Top Ten Adult Manifestations of Childhood Hip Disorders

Congenital, developmental, and acquired conditions of the pediatric hip frequently present with sequelae in the adult. There is substantial overlap in the end-stage results of these pathologic conditions, including osseous changes, chondral/labral injuries, and premature osteoarthritis. This review discusses the top 10 etiopathogeneses of pediatric hip conditions and presents associated dysmorphisms in the adult on an illustrative, multimodality, case-based template. Quantitative imaging metrics and the role of advanced imaging techniques are reviewed. The ultimate goal is enhanced understanding of the expected evolution of childhood hip pathologic conditions and their associated complications for general radiologists.

Key points

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Pediatric hip pathologic conditions arise from various etiopathogeneses but frequently display common morphologic and functional outcomes.
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Specific radiographic views and quantitative imaging metrics are useful for assessing mechanics and congruity of the hip joint.
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Altered joint mechanics in the adult arising secondary to pediatric hip pathologic conditions can result in labral and chondral injury with premature osteoarthritis.

Introduction

To accurately assess the hip, the practicing radiologist should have familiarity with its anatomic components and the standard imaging techniques used to visualize them. The hip is a ball-in-socket joint with the femoral head articulating within the acetabulum. The femoral head and acetabulum are lined with hyaline cartilage to absorb shock and decrease friction during articulation. The fibrocartilaginous labrum attached to the bony acetabular rim both stabilizes the hip and seals in joint fluid to promote even load-bearing. Any incongruence in femoral head-acetabular articulation can promote uneven cartilage wear and weight-bearing and premature cartilage breakdown. Both femoral head dysplasia and acetabular dysplasia can result in pathologic weight-bearing, early breakdown of articular cartilage, labral loading and injury, proliferative bone formation leading to CAM (an abbreviation for “camshaft,” an automotive analogy describing the shape, which the femoral head and neck resembles) and pincer impingement, and premature osteoarthritis. These pathologic outcomes are common endpoints for a wide variety of different pediatric hip pathologic conditions.

This review discusses the top 10 etiopathogeneses of pediatric hip conditions and presents associated dysmorphisms in the adult on an illustrative, multimodality, case-based template. Quantitative imaging metrics and the role of advanced imaging techniques are reviewed. Imaging discussion is supplemented with case presentations, key radiology pearls, and discussion of treatment modalities. The ultimate goal is enhanced understanding of the expected evolution of childhood hip pathologic conditions and their associated complications for general radiologists.

Imaging techniques and normal anatomy

Five basic radiographic views are generally sufficient to accurately evaluate the adult hip: the anterioposterior (AP), lateral, frog-leg-lateral, Dunn, and false profile views ( Fig. 1 ). Radiographic technique for each of these views is summarized in Table 1 . Frequently referenced anatomic hip landmarks are summarized in Fig. 2 . Specific imaging metrics frequently used for quantitative analysis of plain radiographs of the hip are summarized in Table 2 . Excellent pictorial summaries of these metrics have been previously published. A summary of several of the more advanced imaging modalities commonly used to evaluate the adult hip is summarized in Table 3 .

Table 1

Radiograph technique

Projection	Patient Position	Tube Position	Clinical Utility	Quantitative Radiographic Metrics
AP	Supine Hips 15° internal rotation	Beam perpendicular to table at 120 cm Crosshairs centered between PS and ASIS	Acetabular morphology	Acetabular depth Acetabular version Acetabular index (sharp index) Tonnis angle LCEA (angle of Wiberg) Femoral head sphericity Femoral head lateralization Congruency
False profile	Standing Symptomatic hip against cassette Symptomatic foot parallel to cassette Pelvis 65° to cassette, facing beam	Beam perpendicular to patient at 102 cm Crosshairs centered on femoral head	Acetabular morphology	ACEA (angle of Lequesne) Congruency
Lateral	Supine Contralateral hip and knee flexed 80° Symptomatic hip 15° internal rotation	Beam parallel to table 45° to symptomatic limb Crosshairs centered on femoral head	Proximal femur	Femoral head sphericity Femoral head neck offset congruency
Frog-leg lateral	Supine Ipsilateral knee flexed 30°–40° Symptomatic hip abducted 45° Heel against contralateral knee	Beam perpendicular to table at 102 cm Crosshairs centered between PS and ASIS	Proximal femur	Femoral head sphericity Femoral head neck offset Alpha angle ^a Congruency
Dunn	Supine Symptomatic hip and knee flexed 90° Symptomatic hip abducted 20°	Beam perpendicular to table at 102 cm Crosshairs centered between PS and ASIS	Proximal femur	Femoral head sphericity Femoral head neck offset Congruency

Criteria for technical adequacy: coccyx in line with pubic symphysis; iliac wings, obturator foramen, and teardrops symmetric; upper border of pubic symphysis to tip of coccyx 1 to 3 cm.

