Talar Neck Fractures

Article Author:
Alan Shamrock
Article Editor:
Doug Byerly
Updated:
5/17/2019 10:52:51 AM
PubMed Link:
Talar Neck Fractures

Introduction

Talar neck fractures are relatively uncommon, but potentially devastating injuries with often life-altering sequelae. The talus is located in the hindfoot and permits pain-free motion of the ankle, subtalar, and transverse tarsal joints. Talar neck fractures are associated with high-energy mechanisms with severe soft tissue injury, bony comminution, and fracture displacement is common. Injury to the talar neck with resulting displacement can lead to permanent stiffness, deformity, and pain with hindfoot arthrosis estimated to occur in greater than 90% of displaced talar neck fractures.[1] The uncommon nature of these injuries partially explains the paucity of high-quality literature to drive evidence-based treatment strategies. Displaced talar neck fractures almost exclusively receive treatment with open reduction internal fixation with nonoperative treatment reserved for the rare nondisplaced injury pattern or fractures in patients who are not surgical candidates. Classic complications following open fixation of talar neck fractures include osteonecrosis or avascular necrosis (AVN), posttraumatic arthritis, and malunion.[2] The high-energy traumatic mechanism is often a feature in these injuries as well as fracture fragment displacement can disrupt the tenuous supply to the talus resulting in necrosis. Unrecognized comminution of the medial talar neck predisposes these injuries to malreduction leading to varus malunion deformity. Many of these injuries ultimately require hindfoot arthrodesis procedures for pain-relief regardless of the timing of fixation and quality of reduction. The high-energy mechanism of talar neck fractures also leads to significant soft tissue injury making surgical wound healing a considerable concern.

Etiology

Anderson first reported a small case series of 18 talar neck fracture-dislocations in 1919 and coined the term “aviator astragalus” to describe this injury pattern.[3] Aviator astragalus referred to the increased incidence of talar neck fractures observed in fighter pilots during war-time following plane crashes. Typically, fractures of the talar neck occur with forced dorsiflexion of the ankle in the setting of a high-energy axial load.[1][4] Common injury mechanisms today include motor vehicle accidents or falls from height. The fracture occurs when the dense cortical bone of the anterior tibia is driven inferiorly and encounters the less dense trabecular bone of the talar neck.[4] Once the weak talar neck becomes disrupted, force propagates through ligamentous structures surrounding the talus including the talocalcaneal ligament and the complex subtalar and posterior ankle ligamentous complexes.[1] This action leads to subluxation or dislocation of the talar body from its articulations with the tibia superiorly and the calcaneus inferiorly. Significant rotational forces such as hindfoot supination are also thought to play a role in the degree of displacement of talar neck fractures as Hawkins reported a 26% rate of concomitant medial malleolus fractures in a series of 27 talar neck fractures.[5]

Epidemiology

Fractures of the talus are the second most common injuries of all tarsal bone fractures, with talar neck fractures accounting for approximately 50% of all talus fractures.[1] Although the most common site of injury in the talus, talar neck fractures remain a rare injury pattern and consist of less than 1% of all bony injuries of the foot and ankle.[4][6]

Pathophysiology

The talar neck represents the junction between the head and body of the talus. It is angled 10-44 medially and 5-50 plantarly respective to the talar body.[1] It contains less trabecular bone than the talar head or body.[7] The trabecular bone in the talar body orients in a direction that facilitates the transfer of weight-bearing force from the tibial plafond through the talar dome.[7] The trabecular bone of the talar neck is oriented in an abruptly different direction predisposing this already weaker anatomic area to fracture.[4]

