Paediatric, Hip Pain

PD

Imaging in Legg Calve Perthes' Disease (Perthes' Disease)

• Perthes' disease is a form of idiopathic osteonecrosis with peak incidence between 5 and 6 years and is approximately three times more common in boys than girls. Many patients with suspected Perthes' disease will therefore require general anaesthesia or sedation for MRI and this should be taken into account when deciding on imaging strategies 1
• Perthes' disease is a diagnosis of exclusion and other causes of avascular necrosis such as sickle cell disease, leukaemia, steroids and Gaucher‘s disease need to be excluded 2
• Early diagnosis is important for joint preservation 3
• AP pelvis and frog leg lateral radiographs are the initial investigation of choice with radiographs being the main imaging modality for both diagnosis and follow-up 4
• Both hips are involved in approximately 15% of patients and it is therefore important to include both hips on radiographs 1,5
• Changes of Perthes' disease can take 3-4 months to become apparent on radiographs 4
• The best investigation will depend on the age of the child. MRI is generally regarded as the investigation of choice but if the child is less than 6 and MRI will likely require GA, then bone scan may be more appropriate
• Using a combination of unenhanced and post gadolinium MRI sequences the diagnosis of Perthes' disease can be confidently made, even in the presence of normal or equivocal radiographs 2
• The normal critical upstroke of enhancement occurs in the first 2 minutes following contrast administration so rapid image acquisition is essential, as is coronal plane acquisition to allow easy comparison with the other hip. After the early vascular phase, the disparity between normal and abnormal is less apparent 6
• Dynamic gadolinium enhanced subtraction MR also allows assessment of revascularisation patterns 7
• MRI can distinguish Perthes' disease from other epiphyseal conditions such as Meyer dysplasia and can find other causes of hip pain such as apophyseal injury or fracture 2
• When the complication of progressive subluxation is suspected MRI can substitute for arthrography which usually requires general anaesthesia 4
• In the past, pin hole scintigraphy (bone scan) was considered the gold standard for assessing prognosis as it could assess the degree and type of revascularisation 8
• Diffusion weighted imaging MRI may be a way of distinguishing between Perthes' disease with favourable and unfavourable prognosis 9

SCFE

Imaging in Slipped Capital Femoral Epiphysis (SCFE)

• SCFE is a Salter Harris I fracture through the proximal femoral growth plate 10
• Can be mechanically stable, where a patient can still bear weight, or mechanically unstable which typically presents as an acute physeal fracture and inability to weight-bear 11
• Early symptoms can be subtle and ambiguous and the diagnosis is easily overlooked. Commonly, the early symptom is that of a dull ache that is exacerbated by exercise. The diagnosis may only become apparent when a stable slip progresses to an unstable one 11
• AP and frog leg or lateral radiographs are the first investigation of choice 12
• Approximately 13% of slipped capital femoral epiphyses may not be visible on AP radiographs 13
• A line drawn along the lateral aspect of the femoral neck should intersect 20% of the femoral epiphysis and, if not present, indicates medial displacement of the epiphysis 14
• Other findings on an AP radiograph include loss of epiphyseal height and variable physeal widening and irregularity 15
• There is a high rate of bilateral involvement, with over 20% at the time of diagnosis and over 50% overall in one study 16
• There is limited evidence for routine screening with MRI although cases of ‘pre-slip’ have been described that were only detectable with MRI
• The earliest imaging finding, evident only on MRI, is focal widening of the physis, with or without synovitis, but without slippage of the femoral head (pre-slip) 15,17
• The MRI diagnosis of an early slipped capital femoral epiphysis relies on recognition of a morphologic change at the head/neck junction and abnormal signal intensity centred at the physis, indicative of oedema 10
• Patients with SCFE are at risk of avascular necrosis, chondrolysis and premature osteoarthritis 12,18

