- Email: [email protected]
MR imaging of the ankle and foot—A review of the normal imaging appearance with an illustration of common disorders
Clinical Chiropractic (2007) 10, 101—111
intl.elsevierhealth.com/journals/clch
RESOURCE DOCUMENT
MR imaging of the ankle and foot–—A review of the normal imaging appearance with an illustration of common disorders Michelle A. Wessely * Department of Radiology/Department of Clinical Research, Institut Franco-Europeen de Chiropratique (IFEC), 24 Boulevard Paul Vaillant Couturier, 94200 Ivry Sur Seine, France Accepted 28 February 2007
KEYWORDS Ankle; Congenital abnormalities; MR imaging; Foot; Normal variants; Trauma
Summary This article aims to provide a brief overview of magnetic resonance imaging (MRI) of the ankle for the clinician. A basic review of MRI protocols for the region is followed by discussion of the most common imaging sequences. The appearance of normal ankle anatomy is reviewed with emphasis on structures prone to injury; congenital and developmental abnormalities and normal variants. These are correlated to annotated images. Imaging of ankle and foot pathology and trauma is then discussed with emphasis on the identification of ankle pathology for the manual physician. Illustrative examples are given with discussion of specific common conditions including avascular necrosis, accessory navicular, Haglund’s syndrome, Morton’s neuroma, osteochondral defects, osteomyelitis, os trigonum syndrome, peroneus quartus, plantar fasciitis and tendinitis/tendinosis. # 2007 The College of Chiropractors. Published by Elsevier Ltd. All rights reserved.
Introduction Non-invasive imaging of the ankle and foot may consist of a variety of approaches including plain film radiography, ultrasound and further imaging such as computed tomography (CT) and magnetic resonance (MR) imaging, depending on the clinical suspicion and the available resources. Whilst the * Correspondence to: Department of Radiology, Institut FrancoEuropeen de Chiropratique (IFEC), 24 Boulevard Paul Vaillant Couturier, 94200 Ivry Sur Seine, France. Tel.: +33 14515 8919; fax: +33 14515 8911. E-mail address: [email protected].
basic imaging techniques may be useful in many clinical circumstances, an increasing number of patients undergo further imaging. It is, therefore, important for the manual physician to have a good knowledge of the basic anatomical appearance of the ankle and foot on MR images. An appreciation of the imaging characteristics of common disorders of the ankle and foot is also useful to aid clinical diagnosis and management of the patient. This article aims to approach the ankle and foot from the basic normal MR imaging appearance to the more complex disorders illustrating the use of MR imaging in the evaluation of patients who present with abnormalities in the ankle or foot.
1479-2354/$32.00 # 2007 The College of Chiropractors. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.clch.2007.02.006
102
M.A. Wessely
Clinical indications The clinical indications for MR imaging of the ankle and foot are wide, though this may depend on the clinical protocols established by the imaging centre and the availability of resources. Based on current evidence, MR imaging of the ankle and foot is considered an imaging modality of choice for conditions such as internal derangements (for example, impingement syndromes) that commonly affect the ankle or for post-operative evaluation.1,2 Although more basic imaging studies can suggest a disorder and, indeed, be able to show dynamically the effect of the condition, it is the anatomical detail that MR imaging affords that sets it apart. An example of this is the os trigonum syndrome, where the flexor hallucis longus tendon may be compromised, leading to posterior impingement syndrome. Although the os trigonum itself is demonstrated well on plain film images, the tendinous involvement can only be inferred; MR images will show clearly the precise location and severity of the soft tissue involvement. Likewise, in cases of trauma, bony and associated soft tissue lesions can be easily identified, and monitored throughout the patient’s management. This is particularly so when surgery is necessary and MR imaging is used to determine the post-surgical response and evaluate intermediate to long-term complications, including avascular necrosis and osteochondral injuries, which may remain undetected with other imaging modalities. Additional miscellaneous conditions may be best evaluated with MR imaging, including Morton’s neuroma. Although ultrasound may in some circumstances be useful in the detection and treatment of this lesion, MR imaging is better able to differentiate from other conditions including malignant soft tissue tumours.
Figure 1 MR imaging of the ankle of a 33-year-old lady with pain on the medial aspect of the mid-foot. On this axial, T1-weighted image, a region of high signal intensity is noted on the medial aspect of the skin, just medial to the navicular (circle). This is a skin marker to indicate the epicentre of pain or swelling noted by the patient and is useful to note when interpreting the final image.
of the lesion and therefore aid the diagnosis. Each slice is usually 4 mm in thickness. MR imaging of the foot is ordinarily performed with the patient in the prone position. Although this
Procedure and sequences MR imaging of the ankle requires that the patient lies supine with the ankle perpendicular to the lower leg. A support may be used to maintain the position during the imaging study. A surface coil is usually employed to increase the signal capture. A skin marker may be added to illustrate to the person reading the image, the region of pain or swelling for the patient (Fig. 1). The sequences selected usually consist of all three planes: sagittal (Figs. 2—4), axial (Figs. 5—7) and coronal (Figs. 8—10), using a combination of T1- and T2-weighted, straight (or STIR) sequences, depending on the clinical scenario. Contrast is used where a mass or infection is suspected in order to determine the character and behaviour
Figure 2 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This is a sagittal, T-1 weighted image demonstrating the fibula with the tendons of the peronei wrapping around the distal aspect. When interpreting the sagittal plane, identifying the fibula, allows the anatomy of lateral slices of the ankle to be more easily determined.
MR imaging of the ankle and foot
Figure 3 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This is a sagittal, T1weighted image in the mid-sagittal plane demonstrating the bone and soft tissue detail well.
103
Figure 5 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This slice is an axial, T-1 weighted image taken in the region of the distal tibia and fibula. Orientation to this image is achieved by using the Achilles’ tendon to determine the posterior aspect and then, opposing this, the anterior aspect. The fibula with the peronei tendons wrapping around it help differentiate the lateral aspect of the ankle from the medial.
position may be difficult for some patients, it allows for the toes to be maintained in the neutral position, and for the patient to be as immobile as possible during the imaging study, therefore limiting motion artefact which can degrade the final image quality. The sequences and planes are the same as in the ankle; however, the sagittal image is performed
along the long axis of the metatarsals, and may be referred to as the long axis; the axial slice perpendicular to the second or third metatarsal long axis and which may be referred to as the short axis,
Figure 4 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This sagittal, T1-weighted image demonstrates one of the most medial slices captured during this study. Notice the position of the medial malleolus.
