Experience in magnetic resonance (MR) imaging of the neonatal musculoskeletal system is rapidly increasing. The exquisite ability of MR to image the soft tissues, especially cartilage, without radiation is its key strength. Although it is not practical or sensible to undertake MR imaging in conditions in which radiography and ultrasound provide adequate information, MR is proving to be a useful adjunct and problem-solving tool in many neonatal musculoskeletal conditions.
Evaluation of the neonatal musculoskeletal system with magnetic resonance (MR) imaging is not commonly needed. Radiography and ultrasound remain the initial imaging modalities for most common and uncommon musculoskeletal conditions encountered in this age group. However, because of the exquisite tissue contrast provided by MR imaging, its use is expanding, especially for evaluation of complex malformations, infections, and tumors of the neonatal musculoskeletal system. The ability of MR to image the abundant cartilage present within the neonate makes MR imaging invaluable in the assessment of the neonatal musculoskeletal system.
MR imaging of the neonate poses several unique challenges that may arise either before or during scanning. Considerations include patient transport, the need for sedation and monitoring, as well as safe patient positioning. When imaging, careful consideration of coil selection, scan parameters, and sequences is vital. The interpretation of images may also be challenging because the appearance of the neonatal musculoskeletal system and type of underlying disorder often differ from those encountered in older children.
This article discusses some practical aspects of MR imaging of the neonatal musculoskeletal system. It reviews the normal neonatal appearance of the musculoskeletal system and focuses on some common and uncommon musculoskeletal disorders for which MR imaging has been shown to be of benefit in the neonate.
Examination technique
Patient Preparation
Close cooperation between the neonatal service and the radiology department is required for successful acquisition of a diagnostic neonatal MR study. We carry out MR examinations in the neonate as far as possible without the use of anesthesia, instead using a feed-wrap-and-snooze technique. This technique is described in a step-by-step approach by Mathur and colleagues.
There are several principles to optimize success in pediatric musculoskeletal imaging. When sedation or general anesthesia are needed, the MR compatibility of any necessary ventilatory or monitoring equipment must be considered. The number of intravenous solutions should be minimized as much as possible. The neonate is wrapped snugly and placed in a regular transfer incubator or, if available, a specialized neonatal MR-compatible incubator. The advantage of an MR-compatible incubator is that fewer patient transfers are required, which reduces the likelihood of disturbing the neonate or dislodging monitoring leads and intravenous lines. The use of a dedicated nurse, familiar with neonatal procedures and associated specialized equipment, helps to smoothly transfer from nursery to MR scanner and back again. Clear and up-to-date communication with the ward about the anticipated study start is important to enable suitable scheduling of feeds, generally 30 to 40 minutes before scan initiation.
Field of View and Coil Selection
It is important to find an appropriate balance between the desired anatomic coverage, required spatial and matrix resolution, and signal/noise ratio. These factors, along with coil sensitivity and magnetic field strength, help determine the field of view (FOV) and slice thickness to be used. The use of small FOVs with similar matrix sizes to those used in adult studies decreases the signal/noise ratio greatly and may create excessive noise and uninterpretable images. However, if the FOV is too large for a given matrix size, then the spatial resolution may not be adequate for evaluation of neonatal anatomy. Generally, selection of a pixel size of just less than 1 mm by 1 mm with slice thicknesses of 3 to 5 mm is adequate.
The volumes to be imaged in the neonate for detailed evaluation may be small, requiring dedicated imaging coils able to acquire the required small FOVs in adequate detail. At present, in our institution, we primarily use either the head coil, and place the entire baby within the coil for larger anatomic coverage or, for smaller regions, use surface coils.
Choice of Scan Sequences and Parameters
As for all pediatric MR imaging, the order of sequence selection is important. The sequences with the highest anticipated yield should be performed first, so that, if the neonate rouses, enough of the study will hopefully have been completed to give diagnostic information. In general, MR imaging studies of the neonatal musculoskeletal system include a variety of standard fast spin-echo and gradient sequences with or without fat suppression, such as T1-weighted (T1-W), T2-weighted (T2-W), spoiled gradient echo or fast low angle shot, and short tau inversion recovery (STIR). Both two-dimensional and three-dimensional sequences are being used.
T1-W images
T1-W images are helpful in the interpretation of bone marrow involvement in patients with yellow marrow, with abnormalities typically appearing as low signal on T1-W images. However, in the neonate, hematopoietic marrow predominates, which also appears low signal on T1-W images, obscuring recognition of focal or more diffuse marrow lesions. Use of in-phase and out-of-phase sequences may help.
