Skeletal Radiology in Children: Non-Traumatic and Non-Malignant


Constitutional Disorders of Bone

Nomenclature

The naming of constitutional disorders of bone can be confusing. Constitutional bone disorders include osteochondrodysplasias and dysostoses. Osteochondrodysplasias consist of dysplasias (abnormalities of bone and/or cartilage growth) and osteodystrophies (abnormalities of bone and/or cartilage texture). Osteochondrodysplasias are due to intrinsic abnormalities in bone and cartilage, and because of gene expression will continue to evolve throughout the life span of the individual.

Dysostoses occur as a result of a more discrete ‘hit’ during skeletal development—typically during blastogenesis in the first 6 weeks of intrauterine life. The phenotype is fixed, therefore, although multiple bones may be involved and the abnormality may grow with the child, the previously normal bones will remain so. Whilst most dysostoses are genetically determined, some are caused by environmental effects—such as amniotic bands or toxic effects of warfarin; in these cases the abnormality may be termed a ‘disruption’.

Some of the confusion between dysplasias and dysostoses/disruptions arises as a result of unfortunate historical mislabelling of conditions. For instance, the constellation of bony changes often called ‘dysostosis multiplex’ seen in the mucopolysaccharidoses, which are technically dysplasias. The 2015 International Nosology and Classification of Genetic Skeletal Disorders includes 436 different conditions subdivided into 42 groups defined by molecular, biochemical and/or radiographic findings. The classification includes 364 different genes—an increase on the 226 identified in the 2011 classification, with an ever-expanding number of genes continuing to be identified. Selected conditions are summarised in Table 73.1 ( Figs 73.1 to 73.31 ).

