|ESSR 2017 / P-0295||
|Ankle and mid foot ligaments revisited: US and MRI with anatomic correlation: A pictorial essay|
Imaging findings OR Procedure Details
We have described the ligaments systematically on the basis of the joints they stabilize. Special anatomic features of these ligaments have been emphasized and illustrated with the help of images, wherever applicable.
General US features of ankle ligaments:
Ankle ligaments are basically bundles of collagen fibres. In general, on ultrasound images they appear as echogenic fibrillar structures similar to those elsewhwere in the body. Any deviations from this appearance has been mentioned during the description of the respective ligament.
The ultrasound beam should be as perpendcular as posiible to the ligament to avoid anisotropy.
High frequency linear transducers with frequencies ranging from 10-18 MHz should be used to evaluate ankle ligaments.
On ultrasound, ankle ligaments are usually scanned along their long axis. Short-axis US can be helpful in equivocal cases but are rarely needed.
Dynamic stress maneuvres may help straighten the ligament and a better US imaging of the ligament. In pathological cases, they can help detect injury and differentiate partial and complete tears.
General MR features of ankle ligaments:
In general, ligaments appear as smoothly outlined hypointense bands on all sequences. Any deviation from this normal appearance has been mentioned during the description of the respective ligaments.
The following ligaments are included in this pictorial essay:
Ankle ligaments: Tibiofibular ligaments, Bassett ligament, Anterior talofibular ligament, Calcaneofibular ligament, Lateral talocalcaneal ligament, Medial ligament complex.
Chopart ligaments: Bifurcate ligament, talonavicular ligament and plantar ligament.
Sinus tarsi ligaments.
The distal tibiofibular joint (tibiofibular syndesmosis) is reinforced by anterior tibiofibular ligament, Bassett ligament and posterior tibiofibular ligament.
Anterior tibiofibular ligament:
Anatomy: It is a stiff flattened band that originates from the anterior tubercle of the tibia, courses obliquely downward and laterally and inserts on the anterior border of distal fibular shaft and lateral malleolus (Fig. 1).
US: An excellent view of the ligament can be obtained on ultrasound with an oblique position of the probe and dorsiflexion of the ankle (Fig. 2).
MR: Anterior tibiofibular ligament has a multifibred structure and a striated appearance on MRI (Fig. 3).
Anatomy:It is the most distal fascicle of the anterior tibiofibular ligament is separated from the rest of the ligament by a septum of fibrofatty tissue and lies somewhat deeper to the rest of the ligament (Fig. 4).
US: It can be visualised on transverse US just inferior to the anterior tibiofibular ligament (Fig. 5).
This ligament is implicated in anterolateral impingement. Laxity of the ankle joint secondary to anterior talofibular ligament injury or abnormal low insertion of anterior tibiofibular ligament lead to increased talar or distal fibular osseous contact with this ligament and a higher potential for impingement. Excision of Bassett ligament (arthroscopically or open surgery) would relieve the pain without causing compromise to ankle stability.
Posterior tibiofibular ligament:
Anatomy: (Fig. 6) It is stronger than anterior tibiofibular ligament. It has two components, superficial and deep.
The superficial component: It originates at the posterior edge of the lateral malleolus, courses superiorly and medially to insert into the medial tibial tubercle. The term posterior tibiofibular ligament is used to indicate this component.
The deep component:It is cone shaped. It originates in the proximal area of malleolar fossa and inserts on the posterior edge of tibia. This component is called the transverse ligament. It provides talocrural stability by preventing posterior talar translation.
US: It is not as well visualised on US as the anterior tibiofibular ligament. Since it is rarely involved in ankle sprains it is not a part of routine US examination. It can be visualized by placing the transducer almost horizontally and medially on the posterior aspect of the tip of lateral malleolus (Fig. 7). Dorsiflexion and eversion of the hindfoot can enhance its visualisation.
MR: It is best seen on coronal MR images (Fig. 8).
Anatomy: It is located posteriorly between the transverse ligament superiorly and the posterior talofibular ligament inferiorly (Fig. 6). The ligament may be divided into two or three bands. It spans the space between fibula and tibia. It runs obliquely upwards from lateral to medial side. Its prevalence in radiological and anatomical studies varies widely from 19% to 100%. The ligament has been implicated in the posterior soft tissue impingement of the ankle. It becomes taut in dorsiflexion of the ankle. Hence, forced dorsiflexion injury of the ankle can cause injury or rupture of the ligament or osteochondral avulsion. In plantar flexion of the ankle, it relaxes and can be trapped between tibia and talus and cause posterior impingement.
