MRI Web Clinic — August 2017

The Calcaneofibular Ligament
Jeffrey A. Simon, M.D.

Clinical History
A 49 year-old male suffered an ankle inversion injury requiring reduction 2-3 weeks prior to imaging and presents with continued pain and swelling. MRI was performed to evaluate for ankle subtalar joint dislocation. (1a) Axial T1-weighted, (1b) axial T2-weighted at the same level, and (1c) coronal fat suppressed proton-density images are provided. (1d) An axial T2-weighted sequence is also provided slightly more superiorly.

What are the findings? What is your diagnosis?

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Figure 1

Findings

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Figure 2:

2a-2b: The axial T1- and T2-weighted images respectively demonstrate intact peroneal tendons (yellow arrows) with an irregular rounded area of intermediate T1/low T2 signal anterior to the peroneal tendons that is larger than normally seen (red arrow) representing torn and anteriorly retracted fibers of the calcaneofibular ligament (CFL). The CFL is torn in its mid portion with the remnant posterior component of the CFL also seen (arrowhead).

2c: The coronal fat-suppressed proton density-weighted image reveals the adjacent peroneus brevis and peroneus longus tendons (yellow arrows) in normal position with surrounding soft tissue swelling. The plump but ill-defined slightly curvilinear structure just superior is the remnant of the torn CFL (red arrow). Acute medial inferior talus marrow contusion (asterisk) from the inversion injury is also seen.

2d: Axial T2 weighted image demonstrate the more cephalad intact anterior talofibular ligament (green arrow).

Diagnosis

Isolated calcaneofibular ligament (CFL) rupture with anterior displacement.

Introduction

Roughly 20 percent of all sports-related injuries occur at the lateral ankle. The calcaneofibular ligament is an important lateral stabilizing ligament of the ankle.  The main function of the ligament is to provide support to the subtalar joint. This ligament courses from the lateral malleolus to the calcaneus, deep to the peroneal tendons, crossing both the talocrural (ankle) and subtalar joints, making this the longest of the stabilizing ankle ligaments. The tendon is most commonly damaged during inversion injuries to the ankle, and usually there is an associated injury to the anterior talofibular ligament (ATFL). The CFL is rarely torn in isolation and only a few case reports exist.1

Anatomy

The calcaneofibular ligament is part of the lateral ankle ligament complex consisting of the ATFL, CFL, and posterior talofibular (PTFL) ligaments.  The CFL is typically 6-8 mm thick and runs along a length of 20 mm in an oblique course from the tip of the lateral malleolus posteriorly and inferiorly, attaching to the trochlear eminence of the calcaneus.  The CFL is situated inferior to the ATFL with occasional fibers that connect between them.2  The CFL is also seated deep to the peroneal tendon complex and is near completely covered by its posteromedial portion.3  The ligament crosses the ankle and subtalar joints, the only ligament that spans 2 separate joints laterally.  The ligament is taut in flexion, extension and varus angulation but relaxes during valgus stress to the ankle.  The CFL is often seen in close apposition to a smaller ligament that lies medial and anterior, the lateral talocalcaneal ligament (LTCL).

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Figure 3:

3-dimensional representations of the lateral collateral ligament complex of the ankle with the peroneus longus and brevis tendons removed just distal to the lateral malleolus are viewed from the anterolateral (left), lateral (middle), and posterolateral (right) perspectives. ATFL = anterior talofibular ligament (blue), CFL = calcaneofibular ligament (red), PTFL = posterior talofibular ligament (green). (Click on image for 3D interactive view. Click-drag to rotate, scroll to zoom.)

Function

The CFL provides lateral stabilization to the ankle joint and subtalar joint.  The ligament allows flexion and extension movements to occur at the ankle and serves as a primary restraint to inversion in neutral or dorsiflexed position at the talocrural joint.  The CFL also serves to resist subtalar joint inversion. This limits talar tilt.  In cases of absence of the LTCL, the CFL has a greater stabilizing role to the subtalar joint.4  The CFL is tense in dorsiflexion and is a secondary stabilizer to the ATFL.5 The CFL increases in length in dorsiflexion and pronation.6  Extreme inversion forces to the ankle can cause injury and ultimately rupture to the CFL. It has been shown that the CFL tension is increased mainly in inversion and dorsiflexion while the ATFL acts as the primary restraint in inversion and plantarflexion.7 The CFL is typically not injured in isolation because the ATFL is the weakest ligament and the great majority of ankle inversion injuries occur with at least some degree of plantar flexion (Figure 4).  The least commonly torn stabilizing ankle ligament is the PTFL.  An anatomic classification of ankle sprains has been developed. A first degree sprain consists of a partial or complete tear of the ATFL; a second degree sprain consists of partial or complete tearing of the both the ATFL and CFL, and a third degree sprain consists of injury to all of the lateral ligaments, including the PTFL.8

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Figure 4:

14 year-old male with ankle pain for months demonstrates ill-defined ligament margins with thickening of the ATFL (green arrow) and areas of thickening and attenuation of the CFL (red arrow) related to chronic sprains with scarring from prior ankle inversion injury.