TABLE 73.1
Clinical and Radiological Features of Selected Osteochondrodysplasias and Dysostoses
Clinical Features Radiological Features
Group 1 ( FGFR3 Chondrodysplasia Group)
Thanatophoric dysplasia (see Fig. 73.1 ) Most common lethal neonatal skeletal dysplasia. A small number of children may survive into infancy.
Markedly short curved limbs
Respiratory distress, small thoracic cage
Inheritance : Sporadic AD mutation
Gene : FGFR3
Short ribs
Severe platyspondyly
Trident acetabula
Irregular metaphyses
Short broad tubular bones of the hands and feet
Small scapulae
Type 1—Normal skull, marked shortness and bowing of the long bones (‘telephone receiver femora’)
Type 2—‘Clover leaf’ skull. Limb shortening milder.
Achondroplasia (see Fig. 73.2 ) Common
Short limbs > short trunk
Narrow thorax with respiratory distress in infancy
Bowed legs
Prominent forehead with depressed nasal bridge
Hydrocephalus and brainstem and spinal cord compression
Inheritance : AD
Gene : FGFR3
‘Bullet-shaped’ vertebral bodies with short pedicles
Decrease of the interpedicular distance of lumbar spine caudally, and posterior vertebral body scalloping (in older child and adult)
Squared iliac wings with small sciatic notch
Flat acetabular roofs
Short ribs
Short wide tubular bones
Large skull vault
Small foramen magnum
V -shaped notches in growth plates (‘chevron deformity’)
‘Trident’ hands
Hypochondroplasia (see Fig. 73.3 ) Variable short stature
Prominent forehead
Milder phenotype than achondroplasia.
Inheritance : AD
Gene : FGFR3
Absence of normal widening of the interpedicular distance of the lumbar spine caudally
Short, relatively broad long bones, variable brachydactyly
Elongation of the distal fibula and of the ulnar styloid process
Group 2 (Type 2 Collagen Group)
Spondyloepiphyseal dysplasia congenita (see Fig. 73.4 ) Short stature with short trunk at birth
Cleft palate
Myopia
Maxillary hypoplasia
Thoracic kyphosis and lumbar lordosis
Barrel-shaped chest
Inheritance : AD
Gene : COL2A1
Oval, ‘pear-shaped’ vertebral bodies. Anisospondyly; i.e., L5 vertebral body smaller than L1 in infancy
Odontoid hypoplasia and cervical spine instability
Short long bones
Delayed ossification of epiphyses of knees, shoulders, hindfoot, pubic and ischial bones
Severe coxa vara developing in early childhood
Horizontal acetabulum
Delayed ossification of pubic rami
Relative sparing of hands
Group 8 ( TRPV4 Group)
Metatropic dysplasia (see Fig. 73.5 ) Short limbs
Relatively narrow chest
Small appendage in coccygeal region (‘tail’)
Progressive kyphoscoliosis
Progressive change from relatively short limbs to relatively short trunk (hence ‘metatropic’)
Inheritance : AD
Gene : TRPV4
Short long bones with marked metaphyseal flaring (‘dumb-bell’)
Platyspondyly with wide intervertebral spaces
Flat acetabular roofs
Short iliac bones
Short ribs with anterior widening
Progressive kyphoscoliosis
Hypoplastic odontoid peg
Spondylometaphyseal dysplasia, Kozlowski type (see Fig. 73.6 ) Short trunk, progressive scoliosis.
Inheritance: AD
Gene : TRPV4
Irregular platyspondyly with anterior wedging
‘Overfaced’ pedicles
Metaphyseal irregularity (especially of proximal femora)
Coxa vara
Group 9 (Ciliopathies With Major Skeletal Involvement)
Ellis–van Creveld (see Fig. 73.7 ) Short stature
Short limbs, more marked distally
Polydactyly
Hypoplasia of the nails and teeth
Sparse hair
Congenital cardiac defects (ASD, single atrium)
Fusion of upper lip and gum
Inheritance : AR
Gene : EVC1, EVC2
Short ribs (in infancy)
Short iliac wings; horizontal ‘trident’ acetabula (pelvis becomes more normal in childhood)
Premature ossification of proximal femoral epiphyses
Laterally sloping proximal tibial and humeral epiphyses
Polysyndactyly; carpal fusions (90% cases)
Cone-shaped epiphyses of middle phalanges
Asphyxiating thoracic dysplasia—Jeune (see Fig. 73.8 ) Often lethal
Respiratory problems with long narrow thorax
Short hands and feet
Nephronophthisis in later life in survivors
Inheritance : AR
Gene : IFT80, DYNC2H1, WDR34, TTC21B, WDR19, IFT172, IFT140
Small thorax with short ribs, horizontally orientated
High clavicles
Short iliac bones
Trident acetabula
Premature ossification of proximal femoral epiphyses
Cone-shaped epiphyses of phalanges
Polydactyly (10% cases)
Cystic renal disease
Group 10 (Multiple Epiphyseal Dysplasia and Pseudoachondroplasia Group)
Pseudoachondroplasia (see Fig. 73.9 ) Short limbs with normal head and face
Accentuated lumbar lordosis
Genu valgum or varum
Joint hypermobility
Inheritance : AD
Gene : COMP
Platyspondyly with ‘tongue-like’ anterior protrusion of the vertebral bodies
Biconvex upper and lower vertebral end plates
Atlantoaxial dislocation
Small proximal femoral epiphyses with cartilage overgrowth
Wide triradiate cartilage
Small pubis and ischium
Pointed bases of the metacarpals
Short tubular bones with expanded, markedly irregular metaphyses, small irregular epiphyses with delayed bone age
Relatively long distal fibula
Multiple epiphyseal dysplasia (see Figs 73.10 and 73.11 ) Joint stiffness ± limp
Early osteoarthritis
Mild limb shortening
Inheritance : AD
Gene : COMP, MATN3, COL11, COL9A1, COL9A2, COL9A3
Small, irregular epiphyses
Delayed ossification
Delayed bone age
Short tubular bones of the hands and feet
Mild acetabular hypoplasia
Early osteoarthritis
a Note, multilayered patella only seen in autosomal recessive MED due to mutations in the DTDST gene (Group 4, sulphation disorders)
Group 11 (Metaphyseal Dysplasias)
Metaphyseal dysplasia, Schmid type (see Fig. 73.12 ) Short limbs, short stature presenting in early childhood
Waddling gait
Genu varum
Inheritance : AD
Gene : COL10A1
Metaphyseal flaring irregularity and increased density—differential for rickets
Most marked at hips
Large proximal femoral epiphyses
Coxa vara; femoral bowing
Normal spine
Cartilage-hair hypoplasia (metaphyseal dysplasia, McKusick type) (see Fig. 73.13 ) Short stature, sparse hair, immunodeficiency, increased malignancy risk
Inheritance : AR
Gene : RMRP
Metaphyseal irregularity.
Brachydactyly with delta epiphyses
Group 12 (Spondylometaphyseal Dysplasias)
Spondylometaphyseal dysplasia, Sutcliffe type (see Fig. 73.14 ) Inheritance : AR, AD
Gene : Some cases are linked to Col2A1
Corner fracture-type appearance of metaphyses: a differential for suspected physical abuse
Platyspondyly with oval vertebral bodies and anterior beaking
Group 18 (Campomelic Dysplasia and Related Disorders)
Campomelic dysplasia (see Fig. 73.15 ) Neonatal
Respiratory distress
Cleft palate
Prenatal onset of bowed lower limbs
Pretibial dimpling
Survivors
Short stature, scoliosis
Learning difficulties
Inheritance : AD (sex reversal)
Gene : SOX9
11 pairs of ribs
Hypoplastic scapulae
Bowing of femora and tibiae
Short fibulae
Progressive kyphoscoliosis
Dislocated hips
Deficient ossification of the ischium and pubis
Hypoplastic patellae
Group 21 (Chondrodysplasia (CDP) Group)
Chondrodysplasia punctata (see Fig. 73.16 ) Phenotype dependent on genetics
Flat nasal bridge, high arched palate
Cutaneous lesions, e.g. ichthyosis
Asymmetrical or symmetrical shortening of long bones
Joint contractures
Cataracts
Inheritance : XLD, XLR, AR, AD
Gene : XLD— EPP, NHDSL
XLR— ARSE
AR— LBR, AGPS, DHPAT, PEX2
AD—Unknown (also some AR types)
Stippled calcification in cartilage, particularly around joints and in laryngeal and tracheal cartilages. Disappears later on in life
Shortening, which may be asymmetrical, of the long bones and/or digits
Coronal cleft vertebral bodies
Punctate calcification is also seen in some chromosomal disorders, fetal alcohol syndrome, neonates of mothers with autoimmune disorders, warfarin embryopathy
Group 22 (Neonatal Osteosclerotic Dysplasias)
Caffey disease (infantile cortical hyperostosis) Usually present in the first 5 months of life
Hyperirritability
Soft-tissue swelling
Inheritance : AD, AR
Gene : AD— COL1A1
AR—Unknown
Commonly affects mandible, clavicle, ulna
May be asymmetrical
Periosteal new bone and cortical thickening
Abnormality limited to diaphyses of tubular bones
Group 23 (Osteopetrosis and Related Disorders)
Osteopetrosis (see Fig. 73.17 ) Several types
Enlargement of liver and spleen
Bone fragility with fractures
Cranial nerve palsies
Blindness
Osteomyelitis
Anaemia
Inheritance : Severe types—AR
