Soft Tissue Injury to the Ankle: Ligament Injuries

Radiography

Radiography aids diagnosis of fractures in the emergency department when acute ankle injury is first presented.

There are published radiographic measurements for evaluation of ankle stability and integrity of the deltoid and syndesmotic ligaments (see eTable 32-2 ; Fig. 32-1 ). Yet radiographic measurements are indirect assessment of ligament integrity, readily affected by gender, body habitus, and ankle rotation. As a result, there is no agreement in the literature on the normal range for these measurements. In fact, stress views of the ankle, once used to identify ligamentous instability, are considered unreliable and obsolete ( Fig. 32-2 ). In other words, once fracture is excluded, radiography has a limited role in the diagnosis and management of ankle sprain.

Magnetic Resonance Imaging

Magnetic resonance imaging has been shown to be highly sensitive and accurate in identifying ligament injuries in the ankle (see eBox 32-2 ). Except in elite athletes, MRI is rarely performed in the acute setting except for detection of syndesmotic injury and associated injuries such as osteochondral talar lesion and occult fracture. In chronic ligamentous injuries, when surgery is contemplated, MRI can play a vital role in identifying the number and extent of ligamentous tears and in the detection of other associated conditions such as high syndesmotic injuries, impingement syndromes, sinus tarsi syndrome, superior peroneal retinacular tears, tears and dislocations of the peroneal tendons, and occult bony injuries.

After injury, the MR appearance of the affected ligament evolves over time. Within 2 weeks after injury, discontinuity and/or attenuation and poorly defined margins of the ligament are common findings. Periarticular edema and fluid in the common peroneal tendon sheath have also been reported. The indistinct margins of the injured ligament improve over time. Periarticular edema is consistently seen throughout the first 6 months after the initial injury. In chronic injury, the ligament is either attenuated or stretched while its borders have become better defined. Over time, the ligamentous defect is replaced by a thickened band inseparable from the joint capsule. Radiographic evidence of talar tilt and shift could also be present.

MR arthrography of the ankle improves visualization of the ankle ligaments and is especially useful in analyzing soft tissue impingement syndromes. The lateral and syndesmotic ligaments, in particular, are more clearly depicted with joint distention during MR arthrography than during routine MRI. Several ligaments attached to the posterior and lateral processes of the talus are also more distinctly seen in combined ankle and posterior subtalar arthrography in a cadaveric study. In light of its invasiveness, additional time requirements, and increased cost, the added benefit of MR arthrography in the routine evaluation of ligaments, however, remains to be determined.

3D MRI technique allows reconstruction of selected anatomic structures in any desired planes and is useful to depict ankle ligaments. Moreover, the dreaded long imaging times in older 3D MRI techniques are now replaced by quick isotropic 3D acquisitions. Although these new 3D techniques show great promise, they require further study and refinement.

With increased use of MRI in diagnosis of ligament injury, reports on incidental findings of abnormal-appearing ligaments in asymptomatic patients, false positives, and pitfalls are beginning to emerge. For example, in a study consisting of 100 patients with no lateral ankle symptoms, only 71% and 90% had intact anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL), respectively. In addition, the highly variable courses and numbers of fascicles of many ligaments could present interpretative pitfalls. An example is the anterior tibiotalar ligament, which is visualized in only 50% of cadavers and 55% of MRI studies of healthy volunteers. Using nonvisualization of the ligament, a common criterion for ligament injury, therefore could confound clinicians and radiologists. In fact, imaging findings rarely predict outcome or alter initial management in acute ankle ligament injuries. More studies are therefore necessary to address uncertainty, prevent overdiagnosis, and standardize work-up and treatment of ligament abnormalities.

Ultrasonography

The superficial ligaments of the ankle can be effectively depicted by ultrasonography. Detailed assessment of the ligaments requires high-frequency, up to 14- to 15-MHz probes, state-of-the-art scanning systems, and a high level of operator skill. Because ankle ligaments are seldom oriented parallel to the probe, and their bony insertions are used as reference structures, detailed knowledge of the anatomy of the ligaments is mandatory to produce an accurate evaluation. The ultrasonographic image of an intact ligament, obtained along the long axis, reveals a parallel-layered echogenic structure with well-defined sharp margins. Putting the ligaments under stress by changing the ankle position often improves visualization. The ankle ligaments are subject to anisotropy and may become hypoechoic if the ultrasound beam is not perpendicular to their fibers. Pathologic ligaments are also generally hypoechoic, but their sonographic features vary depending on the age of the injury (see eBox 32-3 ).