Water-sensitive images
STIR and fat-suppressed TSE T2-W imaging are the most commonly used water-sensitive images. Fat-suppressed T2-W imaging is the preferred method when magnetic field inhomogeneity is not a concern because it is more efficient than STIR imaging. Fat-suppressed T2-W imaging is also the method used when contrast enhancement is present because STIR suppresses any signal that has a short T1, including gadolinium.
Proton density
Proton density imaging has a high signal/noise ratio that can provide excellent spatial resolution for evaluation of musculoskeletal structures. It is one of the most commonly used sequences in musculoskeletal imaging in older children and adults and also works well in neonates, particularly with fat suppression.
Gradient echo sequences
Gradient echo (GRE) images are particularly useful for imaging cartilage and for looking for magnetic susceptibility artifacts, as seen in hemorrhage. Hyaline epiphyseal and physeal cartilage is of high or intermediate signal, whereas hemorrhage shows as blooming. This sequence is particularly useful in distinguishing between cartilage and adjacent joint fluid. With increasing T2 weighting, signal contrast is increased between cartilage (lower signal) and fluid (higher signal). Three-dimensional gradient sequences are often used for dedicated joint imaging and multiplanar reconstruction.
Use of 3 Tesla MR imaging
The experience with 3 Tesla (3T) MR imaging of the neonate is still in its infancy. With 3T, there is increased signal available, which is used to decrease overall examination time and/or increase image resolution. In practice, for neonatal imaging, a combination of these benefits is usually used to both reduce overall scan time and improve spatial resolution. Early experience with pediatric 3T MR imaging has shown that it can provide good image quality even at small FOVs, showing cartilage, ligaments, and nerves in good detail. In addition, the ability to decrease examination time helps to decrease motion artifact and the need for sedation, which can reduce potential patient complications and aid work flow. However, changes in imaging parameters are required when moving from 1.5T to 3T. The T2 relaxation times at 3T are slightly reduced, whereas the T1 relaxation times are more prolonged, making it difficult to achieve the same contrast resolution. Artifacts related to movement, flow, susceptibility, and chemical shift can cause a problem at higher magnet field strength. Although certain devices and implants may not be safe at 3T, this is not a significant problem in this age group, given the rarity of implants in this patient population. The increased acoustic noise of the 3T scanner may also be problematic, especially for the sleeping neonate.
Use of Contrast
At present, contrast product guidelines warn that the safety and efficacy of gadolinium-based contrast agents have not been established in patients less than the 2 years of age. The pharmacokinetics of the neonatal population has not been well studied; however, it is known that the glomerular filtration rate of neonates and young infants is lower than that of adults, and that the pharmacokinetic volume of distribution is also different. It is also unclear whether 1 type of MR contrast agent is better than another in this patient population.
Despite this caveat, contrast is used because it can add useful information when performing MR imaging of the neonatal musculoskeletal system, similarly to studies in older children. We generally use a similar dosages to those for infants when contrast is needed.
Following contrast agent injection, there is prominent enhancement of the normal cartilaginous physis, the juxtaphyseal tissues, and the subperiosteal fibrovascular tissues. After 30 to 60 minutes, sufficient contrast extravasates into the joint space to act as an indirect arthrogram. In inflammatory conditions such as infection and arthritis, the epiphyseal vascular channels may become even more prominent. In the case of infection or concern for avascularity, contrast administration can be helpful in showing areas that may need drainage or debridement. Tumors and vascular malformations can become more conspicuous following contrast administration, and may be better characterized by their enhancement characteristics or show areas of internal necrosis.
Normal MR imaging appearance of the neonatal musculoskeletal system
Intramembranous ossification is responsible for the development of the facial bones and cranium, whereas the skull base, long and tubular bones, clavicles, and vertebral column develop by endochondral ossification from cartilaginous models. Thus, hyaline cartilage is more abundant within the neonate than in the older child, particularly within the epiphyses and growth plates.
Epiphyseal hyaline cartilage, also known as the chondroepiphysis, is the precursor to the ossified end of long bones. In the neonate, the epiphyses are predominantly all cartilaginous, converting to bone later with subsequent development and growth of the secondary ossification center. The chondroepiphyses are of homogeneous intermediate signal intensity (SI) on T1-W images and are low SI on water-sensitive images. The cartilaginous ends of bones are supplied by a unique vascular arrangement coursing through the cartilage embedded within tubular structures called epiphyseal vascular canals. These vascular canals contain arterioles, venules, capillaries, and loose connective tissues. Articular cartilage is also hyaline but it has a more organized structure than epiphyseal cartilage and appears as a thin, hyperintense rim surrounding the developing epiphysis on water-sensitive images.
