Introduction

Sickle cell disease (SCD) is a hereditary red cell disorder with clinical manifestations secondary to sickling and consequent vaso-occlusion. SCD encompasses a group of disorders that occur because of a point mutation in the beta globin gene, resulting in the production of abnormal haemoglobin. Under conditions of hypoxia and dehydration, the abnormal haemoglobin tetramer can polymerise, causing alteration in red cell rheology, activation of local vasoactivity and inflammation leading to vaso-occlusion and haemolysis [1,2,3].

SCD affects approximately 1 in 2,000 live births, and up to 1 in 300 births in some urban areas in the United Kingdom [4]. Previously considered a disease of childhood, now, 99% children born in London are expected to live into adulthood [5]. Musculoskeletal complications of SCD are a significant cause of morbidity in children.

Musculoskeletal complications are a result of abnormal sickling of the red blood cells leading to vaso-occlusion and subsequent ischaemia and infarction. Furthermore, the high red cell turnover in SCD results in conditions promoting the increased production of red blood cells [2]. Haematopoietic marrow hyperplasia and extramedullary haematopoiesis can result in bone expansion and pathologic fractures, augmented by osteoporosis. Dactylitis (Fig. 1), avascular necrosis (AVN), bone infarcts, the premature closure of epiphyseal plates and the halting of long bone growth are sequalae of vaso-occlusion and subsequent ischaemia [2]. There is decreased blood flow through small vessels supplying bones due to vaso-occulsion. This forms zones of ischaemia in which pathogens can invade and replicate, causing infectious sequalae such as septic arthritis and osteomyelitis [1].

Fig. 1
figure 1

Dorsopalmar radiograph of the right fourth and fifth fingers shows dactylitis in a 1-year-old boy with sickle cell disease who presented with painful swelling. There is periostitis along the fourth metacarpal shaft (arrows) and coarse trabecula of the proximal phalanges (broken arrows)

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Bone and epiphyseal infarctions

Microcapillary obstruction due to abnormally shaped red cells interacting with activated white cells, platelets and endothelium leads to bony infarction in SCD [6]. If this happens in the diaphyses, medullary infarcts occur and if this process takes place in the epiphyses, AVN is seen. The anterior superior portion of the proximal epiphysis of the femur is most severely involved, where maximal weight-bearing forces occur [7]. In SCD, the entire epiphysis of the long bone is involved compared to other conditions in which only the weight-bearing region is affected. Initially, epiphyseal infarcts affect the subchondral region which has minimal collateral circulation. In early disease, the overlying articular cartilage often remains viable due to nutrition from adjacent synovial fluid. As the disease progresses within the subchondral bone, microfractures occur with progressive collapse of necrotic cancellous bone and eventually joint destruction ensues [8].

AVN is uncommon in the first decade of life. Estimates suggest that the prevalence of AVN of the femoral head is up to 12% in patients with SCD under 21 years of age [9, 10]. If left untreated, AVN of the femoral head leads to collapse of the femoral head in 87% of patients within 5 years of diagnosis [11]. Bilateral disease is common and may occur in up to 91% of patients [12].

In SCD, medullary bone infarcts occur with greater frequency than in osteomyelitis, although trying to distinguish both conditions from one another is difficult on imaging [13]. Radiographs are usually normal in the acute stages of medullary infarction; patchy lucency and periosteal reaction develop as the infarction becomes more established (Figs. 2 and 3). As the medullary infarct becomes chronic, sclerosis is seen with a serpiginous border. In epiphyseal infarction, initially the radiographs are normal, but in later stages flattening, subchondral collapse and sclerosis are seen.