Figure 6 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. An axial, T1-weighted image slightly more inferior than in the previous figure. It is useful to start from superiorly and to work inferiorly to retain an orientation to the image. Note the most distal tip of the lateral malleolus and the sickle-shaped Achilles’ tendon.
104
M.A. Wessely
Figure 7 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This is a T1-weighted axial slice of the most distal slice obtained during this study. Note the insertion of the Achilles’ tendon on the calcaneus.
Figure 9 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This image is also in the coronal plane, slightly more anterior to the previous slice. Note the changing form of the bony structures, and the appearance of the sustentaculum tali.
and the coronal image in a plane connecting the second and fifth metatarsals. These slight variations are useful to know in order to better orientate the anatomical structures when interpreting the final MR image.
Normal imaging appearance
Figure 8 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This is one of the most posterior slices in the coronal plane on this, a T1-weighted image, where one’s orientation is based around the fibula, a lateral structure. Once determined, the remaining structures are more easily identified.
Figure 10 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This is the most anterior slice of a coronal, T1-weighted sequence. It is useful to start with the most posterior slice and then work forward to remain orientated to the images. This slice was performed in the posterior aspect of the mid-foot.
The main structures to be evaluated on MR imaging of the ankle and foot will be discussed, although, owing to the wide variation in appearances and the
MR imaging of the ankle and foot anomalous soft tissue structures, it will be necessary for the reader to regard this text as an introduction to the basic interpretation of this region. Although there are a variety of methods to evaluate imaging of the ankle and foot, it is useful to approach the interpretation by identifying individual anatomic structures. These can be divided into those comprising the soft tissues, including tendons, ligaments and fascia; neural and bony structures. For the purpose of this article, the emphasis will be placed on those structures that are commonly implicated in the development of clinical syndromes, namely the soft tissue and bony structures. The soft tissue structures include the tendons. In order to be able to identify the different tendons, the ankle and foot may be divided into four sections: anterior, posterior, medial and lateral in order to better orientate the position of the tendons. About the ankle and foot, the posterior tendons include the Achilles’ and plantaris along with their bursae (Fig. 11). Medially, the flexor tendons pass including tibialis posterior, flexor digitorum longus and flexor hallucis longus (mnemonically referred to as ‘‘Tom, Dick and Harry’’). The posterior tibial artery, nerve and vein are located between flexor digitorum longus and flexor hallucis longus (Fig. 12). Laterally, the peroneus tendons consisting of peroneus longus and brevis are located (Fig. 13). Anteriorly, the
Figure 11 MR imaging of the ankle in the axial plane, a T1-weighted image of a patient with ankle discomfort. The posterior tendon structures can be identified with the most posterior structure representing the Achilles’ tendon with its low signal intensity (circle). The tendon may sometimes demonstrate a small focus of increased signal in its centre, although this is not visible in this patient. Just anteromedial to the Achilles’ tendon, is a region of grey/intermediate signal that represents the soleus muscle.
105 tendons consist of the tibialias anterior, which lies the most medially, then the extensor hallucis longus, extensor digitorum longus and peroneus tertius3 (Fig. 14). These structures tend to be affected the least about the ankle. In addition to the tendons, the ligaments may be visible using MR imaging; however, owing to the possibility of detecting lesions of the ligaments by clinical examination and, if necessary, ultrasound, MR imaging is not used systematically for the evaluation of the ligaments about the ankle and foot. Despite this, note may be made of those ligaments that may be more often involved in clinical syndromes, including the medial ligament complex (deltoid) and lateral ligament complex. These ligaments are best evaluated using the axial images.
Normal variants and developmental anomalies A number of normal variants of the osseous and soft tissue structures may be encountered about the foot and ankle. It is important to be familiar with these
Figure 12 MR imaging of the ankle in the axial plane, a T1-weighted image demonstrating the medial soft tissue structures. The hatched oval represents the tibialis posterior tendon, located the most anteriorly, and the flexor digitorum longus more posteriorly (hint–—use the achilles tendon to orientate to the image). The arrow points to a small intermediate signal intensity that represents the posterior tibial vein. Directly posterior to this is an oval within which are located two small round structures, the most medial of which is the posterior tibial artery, and laterally the tibial nerve. The smaller oval structure surrounding the low signal intensity structure represents the tendon of flexor hallucis longus.
106
M.A. Wessely
Figure 13 MR imaging of the ankle, axial plane with a T1-weighted sequence demonstrating the two small, low signal intensity structures enclosed within an white oval. These structures represent the peronei tendons. The more lateral structure (hint–—note the lateral malleolus) represents the peroneus longus tendon and the more medial, the peroneus brevis tendon. Note their intimate association with the posterior aspect of the lateral malleolus.
so as to not to confuse them with pathologies, for example the presence of peroneus quartus, a supplementary muscle with that can have clinical significance (Fig. 15). Developmental anomalies about the foot and ankle are more clinical important since provocation of pain syndromes may occur, for example in the case of accessory ossicles. About the ankle, the two most common accessory ossicles are the os trigonum and the accessory navicular bone. With an os trigonum, the patient will tend to complain of pain in the posterior aspect of the ankle that is worsened by plantar flexion. This is particularly the case in patients who dance, run down hills or play football. The accessory bone is located posterior to the distal tibia, behind which the tendon of the flexor hallucis longus passes, slightly medially to the os trigonum. During forced plantar flexion, the patient may develop pain in the posterior ankle region, and it is owing to this irritation of the tendon by the os trigonum that this clinical situation has also been termed posterior impingement syndrome.4,5 Although the os trigonum will be detectable on a radiograph, the relationship between the tendon and bone will be better demonstrated using MR imaging. MR imaging will demonstrate an increased signal
Figure 14 MR imaging of the ankle, an axial slice using a T1-weighted sequence to demonstrate the anterior tendon structures. Using the lateral malleolus and achilles tendon to orientate oneself, note that there are a number of low signal intensity structures lying anterior to the tibia and fibular. From medial to lateral, these represent the tibialis posterior (1), the extensor hallucis longus (2), the extensor digitorum longus (3) and the position of the peroneus tertius (4).
