Paediatric musculoskeletal radiology

Skeletal trauma

 

Although children may have the same types of fractures as adults, they also have a number of injuries which are unique to them. The cause of those differences is the presence in children of the cartilaginous growth plate (physis) that is the weakest part of the bone. Also, the bones in children are somewhat softer and more elastic than those of adults and

Figure 10. Classicification of growth plate injuries. Types 1-5 are those of Salter and Harris, white types 6 and 7 have been added by Ogden. produce types of diaphyseal fractures which do not occur in adults. A major difference in fractures in children, as opposed to adults, is the occurrence of growth disturbances, particularly following some physeal fractures.

Physeal and epiphyseal injuries

Because the ligaments in children are relatively strong around the joints, as compared to the strength of the cartilaginous growth plate, many injuries, which in an adult would cause ligamentous injuries, will cause a fracture through the growth plate. The physis is involved in 6-18 % of limb fractures in children. Eighty percent of physeal fractures occur between 10 and 16 years of age. Many, but not all, physeal fractures go through the hypertrophic zone of the physis. The cartilage in this zone consists of large cells and contains relatively less matrix than resting cartilage and is, therefore, weaker. In some cases physeal fractures extend into the other parts of the growth plate or into the metaphysis on a microscopic level. Physeal fractures may extend grossly into the metaphysis or epiphysis.

Except in the hip, the blood supply of the metaphysis and epiphysis is separate so that fractures through the growth plate usually do not

Figure 11. Salter 1 fracture of the proximal humeral epiphysis. Note the angulation of the right epiphysis as compared to the normal left.

interfere with the vascular supply to the epiphysis or the metaphysis. Healing is usually good in these fractures. However, in some cases growth disturbances do occur. Salter and Harris devised a classification of growth plate injuries based on their location. This system has been expanded by Ogden who added several categories and subdivided the original group (Fig. 10).

Type 1 fractures
Type 1 fractures pass only through the growth plate (Fig. 11). They account for approximately 5 % of growth plate fractures. Often, these fractures may involve a very small part of the metaphysis that is not visible radiographically. Diagnosis may be difficult if no displacement is seen. There is usually a somewhat greater separation at the fractured growth plate than on the opposite side or there is angulation at the growth plate. In the neonate, these fractures are very difficult to diagnose, particularly if the epiphysis is not yet ossified. They may only be manifest after a few days when periosteal elevation becomes evident (Fig. 12). The prognosis on these types of fractures is very good.

Type 1 fractures may occur in children with neurological impairment such as in myelodysplasia. These children may still walk on these fractures and this results in considerable widening and irregularity at the fracture site. This appearance can sometimes be confused with osteomyelitis (Fig. 13). A similar appearance can occur in the upper extremity - particularly in the distal radius in young adults who keep on doing their sport

	Figure 12. Salter 1 fracture of the left femoral neck in 4-day-old infant. Initially this was confused with a dislocation of the hip. The callous formation about the femoral shaft was evidence of fracture which was confirmed with ultrasound and showed the femoral head to be well seated in the acetabulum. Poznanski AK: in Resnick D, Pettersson H (ed.) Skeletal Radiology: NICER Series on Diagnostic Imaging. Coconut Creek, Florida: Merit Communications, 1992, p. 270.
	Figure 13.Nonimmobilized fracture of a distal tibial growth plate in a child with myelodysplasia who can walk. There is widening and irregularity of the growth plate which is due to inability to heal because of motion. This is a characteristic appearance of a fracture that has not been immobilized in a child who has no sensation in the extremity. Clinically, these types of injuries must be separated from osteomyelitis as they present with swelling and redness of the extremity. The appearance, however, is very characteristic of a nonhealing Salter fracture and should be treated as such. An additional due is the tilting of the talus which causes increased stress on the growth plate. Poznanski AK: in Resnick D, Pettersson H (ed.) Skeletal Radiology: NICER Series on Diagnostic Imaging. Coconut Creek, Florida. Merit Communications, 1992, p. 264.
	Figure 14. Salter 2 fracture of the distal femur. The fracture goes through the lateral part of the growth plate and extends into the metaphysis.

after a growth plate injury. Also distraction injuries in young gymnasts may cause similar lesions.