Fig. 2
figure 2

Acute bone infarcts in a 15-year-old boy who was admitted with painful sickle cell disease crisis of the chest and left leg. a Coronal short tau inversion recovery magnetic resonance image (MRI) of the left tibia shows a heterogeneous hyperintense area in the tibial diaphysis (arrow) with associated periosteal and soft tissue oedema (broken arrows). b Sagittal T1-weighted MRI of the same area shows heterogeneous high signal intensity of the mid/distal tibial diaphysis (arrow) and background change of marrow reconversion (asterisk)

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Fig. 3
figure 3

Acute infarcts with extraosseous soft tissue abnormality in an 11-year-old boy with sickle cell disease and painful swelling of the left elbow. a Coronal T1-WI magnetic resonance image (MRI) of the left elbow show heterogeneous low bone marrow signal throughout the distal humerus and imaged radius and ulna. Note the areas of low signal intensity in the medial epicondyle (broken arrow) indicating infarct. b Coronal short tau inversion recovery MRI shows heterogeneous high signal intensity of the distal humerus with considerable high signal intensity of the oedematus soft tissues surrounding the elbow (arrows). c Coronal fat-suppressed T1-weighted MRI after intravenous injection of contrast material shows serpiginous areas of enhancement in the distal humerus (broken arrows) consistent with acute bone infarcts and surrounding soft tissue enhancement (arrows)

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Infarction of the small bones of the hands and feet results in a painful dactylitis (Fig. 1) accompanied by leucocytosis and fever, termed “hand-foot” syndrome. Because red marrow does not persist in the hands and feet of older children, this condition is not usually seen in patients beyond 5 years of age. Infarction of epiphyses is very rarely associated with premature fusion and shortened fingers [14]. On radiographs, soft tissue swelling, periosteal new bone formation and a mixed pattern of sclerosis and lucency can be seen. Initial radiographs may be normal although these changes can be present within 10 days from the onset of symptoms. Symptoms can be similar to osteomyelitis or cellulitis, but the symptoms of dactylitis spontaneously resolve within a month [15].

Magnetic resonance imaging (MRI) is of value to define the presence and extent of disease. T1-weighted images show low signal and T2-weighted images demonstrate high signal in the infarcted region, indicative of oedema [1] (Fig. 4).

Fig. 4
figure 4

Acute pelvic infarcts in a 14-year-old girl with sickle cell disease who presented with bilateral hip pain. a, b Coronal (a) and axial (b) short tau inversion recovery magnetic resonance images (MRI) of the pelvis at the level of the left ischium show heterogeneous bone marrow oedema involving the right iliac bone, left proximal femoral diaphysis and left ischium (arrows) with adjacent soft tissue oedema (broken arrow) consistent with acute infarcts. c Coronal fat-suppressed T1-weighted MRI after intravenous injection of contrast shows heterogeneous enhancement of the left ischium with non-enhancing areas of bone infarct in the left (broken arrow) ischium and right iliac bone (arrow)

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The use of intravenous contrast may better depict soft tissue changes and peripheral enhancement in the infarction. The classical appearance of a serpiginous double line sign can be seen. This is best depicted on the T2-weighted sequence and represents the junction between the viable and non-viable bone. The inner bright line represents granulation tissue, while the outer serpiginous low signal intensity line corresponds to the adjacent sclerotic bone. As the infarct becomes chronic, reduced signal is demonstrated on both T1- and T2-weighted sequences representing fibrosis and sclerosis (Fig. 5). The prognostic value of MRI is dependent on the size and location of the lesion. Small lesions tend not to collapse, while larger lesions with articular surface involvement are more likely to collapse; Shimizu et al. demonstrated a 74% rate of femoral head collapse; the AVN affected greater than two-thirds of the weight-bearing area [16]. Secondary osteoarthritis can occur with joint space narrowing, subchondral sclerosis and osteophytic change.

Fig. 5
figure 5

Avascular necrosis in a 14-year-old girl with sickle cell disease. a Anteroposterior pelvic radiograph shows sclerosis, flattening and fragmentation of the right femoral epiphysis. Note the diffuse osteopenia of the right femoral head-neck and widening of the right femoral head (broken arrow) compared with the normal contralateral side. Note also the “H”-shaped fifth lumbar vertebra (arrow). b, c Correlation with coronal T1-weighted (b) and short tau inversion recovery (c) MRI show established avascular necrosis, joint effusion and cartilage loss in the weight-bearing portion of the joint

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Treatment of AVN in children is difficult. If asymptomatic AVN of the femoral head is not treated, up to 95% of cases develop progressive collapse, which has been demonstrated in up to 87% within five years of diagnosis [17].