Figure 15 MR imaging of the ankle in the axial plane, using a T1-weighted sequence in a 57-year-old gentleman complaining of discomfort in the posterior aspect of the ankle. The region outlined by the white oval contains three structures with low-signal intensity. The lateral two, indicated by the white arrows, represent the tendons of peroneus longus (left) and brevis (right). However, in this image, there is a third region of low signal intensity noted (black arrow). This represents the peroneus quartus, which may be, on occasion, associated with peroneus brevis tears, due to the increased pressure on the peroneal retinaculum, which is stretched around the tendons.
MR imaging of the ankle and foot intensity on the fluid sensitive sequences (T2weighted or STIR) corresponding to inflammation in and about the tendon of flexor hallucis longus. Associated bone marrow edema may also be visible. In the case of an accessory navicular, the patient may complain of discomfort and pain on the medial side of the mid-foot, with the possible presence of swelling in the region. On radiographs, a prominent navicular (bicornuate) or accessory navicular may be demonstrated. However, with MR imaging, the relationship of the accessory bone with the surrounding soft tissue structures can be appreciated to a fuller extent (Fig. 16). Ultrasound may also be a modality that is able to detect the dynamic relationship of the soft tissues structures; however, the detail that is achieved with MR imaging provides the accurate clinical imaging information. The posterior tibialis tendon is particularly important to determine since there is a higher incidence of tears in the presence of an accessory navicular. Additional pathology that may be arise may include the development of a painful bursa, or the development of bone marrow edema in the accessory navicular and navicular bone.
Trauma and associated disorders Trauma to the ankle and foot constitute a major proportion of injuries to the musculoskeletal system. Although radiography is useful in identifying
107 the basic injury in many cases, further imaging may be necessary if symptoms persist, complications develop or, in the case of an athlete, to determine exactly the degree of injury sustained.6 MR imaging is well placed to assess such injuries, being able to determine the osseous and soft tissue relationships aiding in the clinical management strategies and prognosis for the patient. Trauma to the ankle and foot may be divided in to acute or chronic presentations. Acute trauma represents a common complaint amongst patients, such as that relating to a sporting activity where an acute twisting injury results in impaction between the osseous structures and tears of the soft tissue structures surrounding the region. In such cases, regions of high signal intensity may be detected soon after the injury within the osseous structures, representing bone marrow edema. The patterns of bone marrow edema may assist in determining the direction of injury and therefore aid in identifying associated soft tissue structures that may also be implicated in the injury. During such injuries, osteochondral defects may develop whereby a fragment of cartilage often attached to the underlying bone develops. Osteochondral defects are particularly well demonstrated using MR imaging7 (Fig. 17). Tears of the tendons about the ankle and foot may also be well evaluated with MR imaging especially when associated bony injuries and additional soft tissue structures need to be evaluated. The Achilles’ tendon is prone to rupture and MR imaging
Figure 16 MR imaging of the ankle in the axial plane in (a) (T1-weighted) and (b) (STIR) and in the coronal plane in (c) (STIR) in a 33-year-old lady with pain along the medial aspect of her mid-foot, which had begun after wearing new shoes. The ovals enclose the region of abnormality, demonstrating a large navicular with an accessory navicular just medial and posterior to the normal navicular bone. In (b), a homogenous region of increased signal is noted in the navicular and accessory navicular which is also visible in (c). This is due to edema created by the altered mechanics in this region, and the irritation created by the presence of the accessory navicular bone.
108
M.A. Wessely
Figure 17 A 57-year-old gentleman suffering from ankle pain and a sensation of the joint ‘catching’ on occasion. MR imaging of the ankle, in the sagittal plane, T1-weighted (a) and STIR (b) sequences demonstrate an abnormality of the dome of the talus. In (a), a region of low signal is noted involving the majority of the articular surface of the talus. This is well visualised as a region of high signal intensity on the STIR sequence where, in addition, irregularity of the articular surface of the talus is noted and represents an osteochondral defect.
may demonstrate the degree of tear to an exquisite detail, allowing the most appropriate clinical management to be applied to the patient (Fig. 18). Chronic trauma may also be well visualised on MR imaging. Chronic trauma may result from repeated injuries such as those sustained in consecutive ankle sprains, or be related to abnormal biomechanics. Illfitting footwear may lead to altered biomechanical stress being placed on the ankle and foot (Fig. 19). An example of a clinical syndrome related to illfitting foot wear that may lead to symptoms is Haglund’s syndrome, whereby the wearing of high heels, or poorly fitting basketball-type shoes, causes chronic irritation to the posterior aspect of the ankle. The condition results in ‘Haglund’s defor-
mity’: retro-calcaneal bursitis, retro-Achilles’ bursitis and thickening of the distal Achilles’ tendon (Fig. 12). Although a number of treatment options are available, surgery is usually performed to modify the surrounding bony structures and to reduce the thickening of the tendon. Similar effects may occur in the bones of the ankle and foot, either due to poor-fitting footwear or in those who place a high demand on their feet, such as long distance runners.
Miscellaneous conditions About the ankle and foot, MR imaging may be used to determine the presence of a range of disorders.
Figure 18 A 51-year-old gentleman with sudden pain in the back of his calf and ankle. MR imaging of the ankle in the sagittal plane, T1-weighted (a), T2-weighted (b) and axial T2-weighted images. Compared to normal, where the achilles tendon is noted as a low signal intensity structure that gradually blends proximally to become the muscle belly, in these sequences there is discontinuity of the tendon (oval in (a)), and a moderate region of increased signal intensity (b and c) in the position of the normal tendon, owing to a complete Achilles’ tendon tear. The retracted fibers of the Achilles’ tendon can also be well seen particularly in (b) (oval) and (c).
