Magnetic resonance imaging of the foot and ankle: correlation of normal anatomy with pathologic conditions.

0198-0211/91/1105-0289$03.00/0 FOOT & ANKLE Copyright 0 1991 by the American Orthopaedic Foot and Ankle Society, Inc

Magnetic Resonance Imaging of the Foot and Ankle: Correlation of Normal Anatomy with Pathologic Conditions Richard D. Ferkel, M.D.,* Bonnie D. Flannigan, M.D.,t and Brad S. Elkins, B.S.* Van Nuys, California and San Francisco, California

ABSTRACT Abnormalities of the foot and ankle can be difficult to diagnose by conventional examination and x-rays. Recently, magnetic resonance imaging (MRI) has emerged as a diagnostic tool for soft tissue and bony imaging. One hundred and ten normal feet and ankles were studied to define normal MRI anatomy. An additional 150 MRI scans were performed to diagnose and characterize various abnormal conditions. MRI demonstrated excellent definition of normal structures and pathologic entities. Surgical correlation with the MRI was done in 42 patients. MRI appears to be a useful examination for patients with certain soft tissue and bony abnormalities. A special oblique view also has been developed to assist in the diagnosis of injuries to the tibialis posterior, flexor hallucis longus, and flexor digitorum longus tendons.

both normal and pathologic anatomy of the foot and ankle. Prior MRI studies have delineated normal ankle morphology in conventional orthogonal (coronal, sagittal, and axial) plane^.^^''-'^ However, image quality and quantity were limited due to technical factors, a lack of clinical experience, and inadequate postsurgical followup. Sartoris and Resnick have described the technical aspects of MRI of the foot and ankle,17 in addition to pathology demonstrated by CAT scan and MR1.18 Isolated cases of tendon ruptures,’ hematomas,’ and osteoid osteoma2*have been reported. The purpose of this study was to identify normal and abnormal morphology using high resolution images, and to correlate pathologic findings with surgical pathology.

EVALUATION OF NORMAL ANATOMY AND PATHOLOGIC ENTITIES

MATERIAL AND METHODS

Clinical detection of foot and ankle abnormalities can be difficult due to swelling and pain. Prior imaging techniques have not been sensitive to soft tissue injury. Computerized axial tomography (CAT) has been shown to be useful in demonstrating osseous structures, however soft tissue abnormalities are often poorly delineated and early vascular abnormalities of the bone may be difficult to detect. Magnetic resonance imaging (MRI) has proven to be an excellent tool for studying the soft tissues of the knee joint, including ligaments and tendons. In addition to superb soft tissue detail, MRI offers additional advantages of direct multiplanar imaging and the lack of ionizing radiation. Applications in the foot and ankle have been limited and few papers have addressed the clinical utility of foot and ankle MRI. Through this study we developed an appreciation for

The majority of MRI scans of the foot and ankle were performed at the Magnetic Resonance Imaging Center at Valley Presbyterian Hospital during 1987 and 1988. Cases referred from other MRI centers for consultation were also reviewed. A total of 260 foot and ankle scans (130 patients) were performed and abnormalities were found in 120 (60 patients). Forty-two of these patients had surgical confirmation of their disease process which allowed direct correlation with the MRI scans obtained preoperatively (Table 1). The remaining patients had clinical diagnoses treated nonsurgically. The normal category (I) listed in Table 1 includes those six volunteers who had bilateral scans in addition to asymptomatic feet and ankles from 49 patients who had bilateral scans. Images were performed on a 1.5 Tesla G.E. MRI Imager (General Electric, Milwaukee, WI). Slices 3 mm thick were obtained with a 1.0 mm interslice gap. Although we had the capability to obtain contiguous 3mm slices, a significant increase in scan time was required, and it was felt that a 1 mm gap would not be clinically important. However, scanning without a gap

’To whom all correspondence and reprint requests should be addressed at: Southern California Orthopedic Institute, 15211 VanOwen St., Suite 300, Van Nuys, CA 91405. t Department of Radiology, Valley Presbyterian Hospital, Van Nuys, California. $ University of California, San Francisco, California. 289