History and Physical

Patients with fractures of the talar neck typically present following a high-energy traumatic mechanism such as motor vehicle accident or fall from height with hindfoot pain, ecchymosis, and swelling. These patients are often victims of polytrauma and likely have other bony, vascular, or soft tissue injuries, so the basic “ABC’s” (airway, breathing, and circulation) of acute trauma care are paramount. A complete neurovascular examination should is necessary with both the dorsalis pedis and posterior tibial artery pulses palpated or evaluated with a doppler if necessary. The cutaneous sensory distribution of all five named nerves of the foot (superficial peroneal, deep peroneal, saphenous, sural, and tibial nerves) should be examined. The motor exam consists of plantar- and dorsiflexion of the great toe and ankle as well as inversion and eversion of the foot, documenting any neurovascular deficits. The skin should undergo close inspection for abrasion or laceration concerning for possible open fracture. If found to be an open fracture, thorough bedside irrigation and debridement is necessary, and intravenous antibiotics and tetanus vaccination provided. Dislocations and bony deformity should undergo reduction, and the extremity placed into a temporizing splint for pain relief and to alleviate pressure from the soft tissues surrounding the talus. If an extruded talus is present, the bone should be thoroughly washed with sterile saline and placed back inside the soft tissue envelope if possible.

Evaluation

The evaluation of a talar neck fracture should begin with plain radiographic imaging with an appropriate plain-film X-ray series consisting of anteroposterior (AP), lateral, and Canale views. The Canale view provides the best visualization of the talar neck and is obtained by angling the x-ray beam 75 degrees from the horizontal and positioning the foot in maximum equinus with varying degrees of eversion (usually 15).[8] Computed tomography (CT) scans have drastically improved the evaluation of talar neck fractures by allowing visualization of complex periarticular anatomy. CT is the best study to assess the degree of displacement, congruity of the articular surfaces, and comminution of these fracture patterns with additional information gained in 93% of cases.[9] Three-dimensional (3-D) reconstructions of CT imaging demonstrates sagittal or coronal alignment and facilitates surgical planning. Magnetic resonance imaging (MRI) has a limited role in the evaluation of talar neck fractures in the acute setting.

In 1970, Dr. Leland Hawkins published a now landmark paper in which he described a classification system for talar neck fractures.[5] This classification system now bears his name and is known as the Hawkins Classification of talar neck fractures. Originally, only types I-III were described, and it was not until 1978 when Canale and Kelly added type IV.[10] A literature review performed by Day et al. revealed Dr. Hawkins’ classic publication had 263 citations and the revision by Canale and Kelly a further 206.[11] The Hawkins Classification is based upon fracture displacement and the presence/location of joint dislocation(s) surrounding the talus.

  • Hawkins I: nondisplaced fracture
  • Hawkins II: fracture with an associated subtalar dislocation
  • Hawkins III: fracture with associated subtalar and tibiotalar dislocation
  • Hawkins IV: fracture with associated subtalar, tibiotalar, and talonavicular dislocations

The value of a classification system rests on its ability to predict outcomes or guide treatment. The Hawkins classification has been shown to be prognostic in nature with more severe injury (Hawkins IV) having a higher rate of osteonecrosis.[4]

  • Hawkins I: 0-13% AVN
  • Hawkins II: 20-50% AVN
  • Hawkins III: 20-100% AVN
  • Hawkins IV: 70-100% AVN

Treatment / Management

Displaced talar neck fractures almost exclusively receive treatment by open reduction and internal fixation with nonoperative treatment reserved for the rare nondisplaced injury pattern or fractures in patients who are not surgical candidates. Nonoperative treatment consists of immobilization with a splint in the acute setting with a transition into a short leg cast when swelling has subsided. Surgical options for talar neck fractures include external fixation or open reduction internal fixation. A spanning external fixator is often selected as a temporizing measure to stabilize the bony injury and allow observation of the soft tissue envelope. The goal of surgery is anatomic reduction, which can be challenging in scenarios of high displacement, comminution, or angulation. A biomechanical study demonstrated that as little of 2 millimeters of malreduction of the articular surface alters contact stresses.[12] Directly visualizing fracture reduction is paramount with a dual incision technique (anteromedial and anterolateral) often necessary. Exposures can be augmented with malleolar osteotomies to aid in the visualization of the talar neck and body. Soft tissue considerations, fracture type, and other associated injuries often dictate the exact surgical approach. There are various reports of screw, plate, and hybrid fixation strategies with an estimated 96% of reported fractures of the talar neck addressed with some combination of plate and/or screw constructs.[13]

Historically, talar neck fractures were treated with the urgency reserved for open fractures or irreducible dislocations as the theory was that prompt reduction and fixation maintained the tenuous blood supply to the talus.[5][10][14] New literature has provided conflicting results.[15] The current understanding is that the risk for osteonecrosis is more related to the degree of displacement at the time of injury.[15] An important distinction is that although delayed fixation is acceptable, delayed fracture reduction is not.