Milder/delayed types—AD
Gene : AR— TCIRG1, CLCN7, RANK, RANKL, CAII
AD— LRP5, CLCN7
Generalised increase in bone density
Abnormal modelling of the metaphyses, which are wide with alternating bands of radiolucency and sclerosis
‘Bone-within-bone’ appearance
Rickets
Basal ganglia calcification (in the recessive form)
Pyknodysostosis (see Fig. 73.18 ) Short limbs with a propensity to fracture
Respiratory problems
Irregular dentition
Inheritance : AR
Gene : CTSK
Multiple Wormian bones, delayed closure of fontanelles
Generalised increase in bone density
Straight mandible
Deficient ossification of terminal phalanges
Resorption of lateral clavicles
Pathological fractures
Osteopoikilosis (see Fig. 73.19 ) Often asymptomatic
May be associated with skin nodules (Buschke–Ollendorff syndrome)
Inheritance : AD
Gene : LEMD3
Sclerotic foci/bone islands, particularly around pelvis and metaphyses
Melorheostosis (see Fig. 73.20 ) Asymmetry of affected limbs
Sclerodermatous skin lesions over affected bones
Vascular anomalies
Muscle wasting and contractures
Inheritance : Sporadic
Dense cortical hyperostosis of affected bones with ‘dripping candle wax’ appearance
Long bones most commonly affected
Group 24 (Other Sclerosing Bone Disorders)
Diaphyseal dysplasia (Camurati–Englemann disease) (see Fig. 73.21 ) Muscle weakness
Pain in the extremities
Gait abnormalities
Exophthalmos
Inheritance : AD
Gene : TGFβ
Sclerotic skull base
Progressive endosteal and periosteal diaphyseal sclerosis
Narrowing of medullary cavity of tubular bones
Isotope bone scan : increased uptake
Group 25 (Osteogenesis Imperfecta and Decreased Bone Density Group)
Osteogenesis imperfecta (see Figs 73.22 and 73.23 ) See Table 73.4
Inheritance : Types I and V—AD
Types II, III and IV—AD, AR
Genes : Type I— COL1A1, COL1A2
Type II— COL1A1, COL1A2, CRTAP, LEPRE1, PPIB
Type III—As for type II plus FKBP10, SERPINH1
Type IV— COL1A1, COL1A2, CRTAP, PKBP10, SP7
Type V—Unknown
See Table 73.4
Group 26 (Abnormal Mineralisation Group)
Hypophosphatasia (see Fig. 73.24 ) Perinatal severe, infantile and
juvenile forms:
Poor dentition with premature loss of teeth, including roots
Inheritance : AR
Gene : ALPL
Juvenile and adult forms:
Inheritance : AD
Gene : ALPL
Low alkaline phosphatase
Phenotypic variability
More severe forms—deficient ossification, with ‘missing’ bones
Metaphyseal spurs
Group 27 (Lysosomal Storage Diseases With Skeletal Involvement (Dysostosis Multiplex Group))
Mucopolysaccharidoses (see Fig. 73.25 )
Abnormality of mucopolysaccharide and glycoprotein metabolism. Differentiation between the types is dependent upon laboratory analysis (of urine, leucocytes and fibroblastic cultures)
Typically present in early childhood
Variable clinical manifestations
Short stature
Distinctive coarse facies
Intellectual impairment (in some)
Corneal opacities (in some)
Joint contractures
Hepatosplenomegaly
Cardiovascular complications
Inheritance : AR, except for MPS type 2 which is XLR
Gene : Hurler/Scheie (type 1H/1S)— IDA
Hunter (type 2)— IDS
Sanfilippo (type 3)— HSS, NAGLU, HSGNAT, GNS
Maroteaux–Lamy (type 6)— ARSβ
Sly (type 7)— GUSβ
Macrocephaly, thick skull vault
‘ J -shaped’ sella turcica
Wide (oar) ribs, short wide clavicles, poorly modelled scapulae
Ovoid, hooked vertebral bodies with gibbus at thoracolumbar junction
Odontoid hypoplasia
Flared iliac wings with narrow base of iliac wings
Small irregular proximal femoral epiphyses, coxa valga, poorly modelled long bones with thin cortices, coarse trabecular pattern
Short wide phalanges with proximal pointing of second to fifth metacarpals
Neurological changes include hydrocephalus, leptomeningeal cysts and a variety of abnormalities best demonstrated by MRI
Morquio syndrome (MPS type 4) (see Fig. 73.25 ) Normal intelligence
Joint laxity
Knock knees
Short stature
Corneal opacities
Inheritance : AR
Gene : GALNS, GLβ1
Hypoplastic/absent odontoid peg (cervical instability may lead to cord compression)
Platyspondyly with posterior scalloping of vertebral bodies
Anterior ‘beak’ or ‘tongue’ of vertebral bodies
Flared iliac wings and constricted iliac bases
Progressive disappearance of the femoral heads
Coxa valga, genu valgum
Irregular ossification of metaphyses of long bones
Small irregular epiphyses
Proximal pointing of second to fifth metacarpals
Mucolipidoses type II (I-cell disease) (see Fig. 73.26 ) Symptoms may be apparent in neonatal period
Craniofacial dysmorphism
Gingival hyperplasia
Joint stiffness
Inheritance : AR
Gene : GNPTα / GNPTβ
Osteopenia with coarse trabeculae
Periosteal cloaking
Pathological fractures
Stippled/punctate calcification
Metaphyseal irregularity
Flared iliac wings
Ovoid vertebral bodies
Broad ribs
Group 29 (Disorganised Development of Skeletal Components Group)
Multiple cartilaginous exostoses (see Fig. 73.27 ) Multiple bony prominences, particularly at the ends of long bones, ribs, scapulae and iliac bones
Secondary deformity and limitation of joint movement
Inheritance : AD
Gene : Type 1— EXT1
Type 2— EXT2
Type 3—Unknown
Multiple flat/protuberant, polypoid/sessile exostoses
Secondary joint deformities
Reverse Madelung deformity (short distal ulna)
Vertebral bodies rarely involved
Skull vault spared
Enchondromatosis (Ollier disease) (see Fig. 73.28 ) Asymmetrical limb shortening
Expansion of affected bones
Occasional pathological fracture
Absence of vascular malformation (Ollier disease)
Presence of vascular malformation (Maffucci syndrome)
Malignancy rare in Ollier disease
Malignancy relatively common in Maffucci syndrome (at least 15%)
Inheritance : Non-genetic
Gene : Non-genetic ( PTHR1 and PTPN11 mutations found in a few patients—significance unknown)
Typically asymmetrical
Shortening of affected long bones
Radiolucencies, particularly in metaphyses, with expansion of bone, cortical thinning and internal calcification
Pathological fractures
Joint deformity
Calcified phleboliths within vascular malformations (in Maffucci syndrome, but not usually seen until adolescence)
Fibrous dysplasia (see Fig. 73.29 ) Pain and deformity of involved bones
Monostotic—only one bone involved
Polyostotic—multiple bones involved
McCune–Albright syndrome consists of polyostotic fibrous dysplasia, patchy café au lait skin pigmentation and precocious puberty (usually in girls)
Inheritance : Sporadic
Gene : GNAS1 (polyostotic)
Asymmetrical thickening of skull vault, with sclerosis of the base, obliteration of the paranasal sinuses, facial deformity
‘Ground-glass’ or radiolucent areas of trabecular alteration in the long bones associated with patchy sclerosis and expansion, with cortical thinning and endosteal scalloping. No periosteal reaction without pathological fracture
Progressive deformities due to fracture/ bone softening: e.g. ‘shepherd's crook’ femoral necks
Group 32 (Cleidocranial Dysplasia and Isolated Cranial Ossification Defects Group)
Cleidocranial dysplasia (see Fig. 73.30 ) Macrocephaly
Large fontanelle with delay in closure
Multiple supernumerary teeth
Excessive shoulder mobility
Narrow chest
Inheritance : AD
Gene : RUNX2
Frontal bossing, wide skull sutures, delayed fontanelle closure, Wormian bones
Supernumerary teeth
Variable clavicular hypoplasia/pseudoarthrosis
Absent or delayed pubic ossification
Group 33 (Craniosynostosis Syndromes)
Pfeiffer syndrome (see Fig. 73.31A ) Craniofacial dysmorphism
Broad, medially deviated thumbs and first toes
Soft-tissue syndactyly of fingers and toes
Inheritance : AD
Gene : FGFR1, FGFR2
Sagittal/coronal/squamous temporal craniosynostosis (‘clover-leaf skull’)
Dysplastic proximal phalanges of thumbs/first toes
Hypoplastic or absent middle phalanges two-thirds and/or three-quarters soft-tissue syndactyly of fingers and toes
Carpal fusions
Apert syndrome (see Fig. 73.31B ) Craniofacial dysmorphism present from birth
Proptosis
High arched/cleft palate
Bifid uvula
‘Mitten/sock deformity’ of hands/feet
Inheritance : AD
Gene : FGFR2
Coronal craniosynostosis
Bony and soft-tissue syndactyly of hands and feet
Progressive carpal/tarsal and large joint fusion
Progressive fusion of cervical spine (commonly C5/C6)
Dislocated radial heads
AD, Autosomal dominant; AR, autosomal recessive; ASD, atrial septal defects; XLD, X-linked dominant; XLR, X-linked recessive.

