaginous coverage.
• Decentering of femoral head and cartilaginous acetabulum:
– Type III A – hyaline cartilage hypoechoic.
– Type III B – cartilaginous acetabulum small, compressed, distorted – struc-
tural anomalies – some echoes and inhomogeneous. Only in untreated and
chronically dislocated hips – sign of severe damage (remark: very uncommon
in Middle Europe).
• Therapy: needs repositioning and fi xation.
406
11 Small Part and Hip Ultrasound
ab
cd
Fig. 11.6 Pathological hips (Graf classifi cation). ( a ) Immature hip, slightly rounded roof
(>3 months of age – type IIa). ( b ) Endangered hip: severely rounded bony roof, displaced cartilagi-
nous roof, dynamic assessment mandatory (type D). ( c ) Dysplastic – decentered hip with fl at bony
roof – type III. ( d ) Luxated hip – by defi nition cartilaginous labrum compressed between femoral
head and iliac bone (type IV)
Luxated Hip – Type IV (Fig. 11.6 ).
US criteria:
• Femoral head displaced from joint space:
– Luxated in cranial, lateral or dorsal position.
• Cartilaginous acetabulum herniated and displaced caudally:
– Pressed in between femoral head and iliac bone – increased inhomogeneous
echoes.
• Sometimes diffi cult to fi nd bony rim – reliable measurements often impossible/
not required.
• Dynamic assessment helps to evaluate for repositionability.
11.2 Other Conditions of Hip Joint
Results in Rosendahl Modifi cation
According to morphology (using Graf angle discrimination):
• Immature, mildly dysplastic, severely dysplastic.
• Using stability: stable, dislocatable, dislocated.
DDH According to Harcke
• Classification: normal, lax with stress, subluxed or dislocated (see
Fig. 11.3b ) .
NOTE : Method more subjective; also includes description of hip stability. Neither
accuracy nor population-based rates of pathological hips based on this technique
have been published.
Hip Assessment Based on Femoral Head Coverage
• All outside accepted limits = DDH – less potential for grading, used as initial
screening tools to assess for normal or abnormal hips.
• In abnormal hips, either Harcke or Graf method can be applied additionally for
treatment decisions.
407
11.2 Other Conditions of Hip Joint
11.2.1 Arthritis and Inflammation of Hip Joint
As in all joints, examination of contralateral (not affected side) helpful for
comparison (start there).
Most common cause: transient synovitis of hip.
US fi ndings and staging:
• Joint effusion, thickening of joint capsule (Fig. 11.5b ).
NOTE : Differentiation (viral, bacterial, septic, rheumatoid) impossible by US.
Usually achieved by clinical data (possibly US-guided arthrocentesis).
11.2.1.1 Capsular Thickening
Can be measured, does not need to be present, no cut-off value, can have varying
echogenicity:
• Appearance not specifi c – depends on kind of infl ammation, age, duration,
transducer used.
• Sometimes CDS shows hypervascularisation of capsule (Fig. 11.5c ).
• Spectral analysis – diastolic hyperemia:
– Unless increased joint pressure, then diastolic perfusion impaired.
11.2.1.2 Joint Fluid/Effusion
Widening of joint space due to fl uid, forces capsule to convex shape:
• Simple/uncomplicated: clear fl uid, up to 10 mm (intraindividual difference
>3 mm) (Fig. 11.5b ).
• Complicated: larger, echogenic particles within, potentially signifi cantly thick-
ened synovial layer:
– Suspect septic/bacterial arthritis (Fig. 11.5c ) .