Septic Arthritis / Osteomyelitis

Imaging in Septic Arthritis / Osteomyelitis

• Osteomyelitis and septic arthritis should be considered in the differential diagnosis of any child with limb pain, even if there is a history of trauma. It is most common in young infants, is usually monoarticular and is frequently localised to the hip or knee joints. It can be a difficult diagnosis to make and with potentially severe consequences and for these reasons referral to a paediatric tertiary centre is generally recommended 19,20
• Osteomyelitis can be present even in a well looking afebrile child 21
• Septic arthritis is a medical emergency and can result from a penetrating injury, haematogenous spread or spread from adjacent sites of infection. Haematogenous spread is more common in neonates and infants, when vessels cross the growth plate and can seed infection from the adjacent metaphysis 18
• In one study less than one third of patients with septic arthritis had any abnormality on radiographs with changes of osteomyelitis and septic arthritis sometimes taking up to 7-10 days to become apparent 20
• After radiographs, hip ultrasound is the next appropriate investigation for possible septic arthritis. It is quick, free of ionising radiation and can evaluate for a hip joint effusion or soft tissue collection. It is, however, not specific and generally cannot distinguish between a transient synovitis or septic arthritis. Other aetiologies such as Perthes disease can also result in a hip joint effusion. A negative hip ultrasound does not exclude the presence of septic arthritis 22
• With negative radiographs and ultrasound and continued suspicion of infection, bone scan and MRI are options. MRI has the advantage of no ionising radiation but, due to the fact many of these children are very young, often requires general anaesthesia or sedation. Bone scan involves ionising radiation but can often be performed without sedation. It is of limited value in distinguishing transient synovitis from septic arthritis 23
• Whilst MRI cannot reliably distinguish between septic arthritis and transient synovitis, the findings of signal abnormality in the bone marrow and signal alterations and enhancement of surrounding soft tissue suggest the diagnosis of septic arthritis 24

mri

Magnetic Resonance Imaging (MRI)

• The best investigation will depend on the age of the child. MRI is generally regarded as the investigation of choice but if the child is less than 6 and MRI will likely require GA, then bone scan may be more appropriate
• Using a combination of unenhanced and post gadolinium MRI sequences the diagnosis of Perthes' disease can be confidently made, even in the presence of normal or equivocal radiographs 2
• Dynamic gadolinium enhanced subtraction MR also allows assessment of revascularisation patterns 7
• MRI can distinguish Perthes' disease from other epiphyseal conditions such as Meyer's dysplasia and can find other causes of hip pain such as apophyseal injury or fracture 2
• When the complication of progressive subluxation is suspected MRI can substitute for arthrography which usually requires general anaesthesia 4
• Diffusion weighted imaging MRI may be a way of distinguishing between Perthes' disease with favourable and unfavourable prognosis 9
• There is limited evidence for routine screening with MRI although cases of ‘pre-slip’ have been described that were only detectable with MRI
• The earliest imaging finding, evident only on MRI, is focal widening of the physis, with or without synovitis, but without slippage of the femoral head (pre-slip) 15,17
• The MRI diagnosis of an early slipped capital femoral epiphysis relies on recognition of a morphologic change at the head/neck junction and abnormal signal intensity centred at the physis, indicative of oedema 10
• With negative radiographs and ultrasound and continued suspicion of infection, bone scan and MRI are options. MRI has the advantage of no ionising radiation but, due to the fact many of these children are very young, often requires general anaesthesia or sedation. Bone scan involves ionising radiation but can often be performed without sedation. It is of limited value in distinguishing transient synovitis from septic arthritis 23
• Whilst MRI cannot reliably distinguish between septic arthritis and transient synovitis, the findings of signal abnormality in the bone marrow and signal alterations and enhancement of surrounding soft tissue suggest the diagnosis of septic arthritis 24

us

Ultrasound

• After radiographs, hip ultrasound is the next appropriate investigation for possible septic arthritis. It is quick, free of ionising radiation and can evaluate for a hip joint effusion or soft tissue collection. It is, however, not specific and generally cannot distinguish between a transient synovitis or septic arthritis. Other aetiologies such as Perthes disease can also result in a hip joint effusion. A negative hip ultrasound does not exclude the presence of septic arthritis 22

radio

Plain Radiographs

• AP pelvis and frog leg lateral radiographs are the initial investigation of choice with radiographs being the main imaging modality for both diagnosis and follow-up 4
• Both hips are involved in approximately 15% of patients and it is therefore important to include both hips on radiographs 1,5
• Changes of Perthes' disease can take 3-4 months to become apparent on radiographs 4
• AP and frog leg or lateral radiographs are the first investigation of choice 12
• Approximately 13% of slipped capital femoral epiphyses may not be visible on AP radiographs 13

bone

Bone Scan

• In the past, pin hole scintigraphy (bone scan) was considered the gold standard for assessing prognosis as it could assess the degree and type of revascularisation 8
• With negative radiographs and ultrasound and continued suspicion of infection, bone scan and MRI are options. MRI has the advantage of no ionising radiation but, due to the fact many of these children are very young, often requires general anaesthesia or sedation. Bone scan involves ionising radiation but can often be performed without sedation. It is of limited value in distinguishing transient synovitis from septic arthritis 23

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