1 Introduction

Injury to neurovascular structures in proximity to long bones is a known complication of traumatic fractures. Injury can result from the initial trauma, a closed reduction attempt, or can be iatrogenic during surgery. Nerve entrapment, however, occurs with less frequency and is more common in the upper extremity as compared to the lower extremity.^1,2 Most describe entrapment of the radial nerve in humerus fractures as well as the median nerves in radius fractures.^3–7 However, superficial peroneal (SPN) and deep peroneal (DPN) nerve entrapment following tibia and fibula fractures has also been reported.^1,2,8–12 To our knowledge, there are only two previous reports of neurovascular entrapment specifically after pilon fractures.^8,12 The DPN and anterior tibial artery and vein lie directly on the distal anterior tibia and are understandably at risk of entrapment in pilon injuries. The exact incidence of this finding is less clear, but recognizing the possibility of entrapment, even in a patient without symptoms, is important to avoid causing neurovascular injury. We report a case of asymptomatic anterior neurovascular bundle entrapment in a high-energy pilon fracture requiring appropriate intraoperative identification and surgical management.

2 Case report

A 37-year-old male with no significant past medical history presented after a 9-foot fall from a fence, landing directly onto his right leg. Physical examination demonstrated a closed deformity of the right ankle. The extremity was swollen from the mid-calf to the dorsal foot, however all lower leg and foot compartments remained compressible. There were no gross motor or sensory deficits, including in the DPN distribution. The patient had a palpable dorsalis pedis pulse.

Initial plain radiographs of the right tibia-fibula and ankle demonstrated a severely comminuted intra-articular fracture of the right distal tibia (OTA 43-C3) as well as a distal fibula fracture (Fig. 1). Given the degree of swelling, comminution, and instability, the patient was taken to the operating room on the day of admission for closed reduction and application of an ankle-spanning external fixator to stabilize the injury and allow for resolution of swelling. Fasciotomies were not performed at the time given compressible compartments and intact motor and sensory exam. A CT scan was obtained after external fixator application for preoperative evaluation and planning, which demonstrated a longitudinal metadiaphyseal fracture along the anterior tibia (Fig. 2).

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Fig. 1 Plain radiograph of the right tibia-fibula demonstrating the initial injury and deformity.

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Fig. 2 Axial CT scan after external fixator application demonstrating the major fracture fragments.

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The patient's right lower extremity remained persistently swollen after the injury despite appropriate management including rest and elevation. On hospital day 14 it was determined that the patient's swelling was adequate for surgery as determined clinically by the “wrinkle sign.” Overall, the patient remained comfortable and tolerated the external fixator. He denied new or worsening sensory or motor changes throughout the hospital course. Daily neurovascular exams did not reveal distal motor or sensory deficits. The patient maintained palpable dorsalis pedis and posterior tibial pulses.

Given the complex morphology of this fracture, a direct anterior approach to the distal tibia was performed. A longitudinal incision was made in line with the third ray starting 10 ​cm proximal to the tibiotalar joint and extending past the tibiotalar joint. Distally, SPN was mobilized out of the field. The deep fascia and the extensor retinaculum were identified and incised in line with the incision. The interval between the extensor hallucis longus (EHL) and extensor digitorum longus (EDL) was identified and bluntly dissected. EHL was retracted medially and EDL was retracted laterally. There was significant comminution upon exposure of the fracture. The anterior neurovascular bundle was easily identified distally. Therefore, dissection of the bundle started distally and was traced proximally. There was difficulty following the course of the bundle proximally as it appeared to fall deep into the zone of injury. Further investigation and meticulous dissection as well as careful debridement of the fracture zone demonstrated entrapment of DPN and anterior tibial artery and vein within the large metadiaphyseal fragment (Figs. 3 and 4). Comminuted cortical fragments were also wedged against the bundle. The fracture was spread open with a lamina spreader, cortical fragments were carefully removed, and the bundle was freed from the fracture site. The bundle was then meticulously dissected further proximally past the most proximal spike of the fracture and was confirmed to be intact throughout. At this point the entire bundle was carefully removed from the fracture as a unit and mobilized out of the field. The fracture was anatomically reduced and fixed with a combination of 3.5-mm lag screws, a medial plate used in buttress fashion, and an anterolateral distal tibial plate. The associated distal fibula fracture was fixed percutaneously with a 4.5-mm cannulated fully threaded screw (Fig. 5). Dorsiflexion external rotation stress test was negative.

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Fig. 3 Clinical photograph of entrapped anterior neurovascular bundle within the large metadiaphyseal fracture fragment. The foot is towards the bottom of the image.

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Fig. 4 Clinical photograph of entrapped anterior neurovascular bundle being presented out of the large metadiaphyseal fracture fragment. The foot is towards the bottom of the image.

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Fig. 5 Postoperative radiographs of the right tibia-fibula.

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Postoperatively, the patient was placed in a splint for two weeks followed by a removable boot while encouraging ankle range of motion exercises. He has been adhering to weight-bearing restrictions. He has denied any new or worsening motor or sensory deficits and has had no notable complications in subsequent follow ups. Radiographic evaluation has demonstrated stable fixation of the pilon fracture. The last follow up was at three months where his weight-bearing status was progressed.

3 Discussion

Pilon fractures continue to present a challenge to orthopedic surgeons. Even if anatomic reduction and restoration of the articular surface is achieved, the risk of intraoperative and postoperative complications is high and functional outcomes vary.¹³ Perioperative complications include malreductions, soft tissue injury, hardware penetration, and wound complications leading to infection. Late complications include post-traumatic arthritis and decreased ankle mobility.

This case is an example of an intraoperative finding that the treating orthopedic surgeon must be aware of to avoid iatrogenic injury. There are few previous reports detailing neurovascular entrapment specifically in pilon fractures and the incidence is unclear.^8,12 In our case, there was very low preoperative suspicion for injury or entrapment given a stable and unremarkable neurovascular examination throughout the two-week hospital course prior to definitive fixation. However, the intraoperative finding of anterior neurovascular bundle entrapment in this high-energy pilon fracture highlights the importance of maintaining a high index of suspicion of entrapment even in patients who present without symptoms.

It is likely that the neurovascular bundle became entrapped within the fracture at the time of the initial trauma given the location of the large metadiaphyseal fracture along the course of the bundle as well as the finding of multiple comminuted cortical fragments wedged against the bundle. A good understanding of anatomy in addition to appropriate identification and management of the neurovascular bundle, especially when in proximity to large fracture fragments, is critical to avoid iatrogenic neurovascular damage.

Financial support and sponsorship

None of the authors received grant support or sponsorship funding for this report.

Informed consent

A written consent was obtained from the patient allowing the authors to use clinical data and images for publication of this case report. Patient identity is present in neither the manuscript nor the images.

Authors contribution

RH conducted the literature review, carried out the case report, and assisted with the surgery. HJD helped conceptualize the report and performed the surgery. HJD provided the revisions for the report. Both authors read and approved the final manuscript.

Ethical committee approval

This study was approved in accordance with the ethical committee at the authors’ institution.