Differential Diagnosis

Differential diagnoses of talar neck fractures include talar body fractures, talar head fractures, rotational ankle fractures, ankle fracture-dislocations, simple ankle dislocations, calcaneal fractures (both tongue and depression type), and subtalar joint simple or fracture-dislocations. These etiologies of traumatic hindfoot pain and deformity can be differentiated using CT imaging.

Prognosis

Given the associated high energy mechanism and severe soft tissue injury often seen in talar neck fractures, the prognosis is poor. The frequently encountered concomitant injuries limit many series of talar neck fractures, as isolated talar neck fractures are unusual. The high association with other lower extremity and axial spine injuries may contribute to worse outcomes.[16][17] In a series of 70 talar neck fractures, Sanders et al. demonstrated that the incidence of foot and ankle reconstructive surgery following fixation increased over time.[6] The authors also reported an association with poor patient-reported outcomes and the development of postoperative complications.[6] Failure to recognize the displacement of fracture fragments and subsequent malreduction can also lead to poor outcomes.[18] Patients with talar neck fractures should receive counseling that residual hindfoot pain is common even after surgery, with 18.6% of patients requiring an arthrodesis procedure by 6 years.[19]

Complications

There are extensive reports of high-rates of complication following talar neck fractures in the literature.[5][10] Reported rates of osteonecrosis of the talus after talar neck fracture range from 11% to 100%.[16][20][21] Posttraumatic arthritis is widely thought to be even more common than necrosis with reports of 30% to 90% of patients affected.[21][22][23][24] Involvement of the subtalar joint accounts for 81% of cases of posttraumatic arthritis.[13][19] Postoperative infection is a concern given the high incidence of open fracture and soft tissue injury with a reported deep infection rate of 21%.[19] Nonunion of talar neck fractures is relatively uncommon (under 5%), while malunion rates range from 20 to 37%.[19][25][26] Varus malunion is the most commonly reported deformity and is a result of unappreciated or malreduced medial comminution.[24]

Consultations

If the examiner identifies a talar neck fracture, a trauma or foot and ankle fellowship-trained orthopedic surgeon is necessary. If unavailable, the patient should be promptly transported to an appropriate facility where orthopedic care is available.

Deterrence and Patient Education

Hindfoot pain, swelling, and ecchymosis should prompt immediate presentation to an emergency department, especially in a mechanism consistent with an axial load applied across the ankle with forced dorsiflexion.

Pearls and Other Issues

The Hawkins sign is a helpful radiographic tool to assess for the development of osteonecrosis following talar neck fracture. This prognostic sign is defined as a lucency beneath the subchondral bone in the talar dome observed approximately 6 to 8 weeks following injury.[13] Typically, the lucency is first visible in the medial aspect of the talus followed by progression laterally. The presence of the subchondral lucency or Hawkins sign correlates with intact talar vascularity and rare progression to osteonecrosis.[4]

Enhancing Healthcare Team Outcomes

Talar neck fractures typically undergo management with dual-incision open reduction and internal fixation techniques. While the prompt reduction of fracture-dislocations is the recommendation, definite fixation can delay until the soft tissue envelope is amenable without an increased risk of osteonecrosis. In a series of 25 patients with 26 displaced talar neck fractures with a mean follow-up of 74 months (Level IV evidence), Lindvall et al. observed a union rate of 88% and concluded that a delay in surgical fixation does not affect the outcome, such as osteonecrosis or union.[15]

Talar neck fractures require the efforts of an interprofessional team that includes physicians, specialists, nursing with specialized orthopedic training, and when necessary, pharmacists, all collaborating across disciplines to achieve optimal patient outcomes. [Level V]



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References

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