normal mri anatomy of the musculoskeletal system · enables the distinction between bone fragments...

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ShoulderAxial Images

Fig. 2.13

Fig. 2.2

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Coronal Oblique Images

-Fig. 2.3A

Fig. 2.3B

Fig. 2.4--

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Fig. 2.2

Fig. 2.5

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Normal MRI Anatomy of theMusculoskeletal SystemJ. Dana Dunleavy, A. Jay Khanna, and John A. Carrino

I Initial Concepts18

Fig. 2.2 An axial illustration of the left shoulder showing theanterior position of the subscapularis muscle and the articu-lar cartilage of the glenoid and humeral head.

Fig. 2.1 An axial T2-weighted image (A) and artist’s sketch (B) of the right shoulder at the level of the glenoid labrum showing the long headof the biceps tendon as it courses along the bicipital groove.

A

B

2 Normal MRI Anatomy of the Musculoskeletal System 19

Fig. 2.4 A coronal proton-density fat-suppressed image (A) and art-ist’s sketch (B) of the right shoulder at the level of the supraspinatusmuscle and the insertion of the conjoined tendon, a site that is very

this level, without evidence of supraspinatus impingement.

A B

Fig. 2.3 Anterior (A) and lateral (B) 3D illustrations of the osseous structures of the right shoulder.

A B


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Fig. 2.5

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Fig. 2.7 -

Sagittal Oblique Images-

-Fig. 2.3B

Fig. 2.8Fig.

2.93Fig. 2.6 A 3D coronal illustration of the right shoulder, identifying

lesser tuberosities of the humerus. Also shown are the coracoclavicu-lar and coracoacromial ligaments and other ligaments that stabilizethe shoulder.

Fig. 2.5 A coronal illustration of the right shoulder at thelevel of the supraspinatus muscle and tendon showing theglenoid and humeral head cartilage and the superior andinferior glenoid labrum.


Fig. 2.7 A 3D coronal illustration of the neurovascular structures ofthe right shoulder and arm showing the subclavian, axillary, and bra-chial arteries, as well as smaller branch vessels such as the anterior

seen coursing anterior to the surgical neck of the humerus.


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Fig. 2.6-

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Fig. 2.3

ElbowAxial Images

-Fig. 2.10

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Fig. 2.11

Fig. 2.8 A 3D sagittal illustration of the rightglenoid showing a labral tear.


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Figs. 2.12 2.13-

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Fig. 2.9 A sagittal proton-density imagewith fat suppression (A) andartist’s sketch (B)muscles. Although it takes some practice to evaluate the shoulder in

on this view.

A

B


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Fig. 2.10 An axial proton-density image (A) andartist’s sketch (B) of the left elbow at the level ofthe humeral epicondyles illustrating the musclearchitecture of the distal arm. The biceps bra-

common extensor tendon show normal thick-ness and low signal intensity.

A

B


Fig. 2.12 A posterior 3D illustration of the right elbowshowing the insertion of the triceps tendon (cut) ontothe olecranon process of the ulna. Also seen are otherneural and ligamentous structures.

Fig. 2.11 Lateral (ulnar side) (A) and posterior (B) 3D illustrations of the left elbow showing the ligamentous structures that stabilize theelbow joint and a tear of the UCL (arrow on B).

A B

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10 The Cervical SpineLukas P. Zebala, Jacob M. Buchowski, Aditya R. Daftary, Joseph R. O’Brien, John A. Carrino,and A. Jay Khanna

Specialized Pulse Sequences andProtocols

indications can vary among institutions, standard MRI of thecervical spine for degenerative pathologies usually includesthe following pulse sequences:

• Sagittal T1-weighted SE• Sagittal T2-weighted FSE• Axial gradient-echo• Axial T2-weighted FSE

A detailed discussion of all the imaging sequences used inthe cervical spine is beyond the scope of this chapter; how-ever, salient features of commonly used sequences are dis-cussed below.

