Paediatric musculoskeletal radiology

Other musculoskeletal disorders

 

Hip effusion

It is important to detect hip effusions in children as increased intracapsular pressure can affect the vascular supply to the fem oral head as it is intracapsular. Permanent damage to the femoral head can occur very quickly. Plain radiographs are not very useful to detect effusion unless there is displacement of the fem oral head. The best diagnostic radiologic method is ultrasound (Fig. 52). If this is not available, radiographs obtained during traction of the hip are of value. If there is a vacuum

	Figure 53. Normal vacuum phenomenon with traction. A 1.5-year-old toddler with a limp. The radiograph was obtained white the leg was pulled. The presence of vacuum almost completely rules out a joint effusion.
a	Figure 54. Child with a limp. a) Before traction. b) After traction. The joint space is several millimetres wider than before which is in dicative of effusion. Hip aspiration confirmed the effusion.
b
a	Figure 55. Legg-Calve-Perthes disease in the left hip and normal variant of ossification in the right. a) The left femoral epiphysis appears normal while the right is fragmented. b) Bone scan. The left fem oral head appears cold which is diagnostic of  LCP while the right is normal. Subsequently the left femoral head became fragmented and had an appearance similar to that seen in Figure 56 a.
b

phenomenon (Fig. 53) it is very unlikely that fluid is present. If there is separation and no vacuum (Fig. 54) this is diagnostic of fluid. If there is no separation the finding is not diagnostic and traction can be repeated. The failure of traction to be diagnostic is due to lack of relaxation and occurs in about 25 % of cases.

Legg-Calve-Perthes disease (LCP)

This is an idiopathic avascular necrosis of the hip which occurs in young children. It presents with pain in the hip or with a limp. The initial radiographic findings may be very subtle or absent (Fig. 55 a). The earliest radiologic sign may be an abnormal bone scan with lack of localization of isotope in the entire femoral head (Fig. 55 b). This is a different pattern than seen in other aseptic necroses where there may be increased

a

Figure 56.Legg-Calvé-Perthes disease (LCP). a) Radiograph in frog leg position. There is marked fragmentation of the left femoral head and apparent increased width of the joint space. b) MRI with gradient echo sequence. The cartilage of the left femoral head is flattened and thickened as compared to the right. There is fragmentation and flattening of the ossified portion (black). There is some fluid within the hip joint (brighter white) and there is separation of the left femoral head away from the acetabulum.

b

activity in the femoral head. Pin hole imaging should be used so as to obtain the necessary resolution. MRI can also detect LCP before radiographs are abnormal. Loss of the normal fatty signal within the bone marrow on T1 weighted images is an early MRI sign of LCP. Bone scintigraphy is probably more sensitive than MRI for early detection since the femoral head appears totally cold on the bone scintigram while the MRI changes may be spotty. Usually, when the child first presents, radiographic changes are already present. The first radiographic sign is separation of the femoral head ossification centre from the tear-drop edge of the acetabulum. This is due to swelling of the cartilage and/or synovitis. Eventually there is a subcortical fracture, fragmentation, sclerosis, and flattening of the femoral head (Fig. 56 a). These are relatively

a

Figure 57. Multiple epiphyseal dysplasia (MED) in a 10-year-old girl. a) There is fragmentation of both femoral heads. This may be difficult separate from LCP disease. When bilateral fragmentation is seen in the hips, radiographs of the knees and hands should be obtained to differentiate LCP from MED. b) Knee of the same girl. The epiphyses of the tibia and femur are fiat and irregular which confirmed the diagnoses of MED. In the lateral view there was evidence of a double ossification centre of the patella. There was irregularity of the carpals on the hand radiograph that was also obtained.

b

late manifestations of the disease although they are often the radiologic findings at the time of onset of symptoms. The course of the disease lasts over several years. There may be eventual reformation of the femoral head or there may be residual deformity. During the time of the disease the femoral head is very soft and is prone to indentations. Therapies include splinting, varus osteotomy of the femur or pelvic osteotomy; all of which help to place the femoral head inside the acetabulum. MRI may be useful to determine containment of the hip since this is an important feature in decisions regarding the management approach as it permits visualization of the cartilaginous portion of the femoral head (Fig. 56 b). Another approach to determine femoral head coverage is to use arthrography. This has the advantage that the hip can be manipulated and the coverage of the femoral head can be determined in various projections.

Legg-Calve-Perthes may be a bilateral condition. Whenever bilateral changes are seen the possibility of multiple epiphyseal dysplasia (MED) should be considered as it can mimic LCP disease (Fig 57). Radiographs of the hands and AP and lateral radiographs of the knees are of value to determine whether there is any flattening of the epiphyses (Fig. 57 b) or if the carpus has decreased in size. These are all signs of MED. A double ossification centre of the patella with one centre in front of the other in the lateral view is a useful sign of MED. In MED the prognosis is worse than in LCP as these patients often develop severe hip and knee arthritis as young adults.