Non-surgical management of AVN of the femoral head should be the initial approach and consists of pain management, activity modification and ambulatory assistive devices [18]. In addition to conventional radiographic imaging, MRI may be used to assess the severity of femoral head involvement. Non-operative treatments may provide benefit in early stages of disease prior to femoral head articular surface collapse. The use of total hip arthroplasty has increased in popularity for treatment of advanced disease. The primary indication is persistent, intractable hip pain despite optimisation of non-operative management, in a medically fit patient [19].

Osteomyelitis

Osteomyelitis is a potentially serious complication, which occurs in SCD with a rate of up to 13% [20]. This is related to tissue infarction and splenic dysfunction. Splenic dysfunction, including shunting, impaired filtration, deformation and stagnation of red blood cells, begins in infancy. Chronic vaso-occlusion and resultant ischemia lead to functional asplenia and the resultant susceptibility to serious bacterial infection is present early in childhood [21].

Osteomyelitis can affect any bone and can be seen in multiple bones simultaneously. In SCD, osteomyelitis characteristically affects the diaphyses of the long bones with the humeri, tibiae and femora being the most common sites [21] (Fig. 6). In contrast, osteomyelitis is typically seen in a metaphyseal distribution in the general paediatric population. Haematogenous infection is the usual route of transmission and Salmonella sp. is the most common causative organism. Burnett et al. demonstrated a ratio of Salmonella to Staphylococcus aureus aof 2.2:1 as the infective organism [22]. Different strains of Salmonella have been implicated including Salmonella enteritidis, Salmonella typhimurium, Salmonella paratyphi B, Salmonella choleraesuis and Salmonella aureus. Ischaemia and sickling in the mesenteric vessels can lead to infarction and subsequent enteric bacteremia related to gram-negative micro-organisms (Enterobacter, Haemophilus influenza and Escherichia coli). Clinical symptoms include pain, swelling and fever. Clinically, there is increased likelihood of osteomyelitis if the child has swelling affecting a single site, with prolonged pain or fever. C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are often elevated [23] and can be correlated with the white blood cell count trend from the time of presentation rather than just considering the absolute white blood cell count. Positive blood cultures can assist in making the diagnosis of osteoarticular infections, with up to 58% of patients reported to be positive [24]. A positive joint or bone sample or positive blood culture would aid the diagnosis; however, a negative blood culture does not exclude osteomyelitis.

Fig. 6
figure 6

Magnetic resonance imaging in a 12-year-old boy presenting with pain and swelling of the right leg and raised inflammatory markers. a Coronal T1-weighted image shows diffuse low marrow signal of the right femur sparing the distal epiphysis, with a subperiosteal collection along the lateral margin of the femur (arrow). b Coronal inversion recovery image shows heterogeneous medullary marrow oedema and high signal of the subperiosteal collection (arrow). c Axial inversion recovery image confirms the subperiosteal collection (arrow)

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Osteomyelitis is often initially investigated with radiographic imaging, though the sensitivity and specificity are low and initial radiographic imaging may be normal in the first 10–14 days of acute osteomyelitis. Gas in the soft tissues, bone lucency, bone destruction and sclerosis can be present in osteomyelitis, but similar changes can be seen in bone infarction [25] (Fig. 7). Ultrasound (US) may be of value in assessing for subperiosteal collections, periosteal elevation and increased vascularity surrounding the periosteum and in the soft tissues. A subperiosteal fluid collection with a thickness of equal to or greater than 4 mm has been reported as a strong predictor of osteomyelitis [3]. If the periosteum is strongly attached, the fluid may be extraperiosteal. US is useful to assess for oedema of the soft tissues, soft tissue abscesses and extension into the adjacent joint. US has a sensitivity of 74% and specificity of 63% in diagnosing osteomyelitis in patients with SCD [26].

Fig. 7
figure 7

Bone infarcts in a 13-year-old boy with sickle cell disease. Coronal T1-weighted (a) and proton density (PD) fast spin (FS) (b) magnetic resonance images show diffuse reduction in bone marrow signal intensity of the humerus with sparing of the epiphysis consistent with red marrow reconversion. Note the slight T1-hyperintense area in the humeral neck with correspondent high PD FS signal (arrows) consistent with an old metaphyseal infarct. No bone marrow oedema. Note the small right glenohumeral joint effusion (broken arrow in a)

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Radio-labelled leucocyte scans, which include technetium-99m (Tc-99m)-sulphur colloid, 99mTc-diphosphonate and 99mTc with gallium, can be used, but these are also often inconclusive in distinguishing between bone infarction and osteomyelitis, particularly in the acute stages and may require sequential imaging [27] (Fig. 8).