T1-weighted images are useful in identifying fracturelines. Because they are sensitive to the presence of gadolin-ium contrast, they are also used for contrast-enhanced imag-ing, which is helpful in assessing neoplasms, infections, andthe postoperative spine. Typically, fat-suppressed postgado-linium T1-weighted images are used to make lesions moreconspicuous. T2-weighted images are sensitive to water(and thus edema) and are useful in identifying areas of po-tential pathology. However, care must be taken with regardto interpreting bone marrow edema because it may be seen

-tion, trauma, and degeneration. Although edema may focusattention toward an abnormality, many of these condi-tions can coexist, so additional analysis is required before

T2-weighted images at speeds up to 64 times faster than-

on T2-weighted FSE images, and therefore fat suppression isused to make these areas more conspicuous. This sequencecan be obtained by applying a fat-suppression pulse toproduce fat-suppressed T2-weighted images or by obtain-

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achieved with STIR or fat-suppressed T2-weighted images.T2-weighted images are also most sensitive for evaluatingthe cord parenchyma for lesions and edema, which are seenas abnormally bright signal, although the sagittal orientation

is subject to linear bright artifact within the cord (Gibbs phe-nomenon). For this reason, axial T2-weighted images serveas a useful tool for detecting cord abnormalities and con-

Gradient-echo images are very susceptible to magneticartifacts; this important characteristic makes them usefulfor detecting small areas of hemorrhage, such as with cer-vical spine trauma and vascular malformations. However,these images can also overestimate the degree of canal andforaminal stenosis secondary to artifact from the adjacentbone. Because of the rapidity with which gradient-echo im-ages are acquired, studies can be obtained with higher reso-lution than that required for other pulse sequences and evenas a 3D volume set, which allows for isotropic voxels andreformations in multiple planes. This volume set can then

-propriate oblique plane.

For evaluation of vascular structures in the neck, MR an-giography can be obtained without contrast, using 2D or 3D

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aging shows fat or subacute thrombus as bright signal andmay be useful in detecting small, subtle thrombi. The 3Dtechniques require more time and are slightly less sensitive

may also be obtained and is extremely accurate.

Traumatic ConditionsAlthough the cervical spine is injured in only 2% to 3% of blunttrauma accidents,1 the potential for instability and critical

-agement of cervical spine injuries important. Patients withsuspected cervical spine injury should be evaluated initiallywith conventional radiographs (AP, lateral, and open-mouth

than does conventional radiography and may reveal frac-tures or details that are not detected with radiography. CT isespecially helpful in assessing fractures of the occipital con-dyles and cervicothoracic junction, where osseous overlapon conventional radiographs makes fracture detection dif-

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of conventional radiography or CT and is useful for the as-sessment of spinal cord injury, ligamentous injury, degreeof spinal stenosis, and additional fracture evaluation. Oc-cult fractures not visible on conventional radiographs or CTimages may be detected by the presence of vertebral bodyedema on MR images. Although MRI is extremely sensitivein identifying cervical spine fractures, their characteristicsand the exact appearance of the osseous components canbe challenging; CT may be a better choice for assessing suchdetails. In addition, MRI is useful for the evaluation of ob-tunded patients or those with cervical spine injury, neuro-

2–7

-cular injury, or soft-tissue injury is suspected in the setting oftrauma. It is also useful in assessing posttraumatic sequelae.8

Imaging spinal gunshot injuries is controversial. Theoreti-cally, a ferrous gunshot fragment may become mobile, butmost bullets are nonferrous, and therefore such patients canusually be imaged without consequences. Unfortunately, theexact composition of a gunshot fragment is seldom known,and therefore MRI remains controversial and dependent onthe clinical need.9,10

It should be noted that there are obstacles to obtainingMRI studies in the trauma setting, especially with regard tocervical spine trauma, because patients may have clinically

following:

• Lack of availability of MRI capabilities on an urgentbasis

• MR-incompatibility of some ventilators, traction de-vices, and other equipment

• Lack of clinical access to patients during the imagingstudy

MRI protocols vary by institution, but commonly used se-quences in trauma evaluation include the following11:

• Sagittal T1-weighted images to assess the alignment ofthe cervical spine, vertebral body integrity, fractures,and spinal cord caliber

• Sagittal T2-weighted images to assess for the presenceof cord edema, compression, and spondylotic changes

• Sagittal STIR images to assess for the presence of para-spinal ligamentous injury and bone marrow edema

• Axial T1-weighted and T2-weighted images to assessfor the presence of posterior element fractures, to eval-

detected on sagittal images• Sagittal T2-weighted gradient-echo images (in some

institutions) to assess for the presence of acute spinalcord hemorrhage and disc herniation (high signal inthe disc even with severe osseous degeneration, which

enables the distinction between bone fragments and adisc herniation)

-tematic approach (see Chapter 3) for the evaluation of cer-vical spine MRI should be used to avoid missing pathologicconditions (see Table 10.1 for important cervical spine struc-tures to evaluate). In addition, it is essential that the inter-

with that of the other available imaging modalities, includ-

views if clinically indicated) and CT (see Chapter 17).