Normal MRI Appearance

MRI is the study of choice in evaluation of the lateral ankle ligamentous complex.  A high resolution extremity coil is best suited for visualization of these small structures. The CFL is best imaged when the ankle is placed in plantar flexion (roughly 20 degrees) as this can lessen the magic angle effect9 which can obscure visualization.  The CFL (and the ATFL) appears as a low signal fiber bundle on all imaging sequences in the normal state. The CFL is best seen on coronal and axial views but is usually not visualized in its entirety on one single image. Multiple continuous images are typically needed to trace the course of the ligament.  The CFL appears band-like extending in the anteroposterior direction and courses parallel to the lateral calcaneal wall with the foot in plantar flexion (Figure 5a).  The CFL on coronal views is more round in shape but occasionally can be imaged in its entirety depending on the obliquity of the slice selection (Figure 5b).

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Figure 5:

The axial T2-weighted image (5a) shows the cord-like intact CFL (red arrow) positioned medial to the peroneal tendons with an intervening fat plane while the coronal image of a different patient (5b) shows a thin, well defined CFL (arrowheads) in its entirety extending from the anterior tip of the lateral malleolus to the calcaneal attachment site.

Clinical Presentation and Physical Exam

Injury to the lateral ligamentous structures usually occur after suffering an inversion type injury to the ankle.  When the ankle is stressed, the vector forces are greatest laterally.  If these forces are greater than the tensile strength of the ligament then the lateral ligaments can tear or rupture.  Typically these injuries occur with the ankle also in plantar flexion and the ATFL is the first ligament to tear.  It is postulated that the CFL could tear in the absence of ATFL if the ankle is inverted in neutral or dorsiflexed position.  On examination, patients can present with tenderness to palpation over the CFL, correlating to a 72 percent chance of ligament injury.10 In addition to pain, edema and ecchymosis are often visualized. Joint instability can be assessed using the anterior drawer test at the ankle which could relate to injury to the ATFL, CFL, or both.  Clinically, a 3 grade system is used to classify the injuries. Grade 1 is a minor injury or sprain. Grade 2 and 3 injuries respectively equate to partial or complete tears.  Lateral ankle stress test maneuvers have been shown to correlate poorly with the degree of ligament disruption.11 Therefore, MR imaging is essential in proper diagnosis.

Pathological MRI Appearance

The typical well-marginated cylindrical or band-like appearance of the CFL seen on multiple contiguous images is changed when there is pathologic injury. Acute CFL (and ATFL) injuries are usually associated with anterolateral and/or lateral soft tissue edema (Figure 6a).  There is characteristic loss of the surrounding fat planes, thickening and heterogeneity of the ligament signal with indistinct margins often seen (figure 6b). Sometimes fluid can be seen in the adjacent peroneal tendon sheath as a result (Figure 7a) and there is most often accompanying partial tearing or rupture of the ATFL (figure 7b). Acute rupture can also result in a wavy irregular appearance as seen in the web clinic case above.  The range of injuries can vary from small to large longitudinal split tears (Figure 8), high grade partial tears, and complete tears of the CFL.

The typical inversion type injury can also secondarily produce injuries to the medial side of the ankle, including contusions of the talus, medial malleolus, or the deltoid ligament (Figure 8, Figure 2c).

More chronic injury to the CFL can result in scarring/thickening or ligament attenuation/non-visualization without surrounding edema. (Figure 9)

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Figure 6:

18 year-old old female suffering a recent ankle sprain with tenderness around the lateral malleolus. The fat suppressed T2-weighted image (6a) reveals subcutaneous edema anterolaterally overlying the ankle (arrowheads) related to the high-grade partial sprain of the CFL (arrows) better delineated on the axial T1-weighted image (6b) by loss of the well-defined fat plane and indistinct and thickened appearance of the CFL.

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Figure 7:

50 year-old with a golfing injury 3 days prior to imaging.