Fig. 8
figure 8

Skeletal technetium 99m skeletal scintigraphy in a 16-year-old girl with sickle cell disease and bilateral osteomyelitis. Anterior (a) and posterior (b) blood pool images show increased tracer distribution in both arms; on the left it appears to extend for the whole length down to the elbow, while on the right there is sparing of the distal third. Appearances are consistent with bilateral humeral osteomyelitis, more extensive on the left

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On MRI, osteomyelitis demonstrates reduced bone marrow signal on T1-weighted sequences and corresponding increased signal on T2-weighted sequences [28]. Contrast-enhanced MRI can demonstrate enhancement of the periosteum and parosteal structures. Rim enhancement has been described in infarcts whereas a more irregular pattern of enhancement has been described in osteomyelitis. Contrast enhancement can be useful to monitor progression of the infection and to assess response to treatment on follow-up imaging. It is important to acknowledge that infarction is much more frequent than bacterial osteomyelitis in SCD [27]. In our experience, no single imaging modality can easily differentiate the two entities. Persistent leucocytosis, fever, significant periosteal elevation, irregular periosteal enhancement, presence of sequestrum and involucrum are indicative of osteomyelitis. In equivocal cases, follow-up imaging can be useful to aid differentiation and the initial imaging acts as a baseline, as typical MRI findings may not be observed in the early phase of the disease.

Chronic osteomyelitis is defined as infection that lasts more than 6 months, and results in necrotic bone (sequestrum), surrounded by pus and a reactive bone sclerosis, called the involucrum [29]. The cortex demonstrates thickening and high signal intensity on MRI. Chronic osteomyelitis can be associated with a sinus tract and cloaca (linear defect in the bone that penetrates the cortex overlying an area of osteomyelitis) which allow for spontaneous drainage of purulent material from the bone to the skin. MRI findings include a linear structure which may contain fluid, granulation tissue or necrotic debris extending from bone or soft tissues to the skin surface, with T1 hypointense signal, hyperintense signal on fluid-sensitive images and post-contrast images demonstrate a “tram-track” pattern of peripheral enhancement [30]. Chronic osteomyelitis with chronic suppuration may develop fistulation and bony sequestrum. This can cause disruption of the growth plate and subsequent growth disturbances [30].

Differentiating bony infarction from osteomyelitis

Differentiating between vaso-occlusive crisis and early osteomyelitis is a diagnostic challenge. Discerning between bony infarction and osteomyelitis on MRI is extremely difficult, due to severe bony infarction having the usual appearances of acute osteomyelitis, namely soft tissue changes, periosteal reaction and patterns of enhancement, and should be interpreted alongside the clinical and biochemical findings [31,32,33]. The cost of MRI, and challenges associated with the use of sedation or general anaesthetic, should also be weighed against the potential diagnostic yield [31].

Important sequences for evaluation include multiplanar T1 and T2-weighted fast-spin echo (FSE) or turbo spin echo (TSE) sequences and short-tau inversion recovery (STIR) or T2-weighted FSE/TSE sequences with fat-suppression (T2-FS). STIR and T2-FS sequences ease the depiction of bone marrow oedema and fluid collections [34].

A further consideration in SCD is epiphyseal growth plate involvement by osteomyelitis which may sometimes only be depicted on gadolinium enhanced T1 sequences and not seen on standard sequences (non-contrast T1, T2, STIR) or other imaging modalities (e.g. radiography, bone scintigraphy). Reduced or complete lack of epiphyseal cartilage enhancement is seen which is indicative of epiphyseal infection [35].