US: It can be seen on transverse US from posterior side spanning the space between the fibula and the tibia. The Achilles tendon can be used as a window to visualize it (Fig. 9).
MR: The intermalleolar ligament is shown on a coronal PD MR image in (Fig. 10).
Lateral collateral ligament complex:
It comprises of three distinct ligaments: the anterior talofibular ligament, the calcaneofibular ligament and the posterior talofibular ligament.
Anterior talofibular ligament:
Anatomy: It originates from the anterior margin of the lateral malleolus, runs anteromedially to its insertion on the talar body. The ligament is oriented horizontally to the ankle in neutral position. It is closely related to the joint capsule and typically composed of two distinct bands. It plays an important role in limiting anterior displacement of the talus and plantar flexion of the ankle. It is the most frequently injured ligament of the ankle (Fig. 4).
US: The examination is performed with patient supine on bed, knee flexed and foot sole placed flat on the examination table. Owing to the nearly horizontal orientation of the anterior talofibular ligament, this ligament is best evaluated with the transducer parallel to the examination table. (Fig. 11).
MR: Typically, it should be seen on two consecutive MR slices. If it is thinner, one of its two bundles may be torn (Fig. 12).
Anatomy: (Fig. 13 and Fig. 14) It is the longest of the three ligaments. It is a strong cordlike structure with a vertical oblique course extending from the lateral malleolus to the lateral surface of the calcaneus. It is the only ligament bridging both talocrural and subtalar joints. In cross section, it is rounded with a diameter of 6-8 mm. It has a length of about 20 mm .
US: It can be seen on ultrasound by placing the probe obliquely and pointing it posteroinferiorly from the lateral malleolus with ankle in neutral position (Fig. 15). It can be seen better with dorsiflexion of the ankle which makes it taut with a nearly vertical orientation.
MR: It is best seen in coronal and transverse planes. It lies just deep to the peroneal tendons and forms a hammock for the peroneal tendons (Fig. 16).
Lateral talocalcaneal ligament:
Anatomy: (Fig. 17) It is a less well-known ligament and is not consistently present. It may be attached to the calcaneofibular ligament but diverging proximally or distally. In 23% of the cases, a lateral talocalcaneal ligament exists anteriorly and independent of the calcaneofibular ligament. In 42% of the cases, the lateral talocalcaneal is absent and is replaced by an anterior talocalcaneal ligament. In these cases, the calcaneofibular ligament acquires more functional significance in providing stability to the subtalar joint.
US: The relationship of calcaneofibular ligament and the lateral talocalcaneal ligament is shown in the US image in (Fig. 18).
The posterior talofibular ligament:
Anatomy: It is the strongest and deepest portion of the lateral collateral ligaments. It is intracapsular but extrasynovial and travels deeply between the posterior aspect of the lateral malleolus and the lateral tubercle of the posterior process of the talus. It has a horizontal course.
US: Because of its deep location, the posterior talofibular ligament cannot be assessed with US.
Medial collateral ligament complex:
Anatomy: It is also known as the deltoid ligament. It is stronger than the lateral collateral ligament. It has a triangular shape with its apex at the medial malleolus and fans out as it progresses downward. It is made of superficial and deep layers of fibres. (Fig. 19).
Anatomy: The deep layer of deltoid ligament courses from the medial malleolus to the talus.
US: It is made up of different fibre bundles and appears striated (Fig. 20).
MR: On fat saturated MR sequences, it may appear markedly hyperintense (in part due to striations) and this should not be mistaken as evidence of injury (Fig. 21).
The delta-shaped superficial layer of deltoid ligament typically has three components extending from the medial malleolus to the navicular (tibionavicular ligament), the spring ligament (tibiospring ligament), and to the calcaneus (tibiocalcaneal ligament). Some authors describe a fourth component of the superficial layer, called the superficial posterior tibiotalar ligament.
Anatomy: It is the most anterior portion of the superficial layer of deltoid ligament. It is a thin ligament with an oblique course. It originates from the anterior border of the anterior colliculus of the medial malleolus and inserts onto the dorsomedial aspect of the navicular. Due to the oblique course it may be difficult to depict it in its entirety on standard transverse or coronal planes.
Anatomy: It is the intermediate component and the thickest part of the superficial layer of the deltoid ligament complex. It originates from the anterior colliculus of the medial malleolus and inserts on the superior aspect of the spring ligament complex (Fig. 22).
US: On US, along the long axis of the ligament, it can be seen inserting on the superior margin of the spring ligament. Between the deeper spring ligament and the more superficial posterior tibial tendon, a fibrocartilaginous nodule designated gliding zone may be seen (Fig. 23).
MR: It is always visible and best seen in the coronal plane (Fig. 24).