7a: A coronal fat-suppressed proton density-weighted image reveals an irregular, ill-defined appearance of the CFL (red arrow) surrounded by edema with adjacent fluid within the peroneal tendon sheath (yellow arrow).

7b: Axial fat-suppressed proton density-weighted image also shows the peroneal tenosynovitis (yellow arrow) with a fluid-filled gap at the ATFL suggestive of ligament rupture (green arrow).

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Figure 8:

16 year-old female with diffuse ankle pain presenting after injury 6 weeks prior with high grade ATFL tear (not included). An axial fat suppressed T2-weighted view reveals a longitudinal split of the CFL (arrows). Incidentally noted is a subacute marrow contusion involving the head of the talus (asterisk).

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Figure 9:

9a: 15 year-old female soccer player with track related injury and pain laterally. The coronal fat suppressed proton density-weighted image shows markedly attenuated CFL ligament fibers (arrows) and lack of surrounding edema consistent with a chronic ligamentous high-grade sprain.

9b: Coronal fat-suppressed proton density-weighted image in another 15 year-old female with pain and swelling for 3 weeks revealing a normal appearance of the CFL (red arrow) and overlying posterolateral subcutaneous swelling.

Treatment

Initial treatment of grade 1 and 2 injuries to the lateral ankle ligamentous complex usually consists of rest and ice along with compression and elevation. The ankle is stabilized in a boot for immobilization.  Most injuries respond well to this conservative treatment with physical therapy also performed.  There is no standard treatment protocol for the rare isolated injuries of the CFL.   Surgery is usually considered for younger persons or athletes with grade 3 sprains.  Surgery is also considered in older patients whose symptoms are refractory to the conservative treatments.

Conclusion

The calcaneofibular ligament is an important component of the lateral ligamentous complex of the ankle. It is unique anatomically in that it crosses both the talocrural and talocalcaneal joints and is intimately associated with the peroneal tendon sheath. In addition to limiting inversion, the ligament assists in stabilizing the subtalar joint. Although the CFL is typically injured in association with ATFL tears, rarely the CFL can tear in isolation if an inversion injury occurs in dorsiflexion. Because physical exam is fairly unreliable in the assessment of ankle ligaments, MRI plays an essential role in the accurate assessment of the status of the CFL.

References

 

  1. Rigby R, Cottom JM, Rozin R. Isolated Calcaneofibular Ligament Injury: A Report of Two Cases. The Journal of Foot and Ankle Surgery. 2015;54(3):487 – 489
  2. Golanó P, Vega J, de Leeuw PAJ, et al. Anatomy of the ankle ligaments: a pictorial essay. Knee Surgery, Sports Traumatology, Arthroscopy. 2010;18(5):557-569.
  3. Sarrafian SK Anatomy of the foot and ankle. Descriptive, topographic, functional, 2nd ed. Lippincott, Philadelphia, 1993; 159–217.
  4. Trouilloud P, Dia A, Grammont P et al Variations du ligament calcaneo-fibulaire. Aplications a` la cine´matique de la cheville (Variations in the calcaneofibular ligament. Applications to ankle kinetics). Bull Assoc Anat 1988; (72):31–35.
  5. Ozeki S, Kitaoka, H, Kaufman K et al. The function of the calcaneofibular ligament and clinical test for its sufficiency. 5th combined meeting of the orthopaedic research societies of Canada, USA, Japan and Europe. Poster 275.
  6. De Asla RJ, et al. Function of the anterior talofibular and calcaneofibular ligaments during in-vivo motion of the ankle joint complex. Journal of Orthopaedic Surgery and Research 2009, 4(7): 1-6
  7. Bahr R, Pena F, Shine J, Lew WD, Engebretsen L: Ligament force and joint motion in the intact ankle: a cadaveric study. Knee Surg Sports Traumatol Arthrosc 1998, 6(2):115-21
  8. Rosenberg ZS, Beltran J, Bencardino JT. From the RSNA Refresher Courses. Radiological Society of North America. MR Imaging of the ankle and foot. Radiographics. 2000;20:S153- 79.
  9. Rosenberg ZS, Beltran J, Bencardino JT. From the RSNA Refresher Courses. Radiological Society of North America. MR Imaging of the ankle and foot. Radiographics. 2000;20:S153- 79.
  10. Puffer, J. The Sprained Ankle. Clin Cornerstone 3:38-49, 2001.
  11. Fujii T, Luo ZP, Ktaoka HB et al. The manual stress test may not be sufficient to diagnose ankle ligament injuries. Clin Biomech 2000, 15(8):619-23.

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