DOI: 10.1148/rg.255045713
RadioGraphics 2005;25:1215-1226
© RSNA, 2005
Fractures of the Calcaneus: A Review with Emphasis on CT1
Aditya Daftary, MB, BS,
Andrew H. Haims, MD and
Michael R. Baumgaertner, MD
1 From the Departments of Radiology (A.D., A.H.H.) and Orthopedic Surgery (M.R.B.), Yale University School of Medicine, 333 Cedar St, Box 208042, New Haven, CT 06520-8042. Received June 23, 2004; revision requested August 5; final revision received December 16; accepted December 17. All authors have no financial relationships to disclose.
Address correspondence to A.H.H. (e-mail: Andrew.haims{at}yale.edu)
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Abstract
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The calcaneus is the most commonly fractured tarsal bone and accounts for about 2% of all fractures. Advances in cross-sectional imaging, particularly in computed tomography (CT), have given this modality an important role in identifying and characterizing calcaneal fractures. Fracture characterization is essential to guide the management of these injuries. Calcaneal fractures have characteristic appearances based on the mechanism of injury and are divided into two major groups, intraarticular and extraarticular. Most calcaneal fractures (70%–75%) are intraarticular and result from axial loading that produces shear and compression fracture lines. Of the two major systems for classifying intraarticular fractures–Hannover and Sanders–the latter is used most often and is helpful in treatment planning and determining prognosis. Extraarticular fractures account for about 25%–30% of calcaneal fractures and include all fractures that do not involve the posterior facet. The article describes in detail calcaneal anatomy, mechanism of calcaneal injuries and their associated fracture patterns, CT features of intra- and extraarticular fractures, and management implications. Familiarity with calcaneal anatomy and fracture patterns is essential for radiologists to guide the treating physicians.
© RSNA, 2005
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LEARNING OBJECTIVES FOR TEST 2
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After reading this article and taking the test, the reader will be able to:
- Describe the clinically relevant anatomic features of the calcaneus.
- Discuss the pathophysiology of calcaneal fractures.
- Identify the appearances of intra-and extraarticular calcaneal fractures and their treatment implications.
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Introduction
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The calcaneus, the largest tarsal bone, is specifically designed to support the body and endure a great degree of force. The most common tarsal bone to be fractured is the calcaneus, and calcaneal fractures account for about 1%–2% of all fractures. These fractures typically occur because of axial loading in men 30–60 years old and usually have poor outcomes. Computed tomography (CT) has revolutionized our understanding of these fractures and their management. The purpose of this article is to explore the anatomy and pathophysiology of intra- and extraarticular calcaneal fractures, with emphasis on their appearances at CT. We also discuss the impact of these CT findings on the management of these fractures.
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Anatomy
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The calcaneus is designed to withstand the daily stresses of weight bearing. A sound understanding of the anatomy of the calcaneus is essential in determining the patterns of injury and treatment goals and options.
The calcaneus has a relatively thin cortex. Traction trabeculae radiate from the inferior cortex, and compression trabeculae converge to support the anterior and posterior articular facets, leaving a "neutral triangle" between them with sparse trabeculations (1) (Fig 1). The cortical bone just inferior to the posterior articular facet is condensed to approximately 1 cm and is called the thalamic portion (2). Thickening of the cortex is also seen in the regions of the sustentaculum tali, medial wall, and critical angle of Gissane.
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Figure 1a. (a) Lateral radiograph of the normal calcaneus. (b) Lateral radiograph of the calcaneus shows compression (light blue arrows) and traction (yellow arrows) trabeculae, with the neutral triangle (brown triangle) in between with sparse trabeculae. The thickened cortical or thalamic portion of the bone supporting the articular facets is shown (T). The critical angle of Gissane (G) and the Boehler angle (B) have also been drawn in. The Boehler angle is normally 20°–40°.
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Figure 1b. (a) Lateral radiograph of the normal calcaneus. (b) Lateral radiograph of the calcaneus shows compression (light blue arrows) and traction (yellow arrows) trabeculae, with the neutral triangle (brown triangle) in between with sparse trabeculae. The thickened cortical or thalamic portion of the bone supporting the articular facets is shown (T). The critical angle of Gissane (G) and the Boehler angle (B) have also been drawn in. The Boehler angle is normally 20°–40°.