MR imaging of the ankle and foot
109
Figure 19 A 33-year-old female presenting with pain in the ankle and foot following surgery for ligamentous tears about the ankle (the low signal intensity regions in the distal tibia are bony screws). MR imaging of the ankle and mid-foot performed in the coronal plane (a) and sagittal plane (b and c), demonstrate that, in the T2-weighted images of (a) and (b), regions of diffuse heterogenous increase signal intensity are noted in the talus, navicular and cuneiforms. This represents bone marrow edema that, on a T1-weighted image (c), is visible as a heterogenous decrease in signal intensity. The patient is thought to have developed the regions of bone marrow edema secondary to the altered mechanical stress placed on the ankle and foot following surgery. No associated soft tissue swelling was noted.
Infection is a major cause of disability amongst predisposed populations such as diabetic patients. Infection in the diabetic carries with it high risks of morbidity and mortality, and thus astute diagnosis and management of the patient is essential. Despite other techniques being available for the detection of infection, primarily osteomyelitis, MR imaging remains the more cost-effective and detailed examination modality to differentiate osteomyelitis from soft tissue infection and aid the visualisation of
associated complications such as abscess formation (Fig. 21). A common disorder to present in the foot is that of a Morton’s neuroma, or interdigital neuroma. Patients are often middle-aged women who develop severe pain in the region of the second or third metatarsal space, radiating to the toes. The etiology is related to chronic trauma to the plantar digital nerve, probably due to footwear such as high heels. MR imaging is a useful technique to differ-
Figure 20 A 40-year-old lady presenting with discomfort in the posterior aspect of her ankle, which was worsened when using high heels. MR imaging of the ankle, in the sagittal plane, STIR sequence demonstrates a retro-calcaneal (oval) and retro-Achilles’ (arrow) bursitis. The Achilles’ tendon is thickened at its most distal aspect due to chronic irritation. This imaging triad of bursitis in the retro-calcaneal and retro-achilles bursa and thickening of the achilles tendon has been referred to as ‘Haglund’s deformity’.
110
M.A. Wessely
Figure 21 A 79-year-old lady presenting with pain and swelling in her toe. MR imaging in the long axis plane, T1weighted (a) and STIR (b) demonstrates a region of decreased signal intensity within the bone in (a), with an associated mass in the soft tissue surrounding the bone both superior and inferiorly. On the STIR sequence (b), the lesion is wellidentified in the proximal phalanx, with increased signal intensity throughout, destruction of the cortices and extension in to the surrounding soft tissues. This is an example of osteomyelitis.
Figure 22 MR imaging of the foot, in the short axis plane, with T2-weighted (a) and T1-weighted with contrast (b), demonstrating a region of high signal intensity about the inferior aspect of the intermetatarsal space between the second and third metatarsal. This region exhibits a moderate degree of enhancement with the addition of contrast (b), due to the presence of an intermetatarsal bursitis.
Figure 23 A 54-year-old lady presenting with severe pain in the base of the ankle. MR imaging of the ankle was performed, in the sagittal plane, T1-weighted (a) and T2-weighted (b) sequences. On the T2-weighted image, a focal region of increased signal intensity is noted in the calcaneus at the insertion of the plantar fascia (oval). On the T1weighted image, the same region is noted, though now with low signal intensity, with thickening of the plantar fascia noted (oval). This is an example of moderate plantar fasciitis.
MR imaging of the ankle and foot entiate a Morton’s neuroma from other conditions such as tumours, as well as to identify the presence of concomitant conditions such as intermetatarsal bursitis (Fig. 22). MR imaging will demonstrate that the lesion will be intermediate signal on T1weighted imaging and of low signal intensity on T2-weighted imaging. If contrast is used, the lesion is well demonstrated with intense uptake. Plantar fasciitis is a condition affecting patients in both ankle and foot that often leads to a moderate to severe degree of discomfort. Whilst MR imaging is not warranted for the simple plantar fasciitis, for those patients with persistent pain, or where surgery is being considered, MR imaging may provide additional clinical information to determine the origin of the pain and identify which anatomic structures are involved8 (Fig. 23). On MR imaging, the plantar fascia/involved muscles are well identified on the sagittal images on the fluid sensitive sequences which will demonstrate regions of increased signal in and about the tendinous insertions in to the calcaneus as well as thickening of the plantar fascia, of more than 5 mm in thickness.
Conclusion MR imaging is an essential imaging technique for evaluating the foot and ankle in a range of disorders.
111 Complications associated with the primary lesions may be detected which may alter the nature and course of clinical management of the patient.
References 1. Beltran J, Shankman S. MR imaging of bone lesions of the ankle and foot. Magn Reson Imaging Clin N Am 2001;9(3):553—66. 2. Bergin D, Morrison WB. Postoperative imaging of the ankle and foot. Radiol Clin N Am 2006;44(3):391—406. 3. Lee MH, Chung CB, Cho JH, Mohana-Borges AV, Pretterklieber ML, Trudell DJ, et al. Tibialis anterior tendon and extensor retinaculum: imaging in cadavers and patients with tendon tear. Am J Roentgenol 2006;187(2):W161—8. 4. Cortes ZE, Harris AM, Baumhauer JF. Posterior ankle pain diagnosed by positional MRI of the ankle: a unique case of posterior ankle impingement and osteonecrosis of the talus. Foot Ankle Int 2006;27(4):293—5. 5. Messiou C, Robinson P, O’Connor PJ, Grainger A. Subacute posteromedial impingement of the ankle in athletes: MR imaging evaluation and ultrasound guided therapy. Skeletal Radiol 2006;35(2):88—94. 6. Morrison WB. Magnetic resonance imaging of sports injuries of the ankle. Top Magn Reson Imaging 2003;14(2): 179—97. 7. Pontell D, Hallivis R, Dollard MD. Sports injuries in the pediatric and adolescent foot and ankle: common overuse and acute presentations. Clin Podiatr Med Surg 2006;23(1): 209—31. 8. Osborne HR, Breidahl WH, Allison GT. Critical differences in lateral X-rays with and without a diagnosis of plantar fasciitis. J Sci Med Sport 2006;9(3):231—7.
