Fractures of the calcaneus and talus, collectively termed “hindfoot fractures” are typically caused by high-impact forces like falls or motor vehicle accidents. Calcaneus fractures are the more common; talus fractures, though less common are often associated with greater morbidity: owing to the bone’s tenuous blood supply of the talus, fractures there have difficulty healing. Hindfoot fractures are caused by axial load, and therefore can be seen with more proximal injuries, such as fracture of the pelvis or spine, as well.
The hindfoot begins at the talocrural (ankle) joint and ends at the calcaneocuboid joint. The bones of the hindfoot are the talus (lower bone of the ankle) and the calcaneus (heel bone). The articulation between the talus and calcaneus is called the subtalar joint. The talus does not sit on top of the center of the calcaneus, but rather toward the lateral-superior edge of the calcaneus.
Fig schematic lateral of the ankle and hindfoot. The tibia is in blue, the talus is in green and the calcaneus is in brown. The midfoot and forefoot bones are all red. The yellow bone is the navicular, seen articulating with the talus; the cuboid is in gray-blue, seen articulating with the calcaneus
The hindfoot functions to bear and distribute weight to the foot while standing, and to permit complex foot movements in coordination with the ankle joint, especially inversion/eversion and axial rotation.
The talus has a complex architecture, enabling it to function as a "ball-joint" between the leg and the foot. The talus can be divided into three anatomical regions: the head, neck, and body. The head articulates with the navicular anteriorly (talonavicular joint). The neck connects the body and head and is the most commonly fractured part of the talus.
The vascular supply to the body enters at the neck. As such, talar neck fractures may impede perfusion of the body and thereby pose a risk of avascular necrosis of the talar body. The talar body articulates with the calcaneus inferiorly (subtalar joint) at three separate articular surfaces: anterior, middle, and posterior. The space between these three articulations is known as the tarsal sinus.
Motions near the hindfoot include plantarflexion/dorsiflexion at the ankle joint; pronation/supination at the subtalar joint; and rotation and translation at the talonavicular joint.
Nearly 70% of the talus is covered by articular cartilage. Unlike the calcaneus, which has many insertions and origins of muscles, the talus does not attach to any muscles. The blood supply to the bone, thus, is limited to a “vascular sling” comprising the artery of the tarsal canal (a branch of the posterior tibial artery that supplies the body) and the artery of the tarsal sinus (supplied by branches of the anterior tibial and peroneal arteries to supply the head and neck). This limited blood supply makes the talus prone to delayed healing and avascular necrosis.
The os trigonum is an accessory bone that develops posterior to the talus. It is present in 2.5-14% of people and is bilateral in 60% of these people. It can be mistaken on x-ray as a fractured bone.
Figure: Os trigonum (circled in red) on plain ankle x-ray. Credit: http://en.wikipedia.org/wiki/Talus_bone#mediaviewer/File:Os_trigonum_1.jpg
The calcaneus articulates with the cuboid anteriorly, but its major articulation is with the talus above it. The calcaneus has three anatomic regions: the anterior process, the body, and the posterior tuberosity. The Achilles tendon inserts at the calcaneal tuberosity on the posterior side of the calcaneus. Near the medial talar articulation is the sustentaculum tali (a horizontal shelf of bone). The calcaneus is likened to a “hard-boiled egg” because its outer cortex is thin and surrounds the softer inner cancellous bone. If damaged, the outer cortex can collapse leading to severe comminution of the underlying cancellous bone.
Patients with a fracture of the hindfoot will present with a history of trauma and significant swelling and pain. It may be difficult to distinguish a fracture from a sprain with an acutely swollen ankle, so re-examination may be necessary after the swelling has subsided. Laceration, blood, or puncture wound, often on the medial aspect of the foot, will indicate an open fracture.
Inability to bear weight is a common sign of hindfoot fractures. Redness, hematoma, and fracture blisters may be present near the heel. “Mondor sign” is a hematoma extending distally along the sole of the foot – it is pathognomic for a calcaneus fracture.
Hindfoot fractures are often accompanied by other injuries because the extent of axial loading necessary to cause a hindfoot fracture is likely to cause other problems too. Fractures and dislocations of the ankle joint may occur in these settings. Additionally, lumbar spine fractures are seen in 10% of patients with calcaneus fractures.
It is important to assess soft tissue damage in addition to the fracture, as the extent of soft tissue damage will dictate the prognosis and when to start definitive treatment. A comprehensive neurological exam should be performed to look for motor or sensory nerve injury. Anterior and posterior tibial pulses and distal capillary refill should be examined via palpation and or Doppler to assess for any vascular deficits.