A complete ligament tear is diagnosed when the parallel fibers are discontinuous and a hypoechoic zone occupies the ligamentous defect. If residual parallel fibers can be seen, a diagnosis of incomplete tear is made. When healing, the ligament always appears thicker than normal on sonograms.

Although ultrasonography and MRI are equally reliable in detecting ligament injuries, ultrasonography, because of its noninvasiveness and portability, has emerged as the first-line imaging modality for managing acute musculo­skeletal injuries in the elite athlete. In fact, in the recent 2012 Olympics, 400 sonographic exams were completed during the 2 weeks of competition. In general practice, however, the use of ultrasonography to diagnose ankle ligament injury is appropriate only for anterior talofibular ligament (ATFL), calcaneofibular ligament (CFL), and anterior inferior tibiofibular ligament (AITFL) tears, based on a consensus paper from the European Society of Musculoskeletal Radiology. For deltoid and spring ligament injuries, these experts recommend ultrasonography only when other imaging modalities are not applicable. Moreover, sonography cannot detect osseous injuries such as associated bone bruises and osteochondral injuries.

Multidetector Computed Tomography

Normal ligaments, if surrounded by fat, can be visualized on CT. When the injured ligament is inseparable from surrounding soft tissue swelling, CT is less useful. CT is superior to MRI in depicting posttraumatic ossifications in the ligaments or small avulsed bone fragments associated with the ligamentous tear. Although 3D CT with volume rendering technique has proved useful in demonstrating the relationships of the ankle tendons with underlying osseous structures, the role of CT imaging of ankle ligaments has not been investigated.

Nuclear Medicine

Bone scintigraphy is a sensitive yet nonspecific method in the evaluation of osseous lesions. Its use in the imaging of ankle ligaments is limited. During the acute and subacute phases, increased bone uptake may be seen at sites of ligamentous avulsions. Increased uptake is also noted at sites of concurrent bony contusions, such as the medial talar dome and medial malleolus. Bone scintigraphy has been used to aid the diagnosis of subtle cases of Lisfranc ligament injuries but has been replaced by MRI (see later section on Lisfranc ligament).

Radiography

Radiography is generally not necessary for acute lateral ankle sprains unless fracture or osteochondral injury is suspected. In fact, talar osteochondral lesions are common, reported in 17% to 23% of patients undergoing arthroscopy and surgery, respectively, for chronic ankle instability after lateral ankle sprain. Arthrography and peroneal tenography, used in the past to diagnose acute ligament injury, have mostly been replaced by noninvasive modalities such as MRI and ultrasonography.

Magnetic Resonance Imaging

Ankle MRI is not cost effective in uncomplicated acute lateral ankle sprain because these injuries are initially treated conservatively. MRI should be limited to those instances in which the clinical diagnosis is unclear or associated injuries such as syndesmotic or high ankle sprain, occult fracture, peroneal tendon dislocation, and avascular necrosis are suggested. If MRI was performed, multiple osseous and soft tissue injuries have been reported in conjunction with lateral ankle sprains. These osseous conditions include malleolar fractures; osteochondral talar or, less commonly, tibial lesions; bone contusions; fractures of the anterior process of the calcaneus or the base of the fifth metatarsal; and posttraumatic arthritis. Concurrent soft tissue conditions that may be seen on MRI include syndesmotic ankle sprains, deltoid injuries, anterior or posterior soft tissue impingement, sinus tarsi syndrome, superior peroneal retinacular injuries, and peroneal tendon tears and dislocations.