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FERKEL ET AL. TABLE 1 MRI Diagnoses in Foot and Ankle Number of feet and ankles (swery)

I. Normal feet and ankles (volunteers and patients) II. No obvious pathology found by MRI 111. Achilles tendon injuries A. Tears/ruptures B. Tendinitis C. Bursitis IV. Other tendon pathologies A. Tibialis posterior 1. Ruptures 2. Tenosynovitis B. Flexor hallucis longus C. Peroneus longus/peroneus brevis V. Ligamentous injuries A. Anterior talofibular B. Anterior tibiofibular C. Deltoid D. Anterolateral impingement

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may be indicated when looking for small structures such as neuromas. A repetition time of 2000 msec was used with echo delay times of 40 msec and 80 msec for coronal and axial images (T2 weighted). A repetition of 500 msec and echo delay time of 20 msec were used for sagittal images. A 24 cm field of view and a 256 x 256 matrix were used. Although several patients were scanned in a standard knee coil, most were scanned using a head coil that allowed images of both extremities to be obtained for comparison purposes. The feet were placed in a standard side-by-side dorsiflexed position. Standard orthogonal planes were obtained in all cases. A T2 weighted modified coronal projection was obtained in cases where evaluation of obliquely oriented tendinous or ligamentous structures was requested. This was a particularly useful view for evaluation of the obliquely oriented segment of the posterior tibialis tendon. RESULTS

Normal structures of the foot and ankle including bone, articular cartilage, muscle, tendon, ligament, fat, and fluid were demonstrated using MRI (Table 2). T1 weighted sequences (i.e., short repetition time [TR] and echo time [TE] times) are adequate for demonstrating normal anatomy; osseous structures are characterized by central high signal intensity (bright) representing the fat contained in bone marrow, outlined by a thin line of low signal intensity (dark) cortical bone. However, T2 weighted sequences (i.e., long TR and TE times) detected and accentuated pathology of soft tissue structures. Fluid appears as intermediate signal intensity on T1 weighted images and becomes brighter on T2 weighted images. Thus, fluid is most easily detected using T2 weighted pulse sequences. Articular cartilage

VI. Inflammation A. Soft tissue B. Osteomyelitis C. Joint effusion D. Sinus Tarsi Syndrome VII. Tumors A. Benign 1. Plantar fibromatosis 2. Ganglion cysts 3. Other B. Malignant-angiosarcoma VIII. Posttraumatic injuries A. Fractures B. Loose bodies C. Osteochondral lesions of the talus D. Avascular necrosis E. Other IX. Other

Total

TABLE 2 Preferred MRI Techniaues Area of pathology

Plane

TE-Weiaht

Achilles Tibialis posterior, flexor hallucis longus, peroneal brevis Anterolateral impingement Ankle ligaments Soft tissue masses Bone

Sagittal, axial Modified coronal oblique, sagittal Axial. coronal

T2 T2

Axial, coronal Coronal, sagittal" Coronal, axial

T1, T2 T1, T2 T1, T2'

T2

The type of view depends somewhat on the location of the lesion. Views should always be done at two planes 90" to each other such as the coronal and sagittal or coronal and axial. a

Fig. 1. Normal T1 weighted axial section through the talar dome. Abbreviations used in figures are found in Table 31


Foot & Ankle/Vol. 1 1, No. 5/April 1991 TABLE 3 Abbreviations Used in Figures abdht abdm abh adh af at ataf atif atnvb cafb cal cb del(tc) del(tt) edb edl ehl fb fld fdb fdl fdmb fdt fhbt fhl fhlm gsv ic int iol Ic m mc nav Pa Pb Pbm PI Pt ptnvb 9P rb ses spring st ta tal tb tP 1 mt 5 mt 5P