Figure: Gross appearance of a closed calcaneal fracture. Note swelling, bruising, and blister formation along the lateral hindfoot. Credit: http://www.orthopaedicsone.com/download/thumbnails/27099874/1.JPG?version=3&modificationDate=1287444363000
The presence and location of talar fractures should be evident on plain films, but the talus may be obscured by the ankle mortise, calcaneus, and midfoot.
Talar neck fractures, caused by excessive dorsiflexion of the foot against the distal tibia, comprise half of all talus fractures. They are classified, with increasing severity, as nondisplaced; displaced but with an intact ankle joint; and displaced subluxation/dislocation of both the subtalar joint and ankles joints. A fourth category is designated in there is disruption of the talonavicular joint as well.
The second most common site of talus fracture is the lateral process – approximately one-quarter of talus fractures occur here. These often occur following axial compression, dorsiflexion, and eversion. They are common in snowboarders.
Fractures of the talar head, body, and posterior process are less common
Calcaneus fractures are more common than talus fractures. They are broadly classified according to whether they involve the subtalar articular surface (intra-articular) or not (extra-articular).
Extra-articular fractures represent only 25% of calcaneal fractures. By definition, they do not involve the subtalar joint or its articular surfaces. Extra-articular fractures typically affect the anterior process, calcanear tuberosity, calcaneal body, and sustentaculum. Intra-articular fractures are both more common and more challenging to treat.
Anterior-posterior, lateral, and oblique/mortise X-rays should be taken of the ankle and foot. Two angles on the lateral x-ray can be helpful in assessing calcaneus fractures. Bohler’s angle is formed from two lines: (1) a line drawn from the superior point of the posterior calcaneal tuberosity to the highest midpoint of the posterior articular facet, and (2) the highest midpoint of the posterior articular facet to the anterior process. This angle should be 20-40 degrees – a decrease in Bohler’s angle suggests a depressed fracture of the posterior facet. The Angle of Gissane is formed from the downward slope of the posterior facet and the upward slope directed anteriorly. This angle should be 100-130 degrees – an increase suggests a fracture of the posterior subtalar articular surface.
Figure: Bohler’s angle as seen on lateral x-ray
“Hawkins sign”, namely a radiolucent line in the subchondral talus (patchy subchondral osteopenia) several weeks following injury on the AP or mortise views of the ankle, is a radiographic indicator of revascularization and absence of avascular necrosis. The radiolucency is the result of bone resorption and is a good sign – it indicates that the bone retained its blood supply.
CT imaging is routinely performed to assess the fracture pattern, degree of displacement, and involvement of articular surfaces since radiographic imaging does not provide sufficient resolution to visualize the articular fragments. Sagittal, coronal, and transverse CT scans are especially helpful for the decisions to perform surgery as well as intra-operative decision-making about technique and needed implants.
MRI is mostly used to detect and quantify the degree of avascular necrosis of talar fractures. It is also used to diagnose osteochondral lesions of the talus.
Figure: CT scan of calcaneus fracture
Calcaneus fractures comprise 2% of all fractures and 60% of tarsal fractures. The annual incidence is approximately 12 per 100,000 per year, significantly less than ankle fractures (187 per 100,000) which may present similarly. According to Mitchell et al (PMID: 20307476), calcaneus fractures occur 2.4 times more often in males and most often affect men in their 20’s. 72% of calcaneal fractures are due to falls from a height and 19% occur in the workplace. A small minority of calcaneus fractures may be non-traumatic stress fractures due to repetitive axial loading, as seen in military personnel or long-distance runners. Ten percent of calcaneus fractures are bilateral. Ten percent will have associated thoracolumbar spine injuries and another 10% will have a hip fracture.
According to Fortin et al (PMID: 11281635), talus fractures are the second most common fractured bone in the foot but are rarer than calcaneus fractures, comprising only 0.1-0.9% of all fractures. The most common site of talus fractures is at the talar neck followed by the lateral process. Talus fractures are significant because of their potential for long-term morbidity and complications.
Shibuya et al (PMID: 24785202) found that open fractures occur in approximately 20% of calcaneus and talus fractures.
Because a high-energy impact is necessary to cause hindfoot fractures, it is possible that the same mechanism will cause other injuries to the lower limb. These include ankle sprains, ankle fractures, talus dislocations, tibial and fibular fractures, pilon fractures, hip fractures, and injuries to the other tarsal and metatarsal bones. In fact, one-quarter of calcaneal fractures are accompanied by other lower limb injuries. A high-energy axial load can also cause injuries outside the lower limb. One of the most common injuries is thoracolumbar spine fractures, occurring in 10% of patients with calcaneal fractures.