Fig. 73.1, Thanatophoric Dysplasia Type 1.

Fig. 73.2, Achondroplasia in a Neonate.

Fig. 73.3, Hypochondroplasia.

Fig. 73.4, Spondyloepiphyseal Dysplasia Congenita.

Fig. 73.5, Metatropic Dysplasia.

Fig. 73.6, Spondylometaphyseal dysplasia Kozlowski type—demonstrates radiological features associated with TRPV4 gene mutations; (A) overfaced pedicles (where the lateral aspect of the vertebral body projects beyond the pedicle) and (B) irregular platyspondyly. The epiphyses are small and irregular (C).

Fig. 73.7, Ellis–van Creveld Syndrome.

Fig. 73.8, Jeune Asphyxiating Thoracic Dystrophy.

Fig. 73.9, Pseudoachondroplasia.

Fig. 73.10, Multiple Epiphyseal Dysplasia.

Fig. 73.11, Multiple Epiphyseal Dysplasia.

Fig. 73.12, Metaphyseal Chondrodysplasia, Schmidt Type.

Fig. 73.13, Metaphyseal Chondrodysplasia, McKusick Type (Cartilage Hair Hypoplasia).

Fig. 73.14, Spondylometaphyseal Dysplasia, Sutcliffe Type.

Fig. 73.15, Campomelic Dysplasia.

Fig. 73.16, Chondrodysplasia Punctata.

Fig. 73.17, Osteopetrosis.

Fig. 73.18, Pyknodysostosis.

Fig. 73.19, Osteopoikilosis.

Fig. 73.20, Melorheostosis.

Fig. 73.21, Diaphyseal Dysplasia (Englemann Syndrome).

Fig. 73.22, Osteogenesis Imperfecta Type II.

Fig. 73.23, Osteogenesis Imperfecta Type III.

Fig. 73.24, Hypophosphatasia.

Fig. 73.25, Mucopolysaccharidosis Type 4 (Morquio), Attenuated Form.

Fig. 73.26, Mucolipidosis Type II (I-Cell Disease).

Fig. 73.27, Multiple Cartilaginous Exostoses.

Fig. 73.28, Multiple Enchondromatosis (Ollier Disease).

Fig. 73.29, Fibrous Dysplasia.

Fig. 73.30, Cleidocranial Dysplasia.

Fig. 73.31, Acrocephalosyndactyly Syndromes.

While the international classification lists only those conditions with a proven genetic basis, there are currently over 2000 malformation syndromes, many of which are associated with skeletal abnormalities and many constitutional disorders of bone for which the genetic basis is unknown. In this chapter, only an approach to diagnosis can be given and only the more common conditions are used as illustrative examples.

Prevalence

Although individually rare, collectively, malformation syndromes and constitutional disorders of bone form a large group. As a rough estimate, approximately 1% of live births have clinically apparent skeletal abnormalities. This figure does not take into account the large numbers of spontaneous abortions or elective terminations, many of which have significant skeletal abnormalities. Nor does it include those dysplasias presenting only in childhood, or those relatively common conditions that may never present for diagnosis because they are mild—for example, hypochondroplasia and dyschondrosteosis—both of which merge with normality in individual cases. In addition, there is wide variation in the incidence of dysplasias between populations—for instance, the rate of achondroplasia is as high as 1 in 6400 live births in Denmark, but only 1 in 10,000 in Latin America. At orthopaedic skeletal dysplasia clinics in England and Scotland, approximately 10,000 patients are seen, 6000 of whom will require repeated hospitalisation for surgical procedures and some will require more prolonged admissions.

Diagnosis

Arriving at an accurate diagnosis requires a multidisciplinary approach, with combined clinical, paediatric, genetic, biochemical, radiological and pathological (molecular, cellular and histopathological) input ( Table 73.2 ). A diagnosis is not always made at the time of first presentation and can sometimes take several years to definitively establish.

TABLE 73.2
Clinical and Radiographic Features Used in the Diagnosis of Constitutional Disorders of Bone and Malformation Syndromes
Family history
Stature—proportions and symmetry
Abnormal body proportion—short trunk (suggests abnormal spine (e.g. platyspondyly) or short limbs
Short limb segments—proximal (rhizomelic), middle segment, i.e. forearms/lower legs (mesomelic), distal (acromelic)
Long bone modelling—under/overtubulation, cortical/medullary texture and density
Evidence of epiphyseal dysplasia (small/delayed epiphyses) or metaphyseal dysplasia (irregular metaphyses, spared/large epiphyses)
Pattern of vertebral changes—anisospondyly (collagen-2), non-widening interpedicular distance/short pedicles ( FGFR3 ), overfaced pedicles/irregular platyspondyly (TRPV4)
Local deformities—polydactyly, focal bone lesions, Madelung deformity
Facies—macrocephaly, microcephaly, dysmorphology
Other—hearing, sight, learning difficulties, hepatosplenomegaly, immunological abnormalities
Bloods/biochemistry—bone biochemistry (hypophosphatasia/rickets), thyroid function tests, storage disorders
Change of phenotype and radiographic changes over time

There are two broad approaches to the diagnosis of osteochondrodysplasias and dysostoses: primary clinico-radiological and primary genetic.