Septic arthritis

Children with SCD are susceptible to joint infection due to sluggish circulation, hyposplenism and reduced bacterial opsonisation. Salmonella sp., Klebsiella pneumoniae, Staphylococcus sp. and Pneumococcus sp. have been implicated as causative organisms. Patients present with bone pain, fever and often have raised ESR and CRP. There is a predilection for large joints with the lower extremities more commonly affected; 40% occur in the hip joint, 25% in the knee joint compared to 20% in the elbow joint and 10% in the shoulder joint [36].

Septic arthritis may occur on a background of other conditions such as osteonecrosis. Early diagnosis, drainage of the joint collection, and the appropriate antibiotic therapy are essential for good functional outcome. Arthrotomy is only used if the joint fluid is too thick to be removed using standard drainage techniques. If left untreated, destruction of the joint ensues. Joint aspiration and fluid culture are often required to determine the causative organism and to adjust the antibiotic regimen. When osteomyelitis develops adjacent to the joint, the infection can spread and involve the joint. This is seen particularly in infection of the proximal femoral metaphysis, which is intra-capsular, with subsequent high risk of destruction of growth structures, femoral head and articular surfaces [36]. In small children, this can have serious implications with development of osteoarthritis of the hip. Once the diagnosis is clinically suspected, US can be used to confirm the presence of effusion and guide percutaneous fluid aspiration for culture. Patients who fail to respond to initial treatment (joint aspiration and antibiotic therapy) may benefit from MRI to assess extent of infection and plan surgical intervention [37].

MRI clearly depicts joint effusions on T2-weighted sequences. Normally the synovium is barely visible; however, this becomes thickened in septic arthritis [32] (Fig. 9). The synovium of a normal joint demonstrates minimal contrast enhancement; however, a hypervascular, inflamed synovium enhances abnormally following contrast administration [32]. Perisynovial oedema related to inflammation of the local vessels is indicative of a septic joint (Fig. 10).

Fig. 9
figure 9

Septic arthritis in a 15-year-old girl with sickle cell disease who presented with painful swelling of the elbow and fever. a, b Sagittal (a) and axial (b) T2-weighted fat-suppressed magnetic resonance images (MRI) show a large elbow joint effusion distending the anterior and posterior articular recess with synovial thickening (arrows), reactive marrow oedema in the distal humerus and marked oedema of the soft tissues (broken arrow) consistant with septic arthritis. c Sagittal fat-suppressed T1-weighted MRI after intravenous injection of contrast material shows synovial enhancement (broken arrow) and enhancement of the surrounding soft tissues

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Fig. 10
figure 10

Serial anteroposterior pelvic radiographs in an adolescent boy with sickle cell disease who presented with bilateral septic hip joints. a Initial radiograph demonstrates subchondral sclerosis and lucencies in the right femoral head and acetabulum (arrows). b Radiograph 3 months after initial presentation, note the remodelling of the right femoral head. There is new sclerosis of the left femoral head with a subchondral lucent line (arrow). c Two years follow-up radiograph shows collapse and fragmentation of the left femoral head with subchondral sclerosis and secondary osteoarthritis of the left hip joint. The right hip shows early subchondral sclerosis and irregularity. d A radiograph 3.25 years from baseline shows an area of avascular necrosis in the right femoral head with cortical collapse (arrow)

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Fig. 11
figure 11

Inflammatory arthritis in a 14-year-old boy with sickle cell disease who presented with pain and swelling of the left shoulder and raised inflammatory markers. Axial (a) and coronal (b) fat-suppressed T1-weighted magnetic resonance images after intravenous injection of contrast show a large glenohumeral joint effusion with synovial enhancement indicating synovitis (arrows). Diffuse oedema is also visible within the humeral epiphysis, proximal diaphysis and surrounding soft tissues

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Arthritis

Both inflammatory and non-inflammatory arthropathies are described in association with SCD, with bone infarcts, hyperuricemia and osteoarticular infections being potential contributory factors [37]. It is not clear whether this is a response in the synovium to the adjacent bone destruction or if this is secondary to AVN of the synovium. Imaging features of arthropathy include periarticular osteopenia, joint destruction and bone erosions, which can be detected on imaging [36] (Fig 11).