abductor hallucis tendon abductor digiti minimi muscle abductor hallucis muscle adductor hallucis (oblique)muscle pre-Achilles fat triangle Achilles tendon anterior talofibular ligament anterior tibiofibular ligament anterior tibial neurovascular bundle calcaneofibular ligament calcaneous cuboid medial (deltoid) ligament-tibiocalcaneal medial (deltoid) ligament-tibiotalar extensor digitorum brevis muscle extensor digitorum longus tendon extensor hallucis longus tendon fibula fluid flexor digitorum brevis muscle flexor digitorum longus tendon flexor digiti minimi brevis muscle flexor digitorum tendons flexor hallucis brevis tendon flexor hallucis longus tendon flexor hallucis longus muscle great saphenous vein intermediate cuneiform interosseous muscles interosseous ligament lateral cuneiform muscle medial cuneiform navicular plantar aponeurous peroneus brevis tendon peroneus brevis muscle peroneus longus tendon peroneus tertius tendon posterior tibial neurovascular bundle quadratus plantae retrocalcanealbursa sesamoid bones calcaneonavicular (spring) ligament sustenaculum tali tibialis anterior talus tibia tibialis posterior first metatarsal fifth metatarsal fifth proximal phalanx

(intermediate signal intensity) is better delineated using T2 weighted images in the presence of joint fluid (bright) which contrasts against the intermediate signal of cartilage. Tendons and ligaments are dark and muscle is of intermediate signal intensity on all pulse sequences. Discussion of normal anatomy and pathologic condi-

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tions has been divided geographically into central, medial, lateral, and posterior compartments. Medial Structures: Normal

Normal anatomical sections demonstrate five structures passing posterior to the medial malleolus and deep to the flexor retinaculum (Fig. l).3~i0~i5 Abbreviations used in figures are found in Table 3. Identification of these five structures in every patient can aid in the diagnosis or exclusion of a ruptured medial tendon. From anterior to posterior these structures are: the tibialis posterior tendon (TP), the flexor digitorum longus tendon (FDL), the posterior tibial artery and nerve (PTNVB), and the flexor hallucis longus tendon (FHL). In the sagittal planes (Fig. 2), the three tendons are identified crossing the ankle joint sequentially from anterior to posterior. The tibialis posterior muscle, originating on the tibia, has multiple insertions on the plantar aspect of the foot, including the navicular tuberosity, cuneiforms, and metatarsals. Figure 3A demonstrates the TP inserting into the navicular tuberosity, which can be a site for rupture. Unlike other joints, the tendons of the ankle make sharp turns on the way to their insertions. In order to better visualize the integrity of TP, FDL, and FHL tendons, we employed a modified coronal oblique (MCO) technique. This technique is performed by using a scan plane oriented at a 45' angle to a true coronal (i.e., parallel to the obliquely oriented segment of tendon as it crosses the ankle joint) and is particularly useful for looking at pathology at the joint level (Fig. 38). Both the TP and FDL can be evaluated by using this 45' angle obliquity (Fig. 3C). The FHL originates in the distal fibula, and the muscle and tendon can be identified on inferior axial sections

Fig. 2. Normal T1 weighted sagittal section (medial).


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:I Digitorurn .ongus FI Hallucis Longus

Tibialis Posterior

B

Fig. 3. A, Normal T1 weighted sagittal section demonstrating TP tendon inserting into the navicular tuberosity. 6,Modified coronal oblique imaging. Upper left inset demonstrates the angle (45') of the scan plane used electronically to obtain sections parallel to the obliquely oriented segments of the shaded and labeled tendons (FDL. FHL, and TP). C, Normal T1 weighted modified oblique coronal through the TP tendon (45O angle).

(Fig. 1). Because the FHL courses below the sustentaculum tali at a more shallow angle than the TP and FDL tendons (Figs. 4A, 5, and 6), the FHL tendon can best be demonstrated using a 30' modified oblique coronal plane (Fig. 48). The medial (deltoid ligament) originates from the distal tibia and has insertions into the talus, calcaneus, and navicular bones. The tibiotalar and tibiocalcaneal insertions are identified in Figures 5 and 7, just deep to the TP. Medial Structures: Pathology

Medial foot pain, valgus hindfoot, and poor strength or difficulty with toe raising are often associated with pathology, involving FHL, FDL, and TP tendons. Figure 8A demonstrates the absence of the TP tendon with fluid in the remaining tendon sheath in a patient who had a surgically proven chronic rupture of the TP tendon (Fig. 88).