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The calcaneus has four articulating surfaces, three superior and one anterior. The superior surfaces—the posterior, middle, and anterior facets—articulate with the talus. The posterior facet is separated from the middle and anterior facets by a groove that runs posteromedially, known as the calcaneal sulcus (Fig 2). The canal formed between the calcaneal sulcus and the talus is called the sinus tarsi. The middle calcaneal facet is supported by the sustentaculum tali and articulates with the middle facet of the talus. The anterior calcaneal facet articulates with the anterior talar facet and is supported by the calcaneal beak. The triangular anterior surface of the calcaneus articulates with the cuboid (3).
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Figure 2. Drawing of the superior surface of the calcaneus shows the anterior (A), middle (M), and posterior (P) facets of the calcaneus, as well as the calcaneal sulcus (S) that runs between the middle and posterior facets. The canal formed by the calcaneal sulcus and overlying talus is the sinus tarsi.
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The lateral surface is flat and subcutaneous, with a central peroneal tubercle for the attachment of the calcaneofibular ligament centrally. The lateral talocalcaneal ligament attaches antero-superiorly to the peroneal tubercle (3) (Fig 3).
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Figure 3. Drawing of the lateral surface of the calcaneus shows the peroneal tubercle (P), as well as the lateral talocalcaneal (LTL), interosseous (IOL), and bifurcate (B) ligaments.
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Medially, the talus is held to the calcaneus firmly by the interosseous ligament and the thick medial talocalcaneal ligaments (4). The sustentaculum tali is seen at the anterior aspect of the medial surface. The groove inferior to it transmits the flexor hallucis longus tendon. The neurovascular bundle runs adjacent to the medial border of the calcaneus (Fig 4). The neurovascular bundle may be injured during trauma or during surgery by the reduction of the sustentacular fragment, which is a key element in the surgical management of calcaneal fractures (5).
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Imaging
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Over the past 10–15 years, there have been dramatic improvements in CT technology. Current multichannel helical CT scanners allow extremely rapid imaging with very thin sections for multiple anatomic regions of the acutely injured patient. Thin-section data provide voxels that are essentially isotropic, which allows for high-resolution multiplanar reconstructions. Image reformation allows trauma patients to be scanned while they are in more comfortable, nonanatomic positions without compromising image quality (6). Multi-planar reconstructions from image data acquired on state-of-the-art scanners provide image quality that is equal or superior to that of directly acquired images produced 10–15 years ago.
Our current protocols for imaging acutely injured patients with suspected calcaneal fractures include a portable lateral radiograph obtained in the trauma room. If a calcaneal fracture or equivocal findings are found, a CT scan of the calcaneus is obtained while the patient is in the CT scanner for routine trauma imaging.
With our 16-channel CT scanner, we image the hindfoot with 0.625-mm collimation, a pitch of 0.5625, 120 kVp, and 200 mA. We reference the ankle joint on the axial images to obtain true sagittal and coronal planes of the hindfoot. For fracture classification, we reformat our images parallel and perpendicular to the anatomic posterior facet off the sagittally reconstructed images (Fig 5 ).
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Figure 5a. Optimal CT reformation planes for evaluation of calcaneal fractures. (a) Sagittal reformatted images of the calcaneus are prescribed off the axial images at the level of the ankle joint. (b) Coronal images are reformatted perpendicular to the sagittal images, also in reference to the ankle joint. (c, d) For fracture classification, particularly with the Sanders classification, we reformat our images parallel (c) and perpendicular (d) to the posterior facet off the sagittal reformatted images.
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Figure 5b. Optimal CT reformation planes for evaluation of calcaneal fractures. (a) Sagittal reformatted images of the calcaneus are prescribed off the axial images at the level of the ankle joint. (b) Coronal images are reformatted perpendicular to the sagittal images, also in reference to the ankle joint. (c, d) For fracture classification, particularly with the Sanders classification, we reformat our images parallel (c) and perpendicular (d) to the posterior facet off the sagittal reformatted images.
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Figure 5c. Optimal CT reformation planes for evaluation of calcaneal fractures. (a) Sagittal reformatted images of the calcaneus are prescribed off the axial images at the level of the ankle joint. (b) Coronal images are reformatted perpendicular to the sagittal images, also in reference to the ankle joint. (c, d) For fracture classification, particularly with the Sanders classification, we reformat our images parallel (c) and perpendicular (d) to the posterior facet off the sagittal reformatted images.