Traditionally, diagnosis was made primarily on the basis of clinical features, such as cleft palate and myopia, combined with careful evaluation of radiographic features. The radiographic evaluation involves multiple elements: identifying the site and nature of abnormalities—for example, whether a dysplasia is affecting epiphyses (epi-), metaphyses (meta-) or the spine (spondylo-); identifying the pattern and distribution of changes (e.g. distal (acro-) ( Fig. 73.32 ) or proximal (rhizo-) shortening); and looking for patterns of bone changes that suggest involvement of a particular gene (e.g. narrow interpedicular distances in FGFR3 conditions). Rapid advances are being made in the field of gene mapping, with many conditions being localised to abnormalities at specific loci on individual chromosomes. Identification of genetic mutations allows ‘families’ of conditions to be recognised, with some common clinical and radiological features. This is reflected in the groupings in the international nosology (see Table 73.1 ) with groups including those with mutations in FGFR3 (the ‘achondroplasia’ group), or the TRPV4 group of disorders, consisting of autosomal dominant (AD) brachyolmia, metatropic dysplasia and spondylometaphyseal dysplasia, Kozlowski type (see Figs 73.5 and 73.6 ). Although classification based on genetic mutations is of value in determining an underlying causative defect, this diagnostic approach does not necessarily arrive at a precise clinical diagnosis.

Fig. 73.32, Acrodysostosis.

With the greater accessibility of genetic testing using ‘panels’ of gene tests established in recent years for particular skeletal phenotypes, it is increasingly common for the radiologist to be presented with a child with a known genetic mutation and asked if this genetic mutation corelates with the child's imaging. Anticipatory genetic testing such as this can be not only a challenge for radiologists but also a great asset in cases where, after extensive clinical (including radiological) work-up, the diagnosis is still uncertain. Currently, National Health Service (NHS) patients in England with undiagnosed dysplasia may benefit from whole genome sequencing as part of the ‘100,000 genomes’ research project.

Because of the large number of relatively rare conditions, it is difficult or impossible for an individual radiologist to be familiar with every feature of every disorder. In addition, many of these conditions may have age-dependent features such that the radiological findings evolve or even resolve with time. For example, in Morquio disease (mucopolysaccharidosis, MPS type 4) the capital femoral epiphyses are well ossified at the age of 2 years, but at 8 years are small and flattened, and by 10 years have typically disappeared (see Fig. 73.25 ).

Each radiologist's personal experience of the individual conditions will be limited because of the vast numbers of conditions involved. Textbooks are also of limited value because of the necessarily restricted number of illustrations and obsolescence. For these reasons, skeletal dysplasias, dysostoses and malformation syndromes as a group lend themselves to computer and web-based applications. Web-based resources include those that allow individuals to refer cases to a group of experts—for example, the European Skeletal Dysplasia Network (ESDN)—or those that allow individuals to attempt to make a diagnosis themselves (e.g. the dynamic Radiological Electronic Atlas of Malformation Syndromes [dREAMS]).

A specific diagnostic label should only be attached to a patient when it is secure. An inaccurate diagnosis may have a profound effect upon the family in terms of genetic counselling, and upon the patient in terms of management and outcome. There may be a need to monitor and re-evaluate the evolution of radiological findings over time before establishing a diagnosis. A significant proportion of cases (approximately 30%) are unclassifiable because the combination of findings does not conform to any recognised condition. It is important that data, both clinical and radiological, and specimens (e.g. bone, tissue and blood) are stored to allow the diagnosis to be revisited as new research emerges. Only in this way will it be possible to ‘match’ conditions and to establish the natural history of a disorder.

Imaging

Prenatal Screening and Investigation

In the UK, all pregnant women are now offered prenatal ultrasound (US) screening at between 18 and 21 weeks’ gestation. Neonatally, lethal skeletal dysplasias may be diagnosed at this stage by demonstrating short limbs, bowed limbs (see Figs 73.1 and 73.22 ) or a narrow thorax. Where there has been a previously affected sibling, specific malformations such as polydactyly, polycystic kidneys or micrognathia may be assessed. Skeletal US findings are highly significant but are not very specific, and in general it is unwise to offer a precise diagnosis on the basis of US alone. Pregnancy terminations offered on the grounds of such findings should subsequently have radiological and histopathological evaluation to determine the precise diagnosis and before genetic counselling is offered.

Many non-lethal conditions, which may present at birth, also can be ascertained on prenatal US. Prenatal US has high precision for predicting lethality. The early diagnosis of a lethal dysplasia can prevent unnecessary and distressing prolongation of life and help to reduce parental expectations and anguish. This practice is leading to a change in the incidence of certain conditions formerly presenting at birth.

Occasionally, other imaging techniques may help to confirm a suspected prenatal diagnosis. Maternal abdominal radiographs are now obsolete; the poor diagnostic quality does not justify the radiation risk to either the fetus or the mother. Low-dose prenatal computed tomography (CT) is being successfully performed in some centres for the evaluation of skeletal anomalies (see Fig. 73.22 ). Magnetic resonance imaging (MRI) is increasingly used for in utero evaluation of specific anomalies, particularly of the central nervous system but more recently of other systems, including the musculoskeletal system, and for the assessment of lung volumes.

Amniocentesis or chorionic villus sampling can be used for biochemical evaluation of fetuses at risk from storage disorders when a previous pregnancy has been affected, but at the cost of a 0.5%–1% risk of miscarriage. Cell-free fetal DNA testing, or non-invasive prenatal testing, is now increasingly available although not yet part of the routine NHS diagnostic armamentarium. This involves the testing of free fetal DNA within maternal blood and although not as accurate as the more invasive tests, does not carry the same risk of miscarriage.

Imaging for Diagnosis

In addition to prenatal US, a skeletal survey is recommended for pregnancy terminations performed for suspected malformation and for spontaneous abortions and stillbirths, with parental consent. Although this may involve anteroposterior (AP) and lateral ‘babygrams’ of the entire fetus/infant, ideally additional views of the extremities should be performed. Cross-sectional post-mortem imaging is increasingly available, including CT, MRI, and (in a research setting) micro-CT.

After live birth, a standard full skeletal survey is indicated when attempting to establish a diagnosis for short stature or for a dysmorphic syndrome. This should include:

  • AP and lateral skull (to include the atlas and axis)

  • AP chest (to include the clavicles)

  • AP pelvis (to include the lumbar spine and symphysis pubis)

  • lateral thoracolumbar spine

  • AP one lower limb

  • AP one upper limb

  • posteroanterior (PA) one hand (usually the left; allows bone age assessment).

Occasionally, additional views will be required, particularly with specific clinical abnormalities, and these may include views of the feet, e.g. if polydactyly is present, or views of the cervical spine if cervical instability is suspected with specific diagnoses ( Table 73.3 ), or both upper and lower limbs if asymmetry or deformity is a clinical feature.