A retracted tendon can often be identified in some cases of tendon rupture. In Figure 9, a retracted TP tendon is seen distally within a fluid-filled synovial sheath cyst related to the rupture site. Sections superior to this image demonstrated absence of the TP tendon. Tenosynovitis is recognized on MRI as fluid within the tendon or sheath surrounding the normal tendon. Figure 10 demonstrates fluid, which is of higher signal intensity than the muscle, surrounding all three tendons consistent with an extensive tenosynovitis. Also, note the diffuse enlargement of the left foot due to the increased amount of subcutaneous edema fluid. T2 weighted images would have been helpful, but were unfortunately not obtained. Figure 11 demonstrates an example of an isolated tenosynovitis involving the FHL tendon. The sagittal image confirms the presence of the intact FHL tendon coursing inferior to the sustentaculum tali enroute to its insertion on the plantar aspect of the distal first phalanx.


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Fig. 4. Views of FHL tendon. A, Normal T1 weighted sagittal image of FHL tendon traveling inferior to sustentaculum tali. B, Normal T1 weighted modified oblique coronal demonstrating the course of FHL distal to sustentaculum tali.

The Achilles tendon (at) is bordered anteriorly by the pre-Achilles fat triangle (af) and is surrounded posteriorly by a subcutaneous bursa and additional fat. A second bursa, the retrocalcaneal bursa, lies just superior and posterior to the calcaneus and anterior to the Achilles' t e n d ~ n . ~ . ' ~ , ' ~ The Achilles tendon is characterized as being of uniform caliber and homogeneous low signal intensity. It generally measures less than 1.0 cm in the AP (Fig. 12) and mediolateral dimension (Fig. 1). Axial sections demonstrate a half moon configuration, and the tendon is convex posteriorly.

Fig. 5.

Normal T1 weighted coronal section anterior to the fibula

Posterior Structures: Normal

The superficial muscles of the calf (gastrocnemius, soleus, and plantaris muscles) form the Achilles tendon which inserts into the posterior aspect of the calcaneus.

Posterior Structures: Pathology

A spectrum of Achilles tendon abnormalities can be observed. A complete rupture of the Achilles tendon is diagnosed by the "Thompson test."*' On MRI, a complete Achilles rupture is identified by loss of continuity of the tendinous structure, retraction of either the proximal or distal tendon fragment, and increased fluid


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may develop multiple longitudinal tears within the substance, which is demonstrated as an irregular, wavy Achilles tendon with increased signal intensity on MRI (Fig. 14). Partial ruptures of the Achilles tendon are usually recognized by fusiform swelling of the tendon itself, as well as a focal region of increased signal intensity consistent with either hemorrhage or fluid at the partial rupture site (Fig. 15A). Note in Figure 158, the asymmetry in appearance of the Achilles tendon. The left Achilles tendon (arrow) is swollen in size and contains focal areas of high signal intensity consistent with fluid or hemorrhage at the partial rupture site. On MRI, chronic tendinitis is seen as a focal fusiform swelling of the tendon often associated with some smaller foci of signal intensity (Fig. 16). Insertional tendinitis is recognized as focal high signal

Fig. 6. Normal T1 weighted axial image through the navicular. The FHL beneath the sustentaculum tali and the TP tendon inserting in the navicular tuberosity are well visualized.

Fig. 7.

Normal T1 weighted coronal section through the fibula.

surrounding the tendon ( ~ i13A ~ and ~ . 13q.8 surgery provides definitive with the previous MR' Scan (Fig. 13c). The Achilles tendon may not have a definitive separation with a palpable defect, but instead

Fig. 8. A, Axial T1 weighted sections of both ankles at the level of the calcaneus demonstrate the absence of the left TP tendon. The normal FDL and FHL tendons on the left are identified as well as are all three medial tendons on the right. In addition, the arrow points to fluid in the region of the ruptured TP tendon. B, At surgery. the TP tendon was completely ruptured and absent below the level of the medial malleolus


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Fig. 9. A, The axial T1 weighted image through the navicular illustrates a retracted TP tendon distal to the rupture site. B, At surgery, a pseudosheath was found at the site of the ruptured TP tendon which was approximately several centimeters proximal to its insertion on the navicular.