Type 2 fractures
These fractures go through the growth plate and then extend into the metaphysis (Fig. 14). The metaphyseal fragment may be small or quite large. This is by far the most common type of fracture accounting for 75 % of all growth plate injuries. The distal radial epiphysis is one of the more common sites of this fracture. The prognosis of this fracture is generally good particularly in the radius. However, when it occurs in the knee or elsewhere in the lower extremity premature growth plate closure may occasionally occur.

Type 3 fracture
This fracture is relatively uncommon, accounting for 8 % of growth plate injuries. Type 3 fractures go through the epiphysis into the physis but do not involve the metaphysis. Some of these fractures are undisplaced and may be difficult to see on radiographs. They may be missed unless

	Figure 15.Salter 4 fracture of the proximal phalanx of the great toe. The fracture goes across the growth plate and involves the metaphysis and the epiphysis.
	Figure 16.Deformity of the ankle secondary to growth disturbance following previous Salter 4 fracture of the distal tibia.

multiple projections including oblique views are obtained. If displacement occurs it must be carefully reduced since lack of reduction will cause an irregularity along the articular surface and may result in arthritis. With good alignment, prognosis is otherwise good as growth arrest is relatively rare. Ogden has subclassified this type into two parts. One in which the physeal component of the fracture extends only to involve one segment of the broken epiphysis. In the other type it extends all the way through the physis resulting in two separate epiphyseal fragments.

Type 4 fracture
In type 4 the fractures extend from the metaphysis into the epiphysis while traversing the physis (Fig. 15). This type most commonly occurs in the elbow and in the distal tibia. The incidence of these fractures

Figure 17.Follow-up of Salter 5 fracture of the left knee. Initially no abnormality was seen. With time, there was closure of the growth plate of the distal femur with shortening of the femur and a cone-shaped deformity of the epiphysis.

account for 12 % of growth plate injuries. Type 4 fractures are the ones most commonly associated with growth arrest and angular deformity (Fig. 16). It is, therefore, very important in these fractures to obtain proper alignment and fixation, as this will minimize the incidence of growth arrest and deformity. Ogden has subclassified type 4 into several subgroups.

Type 5 fracture
This is the rarest of the Salter Harris fractures, accounting for less than l % of growth plate injuries. These fractures are compressions of the growth plate and may involve either the whole growth plate or one side of it. They are very difficult to diagnose at the time of the initial injury. They may only be noted on follow-up. There may be a closure of the growth plate resulting in shortening, cone-shaped deformity or considerable angular deformity (Fig. 17).

Type 6 fracture
This is a type described by Ogden and is an injury to the peripheral zone of Ranvier at the edge of the physis (Fig. 10). This fracture eventually may form an osseous bridge at the edge of the physis causing angular deformity in that area.

Type 7 fracture
This is really not a growth plate fracture as it involves only the epiphysis. The fracture goes through the cartilage of the epiphysis or through

a	Figure 18. Bowing fracture in a 5-year-old boy. a) Note the bowing of the radius and ulna. b) Follow-up study 4 weeks later: There is periosteal elevation on the radius confirming the bowing fracture. Poznanski AK: in Resnick D, Pettersson H (eds) Skeletal Radiology: NICER Series on Diagnostic Imaging. Coconut Creek, Florida: Merit Communications, 1992, p. 252.
b

the epiphyseal ossification centre (Fig. 10).

Triplane fracture
In the ankle an additional growth plate fracture may be seen. It is the triplane fracture in which there is a combination of several of the types. It is seen only in the ankle and only as the growth plate starts to dose.

Imaging of growth plate injuries
Most growth plate injuries can be seen well with conventional radiographs. However, multiple views are often necessary for better evaluation. In some cases, particularly when the ends of the bones are mainly composed of cartilage such as in the elbow, magnetic resonance imaging is of considerable value. Computed tomography or MR are also important in evaluating type 3 and 4 fractures to determine whether the alignment is proper.

Figure 19. Greenstick fracture of the ulna. There is a break in one cortex while the other cortex shows no break. There is also some bowing of the radius which was more bowed than the opposite side. It is not unusual to have a bowing fracture of one of the forearm bones with a greenstick fracture of the other. Poznanski AK: in Resnick D, Pettersson H (eds): Skeletal Radiology: NICER Series on Diagnostic Imaging. Coconut Creek, Florida: Merit Communications, 1992, p. 254.