-nism of injury. Although six categories have been described

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extension12) (Fig. 10.1 -

• Hyperextension• Axial loading

to determine from an analysis of the clinical situation (in the

choose to broadly classify cervical spine injuries as follows:

• Secondary to blunt trauma• Secondary to penetrating trauma

Anatomy Evaluation

Spinal column/vertebral bodies

AlignmentVertebral body fracturePosterior element fractureEdemaDegenerative change

Ligaments Anterior longitudinal ligamentPosterior longitudinal ligamentInterspinous and supraspinousligaments

Evaluation for edema/rupture

Spinal cord EdemaHemorrhageCompressionSyrinx

Epidural space HematomaDisc herniationOsseous fragment

Vascular Vertebral artery

Source: Takhtani D, Melhelm ER. MR imaging in cervical spine trauma. Magn

10 The Cervical Spine 231

Fig. 10.1 An artist’s representation of the Allen-Ferguson mechanis-

Chapman JR, Anderson PA. Cervical spine trauma. In: Frymoyer J,

Ducker TB, Hadler NM et al, eds. The Adult Spine: Principles and

permission.)

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In addition, cervical spine injuries can be subdividedbased on the region of injury within the occipitocervicalspine:

• Occipitocervical junction• Suboccipital cervical spine (C1-C2)• Subaxial cervical spine (C3-C7)

-tion system has been described as an approach that recog-

injury, and integrity of the discoligamentous complex.13 Asystematic evaluation of these three components can beused to guide the treatment of patients with cervical spinefractures.

Flexion-compression injuries range from the minor anteriorcompression of the anterosuperior end plate (Fig. 10.2) toa severe teardrop or quadrangular fracture. These injuriesare associated with retrolisthesis, kyphosis, and circumfer-ential soft-tissue disruption. The radiographic evaluation

following:

• Anterior and middle column compromise• Vertebral body-height loss• Translation• Angulation• Posterior element competence

Although conventional radiographs and CT scans can evalu-ate fracture pattern, alignment, angulation, and translation,MRI provides additional diagnostic value and can assist withthe determination of treatment options for such patients be-cause it facilitates the assessment of spinal cord compressionand posterior element compromise.

Flexion-distraction forces can lead to facet subluxations,dislocations, or fracture-dislocations. These injuries repres-ent a spectrum of osteoligamentous pathology, rangingfrom the purely ligamentous dislocation to fracture of thefacet and lateral mass. MRI helps assess the compromise ofposterior musculature, interspinous ligaments, ligamentum

distraction injuries.14 The role of MRI in the treatment algo-

A B

Fig. 10.2 arrow on eachminimal loss of height.


rithm of patients who present with bilateral cervical facetdislocations (Fig. 10.3) without neurologic compromise isthe subject of substantial debate in the literature and amongspine surgeons.14–16 The treatment options include MRIbefore attempting closed reduction or surgical interven-tion; closed reduction with traction while monitoring thepatient’s neurologic examination; and surgical interventionvia anterior, posterior, or combined approaches.14–16 One ofthe purposes of obtaining an MRI study before the reductionof bilateral facet dislocations is to rule out the possibility ofan extruded disc fragment that may displace into the spinalcanal during a closed reduction (Fig. 10.4).

11:

• Alignment• Fractures• Ligamentous injury

• Cord abnormalities• Acute disc herniations• The cause of anterior subluxation, either chronic de-

Facet joint injuries may be seen on parasagittal or axial im-ages, which show increased signal on T2-weighted imagessecondary to edema from facet capsule tears.11,17–19 Injuryto posterior ligaments may be seen as areas of hyperinten-sity on T2-weighted images, especially fat-suppressed T2-weighted or STIR images (Fig. 10.5).

Cervical spine extension injury results in the posteriortranslation or rotation of a vertebral body in the sagittalplane.6,11,20 Hyperextension injuries often are produced byrear-impact motor-vehicle collisions or direct facial trauma.

Fig. 10.3 Artist’s sketches illustrating the pathology in bilateral facetdislocation. (A) -

dislocation. (B)50% translation of the superior vertebral body relative to the inferior

one and displacement of the intervertebral disc. (C)

the spinal canal and compressed the spinal cord during the reductionmaneuver.