intl.elsevierhealth.com/journals/clch
RESOURCE DOCUMENT
MR imaging of the ankle and foot–—A review of the normal imaging appearance with an illustration of common disorders Michelle A. Wessely * Department of Radiology/Department of Clinical Research, Institut Franco-Europeen de Chiropratique (IFEC), 24 Boulevard Paul Vaillant Couturier, 94200 Ivry Sur Seine, France Accepted 28 February 2007
KEYWORDS Ankle; Congenital abnormalities; MR imaging; Foot; Normal variants; Trauma
Summary This article aims to provide a brief overview of magnetic resonance imaging (MRI) of the ankle for the clinician. A basic review of MRI protocols for the region is followed by discussion of the most common imaging sequences. The appearance of normal ankle anatomy is reviewed with emphasis on structures prone to injury; congenital and developmental abnormalities and normal variants. These are correlated to annotated images. Imaging of ankle and foot pathology and trauma is then discussed with emphasis on the identification of ankle pathology for the manual physician. Illustrative examples are given with discussion of specific common conditions including avascular necrosis, accessory navicular, Haglund’s syndrome, Morton’s neuroma, osteochondral defects, osteomyelitis, os trigonum syndrome, peroneus quartus, plantar fasciitis and tendinitis/tendinosis. # 2007 The College of Chiropractors. Published by Elsevier Ltd. All rights reserved.
Introduction Non-invasive imaging of the ankle and foot may consist of a variety of approaches including plain film radiography, ultrasound and further imaging such as computed tomography (CT) and magnetic resonance (MR) imaging, depending on the clinical suspicion and the available resources. Whilst the * Correspondence to: Department of Radiology, Institut FrancoEuropeen de Chiropratique (IFEC), 24 Boulevard Paul Vaillant Couturier, 94200 Ivry Sur Seine, France. Tel.: +33 14515 8919; fax: +33 14515 8911. E-mail address: [email protected].
basic imaging techniques may be useful in many clinical circumstances, an increasing number of patients undergo further imaging. It is, therefore, important for the manual physician to have a good knowledge of the basic anatomical appearance of the ankle and foot on MR images. An appreciation of the imaging characteristics of common disorders of the ankle and foot is also useful to aid clinical diagnosis and management of the patient. This article aims to approach the ankle and foot from the basic normal MR imaging appearance to the more complex disorders illustrating the use of MR imaging in the evaluation of patients who present with abnormalities in the ankle or foot.
1479-2354/$32.00 # 2007 The College of Chiropractors. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.clch.2007.02.006
102
M.A. Wessely
Clinical indications The clinical indications for MR imaging of the ankle and foot are wide, though this may depend on the clinical protocols established by the imaging centre and the availability of resources. Based on current evidence, MR imaging of the ankle and foot is considered an imaging modality of choice for conditions such as internal derangements (for example, impingement syndromes) that commonly affect the ankle or for post-operative evaluation.1,2 Although more basic imaging studies can suggest a disorder and, indeed, be able to show dynamically the effect of the condition, it is the anatomical detail that MR imaging affords that sets it apart. An example of this is the os trigonum syndrome, where the flexor hallucis longus tendon may be compromised, leading to posterior impingement syndrome. Although the os trigonum itself is demonstrated well on plain film images, the tendinous involvement can only be inferred; MR images will show clearly the precise location and severity of the soft tissue involvement. Likewise, in cases of trauma, bony and associated soft tissue lesions can be easily identified, and monitored throughout the patient’s management. This is particularly so when surgery is necessary and MR imaging is used to determine the post-surgical response and evaluate intermediate to long-term complications, including avascular necrosis and osteochondral injuries, which may remain undetected with other imaging modalities. Additional miscellaneous conditions may be best evaluated with MR imaging, including Morton’s neuroma. Although ultrasound may in some circumstances be useful in the detection and treatment of this lesion, MR imaging is better able to differentiate from other conditions including malignant soft tissue tumours.
Figure 1 MR imaging of the ankle of a 33-year-old lady with pain on the medial aspect of the mid-foot. On this axial, T1-weighted image, a region of high signal intensity is noted on the medial aspect of the skin, just medial to the navicular (circle). This is a skin marker to indicate the epicentre of pain or swelling noted by the patient and is useful to note when interpreting the final image.
of the lesion and therefore aid the diagnosis. Each slice is usually 4 mm in thickness. MR imaging of the foot is ordinarily performed with the patient in the prone position. Although this
Procedure and sequences MR imaging of the ankle requires that the patient lies supine with the ankle perpendicular to the lower leg. A support may be used to maintain the position during the imaging study. A surface coil is usually employed to increase the signal capture. A skin marker may be added to illustrate to the person reading the image, the region of pain or swelling for the patient (Fig. 1). The sequences selected usually consist of all three planes: sagittal (Figs. 2—4), axial (Figs. 5—7) and coronal (Figs. 8—10), using a combination of T1- and T2-weighted, straight (or STIR) sequences, depending on the clinical scenario. Contrast is used where a mass or infection is suspected in order to determine the character and behaviour
Figure 2 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This is a sagittal, T-1 weighted image demonstrating the fibula with the tendons of the peronei wrapping around the distal aspect. When interpreting the sagittal plane, identifying the fibula, allows the anatomy of lateral slices of the ankle to be more easily determined.
MR imaging of the ankle and foot
Figure 3 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This is a sagittal, T1weighted image in the mid-sagittal plane demonstrating the bone and soft tissue detail well.
103
Figure 5 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This slice is an axial, T-1 weighted image taken in the region of the distal tibia and fibula. Orientation to this image is achieved by using the Achilles’ tendon to determine the posterior aspect and then, opposing this, the anterior aspect. The fibula with the peronei tendons wrapping around it help differentiate the lateral aspect of the ankle from the medial.
position may be difficult for some patients, it allows for the toes to be maintained in the neutral position, and for the patient to be as immobile as possible during the imaging study, therefore limiting motion artefact which can degrade the final image quality. The sequences and planes are the same as in the ankle; however, the sagittal image is performed
along the long axis of the metatarsals, and may be referred to as the long axis; the axial slice perpendicular to the second or third metatarsal long axis and which may be referred to as the short axis,
Figure 4 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This sagittal, T1-weighted image demonstrates one of the most medial slices captured during this study. Notice the position of the medial malleolus.