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Figure 5d. Optimal CT reformation planes for evaluation of calcaneal fractures. (a) Sagittal reformatted images of the calcaneus are prescribed off the axial images at the level of the ankle joint. (b) Coronal images are reformatted perpendicular to the sagittal images, also in reference to the ankle joint. (c, d) For fracture classification, particularly with the Sanders classification, we reformat our images parallel (c) and perpendicular (d) to the posterior facet off the sagittal reformatted images.
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Mechanism of Injury, Fracture Type, and Classification
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Fractures of the calcaneus have been described since the times of Hippocrates. They have historically had a poor prognosis, since they are usually caused by direct trauma that injures the articular surfaces, calcaneal fat pad, and peroneal tendons, with resultant change in mechanical forces acting at the ankle joint. Calcaneal fractures are divided into two major categories, intraarticular and extraarticular. Accurate description of calcaneal fractures, including the position and displacement of fracture fragments, is extremely useful to surgeons, with significant implications for the management of these fractures (7).
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Intraarticular Fractures
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Approximately 75% of calcaneal fractures are intraarticular and result from axial loading, which produces two separate fracture lines: shear and compression (8). A shear fracture occurs in the sagittal plane and runs through the posterior facet, dividing it into anteromedial and posterolateral fragments (Fig 6). The fracture line may extend anteriorly to involve the cuboid facet. The position of this fracture line depends on the position of the foot at the time of the shear force. If the hindfoot is in varus position, the line extends more anteromedially; if the hindfoot is in valgus position, the line tends to be more posterolateral. If the foot is in extreme valgus position, the fracture line may be lateral to the posterior facet and extraarticular. A sagittal shear fracture splits the calcaneus into two fragments: the anteromedial or "sustentacular" fragment and the posterolateral or "tuberosity" fragment (9). The medial fragment is not substantially displaced relative to the talus because of the medial talocalcaneal and interosseous ligaments. The lateral fragment is dislocated laterally and remains impacted following release of the axial load, leading to a "step off" in the posterior facet (, Fig 7a, 7b). Occasionally, the talus continues to impact on the lateral edge of the medial fragment, creating a "double split" in it (Fig 7c). The resultant fragment is called the "middle fragment" and typically is displaced by about 1–2 mm.
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Figure 6a. Diagrams of the superior (a) and lateral (b) surfaces of the calcaneus show the shear (solid black line) and compression fracture lines from joint depression (blue lines) and tongue (red lines) type fractures. The shear fracture splits the calcaneus into the anteromedial (or sustentacular) and posterolateral (or tuberosity) fragments. The compression fracture runs in the coronal plane, with the anterior limb running through the critical angle of Gissane and the posterior limb extending either horizontally toward the tuberosity as a tongue type fracture (red line) or more vertically, just posterior to the posterior facet, as a joint depression type fracture (blue line).
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Figure 6b. Diagrams of the superior (a) and lateral (b) surfaces of the calcaneus show the shear (solid black line) and compression fracture lines from joint depression (blue lines) and tongue (red lines) type fractures. The shear fracture splits the calcaneus into the anteromedial (or sustentacular) and posterolateral (or tuberosity) fragments. The compression fracture runs in the coronal plane, with the anterior limb running through the critical angle of Gissane and the posterior limb extending either horizontally toward the tuberosity as a tongue type fracture (red line) or more vertically, just posterior to the posterior facet, as a joint depression type fracture (blue line).
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Figure 7a. (a) Coronal CT image shows the shear fracture line (arrow) separating the anteromedial or sustentacular fragment (S) and the posterolateral or tuberosity fragment (T). Note that the articulation of the posterior facet with the talus is maintained medially and is more angulated laterally. (b) Sagittal image of the same patient shows depression of the tuberosity fragment (T). (c) Coronal CT image of a different patient shows two shear fracture lines (arrows) that separate the sustentacular (S), middle (M), and tuberosity (T) fragments, an example of the "double split."