An axial image of the same patient clearly demonstrates fluid in the subtendinous fat consistent with fluid in the retrocalcaneal bursa (Fig. 178). Lateral Structures: Normal

Fig. 10. Tenosynovitis of all three left medial ankle tendons can be identified in this T1 weighted axial section. The diffuse edema of the left ankle has caused a huge size increase compared with the right ankle.

intensity of the distal Achilles tendon at its insertion into the calcaneus (Fig. 17A). Note the fluid within the retrocalcaneal bursa on the T2 weighted image (arrow).

The ligament most commonly injured in ankle sprains is the anterior talofibular ligament. In addition, the posterior talofibular, calcaneofibular, and tibiofibular ligaments can be disrupted. The anterior talofibular ligament is best visualized in the axial (Fig. 18) and coronal (Fig. 5) planes. The lateral compartment’s ligamentous anatomy has been a confusing area in the past. The anterior talofibular ligament can be differentiated from the anterior tibiofibular ligament by noting the bony structures of the ankle joint. Proximal to the tibiotalar joint, the tibia and fibula are the only bony structures identified, whereas distal to the joint three bony structures are seen, the medial malleolus (tibia), the talus, and the lateral malleolus (fibula) (Fig. 1). Furthermore, inferior to the distal tip of the medial malleolus only the lateral malleolus and talus can be seen (Fig. 18). The


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Because of its oblique course from the distal tibia to the fibula, the anterior tibiofibular ligament is also visualized inferior to the tibiotalar joint (Figs. 1 , 5, and 7). However, this ligament is superior to the anterior talofibular ligament. The calcaneofibular ligament runs posteriorly and obliquely from the fibula to the lateral calcaneus (Fig. 7). The posterior talofibular ligament can also be easily visualized (Fig. 18). The peroneus longus and brevis tendons, originating from the fibula, are routinely seen posterior to the lateral malleolus (Fig. 19). The peroneus brevis tendon lies anterior and superior to the peroneus longus tendon (Figs. 6 and 7). The peroneus brevis inserts on the fifth metatarsal. The peroneus longus tendon crosses under the lateral part of the cuboid and inserts into the medial cuneiform and first metatarsal. Lateral Structures: Pathology

Fig. 11. Tenosynovitis of the FHL tendon is clearly visualized because fluid lights up surrounding the dark tendon on this T2 weighted sagittal image.

Common injuries of the lateral ankle region include disruption of the anterior talofibular ligament and tibiofibular ligament as described above. Traumatic disruption of the anterior tibiofibular ligament is demonstrated in Figure 20A. Note the fluid (white) anterior to the talus and fibula. In contrast, a normal appearing anterior tibiofibular ligament on the asymptomatic foot in the same patient is demonstrated in Figure 208. Recently there has been renewed interest in chronic lateral ankle pain after an inversion stress injury. The etiology of this pain is felt to be due to accumulationof fibrous debris and/or a meniscoid type lesion in the anterolateral gutter producing so-called anterolateral impingement syndrome (Fig. 2l).’ Subsequent arthroscopic debridement alleviated both patients’ pain totally and allowed both of them to return to full activity. Central Structures: Normal

Fig. 12. Normal T1 weighted sagittal image demonstrating the normal appearance of the Achilles tendon.

anterior talofibular ligament lies distal to the tibiotalar joint and almost completely inferior to the fibula (Figs. 38,5, and 18). It is best visualized on sections which include only the talar head and distal fibula.

The central structures of the ankle include the tibia, the talus, and the calcaneus with their corresponding tibiotalar or ankle joint and the subtalar joint with the sinus tarsi regions (Figs. 4A, 5, and 7). The structures anterior to the tibiotalar joint include the tibialis anterior, extensor hallucis longus, the anterior neurovascular bundle, and the extensor digitorum longus (Fig. 1).3.10. l 5 These structures are less commonly injured than the tendinous structures medially and laterally. Pathology of the tibiotalar and subtalar joints is often difficult to visualize with one plane standard x-ray. Both CAT scan and now MRI have greatly improved our diagnostic accuracy. Not only can the integrity of the bony cortex be appreciated, but also the vascularity of the bone can be assessed via MRI and the location of lesions in the bone can be exactly determined.