Abbreviations: ACEA, anterior center edge angle; ASIS, anterior superior iliac spine; OA, osteoarthritis; PS, pubic symphysis.

a Approximate; true angle traditionally measured on cross-sectional oblique CT or MR imaging.

Table 2

Hip imaging metrics (hip pathologic condition by morphology)

	Imaging Modality	Normal	Clinical Significance (Abnormal)	Common Pertinent Hip Pathologic Conditions
CAM deformity
Alpha angle	Axial MR imaging or CT	<55⁰	CAM deformity	LCPD SCFE Intraarticular osteoid osteoma of hip AIIS avulsion
Femoral head neck offset	Any lateral radiograph	>0.17	CAM deformity	LCPD SCFE Intraarticular osteoid osteoma of hip AIIS avulsion
Pincer deformity, acetabular dysplasia
LCEA	AP radiograph	25°–40⁰	Decreased: structural instability Increased: pincer impingement	DDH PFFD Charcot hip Inflammatory/infectious arthritis LCPD
ACEA	AP radiograph	20°–45⁰	Decreased: structural instability Increased: pincer impingement	DDH PFFD Charcot hip Inflammatory/infectious arthritis LCPD
Acetabular depth	AP radiograph	Floor of acetabulum does not abut/cross ilioischial line on AP radiograph	Pincer impingement	Infectious/inflammatory arthritis
Femoral head lateralization	AP radiograph	>10 mm	Structural instability	DDH Charcot hip
Acetabular index (Sharp index)	AP radiograph	<45⁰	Structural instability	DDH PFFD Charcot hip LCPD
Tonnis angle	AP radiograph	0°–10⁰	Increased: structural instability Decreased: pincer impingement	DDH PFFD Charcot hip LCPD
Joint alignment
Acetabular version	AP radiograph	13°–20⁰ anteversion	Pincer impingement	SCFE
Femoral version	Axial MR imaging or CT	8°–14⁰ anteversion	Excessive retroversion risk factor for poor outcomes after corrective FAI surgery	DDH FAI SCFE
Joint congruity
Femoral head sphericity	AP and lateral radiograph	Any portion of femoral head >2 mm beyond standard Mose template	Joint wear and early OA	DDH PFFD Charcot hip LCPD Infectious/inflammatory arthritis IHC

Abbreviations: ACEA, anterior center edge angle; FHC, femoral head center.

Table 3

Summary of basic and advanced hip imaging modalities

Imaging Modality	Views/Sequences	Clinical Utility
Plain radiograph	AP Lateral Frog-leg lateral Dunn False profile	Evaluate acetabular and femoral morphology and congruence Preoperative and postoperative assessment Routine surveillance imaging
CT	Axial, coronal, and sagittal views 3D modeling	Assess complex fractures and hip dysmorphologies Preoperative planning with automated hip measurements Assessment of hip version
MR imaging	Conventional 3 T imaging: dedicated hip coils, parallel imaging, isotropic MR MR arthrography, ± traction Biochemical MR imaging: dGEMRIC, T2 and T2*, T1 rho, Na+ mapping 3D modeling Virtual ROM analysis Open MR imaging (functional imaging) 3D printing Advanced metal suppression MR fingerprinting	Assessment of cartilage and labral injuries Biochemical cartilage mapping (dGEMRIC, T2/T2*, T1 rho, Na ⁺mapping) Automated analysis of joint parameters, for example, alpha angle via 3D modeling Subject-tailored preoperative virtual planning Dynamic ROM simulation Real time in vivo functional imaging

Abbreviations: AP, anterior posterior; dGEMRIC, delayed gadolinium-enhanced MR imaging of cartilage; Na ⁺, sodium; ROM, range of motion.

Two scenarios are generally encountered when evaluating adult hip disease arising secondary to childhood hip pathologic conditions in daily clinical practice:

The disease process and pathophysiology are known, in which case the radiologist is following hip morphology for interval change.
The disease process is unknown, and the radiologist is evaluating hip morphology to assist in diagnosis of the underlying pathologic condition.