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Figure 7b. (a) Coronal CT image shows the shear fracture line (arrow) separating the anteromedial or sustentacular fragment (S) and the posterolateral or tuberosity fragment (T). Note that the articulation of the posterior facet with the talus is maintained medially and is more angulated laterally. (b) Sagittal image of the same patient shows depression of the tuberosity fragment (T). (c) Coronal CT image of a different patient shows two shear fracture lines (arrows) that separate the sustentacular (S), middle (M), and tuberosity (T) fragments, an example of the "double split."
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Figure 7c. (a) Coronal CT image shows the shear fracture line (arrow) separating the anteromedial or sustentacular fragment (S) and the posterolateral or tuberosity fragment (T). Note that the articulation of the posterior facet with the talus is maintained medially and is more angulated laterally. (b) Sagittal image of the same patient shows depression of the tuberosity fragment (T). (c) Coronal CT image of a different patient shows two shear fracture lines (arrows) that separate the sustentacular (S), middle (M), and tuberosity (T) fragments, an example of the "double split."
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The compression fracture line is produced by wedging of the anterolateral process of the talus into the angle of Gissane. The resultant compression fracture runs through the coronal plane and can extend medially to split the middle facet and the anteromedial fragment (Fig 6a). As mentioned, significant displacement of this fracture is prevented by the medial talocalcaneal and interosseous ligaments (10). When viewed laterally, the compression fracture appears as an inverted "Y," with the posterior limb extending horizontally toward the tuberosity as a "tongue type" fracture, or more vertically as a "joint depression type" fracture (10) (Fig 6b). The primary difference between these two fracture types is the connection of the tuberosity or posterolateral fragment to the lateral portion of the posterior facet, which is present in the tongue type and absent in the joint depression type (4) (Fig 8). The anterior limb of this fracture results in the formation of an anterolateral fragment, which is connected to the cuboid facet. This fracture causes buckling of the lateral wall, resulting in loss of height and marked widening of the calcaneus.
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Figure 8a. (a) Sagittal reformatted image of a tongue type fracture shows the fracture line, which exits the posterior aspect of the calcaneus (arrows). (b) On a sagittal reformatted image of the more common joint depression type fracture, the fracture line does not communicate with the tuberosity and runs just posterior to the articular surface (arrows).
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Figure 8b. (a) Sagittal reformatted image of a tongue type fracture shows the fracture line, which exits the posterior aspect of the calcaneus (arrows). (b) On a sagittal reformatted image of the more common joint depression type fracture, the fracture line does not communicate with the tuberosity and runs just posterior to the articular surface (arrows).
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Intraarticular calcaneal fractures produce typical features, including (a) loss of height due to impaction and rotation of the tuberosity fragment, (b) increase in width due to lateral displacement of the tuberosity fragment, and (c) disruption of the posterior facet of the subtalar joint (9) (Fig 9). In addition to the osseous injuries, extraosseous abnormalities must also be considered in the management of these fractures. Tendons can be directly injured by sharp fracture fragments or entrapped between them. Tendon entrapment can be an impediment to reduction (Fig 10). Medially, there are greater stretching forces, which result in fracture blister formation. In rare cases, compartment syndromes can occur and may be unrecognized (11). Because of the axial load mechanism, calcaneal fractures can be associated with burst fractures of the spine, commonly at the thoracolumbar junction.
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Figure 9a. Common findings associated with calcaneal fractures. (a) Sagittal reformatted image shows marked impaction and rotation of the lateral aspect of the posterior articular facet (arrows). (b) Coronal reformatted CT image of the calcaneus shows widening (arrows), primarily caused by displacement of the posterolateral or tuberosity fragment (T).
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Figure 9b. Common findings associated with calcaneal fractures. (a) Sagittal reformatted image shows marked impaction and rotation of the lateral aspect of the posterior articular facet (arrows). (b) Coronal reformatted CT image of the calcaneus shows widening (arrows), primarily caused by displacement of the posterolateral or tuberosity fragment (T).
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Various classification systems of calcaneal fractures based on CT and plain radiographic appearances have been developed for improving management of these fractures. There is still no consensus on surgical versus conservative management of these fractures, which is due, in part, to the lack of standardized fracture classification and understanding of fracture anatomy (12). CT classification of these fractures has been influential in improving our understanding and in standardizing management of these fractures (13). Some classification systems describe changes only at the articular surfaces and are less helpful (14). At present, the two major systems for classifying calcaneal fractures include the Hannover and Sanders classifications (13,15–17).