Figure 6 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. An axial, T1-weighted image slightly more inferior than in the previous figure. It is useful to start from superiorly and to work inferiorly to retain an orientation to the image. Note the most distal tip of the lateral malleolus and the sickle-shaped Achilles’ tendon.
104
M.A. Wessely
Figure 7 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This is a T1-weighted axial slice of the most distal slice obtained during this study. Note the insertion of the Achilles’ tendon on the calcaneus.
Figure 9 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This image is also in the coronal plane, slightly more anterior to the previous slice. Note the changing form of the bony structures, and the appearance of the sustentaculum tali.
and the coronal image in a plane connecting the second and fifth metatarsals. These slight variations are useful to know in order to better orientate the anatomical structures when interpreting the final MR image.
Normal imaging appearance
Figure 8 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This is one of the most posterior slices in the coronal plane on this, a T1-weighted image, where one’s orientation is based around the fibula, a lateral structure. Once determined, the remaining structures are more easily identified.
Figure 10 MR imaging of the ankle of a 33-year-old lady with hind and mid-foot pain. This is the most anterior slice of a coronal, T1-weighted sequence. It is useful to start with the most posterior slice and then work forward to remain orientated to the images. This slice was performed in the posterior aspect of the mid-foot.
The main structures to be evaluated on MR imaging of the ankle and foot will be discussed, although, owing to the wide variation in appearances and the
MR imaging of the ankle and foot anomalous soft tissue structures, it will be necessary for the reader to regard this text as an introduction to the basic interpretation of this region. Although there are a variety of methods to evaluate imaging of the ankle and foot, it is useful to approach the interpretation by identifying individual anatomic structures. These can be divided into those comprising the soft tissues, including tendons, ligaments and fascia; neural and bony structures. For the purpose of this article, the emphasis will be placed on those structures that are commonly implicated in the development of clinical syndromes, namely the soft tissue and bony structures. The soft tissue structures include the tendons. In order to be able to identify the different tendons, the ankle and foot may be divided into four sections: anterior, posterior, medial and lateral in order to better orientate the position of the tendons. About the ankle and foot, the posterior tendons include the Achilles’ and plantaris along with their bursae (Fig. 11). Medially, the flexor tendons pass including tibialis posterior, flexor digitorum longus and flexor hallucis longus (mnemonically referred to as ‘‘Tom, Dick and Harry’’). The posterior tibial artery, nerve and vein are located between flexor digitorum longus and flexor hallucis longus (Fig. 12). Laterally, the peroneus tendons consisting of peroneus longus and brevis are located (Fig. 13). Anteriorly, the
Figure 11 MR imaging of the ankle in the axial plane, a T1-weighted image of a patient with ankle discomfort. The posterior tendon structures can be identified with the most posterior structure representing the Achilles’ tendon with its low signal intensity (circle). The tendon may sometimes demonstrate a small focus of increased signal in its centre, although this is not visible in this patient. Just anteromedial to the Achilles’ tendon, is a region of grey/intermediate signal that represents the soleus muscle.
105 tendons consist of the tibialias anterior, which lies the most medially, then the extensor hallucis longus, extensor digitorum longus and peroneus tertius3 (Fig. 14). These structures tend to be affected the least about the ankle. In addition to the tendons, the ligaments may be visible using MR imaging; however, owing to the possibility of detecting lesions of the ligaments by clinical examination and, if necessary, ultrasound, MR imaging is not used systematically for the evaluation of the ligaments about the ankle and foot. Despite this, note may be made of those ligaments that may be more often involved in clinical syndromes, including the medial ligament complex (deltoid) and lateral ligament complex. These ligaments are best evaluated using the axial images.
Normal variants and developmental anomalies A number of normal variants of the osseous and soft tissue structures may be encountered about the foot and ankle. It is important to be familiar with these
Figure 12 MR imaging of the ankle in the axial plane, a T1-weighted image demonstrating the medial soft tissue structures. The hatched oval represents the tibialis posterior tendon, located the most anteriorly, and the flexor digitorum longus more posteriorly (hint–—use the achilles tendon to orientate to the image). The arrow points to a small intermediate signal intensity that represents the posterior tibial vein. Directly posterior to this is an oval within which are located two small round structures, the most medial of which is the posterior tibial artery, and laterally the tibial nerve. The smaller oval structure surrounding the low signal intensity structure represents the tendon of flexor hallucis longus.
106
M.A. Wessely
Figure 13 MR imaging of the ankle, axial plane with a T1-weighted sequence demonstrating the two small, low signal intensity structures enclosed within an white oval. These structures represent the peronei tendons. The more lateral structure (hint–—note the lateral malleolus) represents the peroneus longus tendon and the more medial, the peroneus brevis tendon. Note their intimate association with the posterior aspect of the lateral malleolus.
so as to not to confuse them with pathologies, for example the presence of peroneus quartus, a supplementary muscle with that can have clinical significance (Fig. 15). Developmental anomalies about the foot and ankle are more clinical important since provocation of pain syndromes may occur, for example in the case of accessory ossicles. About the ankle, the two most common accessory ossicles are the os trigonum and the accessory navicular bone. With an os trigonum, the patient will tend to complain of pain in the posterior aspect of the ankle that is worsened by plantar flexion. This is particularly the case in patients who dance, run down hills or play football. The accessory bone is located posterior to the distal tibia, behind which the tendon of the flexor hallucis longus passes, slightly medially to the os trigonum. During forced plantar flexion, the patient may develop pain in the posterior ankle region, and it is owing to this irritation of the tendon by the os trigonum that this clinical situation has also been termed posterior impingement syndrome.4,5 Although the os trigonum will be detectable on a radiograph, the relationship between the tendon and bone will be better demonstrated using MR imaging. MR imaging will demonstrate an increased signal
Figure 14 MR imaging of the ankle, an axial slice using a T1-weighted sequence to demonstrate the anterior tendon structures. Using the lateral malleolus and achilles tendon to orientate oneself, note that there are a number of low signal intensity structures lying anterior to the tibia and fibular. From medial to lateral, these represent the tibialis posterior (1), the extensor hallucis longus (2), the extensor digitorum longus (3) and the position of the peroneus tertius (4).