Diaphyseal fractures

Fractures of the diaphysis are relatively common in children. Toddlers are prone to have oblique fractures, particularly at the tibia, when they are just beginning to walk. These may not be identified on conventional radiographic views, although the chance of detection is increased if oblique views are obtained. If there is question of such fracture, follow-up films after casting will show presence of periosteal elevation. If diagnosis needs to be made immediately a bone scan is of value.

Bowing fractures of the diaphysis
These occur from multiple microfractures along a bone leading to a bowed appearance without evidence of an actual fracture (Fig. 18). This fracture is due to the fact that the children's bones are more elastic than the adult and will bend a small amount. It is most common in the forearm. Comparison with the opposite extremity may be needed to determine if the bowing is abnormal or a normal variant. A bone scan may be

a

Figure 20.Torus fracture in 3-year-old child. a) There is a buckle along the ulnar side of the distal radius. b) Follow-up view 6 weeks after in jury. There is a linear area of density across the radius which is evidence that the fracture was across the entire bone. Some periosteal changes are also seen. Poznanski AK: in Resnick D, Pettersson H (eds): Skeletal Radiology: NICER Series on Diagnostic Imaging. Coconut Creek, Florida: Merit Communications, 1992, p. 253.

b

used for diagnosis or follow-up radiograph several weeks later will show periosteal elevation confirming the fracture.

Torus and greenstick fractures
Another manifestation of the relative greater elasticity of children's bones is the greenstick fracture. Here there is a fracture of only one cortex and bending or a buckling of the cortex on the opposite side of the bone (Fig. 19). A torus fracture (buckle fracture) is simply a buckling of the cortex (Fig. 20 a). Torus fractures may be subtle and the fracture may not be initially apparent. On follow-up, a linear area of sclerosis is seen since these buckle fractures actually go across the entire bone (Fig. 20 b).

Healing of diaphyseal fractures
Children's fractures generally heal better and faster than those of adults. How rapidly the fracture heals is dependent upon the age of a child and the bone involved. In the infant and newborn some callous may be seen

Figure 21. Abundant callous following a fracture in an infant with myelomeningocele. Note the marked callous formation about the fracture. These fractures heal very well. Poznanski AK: in Resnick D, Pettersson H (eds): Skeletal Radiology on Diagnostic Imaging. Coconut Creek, Florida: Merit Communications, 1992, p. 263.

in a matter of days while in a teenager it may take several weeks. Callous is particularly prominent in children with neurological deficits, such as myelodysplastics (Fig. 21). In infants and young children remodelling is excellent and even if the bones are left in an angular position or overriding position, they often remodel to normal within a relatively short time. Non-union is relatively rare in children's fractures. Overgrowth of fractured bones can occur in children when there is complete apposition and alignment due to hyperemia. This is particularly true in the femur. Because of this the femora are often cast with some overriding of the fracture fragments.

Avulsion fractures

These fractures are really a form of growth plate fractures and represent an avulsion of an apophysis (Fig. 22). The most common location for these is the pelvis. In the pelvis the most common location is at the ischial attachment of the hamstring muscles. Initially, what is seen is an area of irregularity (Fig. 22 a). On follow-up there may be extra calcification that may have the appearance of an extra bone (Fig. 22 b).

a

Figure 22. a) Irregularity of the right ischium due to an avulsion fracture in young soccer player. b) Old avulsion fracture of the ischium. A large ossification area is separated from the main portion of the ischium. This girl had a previous history of pain in this region after sports in jury. Poznanski AK: in Resnick D, Pettersson H (eds): Skeletal Radiology: NICER Series on Diagnostic Imaging. Coconut Creek, Florida: Merit Communications, 1992, p. 257.

b

Stress fractures

These occur in children as in adults. A location of stress fractures seen mainly in children is in the tarsal bones, particularly the cuboid and the calcaneus. These are seen in toddlers who may stop walking or who may present with a limp. Initially, notching may be seen radiographically and only later there may be evidence of a sclerotic line in the bone. The bone scan shows an area of increased activity.