The Hannover classification assigns one point to each of a possible five fragments and one point to involvement of each of three articular surfaces (17). One to four points are also assigned for soft-tissue damage and comminution or involvement of other tarsal bones, yielding a maximum of 12 points.
The Sanders classification is used more commonly and is based on the pathophysiology proposed by Soeur and Remy; it relies on sagittally reconstructed CT images reformatted parallel and perpendicular to the posterior facet of the subtalar joint (13,15,16) (Fig 5). Type I fractures are nondisplaced. Type II fractures (two articular pieces) involve the posterior facet and are subdivided into types A, B, and C, depending on the medial or lateral location of the fracture line (more medial fractures are harder to visualize and reduce intraoperatively). Type III fractures (three articular pieces) include an additional depressed middle fragment and are subdivided into types AB, AC, and BC, depending on the position and location of the fracture lines. Type IV fractures (four or more articular fragments) are highly comminuted (Fig 11). The Sanders classification has been shown to have good interobserver variability, making it useful in clinical practice (18).
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Figure 11. Schematic depicts the Sanders classification of intraarticular fractures of the calcaneus in coronal and axial views. Type I fractures are nondisplaced and are not shown. Fracture lines A, B, and C describe the position of the primary fracture line in relation to the posterior facet and the subtalar joint. Types II and III fractures have two or three fragments, respectively, which are then subdivided, depending on the medial or lateral position of the primary fracture line. Type IV fractures are severely comminuted. (Reprinted, with permission, from reference 13.)
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The Sanders classification system is useful not only in treatment planning but in helping to determine prognosis (13). In their series of 120 intraarticular calcaneal fractures, type I fractures were treated without surgery (13). Patients with type II and type III fractures who underwent surgery experienced excellent or good clinical results in 73% and 70% of cases, respectively (13). Alternatively, only 9% of patients with type IV fractures had excellent or good clinical results after surgical treatment (13). Sanders et al have shown that although anatomic reduction is necessary for a good clinical outcome, success is not guaranteed, possibly related to cartilage necrosis at the time of injury (13).
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Surgical Perspective
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Although the severity of the deformity and the potential for sequelae from calcaneal fractures can generally be determined from radiographic studies alone, CT represents a spectacular tool for surgical decision making. With radiography, relatively easily repaired fractures (which may be severely displaced) cannot be distinguished from those that are surgically not repairable. When a lateral surgical approach (the most common strategy) is used, the entire calcaneus is rebuilt in reference to the sustentacular fragment. Only CT can give a clear understanding of the size of this fragment and the number of fracture lines that must be identified and surgically reduced. In addition, CT shows the location and plane of variable fracture lines that separate the anterolateral fragment. This "road map" guides the surgeon in the amount of dissection necessary to visualize and control this aspect of the pathologic anatomy. The precise location of the lateral wall, particularly in relation to the lateral malleolus and peroneal tendons, is much more easily appreciated with CT than with axial radiography. CT can clearly demonstrate the number of different fractures and their location along the posterior facet. This depiction allows the surgeon to estimate the feasibility of achieving an anatomic reduction that is secure enough to begin early motion, which is the goal of surgery for a displaced intraarticular fracture.
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Extraarticular Fractures
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Extraarticular fractures account for approximately 25%–30% of all calcaneal fractures. All fractures that do not involve the posterior facet are included in this category. Extraarticular calcaneal fractures are classified as (a) anterior process fractures; (b) fractures of the mid calcaneus, which includes the body, sustentaculum tali, peroneal tubercle, and lateral calcaneal process; and (c) fractures of the posterior calcaneus, which include those of the tuberosity and medial calcaneal tubercle (2).
When contemplating extraarticular calcaneal fractures, it is important to differentiate complex fractures that separate articular facets and distort the three-dimensional anatomy of the subtalar joint from the more simple extraarticular fractures.
Anterior process fractures are uncommon and are usually produced by forced inversion that results in increased tension across the bifurcate ligament (Fig 3b), which connects the anterior process to the cuboid and navicular (2) (Fig 12). Other mechanisms include forced abduction of the forefoot with a fixed calcaneus and exaggerated dorsiflexion (19). Patients often present with localized pain and commonly without deformity. The fracture is best seen on oblique views and may not be seen on anteroposterior and lateral views. CT is particularly helpful for evaluation of anterior process fractures. Protected weight bearing is the usual treatment for small fractures. Displaced fractures involving more than 25% of the calcaneocuboid articular surface are usually treated with open reduction and internal fixation (2). Nonunion is the most common complication.
