Developmental Hip Dysplasia

KEY FACTS

Imaging

• Shallow acetabulum ± subluxation of femoral head
• US useful before 6 months of age
• Normal hip

Capsular laxity: > 50% bony coverage femoral head at rest, with < 50% bone coverage on stress examination or normal movement
• Subluxation: < 50% bony coverage at rest
• Dislocation: Femoral head lies completely outside of bony acetabulum at rest
• Modified Graf staging

Type Ia = mature hip, angular bony promontory, α > 60°, β < 55°

Type Ib = mature hip, roundish bony promontory, α > 60°, β < 55°

Type IIa = physiologic immaturity < 3 months, α = 50-60°, β = 55-77°

Type IIb = immaturity > 3 months, α = 50-60°, β = 55-77°

Type IIc = critical hip, subluxation, α = 43-49°, β > 77°

Type III = dislocated hip, α < 43°

Type IV = dislocated hip, inverted labrum, α < 43°
• Roundish anterior acetabular rim can be physiological and often seen in immature hips
• Obtain single image showing deepest part of acetabulum, triradiate cartilage, center of femoral head, straight iliac contour

Top Differential Diagnoses

• Physiologically immature hip in neonate or premature baby

Diagnostic Checklist

• Key to diagnosis rests on obtaining correct coronal (longitudinal) view
• Be clear with respect to definitions of capsular laxity, subluxation, and dislocation

Useful to have these definitions written on US report
• If in doubt, repeat US in 2-4 weeks

TERMINOLOGY

Abbreviations

• Developmental dysplasia of hip (DDH)

Synonyms

• Congenital dysplasia of hip (CDH) (less appropriate)

Definitions

• Underdevelopment of acetabular component of hip joint

IMAGING

General Features

• Best diagnostic clue

Shallow acetabulum ± subluxation of femoral head
• Morphology

Ranges from shallow acetabulum to complete dislocation with false acetabulum

– Secondary hypoplasia of femoral head

Ultrasonographic Findings

• Both morphology (coronal and transverse views) and dynamic evaluation
• Morphology: Graf technique

Coronal (“egg in spoon”) view

– Most important image

– Obtained from lateral approach with hip and knee in slight (~ 20°) flexion; infant in decubitus (or supine) position

– Align transducer 10-15° obliquely (usually posteriorly) from coronal plane to obtain straight iliac line

– Obtain single image showing deepest part of acetabulum, triradiate cartilage, center of femoral head, straight iliac contour

Position too anterior → false-positive result; too posterior→ false-negative result

– Normal hip

Sharp edge to ossified acetabular roof (promontory)

Roundish anterior acetabular rim can be physiological and often seen in immature hips

Transverse (“ice cream cone”) view

– Shows femoral head overlying triradiate cartilage

3 lines drawn on coronal view to assess acetabular morphology

– Line along straight contour of ilium (iliac line)

– Line along osseous acetabular roof

– α angle measured at intersection between iliac line and line along osseous acetabular roof

α angle is acetabular angle

Reflects steepness of acetabular roof

Greater the angle, more mature hip; smaller the angle, more dysplasia of hip

– Line from promontory to tip of labrum

– β angle measured at intersection between iliac line and line from acetabular promontory to tip of labrum

Represents elevation of acetabular labrum

Displacement of femoral head; restraint of cartilaginous roof coverage

β angle less critical than α angle

Modified Graf staging

– Type Ia = mature hip, angular bony promontory, α > 60°, β < 55°

– Type Ib = mature hip, roundish bony promontory, α > 60°, β < 55°

– Type IIa = physiologic immaturity < 3 months, α = 50-60°, β = 55-77°

– Type IIb = delayed ossification = immaturity > 3 months, α = 50-60°, β = 55-77°

– Type IIc = very deficient acetabulum = subluxation, α = 43-49°, β > 77°

– Type III = dislocated hip, α < 43°

– Type IV = severe dysplasia = dislocated hip, inverted labrum, α < 43°
• Dynamic testing: Apply Barlow maneuver (i.e., posterior force on adducted and flexed hip)

Attempt to displace femoral head from acetabulum during real-time imaging

Lack of relaxation by infant can limit acquisition of optimal stress view and can produce false-negative examination

Acetabular bony coverage

– Portion of femoral head contained within bony acetabulum

– Center of femoral head relative to iliac straight line

– Capsular laxity: > 50% bony coverage femoral head at rest, < 50% bone coverage on stress examination or active movement

– Subluxation: < 50% bony coverage at rest

Some centers define subluxation as < 33% bony coverage and 33-50% as indeterminate

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Apr 9, 2020 | Posted by admin in MUSCULOSKELETAL IMAGING | Comments Off

KEY FACTS

Imaging

TERMINOLOGY

Abbreviations

IMAGING

General Features

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Radiology Key

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Developmental Hip Dysplasia

Developmental Hip Dysplasia

Top Differential Diagnoses

Diagnostic Checklist

Synonyms

Definitions

Ultrasonographic Findings

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Developmental Hip Dysplasia

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