In neonates and young children, the physis is flatter and less undulating than in older children. Two distinct regions of the physis are seen on MR imaging. The first is the cartilaginous zone, which is of intermediate to high SI on water-sensitive images. This zone is easy to separate from epiphyseal cartilage, which is of lower SI. On T1-W images, the physis is difficult to visualize separately from the adjacent unossified epiphysis. The second zone of the physis is that of provisional calcification. This zone is of low SI on all sequences because it contains a more mineralized matrix.
The epiphyseal vasculature courses through the cartilaginous ends of the long bones within the cartilage canals. The vasculature extends across the physis from the metaphysis into the epiphysis until approximately 12 to 18 months of age when the physis acts as a barrier between the epiphyseal vascularity and the metaphyseal vascularity. This anatomic fact is of clinical importance because of the rapid spread of infection within bone and cartilage within the neonate. The cartilage canals have a linear parallel appearance before development of the ossification centers and converge around the ossification center.
Fibrocartilage appears similar to that seen in older children and adults, with low signal on all standard sequences. Khanna and Thapa recently reviewed the MR appearances of developing cartilage.
Bone
Long bones
In the third-trimester fetus, and in the newborn, the diaphyseal cortex is thick, with only a small central medullary cavity that eventually enlarges to form the mature marrow cavity. During this time, the SI of cortical bone is low on all sequences. Bones typically appear low signal on T1-W images because of both the presence of hematopoietic marrow and increased trabeculation. The marrow space starts enlarging within the first week of life. It is initially entirely hematopoietic and vascular with low T1-W SI, and high SI on water-sensitive images. Marrow conversion to fatty marrow begins during the first year of life but is not well advanced in the neonatal period. On MR imaging, the characteristics of normal marrow depend on the relative amounts of the marrow constituents, including hematopoietic elements and marrow fat. Normal neonatal hematopoietic marrow is lower than or equal to muscle SI on T1-W imaging and of increased signal on T2-W imaging and following contrast enhancement.
The bony envelope
The periosteum is a thin, low-SI structure that parallels the bone cortex. It is loosely attached along the shaft of the bone, but tightly held at the level of the physis where it is termed the perichondrium. The perichondrium surrounds the physeal cartilage and allows for circumferential growth. It is most prominent in newborns.
There is a layer of fibrovascular tissue that separates the periosteum from the cortex. This layer is most easily seen at the metaphysis where it appears as a metaphyseal stripe on longitudinal images, and a cuff on transverse images. It has a high SI on water-sensitive images and enhances vividly after contrast administration. In areas of loose attachment of the periosteum, subperiosteal collections of blood, pus, or tumor can form.
Spine
The various structures of the spine also undergo marked changes during infancy. These structures have 3 distinct stages of evolution. The description in this article compares the T1-W SI of the bone and cartilage with that of skeletal muscle. Stage 1, from birth to approximately 1 month of age, shows prominent hyperintense cartilage at the superior and inferior margins of the vertebral body, and hypointense ossification centers. A central band of higher SI is occasionally seen corresponding with the radiolucent band seen on radiographs. At this stage, the vertebral body is ovoid in shape. Stage 2 is from approximately 1 to 6 months, and shows increasing SI in the ossification centers, from the endplates inwards, with decreasing prominence of the cartilage. Stage 3, from approximately 7 months, shows increasingly rectangular vertebral bodies that are centrally intense, with a further decrease in the amount of cartilage. The neonatal spinal marrow signal is lower than that of the adjacent disc.
Normal MR imaging appearance of the neonatal musculoskeletal system
Intramembranous ossification is responsible for the development of the facial bones and cranium, whereas the skull base, long and tubular bones, clavicles, and vertebral column develop by endochondral ossification from cartilaginous models. Thus, hyaline cartilage is more abundant within the neonate than in the older child, particularly within the epiphyses and growth plates.