The normal ATFL is a band of low signal extending from the lateral talar head to the tip of the fibula (see eFig. 32-4A ). Representing a capsular thickening, this ligament is often best seen on fluid-sensitive images where the ligament is highlighted by joint fluid. It has a variable number of fascicles that are separated by fat. Signs of ATFL injury include nonvisualization of the ligament, discontinuity of the ligament, irregular contour, or heterogeneous increased signal intensity. The “bright rim sign” is a newly added criterion for ATFL tear. This sign, seen on T2-weighted axial image, consists of a dotlike or curvilinear high signal intensity adjacent to the focus of cortical disruption on either the fibular or talar attachment of the ATFL. This bright dot is thought to represent chemical shift artifact at the site of cortical avulsion at ATFL attachment. The avulsed or peeled-off cortex exposes the underlying fatty marrow to joint fluid, leading to formation of chemical artifact that is seen as the reported bright rim or dot. Adding this new criterion significantly improved the sensitivity of detecting ATFL tear, with a sensitivity of 90.9% to 96.9% when compared to arthroscopic findings. The authors, however, did not find increased specificity when this new criterion was added. Pitfalls in diagnosis may arise when the ligament is assessed at 1 to 2 cm above the tip of the fibula, where a physiologic gap occurs between the fascicles. The ligament can be distinguished from the more superiorly located AITFL by two major criteria. On axial images, the talus appears oblong at the ATFL ligament origin (see eFig. 32-4A ), whereas the talus is square at the talar dome where the anterior tibiofibular ligament is visualized. The shape of the fibula at site of ligament insertion also helps differentiate the ATFL from the AITFL. The ATFL inserts at the level of the fibular malleolar fossa where the fibula demonstrates a normal medial notch, whereas the fibula is round at the insertion of the AITFL (see eFig. 32-4 ).

The CFL is found deep to the peroneal tendons along the lateral wall of the calcaneus. The course of CFL is frequently oblique and highly variable. As a result, sequential images in both axial (see eFig. 32-4B ) and coronal images are necessary to depict the ligament's origin and insertion sites ( Fig. 32-3A ).

The PTFL can be consistently visualized on routine axial MR images (see eFig. 32-4B ). The ligament is fan shaped with a broad insertion into the fibular malleolar fossa. Its other insertion is at the lateral tubercle of the talus. Its fascicles are separated by fibrofatty tissue, similar to the anterior cruciate ligament of the knee, resulting in a normally striated appearance of the ligament. This striation should not be confused with a tear.

MRI features of injury to the lateral collateral ligaments include disruption, nonvisualization, thickening, attenuation, heterogeneity, and wavy appearance of the ligaments (see eBox 32-2 ; Figs. 32-4 to 32-8 ). Acute ligamentous tears are associated with adjacent soft tissue edema and with fluid extravasation outside the joint capsule (see Fig. 32-4A ). Obliteration of the fat normally highlighting the ligaments is a reliable sign for ligament injury. Complete tear of the CFL allows communication between the common peroneal tendon sheath and the ankle joint (see Fig. 32-7B ). Fluid within the common peroneal tendon sheath was noted in 52% of patients within 2 weeks of acute sprain but was more common in cases of CFL tears. In contrast, at 7 weeks, 75% of patients with fluid in the peroneal tendon sheath had an intact CFL. This increased incidence of fluid in the peroneal tendon sheath is thought to represent tenosynovitis resulting from the added stress to the peroneal tendons as they attempt to stabilize the lateral laxity of the ankle joint.

Ligaments commonly heal through filling of the defect with a fibrous scar that may occur as early as 7 days after the injury. Scar formation is typically ligament specific. The location of the sprain also influences healing: The closer the site of ligamentous injury to the bony attachment, the greater the likelihood of delayed healing. A study using MRI to track the changes in the injured ligaments over time showed progression from an obvious defect to a hypoplastic or hyperplastic appearance of the ligament. For example, 50% of the imaged ATFL ligaments had a defect at 2 weeks. By the seventh week, only 11% of the ATFL ligaments displayed a defect. During healing, the margins of the ATFL also became better defined.

Concomitant ATFL and CFL injury is frequent (see Fig. 32-4 ); syndesmotic and deltoid tears or contusions are often seen in conjunction with lateral collateral ligament tears (see Fig. 32-5 ).

Thirty-five percent of cases of lateral ligament injuries had bone bruises, predominantly in the talar dome. Bone contusions in the medial tibia, talus, and calcaneus and more subtle ipsilateral bone contusions of the distal fibula are other common findings associated with acute tears (see Fig. 32-5 ). These talar and navicular bone contusions result from talar head rotational instability.

Using surgery as the gold standard, MRI was demonstrated to be 74% sensitive and 100% specific for detecting complete lateral ligament tears. In another study, MRI correctly detected 92% of surgically proven cases of lateral ligament tears. In a recent study using arthroscopy as gold standard, the sensitivity, specificity, and accuracy of MRI in detecting ATFL injury is 97%, 100%, and 97%, respectively.