Pathological fractures
Pathological fractures can occur in children as in adults. In children they may be associated with severe osteopenia in chronic conditions such as in Crohn's disease or juvenile rheumatoid arthritis. They may be seen in the neonate who has been very sick in intensive care. Osteogenesis imperfecta is associated with fracture both in the neonatal form and later in milder forms. It is sometimes difficult to separate osteogenesis imperfecta in the toddler from the battered child syndrome. In arthrogryposis and other contracture syndromes unsuspected fractures may be seen possibly related to attempts to straighten the limbs. Growth plate fractures

Figure 23.Frostbite. This child has severe frostbite deformity on the right and milder involvement on the left. There is closure of several growth plates in the phalanges and metacarpals in both hands. There is loss of the middle and distal phalanges of the right index finger secondary to necrosis. The latter finding is more the type of frostbite damage that can occur in adults. Closure of the growth plates with shortening of the hand bones is a finding specific to children. The short distal and middle phalanges bilaterally and the short right metacarpals are due to damage of their growth plates. The thumbs are relatively less affected than the other fingers. Poznanski AK: in Resnick D, Pettersson H (eds): Skeletal Radiology: NICER Series on Diagnostic Imaging. Coconut Creek, Florida: Merit Communications, 1992, p. 265.

may occur in neurogenic disorders. Another situation where growth plate fractures can occur is in renal osteodystrophy.

Physical agents causing trauma

Cold injury, burns and electrical injury all can cause closure of growth plates with resultant alterations in the length and angulation of the hand bones (Fig. 23). In frostbite the thumbs are often spared as they have a better vascular supply than do the other fingers. The thumbs are also more protected as they are often clasped within the hand when the child is exposed to cold.

Child abuse

Abused children can have a variety of different fractures. The characteristic fracture is the corner fracture where all that may be seen is a break of a small corner of metaphysis (Fig. 24). Actually, these fractures go through the entire distal portion of the metaphysis. They are often very difficult to identify initially (Fig. 24 a), but subsequently periosteal changes may occur which make their diagnosis easier (Fig. 24 b). The bone scan is also positive in these fractures. These corner fractures are

a

b

Figure 24. a) Child abuse with corner fracture in 4-month-old who presented with swelling of the leg. There is a very small ossification fragment along the anterior part of the distal tibial metaphysis which is barely apparent. The bone scan taken at the same time showed considerable increased activity in the entire tibia and child abuse was suspected. This was confirmed with clinical history and further radiographs. b) Subsequent film 12 days later. There is considerable healing at the fracture site with periosteal changes. The fracture now has become very obvious. Poznanski AK: in Resnick D, Pettersson H (eds): Skeletal Radiology: NICER Series on Diagnostic Imaging. Coconut Creek, Florida: Merit Communications, 1992, p 272.

not the only fractures that are seen in child abuse. Any diaphyseal or physeal fracture may occur in this population. Child abuse should be suspected if there is a presence of multiple metaphyseal fractures, posterior rib fractures or fractures showing different degrees of healing suggesting that they occurred at different times. Suspicion is also aroused if a child has skull fractures and bilateral fractures or a severe epiphyseal injury which does not fit with the type of trauma that has occurred. Generally, in the presence of suspected child abuse one should obtain a complete skeletal survey. The bone scintigram should also be obtained as it is much more sensitive than radiographs for the detection of posterior rib fractures which are so characteristic of child abuse. Although radiological evidence is very important in the diagnosis of child abuse it

a,b

Figure 25. Developmental dysplasia of the hip in the neonate. a) Plain radiographs. The acetabulae are not particularly steep. There is a somewhat poor development of their upper lip. b) Hilgenreiner line is drawn through the Y cartilage on the radiograph in A. The acetabular angles also drawn measure 30° bilaterally which is within normal limits for a neonate. c) MRI (with gradient echo sequence) in coronal plane. Note the lateral and somewhat superior displacement of the femoral heads. The cartilage appears light grey in this sequence. There is some fluid in the hip joint (appears white). The ossified bones appear black. MRI is not usually used in the diagnosis of DDH but it nicely illustrates the pathology.

c

is not the only information needed. Social history is also very important. Other possible causes of multiple fractures such as osteogenesis imperfecta must be considered. Radiologically one of the more helpful signs which defines osteogenesis imperfecta is the presence of multiple wormian bones in the skull. However, even that is not an absolute separation as some cases of osteogenesis imperfecta are not associated with wormian bones and in some normal children wormian bones can occur.

 

Andrew K. Poznanski