Epiphyseal hyaline cartilage, also known as the chondroepiphysis, is the precursor to the ossified end of long bones. In the neonate, the epiphyses are predominantly all cartilaginous, converting to bone later with subsequent development and growth of the secondary ossification center. The chondroepiphyses are of homogeneous intermediate signal intensity (SI) on T1-W images and are low SI on water-sensitive images. The cartilaginous ends of bones are supplied by a unique vascular arrangement coursing through the cartilage embedded within tubular structures called epiphyseal vascular canals. These vascular canals contain arterioles, venules, capillaries, and loose connective tissues. Articular cartilage is also hyaline but it has a more organized structure than epiphyseal cartilage and appears as a thin, hyperintense rim surrounding the developing epiphysis on water-sensitive images.
In neonates and young children, the physis is flatter and less undulating than in older children. Two distinct regions of the physis are seen on MR imaging. The first is the cartilaginous zone, which is of intermediate to high SI on water-sensitive images. This zone is easy to separate from epiphyseal cartilage, which is of lower SI. On T1-W images, the physis is difficult to visualize separately from the adjacent unossified epiphysis. The second zone of the physis is that of provisional calcification. This zone is of low SI on all sequences because it contains a more mineralized matrix.
The epiphyseal vasculature courses through the cartilaginous ends of the long bones within the cartilage canals. The vasculature extends across the physis from the metaphysis into the epiphysis until approximately 12 to 18 months of age when the physis acts as a barrier between the epiphyseal vascularity and the metaphyseal vascularity. This anatomic fact is of clinical importance because of the rapid spread of infection within bone and cartilage within the neonate. The cartilage canals have a linear parallel appearance before development of the ossification centers and converge around the ossification center.
Fibrocartilage appears similar to that seen in older children and adults, with low signal on all standard sequences. Khanna and Thapa recently reviewed the MR appearances of developing cartilage.
Bone
Long bones
In the third-trimester fetus, and in the newborn, the diaphyseal cortex is thick, with only a small central medullary cavity that eventually enlarges to form the mature marrow cavity. During this time, the SI of cortical bone is low on all sequences. Bones typically appear low signal on T1-W images because of both the presence of hematopoietic marrow and increased trabeculation. The marrow space starts enlarging within the first week of life. It is initially entirely hematopoietic and vascular with low T1-W SI, and high SI on water-sensitive images. Marrow conversion to fatty marrow begins during the first year of life but is not well advanced in the neonatal period. On MR imaging, the characteristics of normal marrow depend on the relative amounts of the marrow constituents, including hematopoietic elements and marrow fat. Normal neonatal hematopoietic marrow is lower than or equal to muscle SI on T1-W imaging and of increased signal on T2-W imaging and following contrast enhancement.
The bony envelope
The periosteum is a thin, low-SI structure that parallels the bone cortex. It is loosely attached along the shaft of the bone, but tightly held at the level of the physis where it is termed the perichondrium. The perichondrium surrounds the physeal cartilage and allows for circumferential growth. It is most prominent in newborns.
There is a layer of fibrovascular tissue that separates the periosteum from the cortex. This layer is most easily seen at the metaphysis where it appears as a metaphyseal stripe on longitudinal images, and a cuff on transverse images. It has a high SI on water-sensitive images and enhances vividly after contrast administration. In areas of loose attachment of the periosteum, subperiosteal collections of blood, pus, or tumor can form.
Spine
The various structures of the spine also undergo marked changes during infancy. These structures have 3 distinct stages of evolution. The description in this article compares the T1-W SI of the bone and cartilage with that of skeletal muscle. Stage 1, from birth to approximately 1 month of age, shows prominent hyperintense cartilage at the superior and inferior margins of the vertebral body, and hypointense ossification centers. A central band of higher SI is occasionally seen corresponding with the radiolucent band seen on radiographs. At this stage, the vertebral body is ovoid in shape. Stage 2 is from approximately 1 to 6 months, and shows increasing SI in the ossification centers, from the endplates inwards, with decreasing prominence of the cartilage. Stage 3, from approximately 7 months, shows increasingly rectangular vertebral bodies that are centrally intense, with a further decrease in the amount of cartilage. The neonatal spinal marrow signal is lower than that of the adjacent disc.