Figure 15 MR imaging of the ankle in the axial plane, using a T1-weighted sequence in a 57-year-old gentleman complaining of discomfort in the posterior aspect of the ankle. The region outlined by the white oval contains three structures with low-signal intensity. The lateral two, indicated by the white arrows, represent the tendons of peroneus longus (left) and brevis (right). However, in this image, there is a third region of low signal intensity noted (black arrow). This represents the peroneus quartus, which may be, on occasion, associated with peroneus brevis tears, due to the increased pressure on the peroneal retinaculum, which is stretched around the tendons.
MR imaging of the ankle and foot intensity on the fluid sensitive sequences (T2weighted or STIR) corresponding to inflammation in and about the tendon of flexor hallucis longus. Associated bone marrow edema may also be visible. In the case of an accessory navicular, the patient may complain of discomfort and pain on the medial side of the mid-foot, with the possible presence of swelling in the region. On radiographs, a prominent navicular (bicornuate) or accessory navicular may be demonstrated. However, with MR imaging, the relationship of the accessory bone with the surrounding soft tissue structures can be appreciated to a fuller extent (Fig. 16). Ultrasound may also be a modality that is able to detect the dynamic relationship of the soft tissues structures; however, the detail that is achieved with MR imaging provides the accurate clinical imaging information. The posterior tibialis tendon is particularly important to determine since there is a higher incidence of tears in the presence of an accessory navicular. Additional pathology that may be arise may include the development of a painful bursa, or the development of bone marrow edema in the accessory navicular and navicular bone.
Trauma and associated disorders Trauma to the ankle and foot constitute a major proportion of injuries to the musculoskeletal system. Although radiography is useful in identifying
107 the basic injury in many cases, further imaging may be necessary if symptoms persist, complications develop or, in the case of an athlete, to determine exactly the degree of injury sustained.6 MR imaging is well placed to assess such injuries, being able to determine the osseous and soft tissue relationships aiding in the clinical management strategies and prognosis for the patient. Trauma to the ankle and foot may be divided in to acute or chronic presentations. Acute trauma represents a common complaint amongst patients, such as that relating to a sporting activity where an acute twisting injury results in impaction between the osseous structures and tears of the soft tissue structures surrounding the region. In such cases, regions of high signal intensity may be detected soon after the injury within the osseous structures, representing bone marrow edema. The patterns of bone marrow edema may assist in determining the direction of injury and therefore aid in identifying associated soft tissue structures that may also be implicated in the injury. During such injuries, osteochondral defects may develop whereby a fragment of cartilage often attached to the underlying bone develops. Osteochondral defects are particularly well demonstrated using MR imaging7 (Fig. 17). Tears of the tendons about the ankle and foot may also be well evaluated with MR imaging especially when associated bony injuries and additional soft tissue structures need to be evaluated. The Achilles’ tendon is prone to rupture and MR imaging
Figure 16 MR imaging of the ankle in the axial plane in (a) (T1-weighted) and (b) (STIR) and in the coronal plane in (c) (STIR) in a 33-year-old lady with pain along the medial aspect of her mid-foot, which had begun after wearing new shoes. The ovals enclose the region of abnormality, demonstrating a large navicular with an accessory navicular just medial and posterior to the normal navicular bone. In (b), a homogenous region of increased signal is noted in the navicular and accessory navicular which is also visible in (c). This is due to edema created by the altered mechanics in this region, and the irritation created by the presence of the accessory navicular bone.
108
M.A. Wessely
Figure 17 A 57-year-old gentleman suffering from ankle pain and a sensation of the joint ‘catching’ on occasion. MR imaging of the ankle, in the sagittal plane, T1-weighted (a) and STIR (b) sequences demonstrate an abnormality of the dome of the talus. In (a), a region of low signal is noted involving the majority of the articular surface of the talus. This is well visualised as a region of high signal intensity on the STIR sequence where, in addition, irregularity of the articular surface of the talus is noted and represents an osteochondral defect.
may demonstrate the degree of tear to an exquisite detail, allowing the most appropriate clinical management to be applied to the patient (Fig. 18). Chronic trauma may also be well visualised on MR imaging. Chronic trauma may result from repeated injuries such as those sustained in consecutive ankle sprains, or be related to abnormal biomechanics. Illfitting footwear may lead to altered biomechanical stress being placed on the ankle and foot (Fig. 19). An example of a clinical syndrome related to illfitting foot wear that may lead to symptoms is Haglund’s syndrome, whereby the wearing of high heels, or poorly fitting basketball-type shoes, causes chronic irritation to the posterior aspect of the ankle. The condition results in ‘Haglund’s defor-
mity’: retro-calcaneal bursitis, retro-Achilles’ bursitis and thickening of the distal Achilles’ tendon (Fig. 12). Although a number of treatment options are available, surgery is usually performed to modify the surrounding bony structures and to reduce the thickening of the tendon. Similar effects may occur in the bones of the ankle and foot, either due to poor-fitting footwear or in those who place a high demand on their feet, such as long distance runners.
Miscellaneous conditions About the ankle and foot, MR imaging may be used to determine the presence of a range of disorders.
Figure 18 A 51-year-old gentleman with sudden pain in the back of his calf and ankle. MR imaging of the ankle in the sagittal plane, T1-weighted (a), T2-weighted (b) and axial T2-weighted images. Compared to normal, where the achilles tendon is noted as a low signal intensity structure that gradually blends proximally to become the muscle belly, in these sequences there is discontinuity of the tendon (oval in (a)), and a moderate region of increased signal intensity (b and c) in the position of the normal tendon, owing to a complete Achilles’ tendon tear. The retracted fibers of the Achilles’ tendon can also be well seen particularly in (b) (oval) and (c).