Despite the ability of MRI to document the extent of ligamentous injury in acute sprain, the ability of MRI findings to affect therapy and predict clinical outcome is moderate, as most acute injuries are initially treated conservatively. On the other hand, imaging of residual chronic pain and instability is indicated, as these chronic lesions are frequently treated surgically.

Ultrasonography

The group of European Society of Musculoskeletal Radiology experts has deemed sonography of ATFL and CFL clinically appropriate but not cost effective. Using MRI as gold standard, sonography of the ATFL reported a sensitivity and specificity of 92% and 83%, respectively. In another study, sonographic findings of ATFL tears were confirmed by arthroscopic surgery, yielding a sensitivity and specificity of 100% and 33%, respectively. A sonographic study on 105 patients who underwent surgery for lateral ankle sprain showed accuracies of 92% for diagnosing CFL lesions.

ATFL on sonography is a flat fibrillar hyperechoic structure connecting the tip of the lateral malleolus to the lateral talus ( Fig. 32-9 ). To avoid hypoechoic anisotropic artifacts, the transducer must be parallel to the long axis of the ATFL when obtaining longitudinal images. The CFL lies deep to the peroneal tendons, which can be used to localize the ligament. Dorsiflexion of the foot stretches the CFL and improves visualization. The proximal segment of the CFL is generally obscured by the lateral malleolus. Because of the close proximity between the CFL and the peroneal tendons, fluid is commonly found in the common peroneal tendon sheath after CFL tears. An indirect sign of CFL tear is lack of motion of the peroneal tendons toward the probe during dorsiflexion. Also, the attenuated or torn CFL allows the peroneal tendons to fall deeper toward the calcaneus. The PTFL is difficult to visualize on ultrasonography, owing to its deep location.

Nonsurgical Treatment

Immediately after injury and after exclusion of fracture, rest, ice, compression, elevation (RICE) treatment is delivered at the field or the emergency room. The ankle is reexamined in 5 days after the initial treatment because delayed physical exam was shown to have higher sensitivity to ankle injuries as pain and swelling resolved. If the exam reveals a stable ankle joint or grade 1 or 2 lesion, the general consensus is nonsurgical management, such as functional rehabilitation.

Functional regimens include elastic wrap, frequent applications of ice, short period of weight- bearing immobilization, and initiation of range of motion exercise during the acute phase of injury. Once swelling has receded, neuromuscular training stressing peroneal muscle strengthening and proprioceptive exercise should begin. Functional bracing that controls inversion and eversion is commonly used during the strengthening period and prophylactically for high-risk activities thereafter. These measures are shown to be cost effective, associated with recovery of ankle range of motion and early return to work. For unstable, or grade 3, sprains, the treatment remains controversial. Because surgical treatment to the lateral complex may induce some serious though infrequent complications, and functional treatment is free of complications, the growing consensus is to treat grade 3 sprains first with a trial of nonsurgical functional regimen. If such trial fails to resolve symptoms after a considerable period, surgical repair could subsequently be performed.

Surgical Treatment

Surgical repair of acute lateral ligament ruptures is rarely indicated. The exception may be in cases of sprains in the competitive athlete, where surgical treatment should be considered on an individual basis. Several studies suggested a decreased incidence of late recurrent instability after surgical intervention, but high-quality evidence studies are not available. Operative indications include instability and arthrosis in chronic ligamentous injuries, which can typically be detected clinically or on routine weight-bearing radiographs. More than 50 procedures designed to stabilize the lateral ankle have been described. These can be categorized into four general groups: (1) direct lateral ligament repair, (2) peroneus brevis tendon rerouting, (3) peroneus brevis tendon loop, and (4) peroneus brevis tendon loop and rerouting.

The postsurgical appearance after ligamentous reconstruction may be assessed by radiography, ultrasonography, and MRI. The presence of suture anchors in the region of the ATFL indicates direct ligamentous repair, whereas detection of a fibular tunnel suggests a peroneus brevis loop or rerouting. T1-weighted MR images, in particular, can clearly depict the rerouted peroneus brevis tendon within the fibular tunnel. The integrity of the rerouted tendon is best assessed by backward tracing of the peroneus brevis from its distal attachment at the base of the fifth metatarsal. The distal attachment of the peroneus brevis is typically not disturbed during surgical intervention.