Another condition in which an aseptic necrosis similar to LCP may be seen is the trichorhinophalangeal syndrome. This is an autosomal dominant disorder which is associated with slowly growing hair and premature baldness in boys as well as a bulbous, pear-shaped nose and deformities of the fingers. Gaucher's disease (Fig. 50) and sickle cell disease may also result in aseptic necrosis. Steroids can cause aseptic necrosis of the hip but the appearance is usually different and the course quite different than in LCP. In steroid necrosis fluid in the hip joint is seen as an initial sign. In contrast to LCP there is increased activity of the femoral head on the bone scintigram.

Slipped capital femoral epiphyses (SCFE)

This is a relatively common cause of limp in teenagers particularly in those who are overweight. It is basically a slow fracture through the growth plate of the proximal femur with remodelling as the slip progresses. The plain radiographs are usually diagnostic, particularly on the frog leg views (Fig. 58 b) since the slip is usually from front to back. On the AP view the findings are more subtle (Fig. 58 a). A line drawn along the superior margin of the femoral neck normally should intersect the femoral head. In SCFE it usually does not. Additional signs on the AP view are relative widening and poor definition of the growth plate (Fig. 58 a) and deformity or bending of the femoral neck. SCFE can be caused by too much force on the growth plate such as may occur with increased weight of the child or from the forces of active sports. Alternatively the

a

Figure 58. Slipped capital femoral epiphysis (SCFE) a) In the neutral position the slip is not seen. There is, however, a wider growth plate in the left hip than on the right which is suggestive of SCFE. The findings in SCFE can be very subtle in the neutral position view. The diagnosis can be missed unless a frog-leg view is obtained. b) Frog-leg view. The slipped capital epiphysis on the left is clearly seen. The reason it is best seen in this view is that the slip is mainly from front to back, rather than side to side.

b

growth plate may be too weak for the normal forces placed upon it, such as in children who have rickets, renal osteodystrophy (Fig. 59), hypothyroidism, or following previous radiation therapy to the hip region. One of the serious complications of treatment of SCFE is chondrolysis which is an arthritis with narrowing and irregularity of the hip joint (Fig.60). Aseptic necrosis of the femoral head may also occur, although, if no attempt is made to reduce the slip the incidence of aseptic necrosis is very low.

	Figure 59. Slipped capital femoral epiphyses in 15-year-old boy with renal osteodystrophy. The growth plates are wide and the metaphyseal margins are irregular. There are also fuzzy margins of the ischia which is evidence of hyperparathyroidism.
	Figure 60. Chondrolysis of the right hip following pinning of bilateral SCFE. The right hip joint is narrow and irregular.

Osteochondritis Dissecans

In this disorder small fragments of bone separate from the articular surface. It is seen in many joints but particularly in the distal femoral epiphysis, the dome of the talus and the proximal fem oral epiphysis. Osteochondritis dissecans may be acquired from trauma, steroids, or other conditions and there is also a congenital familial form. Although osteochondritis dissecans is readily diagnosable in adults it is difficult to diagnose in the knees of children because of the common normal variant of irregular ossification of the distal femoral epiphysis (Fig. 61). These epiphyseal irregularities and abnormal centres are commonly seen in a large percentage of normal children, more commonly in young children. They usually do not represent a loose fragment in a very young child but represents uneven ossification of the epiphysis. Magnetic resonance imaging can be of value to prove that these are well within the

Figure 61. 10-year-old boy with pain in the knees. An apparent fragment is seen in the lateral condyle. There was a question whether this represented a normal variant or osteochondritis dissecans. On the plain films alone it is very difficult to make this distinction in children, because normal ossification variants can mimic the disease. MRl, however, confirmed that in this case the defect was simply a normal variant.

cartilage of the epiphysis.

Joint disease

Juvenile rheumatoid arthritis (JRA) is the most common joint disease in children. The term juvenile chronic arthritis has been used in countries other than the USA for the same condition. Radiological signs are usually secondary in very young children since the bone ends are covered by a thick layer of cartilage and erosion of cartilage may not be detected until maturity. One of the roles of radiology is to determine whether the clinical signs are due to JRA or due to some mimic of joint disease. Radiologic studies are also of value to determine the activity of the disease and to determine whether it is improving or getting worse. Radiologic evaluation is often more objective than the clinical exam and is a good way to monitor the efficacy of therapy. JRA can occur in very young children one or two year of age who are often not very good historians and cannot localize pain well.