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Figure 12. Anterior oblique radiograph of the foot shows a fracture of the anterior process of the calcaneus (arrow). There was minimal involvement (<25%) of the calcaneocuboid articulation, and the fracture was treated conservatively.
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The mechanism for calcaneal body fractures is similar to that for intraarticular fractures. However, this category includes those fractures that do not involve the posterior facet. These fractures are associated with extensive soft-tissue swelling and injuries to the appendicular and axial skeleton. CT assessment is important for excluding articular surface involvement and determining the extent of the fracture. Patients with calcaneal body fractures usually have a better prognosis than those with intraarticular fractures, and management is usually conservative. Nonunion is uncommon with these fractures.
The sustentaculum tali is rarely injured alone, and fracture may occur as a result of axial loading and inversion (10). Pain and swelling are usually noted below the medial malleolus and with flexion of the flexor hallucis longus tendon as it passes under the sustentaculum. Axial and coronal CT images are useful for diagnosing nondisplaced fractures (Fig 13). Fractures are usually treated conservatively, with no weight bearing for about 6 weeks. Large single fragments or persistent displacement may be treated with fixation by using a cannulated screw (2). Injury to the flexor hallucis longus tendon and nonunion are common complications. Triggering of the flexor hallucis longus may occur from stenosis of the tendon sheath.
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Figure 13a. Coronal (a) and axial (b) CT images illustrate an isolated sustentacular fracture (arrows). In this case, the posterior articular facet was spared. S = sustentacular fragment.
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Figure 13b. Coronal (a) and axial (b) CT images illustrate an isolated sustentacular fracture (arrows). In this case, the posterior articular facet was spared. S = sustentacular fragment.
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Avulsion fractures of the calcaneal tuberosity tend to occur in elderly osteoporotic patients from avulsion of the Achilles tendon with its bony insertion (20). The fracture is subcutaneous, and fragment displacement may result in skin compromise and sloughing if the fracture is not identified and addressed soon after injury. Other than compartment syndrome, this fracture is perhaps the only closed calcaneal fracture for which urgent surgical treatment is needed (Fig 14). Initial conservative management with immobilization in slight equinus position followed by open reduction and internal fixation is the usual treatment; however, repeat displacement is possible because of the strong pull from the tricepssurae mechanism (medial and lateral gastrocnemius and soleus muscles).
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Figure 14a. Lateral radiograph (a) and T1-weighted magnetic resonance (MR) image (b) show a displaced avulsion type fracture of the calcaneal tuberosity. The Achilles tendon (T) is seen on the MR image.
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Figure 14b. Lateral radiograph (a) and T1-weighted magnetic resonance (MR) image (b) show a displaced avulsion type fracture of the calcaneal tuberosity. The Achilles tendon (T) is seen on the MR image.
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The abductor hallucis, flexor digitorum, and plantar fascia attach to the medial process of the calcaneus. Fractures of the medial process usually occur after a fall from a height with vertical sheer when the foot is in valgus position. Observations in recent literature suggest that this injury may actually be the first component of a more complex injury in younger patients (21). The fracture is well seen on an axial calcaneal radiograph, but CT images should be obtained to assess for intraarticular or sustentacular extension (Fig 15).
Open reduction and internal fixation with an oblique tension band wire is often the treatment of choice for medial process fractures (21). Long-term complications are uncommon with these fractures.
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Conclusions
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Calcaneal fractures are complex injuries that commonly occur in male patients and that result in substantial morbidity. Recently, there has been an exponential proliferation of CT examinations of trauma patients who have sustained multiple injuries. In addition, dramatic advances have occurred in imaging technology, particularly multi-detector CT and image processing. This combination has resulted in dramatic improvements in the visualization of calcaneal injuries, which in turn has led to improved fracture characterization for the trauma patient. Radiologists must be familiar with injuries of the calcaneus, their anatomy, mechanisms, classification, and implications to help guide the treating physicians.
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Acknowledgments
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The authors thank Salvador Beltran, MD, Girona, Spain, for his excellent anatomic drawings.
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Abstract
LEARNING OBJECTIVES FOR TEST...