Neonatal musculoskeletal disorders and the use of MR imaging
Abnormalities of the spine, pelvis, and extremities are common in neonates. In many cases, the abnormality is evident on clinical examination, as in the absence of all or part of a limb, and no imaging is required. Other conditions, such as developmental dysplasia of the hip, are more difficult to diagnose and may require imaging. Imaging is useful in confirming the diagnosis or assessing for potential complications. Imaging can also provide information for preoperative planning, or can be used in follow-up. Radiographs remain the first-line imaging modality for almost all conditions, giving an overview of skeletal density and ossification, alignment, and presence of calcification. Ultrasound is also widely used because it has several advantages: lower cost than MR imaging, can be performed portably, and seldom requires sedation. Despite the distinct role of ultrasound in certain conditions, its sensitivity remains operator dependant. The role of MR imaging in neonatal musculoskeletal conditions is expanding, with its greatest advantage being its multiplanar capability to visualize the nonossified elements of the musculoskeletal system.
Congenital and Developmental Conditions
Neonates with certain skeletal dysplasias with underlying cartilage abnormalities, such as achondrogenesis II and hypochondrogenesis, have been shown histologically to have increased size and number of cartilage canals. MR imaging can reveal these abnormalities in the number and distribution of the cartilage canals.
Congenital anomalies are those that occur early during the embryonic period, whereas developmental deformities occur later in fetal or neonatal life. Limb buds appear in the upper body by the 23rd gestational day and appear for the lower limbs a few days later. Development can be affected by genetic, vascular, nervous, and teratologic influences, the timing of which is reflected both in the specific musculoskeletal abnormality and any concurrent anomalies, such as the many associated findings commonly identified with abnormalities of the radius.
Upper extremity
Congenital and developmental disorders of the upper limb occur less commonly than those of the lower limbs. Of the disorders that present in the neonatal period, many do not require MR imaging at this time. For example, radiography provides all the information required in cases of polydactyly or congenital amputations. Other entities, such as radioulnar synostosis, may not present until later in life, and those abnormalities involving the radius that may be associated with syndromes are generally further worked up with ultrasound. However, MR imaging can be helpful in unique anomalies that are rarely encountered, such as intrathoracic development of a right upper limb.
Lower extremity
Depiction of the unossified skeletal structures of the lower limbs with MR imaging is more important in planning treatment of children with a broader variety of congenital deformities of the lower extremities.
Developmental dysplasia of the hip
In infancy, the most common clinical concern of the lower limb is developmental dysplasia of the hip (DDH). Hip dysplasia in the neonate may also arise from multiple causes including neuromuscular conditions, such as cerebral palsy and arthrogryposis, as well as teratologic causes or ligament laxity. In most cases, DDH is diagnosed clinically and with ultrasound. Radiography may be used once the femoral head ossification centers have appeared. In certain refractory cases of DDH, as well as in other causes of hip dysplasia, MR imaging has a role both in preoperative planning and postoperative care.
MR can show the cartilaginous parts of the pelvis and hip and analyze the relationship of the femoral head to the acetabulum and labrum without the radiation required with computed tomography (CT). An MR classification of DDH has been described, but this is not in common use, especially for the neonatal age group. With MR, the sequences used should be limited to 1 or 2 in total in the coronal and/or axial planes so that studies can be completed without need for sedation. Generally, cartilage-specific GRE or fat-suppressed T1-W sequences are used. Fat-saturated spin-echo T1-W images or gradient sequences with flip angles of 34° to 45°, show epiphyseal cartilage appearing bright, with ossified bone, and the labrum appearing dark.
MR imaging is helpful to confirm satisfactory concentric hip reduction in casts. With MR imaging, it is possible to see potential impediments to reduction, such as an inverted labrum or prominent pulvinar fat. Other causes of inability to concentrically reduce the hip include a redundant ligamentum teres, whereas the capsule, iliopsoas tendon, or transverse acetabular ligaments may all become interposed, also preventing hip relocation. Routine MR imaging has been recommended by some investigators in all casted open or closed reduced dislocations to confirm reduction because up to 4% to 14% of patients may not have satisfactory reduction in casts. This recommendation has not yet been widely adopted. MR imaging has also been used to evaluate the degree of abduction and extent of femoral head perfusion. Relative increased abduction is associated with an increased risk of vascular compromise. Gadolinium enhancement may show abnormalities of the femoral head and physeal vascularity with reduced perfusion. Timely correction of potential ischemia of the femoral head may obviate the development of chondronecrosis.