Limb length discrepancy

Leg length discrepancy is the arithmetic difference between corresponding leg lengths and is classified as mild (<2 cm), moderate (2–5 cm), or severe (>5 cm). Complications of SCD associated with disproportionate leg growth include AVN, septic arthritis, osteomyelitis, bone infarcts and atypical skeletal development. Local ischaemic events secondary to compromised blood supply result in infarction of long bone articular surfaces. Repeated infection involving the growth plate and bone marrow hyperplasia ensue and limb length discrepancy results [38]. True leg length discrepancy due to leg shortening is common in homozygous SCD [38]. Figure 12 shows physeal growth arrest due to disturbance or complete cessation of normal growth of skeletally immature bone at the physeal growth plate.

Fig. 12
figure 12

Avascular necrosis in a 16-year-old boy with sickle cell disease. a Anteroposterior pelvic radiograph shows expansion of the left femoral head and neck, dysplasia of the acetabulum, relative uncovering of the femoral head and coxa magna. Note the irregular areas of sclerosis in the femoral head and neck (arrow). b Coronal computed tomography image (bone windows) shows a central sclerotic physeal bar (arrow). Note the prominent supraacetabular fossa (broken arrow). Normal right hip. This patient went on to have a total hip replacement 3 years later

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Red marrow hyperplasia

Red marrow is haematopoietically active and responsible for the creation of cellular contents of blood, whereas yellow marrow is composed of 80% fat [14]. With ageing, conversion of red to yellow marrow occurs symmetrically beginning peripherally. In long bones, conversion begins in the epiphyses followed by the mid diaphyses and then the metaphyses. At maturity, a small amount of red marrow is typically seen in the proximal metaphysis of the long bones [32,33,34].

In red marrow hyperplasia, red marrow cells replace the yellow marrow in a reconversion process due to the elevated haematopoietic demand in SCD. It begins in the proximal metaphysis, followed by the distal metaphysis and then the diaphysis (Fig. 13). The bones of the hands and feet are last to undergo reconversion [39]. Epiphyses may undergo reconversion, but only in extreme cases of demand. Haemolysis leads to chronic medullary hyperplasia, which results in expansion of the marrow spaces, enlargement of the haversian canals and leads to cortical thinning and irregular, diffuse trabeculation. This may affect bone growth in the appendicular skeleton and delayed bone age is seen [39].

Fig. 13
figure 13

Red marrow reconversion in an 11-year-old girl with sickle cell disease. Long field of view coronal T1-weighted magnetic resonance image shows diffuse reduced bone marrow signal of both femurs and visualised pelvis in keeping with red marrow reconversion.

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Muscle and soft tissue manifestations

Vaso-occlusive episodes involving the muscles, fascia and soft tissues can result in complications such as muscle necrosis, fasciitis, soft tissue haematomas (Figs. 14 and 15) and added superinfection.

Fig. 14
figure 14

Subperiosteal haematoma in an 8-year-old girl with sickle cell disease who presented with a right scalp mass. Longitudinal ultrasound image shows a focal crescentic hypoechoic mass (asterisk) in the right parietal region, which crossed sutures and measured 20 mm (length) × 6 mm (depth). No internal vascularity or solid component. Findings were consistent with subperiosteal haematoma

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Fig. 15
figure 15

Subperiosteal haematoma in a 16-year-old boy with sickle cell disease who presented with anterior lower leg swelling and pain. No raised inflammatory markers. a Lateral radiograph of the right tibia shows focal soft tissue swelling anterior to the mid tibial shaft (arrow). b Long axis ultrasound of the anterior mid-shaft of the tibia shows an elongated, predominantly hypoechoic collection at the site of the palpable swelling (arrows). The tibial cortex is intact and no vascularity was noted within the mass

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Literature related to skeletal muscle involvement in SCD is relatively sparse, maybe because sickle myonecrosis episodes are relatively rare or might be overlooked because the symptoms may be attributed to skeletal pathology [40]. Frequently, soft tissue involvement coexists with bone marrow abnormalities [15]. Vaso-occlusive crisis involving the skeletal muscle may lead to myositis (Fig. 16), muscle infarction and myonecrosis. Painful vaso-occlusion and muscle infarction can cause long-term debilitating sequelae for these patients, with potential muscle atrophy, myofibrosis and contractures [41].