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Fig. 13. A, This T1 weighted sagittal

view shows an Achilles tendon ruptured at the musculotendinous junction (large arrow). B, The high signal intensity at the rupture site is also well demonstrated in the axial plane (T1 weighted).C, This surgical photo demonstrates the ruptured Achilles corresponding to the previously presented MRI scan.

Central Structures: Pathology

The most common pathology seen in the central compartment includes osteochondral lesions of the talus (OLT), loose bodies, avascular necrosis of the talus, and subtalar pain. The MRI in Fig. 22 demonstrates the presence of a loose body in the medial gutter that was subsequently proven surgically to be an osseous fragment. OLT are well visualized using MRI and can provide information on the integrity of the

overlying cartilage and underlying bone (Fig. 23). Coronal and axial images are both important to anatomically localize the lesion for both diagnostic as well as surgical purposes. Foot Structures: Normal

The four muscles of the leg’s anterior compartment, tibialis anterior, extensor hallucis longus, extensor digitorum longus, and peroneus tertius, have tendons that


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Fig. 14. T1 weighted sagittal image shows a shredded Achilles tendon. The tendon is continuous and wavy in contour.

Fig. 16. Chronic tendinitis of the Achilles tendon is seen in the T1 weighted sagittal view. As a result, there is fusiform thickening with a foci of high signal intensity. The oil droplet is often used !o exactly locate the area in which the patient is having the most discomfort.

Fig. 15. A, This sagittal T2 weighted double-echo study shows a focal area of increased signal intensity within the Achilles tendon which is consistent with a partial tear. B, Because of the partial tear, the left Achilles tendon is increased in size compared with the right. The axial T1 weighted view also demonstrates the increased signal within the tendon.


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Fig. 18. Normal T1 weighted axial image of the talar head and distal fibula.

Fig. 19. Normal T1 weighted sagittal image demonstrating peroneus longus and brevis tendons posterior to the fibula.

lie on the dorsal aspect of the foot (Fig. 1). In addition, extensor digitorum brevis originates from the dorsolatera1 aspect of the calcaneus. Also, the deep peroneal nerve and anterior tibia1 artery lie between and deep to

the extensor hallucis longus and extensor digitorum longus tendons. MRI can greatly assist in evaluation of the plantar surface of the foot. Lying deep to the plantar aponeurosis, there are four layers of intrinsic muscles


of the foot (Figs. 12 and 24). The most superficial layer consists of the abductor hallucis, flexor digitorum brevis, and abductor digiti minimi; while layer 2 contains quadratus plantae, the lumbricals, and FHL and FDL tendons. Flexor hallucis brevis, adductor hallucis (oblique and transverse), and flexor digiti minimi are in layer 3. Finally, the interosseous muscles, tibialis posterior, and peroneous longus tendons are located in layer 4. Foot Structures: Pathology

Two well-encapsulatedsoft tissue masses were identified involving the dorsal aspect of the right ankle in a 30-year-old female (Fig. 25A). One tumor was located at the level of the dorsal intermediate cuneiform, and a second, smaller lesion was identified lying dorsal to the second metatarsal. Subsequent surgical biopsy demonstrated angiosarcoma of the right foot (Fig. 258). Neither MRI or surgery showed evidence of osseous invasion. However, because of the invasive nature of the tumor, the patient eventually underwent below-theknee amputation. Ganglion cysts can commonly occur on the dorsum Fig. 20. (left) A, These T2 weighted double echo axial images demonstrate a ruptured left anterior tibiofibular ligament as well as an extensive amount of fluid. 8,This axial T1 weighted section of the same patient demonstrates the intact left anterior tibiofibular ligament.