TABLE 73.3
Disorders With Instability in the Cervical Spine
Cervical Spine Instability With Odontoid Peg Absence or Hypoplasia
  • Achondroplasia

  • Chondrodysplasia punctata

  • Diastrophic dysplasia

  • Dyggve Melchior–Clausen disease

  • Hypochondrogenesis

  • Infantile hypophosphatasia

  • Kniest dysplasia

  • Metaphyseal chondrodysplasia, McKusick type

  • Metatropic dysplasia

  • Morquio disease (MPS type 4) and other mucopolysaccharidoses (MPS)

  • Mucolipidoses (MLS)

  • Multiple epiphyseal dysplasia

  • Neurofibromatosis type 1

  • Opsismodysplasia

  • Pseudoachondroplasia

  • Pseudodiastrophic dysplasia

  • Spondyloepiphyseal dysplasia congenita

  • Trisomy 21

Cervical Spine Instability With Cervical Kyphosis (C2/C3)
  • Diastrophic dysplasia

  • Spondyloepiphyseal dysplasia congenital

Lethal
  • Atelosteogenesis

  • Campomelic dysplasia

If a diagnosis cannot be established, then (limited) follow-up imaging is indicated (e.g. at 1 and 3 years), to evaluate progression and evolution of radiographic appearances.

Conditions with decreased bone density may be assessed and monitored by means of dual-energy x-ray absorptiometry (DXA). The roles of quantitative US and high-resolution peripheral quantitative CT for assessment of bone density are yet to be fully determined in children.

Imaging for Complications

When a confident diagnosis is established, further imaging is essential to monitor the progress of potential complications. Complications may result as part of the natural evolution of the condition, but may also be iatrogenic.

Radiography and MRI of the cervical spine in flexion and extension will monitor instability; AP and lateral views of the spine will monitor kyphosis and scoliosis. In children with reduced bone density, a lateral spine DXA should replace radiographs to diagnose vertebral fractures. Long limb radiographic views, CT scanograms or increasingly images from low-dose, upright biplanar systems such as the ‘EOS’ system (EOS Imaging, France), will help to assess asymmetry, genu varum and genu valgum, and to monitor progression of limb length discrepancy. CT or MRI may monitor the development of hydrocephalus or the presence of neuronal migration defects and structural defects, such as the absence of the corpus callosum. CT may also demonstrate encroachment on the cranial nerve foramina and both CT and MRI are of value in assessing spinal cord compression.

US can demonstrate associated organ anomalies (e.g. cystic disease of the kidneys or hepatosplenomegaly) and echocardiography may reveal associated intracardiac abnormalities.

Arthrography, US, CT and MRI are of value in the assessment of joint problems, particularly when surgical intervention is proposed or following surgery.

Technetium skeletal scintigrams are occasionally used to determine the extent of bony involvement in specific disorders (e.g. asymptomatic lesions identified in chronic recurrent multifocal osteomyelitis [CRMO]). However, in patchy disorders such as fibrous dysplasia, radiographically affected areas may not demonstrate abnormal uptake of radionuclide.

In recent years, whole-body MRI has become an increasingly feasible, radiation-free option for global assessment of multifocal disease, as technological advances in rolling table platforms, phased array coils and the use of multiple radiofrequency input channels have allowed for faster, higher-resolution imaging. Fat-suppressed images (short tau inversion recovery [STIR]) and diffusion-weighted imaging (DWI) can increase the sensitivity for detection of focal lesions, although ongoing research is still required in this area to fully understand the range of normal findings in healthy children.

Management

Only when an accurate diagnosis has been established can the prognosis and natural history be given. For example, myopia can be corrected and retinal detachment prevented in Stickler syndrome (hereditary arthro-ophthalmopathy); cord compression can be prevented in conditions with instability of the cervical spine (see Table 73.3 ) or with progressive thoracolumbar kyphosis and spinal stenosis, as in achondroplasia.

Conditions previously considered lethal in the perinatal period can now be treated with pharmacological therapies: for example, the success of enzyme replacement therapy with asfotase alfa in selected cases of severe perinatal hypophosphatasia. Enzyme replacement therapy is also an option in mucopolysaccharidoses, where the specific enzyme deficient in each subtype is supplemented intravenously. This can improve symptoms; however, it cannot reverse already established changes.

In some conditions, cure may be achieved: for example, in the severe form of osteopetrosis (which is lethal in childhood unless treated), by means of a compatible bone marrow transplant in the first 6 months of life. Bone marrow transplantation has also been used with some success in selected patients with mucopolysaccharidoses.

Growth hormone therapy is used in selected disorders to influence final height. Growth hormone stimulates type I collagen production and is being used, in particular, to augment growth rate in children with osteogenesis imperfecta (OI) ( Table 73.4 ).

TABLE 73.4
Osteogenesis Imperfecta Clinical (Based on the Sillence Classification) and Radiological Findings
I II III IV V a
Clinical Findings
Incidence 1 : 30,000 1 : 30,000 Rare Unknown (rare) Unknown (rare)
Severity Mild Lethal Severe Mild/moderately severe Moderate
Death Old age Stillborn By 30 years Old age Old age
Sclerae Blue Blue Blue, then grey White White
Hearing impairment Frequent Rare Rare Rare
Teeth IA normal DI IVA normal Normal
IB DI IVB DI
Stature Normal Short Normal/mildly short Normal/mildly short
Radiological Findings
Fractures at birth <10% Multiple Frequent Rare Rare
Osseous fragility Moderate/mild Severe Moderate/severe Moderate/mild Moderate
Deformity Mild Severe Variable Moderate/severe
DI , Dentinogenesis imperfecta.

a Other radiological findings in type V osteogenesis imperfecta (OI) include dense metaphyses in the paediatric age range, healing of fractures with hyperplastic callus formation, ossification of the interosseous membrane and dislocated radial head.

Bisphosphonates are pyrophosphate analogues that inhibit osteoclast function. They have been used in OI to improve bone density and have been used to treat bone pain and osteopenia in a variety of rheumatological and dermatological conditions. The radiological hallmark of bisphosphonate therapy, so-called ‘bisphosphonate lines’, are now well recognised ( Fig. 73.33 ).

Fig. 73.33, Bisphosphonate Lines in a Patient With Osteogenesis Imperfecta.