It is the thinnest component of the superficial layer. It originates from the anterior colliculus of the medial malleolus, descends vertically, and inserts on the medial border of the sustentaculum tali.
MR: It is best visualized in the coronal plane (Fig. 25).
The main function of the deltoid ligament is to stabilize the medial aspect of the ankle joint. It also holds the calcaneus and navicular against the talus and reinforces the action of the spring ligament on which the head of the talus rests.
The spring ligament complex includes three ligaments extending the calcaneus and the navicular bones (Fig. 26):
Superomedial Calcaneonavicular Ligament:
Anatomy: It is the broadest and clinically most important part of the complex. It originates from the medial aspect of the sustentaculum tali and attaches broadly on the superomedial aspect of the navicular bone close to the talonavicular joint. Between the spring ligament and the posterior tibial tendon, a loose connective tissue nodule provides a gliding layer (Fig.23 and Fig. 24).
US: The ligament is scanned along the long axis by placing one tip of the US probe inferior to the medial malleolus, over the sustentaculum tali, and tilting the other end slightly superiorly toward the superomedial aspect of the navicular bone (Fig. 27).
MR: The inner portion of the ligament articulates directly with the talar head and has a very smooth surface similar to an articular surface (Fig. 28).
Medioplantar Oblique Calcaneonavicular Ligament:
It originates just anterior to the middle articular facet of the calcaneus, has a medial oblique course and attaches at the medioplantar portion of the navicular bone. It is best seen in the transverse oblique plane on MR.
Inferoplantar Longitudinal Calcaneonavicular Ligament:
It originates from the coronoid fossa of the calcaneum, runs slightly obliquely to attach at the inferior beak of the navicular bone. It is well seen on transverse, sagittal, and coronal MR images.
It is a short and stout Y shaped ligament with two components, calcaneocuboid and calcaneonavicular ligaments (Fig. 29, Fig. 30 and Fig. 31). It is intimate with the superior aspect of the calcaneocuboid joint and inferior aspect of the talonavicular component of talocalcaneonavicular joint.
This ligament can be injured in inversion injuries of the ankle or foot.
Short and long plantar ligaments:
The short plantar ligament originates from the anterior calcaneal tubercle and attaches to the adjacent part of the plantar surface of the cuboid bone. It is short but strong and sustains the lateral plantar arch.
The long plantar ligament originates from the plantar surface of calcaneus, anterior to the calcaneal tuberosity and attaches to the plantar surface and tuberosity of cuboid bone. It lies on the lateral side of the short plantar ligament and is separated from it by a layer of loose areolar tissue. Some of its superficial fibres may attach to the bases of second to fifth metatarsals.
(Fig. 32, Fig. 33 and Fig. 34).
The dorsal talonavicular ligament:
It extends from the dorsal surface of the neck of the talus to the navicular (Fig. 35). It is covered by extensor tendons. On MRI, it is best visualized in sagittal plane (Fig. 36). Dorsal talonavicular ligament tears have been described after inversion injuries associated with forcible plantar strain (Fig. 37).
Sinus tarsi ligaments:
Sinus tarsi and canalis tarsi is a space located between the subtalar joint and the talocalcaneonavicular joint. It contains fat, blood vessels, nerve endings and ligaments.
The primary intrinsic ligaments of the sinus tarsi include cervical and interosseous ligaments. These ligaments limit inversion and maintain talocalcaneal alignment. Acute injury to these ligaments leads to subtalar sprain. Chronic injury causes sinus tarsi syndrome which causes lateral foot pain, tenderness and subtalar joint instability.
Cervical ligament: is located at the lateral border of the sinus tarsi (Fig. 38, Fig. 39, Fig. 40 and Fig. 41)). It originates from the superior surface of calcaneus and attaches at the inferolateral aspect of talar neck.
Interosseous ligament: is located medially in the canalis tarsi and extends from the sulcus tali to the sulcus calcanei (Fig. 42, Fig. 43, Fig. 44 and Fig. 45).
Lisfranc ligament is an oblique ligament between the medial cuneiform and the base of the second metatarsal. It is a complex ligament made up of three parts: a dorsal part, main central part and a plantar part. The plantar component may also extend to the base of the third metatarsal. As this ligament complex has a deep interosseous location, it cannot be seen with ultrasound. On MR, it can be identified on axial images (Fig. 46, Fig. 47 and Fig. 48).
Tarsometatarsal joint ligaments (Fig. 49 and Fig. 50):
At the Lisfranc joint, ligaments connecting the midtarsal bones to the bases of metatarsals and cuneiforms to the bases of metatarsals are present. Ultraound and MR are well suited to evaluation of these ligaments.
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