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of the foot, originating either from extensor tendon sheaths or from the joint itself. MRI is particularly helpful in determining the site of origin of cysts. Figure 26A demonstrates a large multilobulated ganglion cyst of high signal intensity on a second echo T2 weighted image. The cyst tail was followed into the subtalar joint (Fig. 26B). At surgery, a large multilobulated ganglion cyst was identified lying superficial to the extensor digitorum brevis muscle with a tail extending into the subtalar joint. Another example of a ganglion cyst is illustrated in Figure 26C. Ganglion cysts are characterized by high signal intensity (fluid) on heavily T2 weighted images. One can differentiate angiosarcoma from ganglion cysts by noting signal intensity. Angiosarcoma behaves like a solid mass, whereas ganglion cysts behave like fluid. Plantar fibromatosis is a not uncommon condition affecting the plantar aspect of the plantar aponeurosis. Figure 27A demonstrates a focal nodule of isointensity to surrounding musculature which involves the plantar aspect of the plantar aponeurosis. It does not appear to penetrate the aponeurosis, and surgical correlation demonstrates an isolated plantar fibroma (Fig. 278). MRI has also been shown to be helpful in the diagnosis and treatment of osteomyelitis. Figure 28 demonstrates evidence of infiltration of the bone marrow involving the second metatarsal head, as well as surrounding edema consistent with osteomyelitis in the diabetic patient. This scan also showed that the first and third metatarsal heads had well preserved bone marrow and were not affected. Plain film radiographs were interpreted as negative.

Fig. 22. A loose body, surrounded by joint fluid, that was surgically identified as a bony fragment can be seen in the medial gutter on the T1 weighted axial image. The anterior structure is a foot holder.

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CONCLUSIONS

In our experience of a large number of patients with symptomatic foot and ankle complaints, MRI was a valuable imaging tool. Newer technology includes the capability of oblique angle imaging (for TP and FHL tendons), and thin slice acquisition and surface coils have allowed substantial improvements in studies as compared with previous reports. Oblique angle imaging allows imaging directly parallel or perpendicular to the structure of interest, often allowing it to be seen in its entirety on one single slice rather than piecing it together with multiple slices. We found this technique improved our accuracy. Thin slices with small gaps are essential for this complex anatomical region where the small bones and ligaments can easily be partially vol-

Fig. 23. Osteochondral lesion of the medial dome of the talus visualized in coronal T1 weighted images. An osseous defect of the superior medial aspect of the talar dome can be seen. At surgery, the cartilaginous surface on this patient was intact, but soft and fibrillated.

Fig. 21. (previous page) These axial images demonstrate anterolateral impingement syndrome on two different patients. Note the thinning of the previously injured anterior tibiofibular ligament in both cases. A, Fluid and scarring around the anterior talofibular ligament are identified in the T2 weighted image. 5, The T1 weighted image depicts scarring deep to the anterior talofibular ligament.


-ig. 24. Normal T1 weighted coronal images. A, Through the cuieiforms. 8, Through the metatarsal bases. C, Through the metatarsal leads.

Fig. 25. A, Two lesions, one dorsal to the second metatarsal and the other dorsal to the intermediate cuneiform are seen on this sagittal T1 weighted image. B, The patient was diagnosed as having angiosarcoma following surgical biopsy of both tumors.

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Fig. 26. A, The axial T2 weighted image demonstrates a ganglion cyst on the dorsolateral surface of the foot associated with the extensor digitorum brevis muscle.6, As identified on this T2 weighted coronal image, the ganglion cyst had a tail extending into the subtalar joint. C, Another ganglion cyst from a different patient is seen on the T2 weighted coronal section. Also, note the extensor tendon within the cyst.


Fig. 27. A, The plantar fibroma does not penetrate the plantar aponeurosis as demonstrated on this T1 weighted coronal section. 8, The excised portion of the plantar fascia with the plantar fibroma attached.