Hindfoot fractures can be missed in patients who have sustained polytraumatic injuries. Thus an axial load mechanism should be a “red flag” suggesting the presence of a hindfoot fracture, and the presence of such a fracture in one limb should prompt close evaluation of the contralateral side (as it may have been subjected to the same axial load).
A missed hindfoot fracture should also be suspected if a diagnosed ankle sprain does not improve with routine treatment. Subtle hindfoot fractures can be caused by the same inversion mechanism that causes sprains, and therefore can be easily misdiagnosed as ankle sprains (PMID: 12322769).
Tenting of the skin with a fracture is a worrisome sign indicative of potential skin necrosis.
Initial treatment of hindfoot fractures should focus on reducing swelling and addressing any open wounds. After the fracture pattern has been identified, definitive treatment can begin.
Definitive treatment for hindfoot fractures can be operative or non-operative depending on the part of the bone fractured, the severity of the fracture, and the patient's risk factors. Non-operative treatment generally involves immobilization and no weight bearing for 6 to 12 weeks followed by progressive weight bearing and ROM exercises.
Operative treatment generally involves open reduction and internal fixation (ORIF) followed by immobilization, no weight bearing and ROM exercises. According to Swanson et al (PMID: 19013401) there is a narrow window of opportunity for surgery–long enough after the injury such that there is resolution of swelling yet not too long that too much soft callus can formed.
The risk of complications of talus fractures is related to the extent of the displacement, degree of damage to the blood supply, and damage to the articular surfaces. A common complication is avascular necrosis due to injury to the vascular sling supplying the talus. The risk of avascular necrosis ranges from 10% or less if the fracture is not displaced to 100% if there is disruption of subtalar, ankle and talonavicular joints.
Extra-articular calcaneus fractures can generally be treated non-operatively unless the fragments are large. In the case of fractures of the calcaneal tuberosity caused by Achilles tendon avulsion, screw fixation may be required to prevent displacement by the force of the Achilles.
Non-displaced fractures are treated non-operatively and either non-operative or surgical fixation may be indicated for displaced fractures. Surgical fixation is a technically challenging procedure and surgical fixation has been shown to be only marginally better than non-operative treatment. In an analysis by Buckley et al (PMID: 12377902), it was shown that surgical fixation has optimal results in young, female patients who are not receiving worker’s compensation. Smokers, diabetics, older patients, patients with vascular disease, and those receiving worker’s compensation tend to do less well.
Figure: Surgical fixation of a lateral process fracture
Figure: x-ray of calcaneus fracture following anatomic reduction and fixation with plate and screws. Credit: http://www.footeducation.com/wp-content/uploads/2010/08/Calcaneus-X-ray-Post-Fixation-277x300.jpg
Because most hindfoot fractures occur in the setting of acute injury, such as falls or motor vehicle accidents, prevention mostly centers on avoiding such accidents. However, certain health conditions can also predispose people to hindfoot fractures. For example, Kathol et al (PMID: 1871285) and Cheng et al (PMID: 9200007) found that diabetes mellitus and low bone mineral density are major risk factors for hindfoot fractures.
Hindfoot fractures can also be sports-related. Chan et al (PMID: 12764342) found that snowboarders are 17 times more likely to sustain fractures to the lateral process of the talus compared to the general population. Additionally, Salzler et al (PMID: 22735197) found that running with minimalist footwear has been implicated in calcaneal stress fractures.
Calcaneus fractures are called “lover’s fractures” because they are the injury a cheating spouse would sustain if jumping from an upstairs bedroom window to escape trouble.
Talus fractures were historically referred to as “Aviator’s astralgus.” In the early 20th century, plane crashes at sub-lethal speeds were common, resulting in high-impact injuries to the foot including talus fractures. Nowadays talus fractures are mostly caused by falls and motor vehicle accidents, so this term is mostly obsolete.
Develop a differential diagnosis of possible foot injuries resulting from high-energy axial loading such as a fall or motor vehicle accident
Recognize the classic signs, symptoms, and history of hindfoot fractures
Identify and differentiate between calcaneus and talus fractures on plain radiographs
Use radiography and CT imaging to calculate Bohler’s and Gissane’s angles
Classify calcaneus fractures according to Sanders Classification using coronal CT images
Determine the appropriateness of operative vs. non-operative management depending on whether fractures are displaced