In many conditions, orthopaedic procedures are invaluable in maintaining or improving mobility. For example, osteotomies prevent or correct dislocations or long bone bowing deformities. Patients with OI may require multiple osteotomies to correct severe deformities, as well as intramedullary rodding to reduce fractures, to maintain alignment and to provide support and stability (see Fig. 73.23 ). Joint replacements may be necessary, especially in those dysplasias (e.g. multiple epiphyseal dysplasia) in which major involvement of the epiphyses may result in premature osteoarthritis. In some conditions, limb-lengthening procedures may be appropriate to improve mobility. This is usually offered in disorders with asymmetric shortening ( Table 73.5 ), but is sometimes offered to selected patients with achondroplasia or other short-limbed dysplasias for cosmetic reasons. With the identification and localisation of specific chromosomal abnormalities associated with particular disorders, the development of gene therapy for clinical use poses many challenges and offers great potential for the future.

TABLE 73.5
Asymmetric Shortening or Overgrowth
  • Beckwith–Wiedemann syndrome

  • Chondrodysplasia punctata (Conradi–Hünermann)

  • Dysplasia epiphysealis hemimelica

  • Epidermoid nevus syndrome

  • Hereditary multiple exostoses

  • Hypomelanosis of Ito

  • Klippel–Trénaunay syndrome

  • Maffucci syndrome

  • McCune–Albright syndrome

  • Melorheostosis

  • Neurofibromatosis

  • Ollier disease (multiple enchondromatosis)

  • Polyostotic fibrous dysplasia

  • Silver–Russell syndrome

  • Sturge–Weber syndrome

Genetic Counselling

When an accurate diagnosis has been made, meaningful genetic counselling can be given, both to the parents and to the affected individual. Most conditions are inherited in an AD or autosomal recessive (AR) manner . In conditions with an AD inheritance, the affected individual has a one in two chance of passing the same abnormality on to his/her offspring. However, many of these conditions arise as a spontaneous mutation, which means that the parents of the affected individual, who are themselves normal, have an extremely low risk of having another affected child . For example, although the FGFR3 mutation in achondroplasia is inherited in an AD manner, most new cases are due to spontaneous mutations . In AR conditions, both the parents are carriers of the disorder, but are not affected, and they have a one in four chance of having another affected child.

Summary Box: Constitutional Disorders of Bone

  • Dysplasias (abnormal bone/cartilage growth) and osteodystrophies (abnormal bone texture) are due to genetic changes with an evolving phenotype.

  • Dysostoses are due to a discrete insult (either genetic or environmental) during development and have a static phenotype.

  • Diagnosis requires synthesis of large volumes of data—clinical, biochemical, radiological and genetic—and it may take years to reach a diagnosis.

  • A final diagnosis allows more specific treatment, anticipation of complications and specific genetic counselling.

Other important, although uncommon, modes of inheritance are the result of somatic or gonadal mosaicism or uniparental disomy. Mosaicism is the presence of at least two cell lines in a single individual or tissue that derive from a single zygote. Somatic mosaicism for AD conditions results in asymmetric or patchy disorders (see Table 73.5 ). It is thought that when not a mosaic, these disorders are lethal. Clinical evidence of somatic mosaicism includes asymmetry, localised overgrowth, pigmentation and haemangiomas. In uniparental disomy, both copies of a chromosome or part of a chromosome are inherited from one parent: for example, paternal uniparental disomy 14 (patUPD14) ( Fig. 73.34 ). Imprinting refers to the situation where a gene's expression depends on the parent of origin: hence, patUPD15 leads to Angelman syndrome, while maternal UPD15 causes Prader–Willi syndrome.

Fig. 73.34, Paternal UPD14.

Osteochondrodysplasias

The clinical and radiographic features of selected osteochondrodysplasias and dysostoses are described in Table 73.1 .

Chromosomal Disorders

Trisomy 21 (Down Syndrome)

Craniofacial abnormalities include brachycephaly, microcephaly, hypertelorism and relatively small facial bones. The iliac wings are flared with relatively sloping acetabula. Frequently there are 11 pairs of ribs and the ribs themselves are gracile. There are often two ossification centres in the manubrium sterni. Atlantoaxial subluxation and instability with hypoplasia of the odontoid process are a frequent cause of myelopathy. There is generalised joint laxity. The vertebral bodies are relatively tall. The hands are short, with fifth finger clinodactyly due to a hypoplastic middle phalanx. Congenital heart lesions include endocardial cushion defects and intra- and extracardiac shunts. Duodenal atresia, duodenal stenosis, Hirschsprung disease and anorectal anomalies are associated.

45XO (Turner Syndrome)

Short stature and lymphoedema may be clinically obvious. Important radiological findings include short fourth metacarpals, a reduced angle between the distal radial and ulnar metaphyses similar to that seen in dyschondrosteosis (Madelung deformity; Figs 73.35 and 73.36 ), flattening of the medial tibial condyle with a transitory exostosis, osteoporosis, scoliosis, coarctation of the aorta, and increased occurrence of urinary tract anomalies, such as horseshoe kidneys.

Fig. 73.35, Dyschondrosteosis (Léri–Weill syndrome).

Fig. 73.36, Compare the Madelung deformity (long ulna) in dyschondrosteosis with the reverse Madelung deformity (short ulna) in a patient with multiple enchondromatosis.

Localised Disorders of the Skeleton

Developmental Dysplasia of the Hip

This may occur as an isolated disorder (increased female incidence, breech presentation, first-born children, oligohydramnios, and when there is a positive family history) or in association with other conditions (e.g. sternomastoid tumour, torticollis, talipes calcaneovalgus, arthrogryposis multiplex and trisomy 21). The incidence in the UK approaches 1 in 400 live births, while in the USA it is 3 to 4 in 1000.

Although guidelines may vary slightly, both in the USA and the UK, US screening is performed on all newborn infants with a positive Ortolani and/or Barlow test, breech presentation or positive family history, Screening programmes for at-risk infants have led to earlier detection and treatment, and cases such as those with bilateral dislocation and formation of pseudoacetabulae are now less common. US is usually performed when the infant is about 6 weeks old. A high-frequency linear probe is used to obtain a coronal view of the hip joint, with the infant lying in a lateral position, with the hip being examined flexed and abducted. Measurements and their interpretation are summarised in Figs 73.37 and 73.38 and in Table 73.6 . The age of the infant is important when interpreting the measurements, with the difference between Graf IIa (‘immature’) and IIb hips explained by patient age being under or over 3 months. Dynamic images can also be obtained, showing the position of the femoral head under gentle stress. The various imaging appearances of developmental dysplasia of the hip (DDH) are illustrated in Fig. 73.38 .

Fig. 73.37, Developmental Dysplasia of the Hip.