Fig. 28. A, Coronal images are best for visualizing foot pathology. This coronal section through the metatarsal heads demonstrates osteomyelitis involving the second metatarsal head. 8, An axial T1 weighted image also demonstrates osteomyelitis of the second metatarsal head. Plain film radiographs were interpreted as negative. Downloaded from fai.sagepub.com at UNIV CALIFORNIA SANTA BARBARA on September 4, 2015

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umed. Currently head and knee coils provide good spatial resolution and this will improve when dedicated foot and ankle coils are developed. We feel it is valuable to simultaneously scan the opposite foot, or ankle, so as to have a normal side for comparison; occasionally certain lesions will occur bilaterally such as OLT and this diagnosis can be made at the time of the scan. T2 weighted pulse sequences are essential for the diagnosis of soft tissue disease. Although T1 weighted scans are easier to obtain and often appear more pleasing to the eye, fluid, inflammation, tumor, and other pathology may appear isointense to other structures and thus be missed. CAT scans still may be the procedure of choice for evaluating some osseous abnormalities, including OLT. However, cartilage integrity can be assessed more accurately with MRI than with CAT.6,’6In some cases, these studies may be complimentary to each other. Soft tissue detail is limited with CAT and thus important diagnoses such as tendon ruptures may be overl o ~ k e d . ~ Acute , ’ ~ , ~ ruptures ~ of the posterior tibialis tendon have been occasionally difficult to diagnose by nonorthopedic physicians. MRI can assist in evaluating the medial joint structures and, as a result, more ruptures may be diagnosed and treated at an earlier stage.’ Ligamentous injuries of the foot and ankle can also be diagnosed with greater accuracy. The future of MRI is exciting as we have only touched the surface of this technology’s abilities. Kinematic MRI of the ankle is currently being developed to assist in the evaluation of ankle biomechanics and instability. In the meantime, MRI has proven a valuable technique for the diagnosis of foot and ankle pathology. REFERENCES Alanen, A.: Magnetic resonance imaging of hematomas in a 0.02T magnetic field. Acta Radiol. [Diagn.], 27(5):589-593,

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Normal anatomy and pathologic conditions of ankle tendons: current imaging techniques.

Magnetic resonance imaging evaluation of tubercular arthritis of the ankle and foot.

[Magnetic resonance imaging of the foot].

A Case of Glomangiomatosis of the Ankle and Foot: Ultrasonographic Appearance Correlated With the Magnetic Resonance Imaging Findings.

Correlation of Magnetic Resonance Imaging With Knee Anterolateral Ligament Anatomy: A Cadaveric Study.

Magnetic resonance imaging of the temporal lobe: normal anatomy and diseases.

Magnetic resonance imaging of the calcaneus: normal anatomy and application in calcaneal fractures.

Magnetic Resonance Imaging of the Craniovertebral Junction Ligaments: Normal Anatomy and Traumatic Injury.

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Importance of Contrast-Enhanced Fluid-Attenuated Inversion Recovery Magnetic Resonance Imaging in Various Intracranial Pathologic Conditions.

Cerebral tubercular thrombophlebitis presenting as venous infarct: Magnetic resonance imaging and pathologic correlation.

Examination of the pathologic anatomy of ankle fractures.

Comprehensive review of the anatomy, function, and imaging of the popliteus and associated pathologic conditions.

Inexpensive technique for performing magnetic resonance-pathologic correlation in cadavers.

High-resolution 3T Magnetic Resonance Imaging of the Triangular Fibrocartilage Complex in Chinese Wrists: Correlation with Cross-sectional Anatomy.

Long bicipital tendon of the shoulder: normal anatomy and pathologic findings on MR imaging.

Magnetic resonance imaging of the normal prostate at 1.5 T.

Diffusion-weighted magnetic resonance imaging of the normal canine brain.

Carotid-cavernous sinus thrombosis caused by Aspergillus fumigatus: magnetic resonance imaging with pathologic correlation--a case report.

Magnetic Resonance Imaging and Pathologic Findings of 26 Cases With Uterine Adenomatoid Tumors.

Strain sonoelastography of inflammatory myopathies: comparison with clinical examination, magnetic resonance imaging and pathologic findings.

Craniovertebral junction: normal anatomy with MR correlation.

Chondrosarcoma: MR imaging with pathologic correlation.

MR imaging of the most commonly injured ankle ligaments. Part I. Normal anatomy.