Fig. 16
figure 16

A 15-year-old boy with sickle cell disease presented with swelling of his left shoulder blade suspicious of collection or haematoma. Ultrasound images of the left (a) and right (b) scapular areas at the same level show oedema of the deep subcutaneous tissues and musculature posterior to the blade of the left scapula, with asymmetry in the thickness of the infraspinatus muscle compared with the asymptomatic right contralateral side (b), suggestive of myositis SC scapula

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Muscle involvement usually presents with symmetrical proximal muscle swelling, most often of shoulders and thighs (although it can involve any muscle), severe pain (which is disproportionate to the patient's usual crisis pain), warmth and decreased range of motion [41]. The same muscle groups may be repeatedly and symmetrically affected, with episodic muscle and fascial necrosis after periods of spontaneous improvement. Compartment syndrome has been described as a complication of myonecrosis [42]. Another complication is the liquefaction of muscle, which can lead to the development of sterile abscess formation. Levels of laboratory markers of myonecrosis such as creatinine phosphokinase and lactate dehydrogenase might be elevated, although they have been reported as normal in some cases, making the interpretation of laboratory results challenging [41].

On MRI, muscle oedema might be focal or diffuse and appear as abnormal increased signal intensity on inversion recovery and fat-supressed T2-weighted images. Myonecrosis can simulate an abscess clinically and radiologically. MRI demonstrates marked muscle oedema, alteration in muscle size and shape, and gadolinium enhancement around irregular mass-like regions of muscle necrosis [43]. US is particularly valuable in assessing muscle oedema (Fig. 16, Fig 17) and myonecrosis in the paediatric population. On US, muscle fibres become relatively hyperechoic. The fibroadipose septae are distended with inflammatory exudate and appear relatively hypoechoic. The affected muscle increases in diameter and with time, if myonecrosis develops, leads to central necrosis and formation of a hypoechoic fluid collection, which has the potential to become infected and pyomyositis [44] (Fig. 18).

Fig. 17
figure 17

An 8-year-old girl with sickle cell disease presented with swelling of the left thigh. Ultrasound images of the right (a) and left (b) thighs at the same level show asymmetric thickening of the left vastus intermedius compared with the asymptomatic right contralateral side suggestive of myositis

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Fig. 18
figure 18

Myonecrosis in a 10-year-old boy with acute sickle cell disease crisis with severe left arm pain, swelling and loss of mobility. a, b Sagittal (a) and axial (b) inversion recovery magnetic resonance (MRI) images show extensive oedema and swelling of the brachialis muscle (asterisks) and anterior joint effusion (arrow). c Fat-suppressed axial T1-weighted MRI after intravenous injection of contrast shows an intramuscular collection (arrow) within the brachialis muscle. There was no bone involvement

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Leg ulcers usually occur over bony prominences as a consequence of venous stasis, which may result in venous thrombosis and hypoxia [15]. On radiographs, they may show associated periosteal reaction [45]. They can be difficult to treat due to the vascular compromise and added infection from commensal organisms commonly present in the skin [46] (Fig. 19, 20).

Fig. 19
figure 19

A 14-year-old boy with sickle cell disease presented with right leg swelling and pain thought to be related to a pain crisis. Arterial phase axial computed tomography scan shows enlargement of the right thigh compared with the asymptomatic left side, with muscle enlargement, subcutaneous oedema and fat stranding

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Fig. 20
figure 20

Cellulitis in a 13-year-old girl who presented with left ankle pain and swelling. Magnetic resonance imaging was requested to exclude bone infarcts. Sagittal (a) and coronal (b) short tau inversion recovery magnetic resonance images of the ankle show extensive subcutaneous oedema. No muscle or bone involvement is demonstrated

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Conclusion

The musculoskeletal manifestation of SCD is wide and varied and often poses diagnostic and therapeutic challenges. A multidisciplinary approach to the treatment of these conditions is important, with collaboration from radiologists, surgeons, physicians, therapists, microbiologists, among others. Musculoskeletal complications are common causes of morbidity and mortality in SCD. Being familiar with the pathophysiology, clinical presentation and imaging manifestations of SCD is helpful for accurate diagnosis and prompt treatment.