A

B C

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A B

C

Fig. 10.4 Bilateral cervical facet dislocation. (A)A sag-

ar-row)(B) and gradient-echo (C)

arrow on each) displaced ante-arrowhead

on each).


include the following6,11,17,19,20:

• Tear(s) of the anterior longitudinal ligament• Avulsion of the intervertebral disc from an adjacent

vertebral bodyFig. 10.6)

More severe and potentially unstable hyperextension inju-ries may be associated with the following6:

• Prevertebral hematoma• Widening of the disc space• Posterior ligament complex edema• Herniated disc

Elderly patients with spondylosis and kyphosis of the cer-

or ligamentous injury because of posterior infolding of the

posterior vertebral osteophytes.6Whiplash injuries often have no associated osseous injury

radiographs may be nondiagnostic because of poor excursionsecondary to pain. However, MRI is of limited value for the

assessment of whiplash; several studies have failed to show-

toms.18,21 In contrast, patients with a fused cervical spine

to assess for acute fracture, instability, or neurologic com-promise. In such patients, the fused cervical spine acts like along-bone fracture, and even minimally displaced fracturesmay be unstable (Fig. 10.7).22

Finally, MRI can assess intervertebral disc injury andsubtle fractures caused by any of the above-mentionedmechanisms.11,17–19,23 Intervertebral disc injury may range

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tear on MRI does not indicate acute traumatic injury and canbe seen in asymptomatic individuals.24,25 Intervertebral discseparation from the adjacent vertebral body may be seen as

11,17,19 Subtlefractures, such as vertebral end-plate fractures, may be best

and hemorrhage not seen on conventional radiographs orCT images.11,17,19

Fig. 10.5 -arrowhead) and interspinous region at C6-C7 and C7-T1,

-arrow

Fig. 10.6arrow -

sion injury to the cervical spine. Note the associated prevertebral-

sociated cord signal change.

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Axial load injuries are caused by the axial transmission offorce through the skull, through the occipital condyles, and

burst fracture or burst fractures of the subaxial cervicalspine. MRI is useful for the assessment of C1 compressionfractures and associated pathologies such as lateral massdisplacement on coronal images, atlantodental interval in-crease on sagittal images, and transverse ligament disrup-tion on axial images.11 For burst fractures, MRI is usefulfor diagnosing associated spinal cord injury caused by anacute herniated disc or retropulsion of osseous fragments(Fig. 10.8). Because a purely axial force subjects the poste-rior capsuloligamentous structures to compression only,these posterior structures should remain intact.11,20 How-

traumatic event that may cause injury to the posterior spinalelements, which can be detected by MRI.20 It is important

other images for evidence of injury to the posterior ligamen-tous and osseous structures because such injury will lead toconsideration of posterior fusion in addition to the anterior

decompression and fusion that is often performed for pa-tients with cervical burst fractures.

Although injury to the occipitocervical junction occurs ina small percentage of blunt trauma victims (0.8% in onestudy26), recognition of such injuries is crucial because of

27–30 A detailed discussion of occipi-tocervical craniotomy and the various measurement tech-niques for evaluation of occipitocervical pathology is beyondthe scope of this chapter, but presented here is an overview

seen on MRI. It is important to keep in mind that MRI studiesof the occipitocervical junction should be reviewed in con-junction with conventional radiographic and CT imaging.

Atlantooccipital Dissociation

Atlantooccipital dissociation is any separation of the atlan-tooccipital articulation. The skull may displace anteriorly,posteriorly, or superiorly, and may be complete (disloca-

BA

Fig. 10.7 Ankylosing spondylitis. (A)-

(B)

nondisplaced “fracture” or injury through the anterior column at C6arrow) and posterior column injury; both injuries manifested as re-

pulse sequence.


tion) or partial (subluxation). Atlantooccipital dissociationcan be a devastating injury.27–30 The primary injury is tothe ligaments that provide structural support to the cervi-cocranial junction. In addition, even without frank disloca-tion, the occiput–C1 junction may be injured, as indicated bypostmortem studies.27,28 Although this injury may be fatal,improvement in resuscitative and medical treatment hasincreased survival rates. CT imaging may be used to assessassociated fractures or relationships among the basion, dens,occipital condyles, and atlas in conjunction with atlanto-

occipital dissociation, whereas MRI is better at detecting in-jury to the cervicocranial ligaments (e.g., transverse, apical,cruciate, atlantooccipital membrane and capsular ligaments,tectorial membrane), brainstem, or spinal cord.11,19,31

Trauma to the Atlas

Axial load to the occipitocervical junction at the atlas may re-

open-mouth odontoid radiographs or coronal CT images.32,33

Fig. 10.8 Cervical burst fracture. Sagittal fat sup-(A) (B) images

arrow on eachmoderate loss of height, retropulsion, and spinal cord

arrowhead on A). (C)

arrow).

BA

C

normal mri anatomy of the musculoskeletal system · enables the distinction between bone fragments...

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