Proximal focal femoral deficiency
Proximal focal femoral deficiency (PFFD) is a congenital condition with unilateral hypoplasia or complete or partial absence of the proximal femur associated with proximal femoral varus deformity. Associated abnormalities include asymmetry in muscle size with decrease in ipsilateral musculature and vessels. Abnormalities of the more distal limb may also be present, including agenesis of the cruciate ligaments and fibular agenesis. Several classification schemes have been proposed based on radiographic appearance or proposed therapy with the most widely known being the Aitken classification. In this classification, class A is a shortened femur with coxa vara and a normal acetabulum. Class B shows no apparent connection between the femoral head and shaft. In class C, the acetabulum is abnormal with a small or absent femoral head, whereas, in class D, both the femoral head and acetabulum are missing. However, cartilaginous connections are not well identified on radiograph and radiographic classification may be unreliable and underestimate the extent of cartilage present.
When radiographic assessment fails to show the femoral head or proximal femur, MR imaging can help to identify the presence or absence of a cartilaginous anlage for the femoral head. MR imaging is more accurate than radiographic evaluation and can delineate the presence of cartilage across a proximal femoral bony gap to enable earlier appropriate intervention. Thin-section coronal and axial imaging is required if a small femoral head is not to be missed.
Congenital pseudarthrosis of the tibia
Congenital pseudarthrosis is an uncommon entity that usually becomes evident within the first year of life with angulation seen within the calf. There is typically unilateral segmental osseous weakness of the tibia resulting in anterolateral angulation of the tibia. MR imaging depicts the morphology of the pseudarthrosis and adjacent soft tissue deformity better than radiography. MR imaging can clearly show the type of pseudarthrosis, its length and structure, and whether there is union or nonunion of the bone. This information is of prognostic significance because the pseudarthrosis and affected periosteum need to be surgically removed. Associated soft tissue abnormalities, such as neurofibroma, can also be shown, although these may be at a site distant from the pseudarthrosis. On MR imaging, the pseudarthrosis appears hyperintense on fat-suppressed and T2-W images, whereas, on T1-W images, it is usually hypointense. Contrast may help to define the lesion.
Congenital patellar dislocation
The patella develops as a sesamoid bone anterior to the femur. Congenital anomalies of the patella include its absence, hypoplasia, or dislocation. Absence or hypoplasia occur as part of several syndromes including nail-patella syndrome and genitopatella syndrome. Congenital dislocation of the patella (CPD) is uncommon.
CPD is believed to arise from failure of internal rotation of the myotome that forms the femur, the quadriceps muscle, and the extensor mechanism of the knee, occurring during the 8th to 10th week of embryologic life. CPD usually presents at birth with characteristic genu valgum, flexion contracture, and external rotation of the tibia. However, some cases with less distinctive features do not present until later in childhood. Casting or surgical intervention is required to realign the maldeveloped, laterally displaced extensor mechanism to reduce or avoid long-term sequelae of knee dysfunction and early knee degeneration.
Radiographs are used to confirm the diagnosis in older infants and children in whom the patella has ossified. Changes are also seen in the appearance of the femur and joint space. However, in the neonate, diagnosis is more difficult. Sonography can be used to identify the presence of a congenital dislocated patella. However, MR imaging provides an overall detailed anatomic perspective and permits better understanding of mutual anatomic relationships of involved structures. Assessment with MR imaging can be performed with a 3D gradient sequence to highlight the cartilaginous patella. MR evaluation should describe the size, shape, and orientation of the developing patella, the size and position of the quadriceps muscle and its tendon, the patellar tendon, and the medial and lateral patellar retinacula. Assessment of the bones, including the femoral sulcus, the menisci, and ligaments of the knee, should also be included. Thin sections are needed to avoid missing a small, hypoplastic patella.
Ankle/foot
Distinct entities of the foot and ankle, other than those related to a more generalized condition, are uncommon in the neonate. The most common concern is clubfoot, which occurs in 1:1000 newborns in North America. The 2 classifications are postural or positional, which can be manipulated back into the correct alignment, or fixed. Imaging is performed after 4 to 12 weeks of unsuccessful conservative treatment, routinely with radiography. MR imaging is rarely needed for clubfoot. Although rarely used, the theoretic advantage of MR imaging is in visualizing the relationships of the cartilage anlagen.
Spine and pelvis
Evaluation of the lumbar neonatal spine is possible with ultrasound caused because of the cartilaginous nature of most vertebral bodies at this stage. The most common clinical finding in an otherwise normal infant, prompting evaluation, is the presence of a sacral dimple. Skilled clinicians can obtain a great deal of detail and information with ultrasound, but MR imaging is the modality of choice for a more detailed evaluation of the spinal column and cord, and any abnormality found on ultrasound is usually followed up with MR imaging ( Fig. 1 ).
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