It is most helpful, therefore, to organize commonly encountered hip pathologic conditions by both morphology ( see Table 2 ) and etiopathogenesis ( Tables 4 and 5 ).

Table 4

Hip pathologic conditions by etiopathogenesis: developmental/congenital

Etiopathogenesis	Pathophysiology/Mechanism	Imaging Features	Abnormal Imaging Metrics	Possible Operative Findings
Developmental/congenital
DDH	Lateralized femoral head Acetabular undercoverage	Coxa valga Femoral lateralization Hip subluxation AD Premature OA/cartilage damage	LCEA/ACEA Acetabular index Tonnis angle	Periacetabular osteotomy Femoral varus osteotomy Hip resurfacing arthroplasty Total hip arthroplasty
PFFD	Abnormal mesenchymal development • Dysmorphic femoral head • Shortened femur Loss of developmental acetabular molding	Coxa vara Femoral head deformity Proximal femoral deficiency AD	LCEA/ACEA Acetabular index Tonnis angle	Various femoral lengthening procedures
Charcot hip ^a	Sensory/autonomic neuropathy Insensate bone imperceptible trauma Hyperemia bone breakdown	Femoral head deformity Femoral lateralization Pseudoarticulation AD Premature OA/cartilage damage	Acetabular index Acetabular depth Tonnis angle	Total hip arthroplasty

General assessment of the above includes AP and lateral radiographs, MR imaging (cartilage/labral assessment), and CT (3D bone morphology, operative planning, and so forth).

Abbreviations: ACEA, anterior center edge angle; AD, acetabular dysplasia; OA, osteoarthritis.

a Congenital neuropathic hip most frequently related to spina bifida, Chiari malformations, and syringomyelia.

Table 5

Hip pathologic conditions by etiopathogenesis: acquired

Etiopathogenesis	Pathophysiology/Mechanism	Imaging Sequela	Abnormal Imaging Metrics	Possible Operative Findings
Acquired
LCPD	Loss of blood flow to femoral head AVN Relative CAM deformity	Femoral head deformity CAM deformity AD Premature OA/cartilage damage	LCEA Acetabular index Femoral head neck offset ratio Alpha angle	Femoral varus osteotomy Periacetabular osteotomy Femoral neck lengthening Innominate osteotomy Shelf procedure
SCFE	Anterior/lateral slippage of femoral neck • Pathologic stress ^a • Pathologic physeal weakness ^b Relative CAM deformity	Femoral head deformity CAM deformity Premature OA/cartilage damage	Acetabular version Femoral head neck offset ratio Alpha angle	Femoral head pinning Proximal femoral osteotomy Femoral head/neck osteochondroplasty
Infectious/inflammatory arthritis	Inflammatory change/hyperemia • Premature triradiate/physeal closure • Femoral head erosion/AVN • Acetabular deformity Possibly idiopathic (eg, JIA)	Femoral head deformity Femoral lateralization Coxa vara/valga Leg length discrepancy AD Joint ankylosis/heterotopic bone Premature OA/cartilage damage	Femoral head sphericity Tonnis angle Acetabular index Femoral head extrusion index	Pelvic acetabuloplasty Femoral varus/valgus osteotomy Epiphysiodesis with contralateral leg lengthening Trochanteric arthroplasty Total hip arthroplasty
IHC	Idiopathic rapid destruction of hip cartilage	Symmetric joint space narrowing Periarticular osteopenia Acetabular protrusion Joint ankylosis/heterotopic bone Premature OA/cartilage damage	Acetabular depth Acetabular index Tonnis angle	Total hip arthroplasty
Osteoid osteoma of the hip	Benign bone tumor • Reactive hyperemia • Bone proliferation	Lucent nidus with surrounding sclerosis (minority of intraarticular cases) Coxa valga Widening of femoral neck (CAM deformity) Premature OA/cartilage damage	Alpha angle Femoral head neck offset ratio	Osteochondroplasty
Traumatic avulsion	Repetitive stress (athletics) Direct trauma	AIIS hypertrophy, malunion, or nonunion Heterotopic bone formation CAM deformity	Alpha angle (concurrent CAM deformity) Femoral head neck offset ratio	AIIS osteochondroplasty Femoral head/neck osteochondroplasty