MR imaging of the ankle and foot
109
Figure 19 A 33-year-old female presenting with pain in the ankle and foot following surgery for ligamentous tears about the ankle (the low signal intensity regions in the distal tibia are bony screws). MR imaging of the ankle and mid-foot performed in the coronal plane (a) and sagittal plane (b and c), demonstrate that, in the T2-weighted images of (a) and (b), regions of diffuse heterogenous increase signal intensity are noted in the talus, navicular and cuneiforms. This represents bone marrow edema that, on a T1-weighted image (c), is visible as a heterogenous decrease in signal intensity. The patient is thought to have developed the regions of bone marrow edema secondary to the altered mechanical stress placed on the ankle and foot following surgery. No associated soft tissue swelling was noted.
Infection is a major cause of disability amongst predisposed populations such as diabetic patients. Infection in the diabetic carries with it high risks of morbidity and mortality, and thus astute diagnosis and management of the patient is essential. Despite other techniques being available for the detection of infection, primarily osteomyelitis, MR imaging remains the more cost-effective and detailed examination modality to differentiate osteomyelitis from soft tissue infection and aid the visualisation of
associated complications such as abscess formation (Fig. 21). A common disorder to present in the foot is that of a Morton’s neuroma, or interdigital neuroma. Patients are often middle-aged women who develop severe pain in the region of the second or third metatarsal space, radiating to the toes. The etiology is related to chronic trauma to the plantar digital nerve, probably due to footwear such as high heels. MR imaging is a useful technique to differ-
Figure 20 A 40-year-old lady presenting with discomfort in the posterior aspect of her ankle, which was worsened when using high heels. MR imaging of the ankle, in the sagittal plane, STIR sequence demonstrates a retro-calcaneal (oval) and retro-Achilles’ (arrow) bursitis. The Achilles’ tendon is thickened at its most distal aspect due to chronic irritation. This imaging triad of bursitis in the retro-calcaneal and retro-achilles bursa and thickening of the achilles tendon has been referred to as ‘Haglund’s deformity’.
110
M.A. Wessely
Figure 21 A 79-year-old lady presenting with pain and swelling in her toe. MR imaging in the long axis plane, T1weighted (a) and STIR (b) demonstrates a region of decreased signal intensity within the bone in (a), with an associated mass in the soft tissue surrounding the bone both superior and inferiorly. On the STIR sequence (b), the lesion is wellidentified in the proximal phalanx, with increased signal intensity throughout, destruction of the cortices and extension in to the surrounding soft tissues. This is an example of osteomyelitis.
Figure 22 MR imaging of the foot, in the short axis plane, with T2-weighted (a) and T1-weighted with contrast (b), demonstrating a region of high signal intensity about the inferior aspect of the intermetatarsal space between the second and third metatarsal. This region exhibits a moderate degree of enhancement with the addition of contrast (b), due to the presence of an intermetatarsal bursitis.
Figure 23 A 54-year-old lady presenting with severe pain in the base of the ankle. MR imaging of the ankle was performed, in the sagittal plane, T1-weighted (a) and T2-weighted (b) sequences. On the T2-weighted image, a focal region of increased signal intensity is noted in the calcaneus at the insertion of the plantar fascia (oval). On the T1weighted image, the same region is noted, though now with low signal intensity, with thickening of the plantar fascia noted (oval). This is an example of moderate plantar fasciitis.
MR imaging of the ankle and foot entiate a Morton’s neuroma from other conditions such as tumours, as well as to identify the presence of concomitant conditions such as intermetatarsal bursitis (Fig. 22). MR imaging will demonstrate that the lesion will be intermediate signal on T1weighted imaging and of low signal intensity on T2-weighted imaging. If contrast is used, the lesion is well demonstrated with intense uptake. Plantar fasciitis is a condition affecting patients in both ankle and foot that often leads to a moderate to severe degree of discomfort. Whilst MR imaging is not warranted for the simple plantar fasciitis, for those patients with persistent pain, or where surgery is being considered, MR imaging may provide additional clinical information to determine the origin of the pain and identify which anatomic structures are involved8 (Fig. 23). On MR imaging, the plantar fascia/involved muscles are well identified on the sagittal images on the fluid sensitive sequences which will demonstrate regions of increased signal in and about the tendinous insertions in to the calcaneus as well as thickening of the plantar fascia, of more than 5 mm in thickness.
Conclusion MR imaging is an essential imaging technique for evaluating the foot and ankle in a range of disorders.
111 Complications associated with the primary lesions may be detected which may alter the nature and course of clinical management of the patient.
References 1. Beltran J, Shankman S. MR imaging of bone lesions of the ankle and foot. Magn Reson Imaging Clin N Am 2001;9(3):553—66. 2. Bergin D, Morrison WB. Postoperative imaging of the ankle and foot. Radiol Clin N Am 2006;44(3):391—406. 3. Lee MH, Chung CB, Cho JH, Mohana-Borges AV, Pretterklieber ML, Trudell DJ, et al. Tibialis anterior tendon and extensor retinaculum: imaging in cadavers and patients with tendon tear. Am J Roentgenol 2006;187(2):W161—8. 4. Cortes ZE, Harris AM, Baumhauer JF. Posterior ankle pain diagnosed by positional MRI of the ankle: a unique case of posterior ankle impingement and osteonecrosis of the talus. Foot Ankle Int 2006;27(4):293—5. 5. Messiou C, Robinson P, O’Connor PJ, Grainger A. Subacute posteromedial impingement of the ankle in athletes: MR imaging evaluation and ultrasound guided therapy. Skeletal Radiol 2006;35(2):88—94. 6. Morrison WB. Magnetic resonance imaging of sports injuries of the ankle. Top Magn Reson Imaging 2003;14(2): 179—97. 7. Pontell D, Hallivis R, Dollard MD. Sports injuries in the pediatric and adolescent foot and ankle: common overuse and acute presentations. Clin Podiatr Med Surg 2006;23(1): 209—31. 8. Osborne HR, Breidahl WH, Allison GT. Critical differences in lateral X-rays with and without a diagnosis of plantar fasciitis. J Sci Med Sport 2006;9(3):231—7.