Fig. 73.38, (A) Dysplastic right acetabulum with dislocated femoral head. (B) Post open reduction and internal fixation of the left femur, with the patient imaged in a spica cast. (C) Postoperative maximum intensity projection Computed tomography images confirm satisfactory reduction of the femoral head.

TABLE 73.6
Graf Angles
Type α Angle (°) β Angle (°) Bony Roof Ossific Rim Cartilage Roof Interpretation
Ia >60 <55 Good Sharp Covers femoral head Mature
Ib >60 >55 Good Usually blunt Covers head Mature
IIa 50–59 >55 Deficient Rounded Covers head <3 months of age (physiological ossification delay)
IIb 50–59 >55 Deficient Rounded Covers head >3 months of age
IIc 43–49 <77 Deficient Rounded/flat Covers head
IId 43–49 >77 Severely deficient Rounded/flat Compressed On point of dislocation
IIIa <43 >77 Poor Flat Displaced up
Echo poor
Dislocated
IIIb <43 >77 Poor Flat Displaced up
Reflective
Dislocated
IV <43 >77 Poor Flat Interposed Dislocated

For milder degrees of hip dysplasia, physiotherapy and/or a Pavlik harness often suffice. When ossification of the proximal femoral epiphysis renders US examination difficult (normally around 9 to 12 months of age), then radiographs are useful for follow-up and monitoring the response to treatment. Radiographs may also be required for preoperative planning in cases of more severe dysplasia. CT and MRI can be useful for assessing the position of the femoral head following operative reduction if there are ongoing clinical concerns (see Fig. 73.38 ). When it occurs, osteonecrosis secondary to surgical treatment for DDH is a relatively benign complication, not significantly affecting general physical function or quality of life.

Idiopathic Avascular Necrosis of the Femoral Head (Perthes Disease)

Osteonecrosis of the femoral head usually presents with pain or limp between 5 and 8 years of age. It is most often unilateral, but when bilateral (approximately 15%) is asymmetrical, helping to distinguish it from epiphyseal dysplasias such as Morquio disease, multiple epiphyseal dysplasia, or a late presentation of hypothyroidism. There are four stages of disease: devascularisation; collapse and fragmentation; re-ossification; and finally remodelling.

The earliest radiographic feature is that of a radiolucent subchondral fissure—the crescent sign ( Fig. 73.39 ). Disease progresses with loss of height, fragmentation and sclerosis of the femoral head (see Fig. 73.39 ). A coxa magna deformity may ensue, with lateral uncovering of the capital femoral epiphysis. There may be associated irregularity of the acetabular margin. The extent of subchondral fracture is said to be a good predictor of the final outcome. Several radiological classification systems, such as the Herring lateral pillar and (modified) Catterall systems, have been developed and shown to be reliable when used by an experienced observer.

Fig. 73.39, Idiopathic Avascular Necrosis of the Femoral Head (Perthes Disease).

While skeletal scintigraphy is highly sensitive and specific for detecting avascular necrosis (AVN), MRI has now largely replaced it. In those with normal signal intensity in the epiphysis, or with marked loss of signal on both T 1 and T 2 weighted sequences (dead bone), intravenous enhancement is not necessary. In those with more equivocal findings, intravenous contrast medium may assist in identifying areas of viable bone. Treatment options in the acute phase are largely supportive, aiming to reduce impact on the fragile femoral head. If there is significant deformity later, corrective osteotomy/leg lengthening may be considered.

Slipped Capital Femoral Epiphysis

This is the commonest hip disorder of adolescence. Anterolateral and rotational forces of the hip muscles on the femoral shaft result in anterosuperior translation of the proximal femoral metaphysis relative to the epiphysis: that is, technically it is the metaphysis rather than the epiphysis that slips ( Fig. 73.40 ). It is more common in boys, in Afro-Americans and in the obese. It most commonly occurs at the time of the pubertal growth spurt at Risser grade 0 (see Fig. 73.49 below). Slipped capital femoral epiphysis (SCFE) is extremely rare before the onset of puberty (adrenarche) and is uncommon in girls after menarche or in boys after Tanner stage 4. Bilateral slips occur in about 25% of Caucasian and up to 50% of Afro-American children. When unilateral, the left side is more often involved (65%). Endocrine disorders associated with SCFE include hypothyroidism, growth hormone deficiency, hypogonadism and panhypopituitarism.

Fig. 73.40, Slipped Capital Femoral Epiphysis.

Radiography remains the investigation of choice. The frog leg lateral is more sensitive for detection of a slipped epiphysis, and in many centres is the radiograph of choice in patients of this age presenting with hip pain. Not performing a frog leg lateral makes SCFE easier to miss, and delayed presentation/diagnosis of slips have worse outcomes. Unstable slips—where the child is unable to weight-bear on the hip—also have a higher rate of complications.

A Klein line is drawn on the AP projection while the slip angle is measured on frog lateral radiographs ( Fig. 73.41 ). Once detected, most SCFEs are fixed in situ. Complications of SCFE include chondrolysis (narrowing of the joint space), AVN and osteoarthritis.

Fig. 73.41, Slipped Capital Femoral Epiphysis Measurements.

Femoral Dysplasia (Idiopathic Coxa Vara/Proximal Focal Femoral Deficiency Spectrum)

The spectrum of femoral dysplasia encompasses all conditions from the mild idiopathic coxa vara, through moderate forms with deficiency of the proximal femur ( Fig. 73.42 ), to severe forms in which only the distal femoral condyles develop.

Fig. 73.42, Proximal Focal Femoral Deficiency.

Idiopathic Coxa Vara

In this condition, there is coxa vara (reduction of femoral neck/shaft angle). A separate fragment of bone (Fairbank triangle)—from the inferior portion of the femoral neck—is characteristic. If the neck/shaft angle is less than 100 degrees, then without surgical intervention the varus deformity will progress.

Proximal Focal Femoral Deficiency

Proximal focal femoral deficiency (PFFD) is bilateral in only 10% of cases. Varying degrees of agenesis of the proximal femur occur (see Fig. 73.42 ); there is an association between severity of femoral dysplasia and severity of acetabular dysplasia. Based on the presence or absence of the femoral head, connection between the proximal femur and femoral head, and the morphology of the acetabulum and shortened femur, Aitken classified PFFD into four groups of increasing severity from A to D. In addition to the femoral shortening, the lower leg also may be short, and the fibula absent or hypoplastic.

Radiography demonstrates the degree of aplasia and, particularly in younger children, MRI and/or arthrography is useful for the visualisation of unossified cartilage. Because PFFD is associated with absence or deficiency of the cruciate ligaments, MRI also has a role in imaging the knee(s) of affected patients.

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