Inflammatory changes in JRA can be detected by the presence of growth disturbances secondary to the associated hyperemia. These may

	Figure 62. Juvenile Rheumatoid Arthritis in a 15year-old girl with long standing disease. Note the markedly broadened distal ends of the proximal phalanges. This is evidence of hyperemia and is often the only sign of JRA in the hand. In this particular child, however, joint changes are also evident at the metacarpal phalangeal joints. There are also irregularities of the carpals indicating joint involvement.
	Figure 63. Juvenile rheumatoid arthritis in a 2.5year-old girl. Note the extensive periosteal changes particularly in the fourth metacarpal and in all the proximal phalanges. The periosteal changes in the proximal phalanges may result in broadening of these bones. The carpals and metacarpal carpal joints appear irregular.

be the only radiographic signs present. A common location of hyperemic change is the distal portion of proximal phalanges, which often have a bulbous configuration (Fig. 62). The condyles of the femur or patella or any other bone end may also be enlarged. Initially the bones may be too long from the hyperemia. Eventually they may become too small as premature closure of the growth plates stops further growth. Periosteal elevation may occur in young children (Fig. 63). The best method for evaluating synovitis is with MRI and enhancement following intravenous injection of gadolinium compounds. In this way one can separate fluid from synovitis. This is otherwise very difficult to do radiographically. With MRI, meniscal deformity and hypoplasia, which are common in JRA, may be detected. Bone scintigraphy has a smaller role in joint disease as correlation with disease is not very good. Loss of cartilage is best evaluated by MRI. Loss of cartilage can be implied in the hand by showing a decrease in the space between the growth plate of the distal radius and the third metacarpal (Fig 1 a). A measurement of this space can then be compared to the length of the second metacarpal or the width of the base of the metacarpals and give a measure of carpal loss. Bone erosion occurs later and is seen particularly in older children. Various joint dislocations may occur. Ulnar dislocation of the wrist is common particularly when associated with short ulna. The cervical spine is occasionally involved in JRA with subluxation at Ct-C2. Eventual fusion of the posterior elements of cervical vertebrae may occur. Temporomandibular joints can also be involved in JRA with associated hypoplasia of the mandible and deformity of the mandibular condyle. MRI with gadolinium can show active synovitis and meniscal damage in the temporomandibular joints.

In evaluating children with joint symptoms it is very important to rule out the many mimics of joint disease. Eight to ten percent of children presenting with joint symptoms have leukemia rather than arthritis. The presence of lucent metaphyseal bands (Fig. 9) is a useful sign of leukemia. Destructive changes also may be seen. Carpal-tarsal osteolysis can in its early stages mimic JRA both clinically and radiographically. It is a hereditary condition which is usually inherited as autosomal dominant. Initially carpal and tarsal bones are destroyed with soft tissue swelling. Eventually the destruction becomes much more severe and even the base of the metacarpals may be destroyed. Often it is only when the destruction becomes great that one can separate it from JRA. The name

Figure 64. Dermatomyositis with extensive calcification in a 12.5-year-old girl. Fortunately, with modern therapy we now rarely see the disease in this form.

carpaltarsal osteolysis is somewhat of a misnomer since elbows and other joints may also be affected.

There are many other mimics of joint disease in children including various other collagen disorders, Gaucher disease, fibrodysplasia ossificans progressiva, osteomyelitis, neuroblastoma, trauma, etc. When unilateral joint disease is present particularly in the hip or knee the possibility of tuberculosis should always be considered.

Juvenile dermatomyositis (JDMS)

In long standing JDMS calcification can be seen in soft tissue (Fig, 64) and there may be considerable bony demineralization. In early disease radiographs are normal MRI has been very useful to localize active myositis in early or late disease as often the muscle involvement is patchy. It is best demonstrated on MRI using a T2 weighted fat suppressed sequence, The affected muscle has a very high signal Without MRI for localization normal muscle may be biopsied since involvement is often not universal MRI is also useful in following the results of therapy.

a

Figure 65.Fibrodysplasia ossificans progressiva. a) There is extensive calcification and ossification in the soft tissues around the shoulders and chest wall. b) Foot of the same girl as in A. The great toe is short with a valgus deformity. The first proximal phalanx is fused to the first metatarsal. The appearance of the foot is characteristic of this disorder and is evident long before the onset of calcification.

b

Fibrodysplasia ossificans progressiva

This is a syndrome in which ossification occurs in the tendons and fascia of muscles with eventual, total immobilization of the patient (Fig. 65 a). The condition usually starts in childhood around the shoulder girdle with swelling and pain. It does not show any initial radiographic findings in the affected area. Early changes can be detected with MRI. A radiographic finding that is present since birth, well before the outset of symptoms which is not related to the ossification, is a foot abnormality with a pathognomonic appearance. The great toe is very short with a valgus deformity and sometimes with absence of the proximal phalanx or fusion of it to the first metatarsal (Fig. 65 b). The foot abnormality precedes the ossifications in the soft tissues.

Figure 66. Fractures in infant with severe osteoporosis associated with prematurity and bronchopulmonary dysplasia. This infant was three months of age and developed fractures white in the hospital. There is callous and periosteal elevation about the fractures.

 

 

 

Andrew K. Poznanski