Tarsal Navicular Fractures

Etiology

While the biomechanics behind stress fractures of the tarsal navicular are somewhat poorly understood, those of traumatic injuries are more comprehensively elucidated. It is known, however, that stress fractures are a chronic overuse injury associated with microfractures of the bone[7] Traumatic injuries can cause a variety of navicular fracture patterns, including avulsion fractures, tuberosity fractures, and body fractures.

Avulsion fractures of the navicular may occur dorsally, medially, or in a plantar direction, depending on the force applied to the midfoot. In the case of foot dorsal avulsion, fractures result from extreme plantar flexion causing undue stress on the deltoid and dorsal capsules.[1] Excessive pull from the posterior tibialis tendon can result in medial and tuberosity fractures, and plantar avulsion fractures are secondary to ligamentous injury.[1]

Navicular body fractures can be caused either by a direct or an indirect force. The Sangeorzen classification, devised in 1989, is the leading system for grading tarsal navicular body fractures.[1] This system classifies tarsal navicular body fractures according to the direction of the fracture line, degree of disruption of surrounding joints, and the direction of foot displacement.[8] In this classification, a Type-1 injury is one that occurs in the coronal plane, with no angulation of the forefoot. A Type-2 injury is one that has a dorsolateral to plantar-medial fracture line with medial displacement of the major fragment and forefoot. A Type-3 injury is a comminuted fracture in the sagittal plane of the bone, with lateral displacement of the forefoot. There are several other theories on the forces causing navicular body fractures, though all are due to axial forces on a foot in plantar flexion.[8][7]

Epidemiology

Midfoot fractures only represent a small portion of all foot injuries, though stress fractures comprise approximately one-third of all stress fractures of the foot.[7]

In the case of traumatic navicular injuries, the vast majority result from motor vehicle accidents, followed by falls and blunt injuries.[9] Stress fractures are most common in young individuals with high functional demand such as competitive athletes.[7]

History and Physical

Patients of avulsion fractures typically present with a significant degree of pain in the midfoot area, particularly during push-off of the fractured segment. Patients who have endured a navicular body fracture are typically unable to bear any weight on the affected extremity and present with a profound degree of swelling on the dorsal and medial aspects of the foot, all of which is due to the mechanism of the injury and disruption of the medial column of the foot.[10] Owing to the risk of compartment syndrome, a thorough neurovascular assessment should take place, with an evaluation of any open wounds. Additionally, navicular body injuries are often associated with additional injuries on the ipsilateral foot, with a recent study showing fifteen patients out of twenty-four having further injuries.[11]

On the other hand, patients who have endured a navicular stress fracture typically have a milder clinical presentation, with an extended history of vague midfoot discomfort. Examination of these patients typically reveals a well-localized source of their pain over the dorsal aspect of the midsection of the navicular.[10]

Evaluation

In a patient with a suspected tarsal navicular fracture, the initial radiographic evaluation is the three-view radiograph of the foot; this includes a non-weight bearing anteroposterior, lateral, and oblique X-ray. However, patients with suspected ligamentous injury or minor injuries may require a weight-bearing radiograph. An external oblique radiograph of the foot is useful in the evaluation of a suspected tuberosity fracture.[10] In evaluating radiographs, the clinician should be aware of the potential for the appearance of an accessory navicular, which is identifiable with a radiograph of the contralateral foot.

The use of computed tomography (CT) can be helpful in high-energy injuries, as it can more precisely delineate complex fracture patterns, the geometry of the talonavicular joint, and can assist in preoperative planning. Additionally, CT can be used to create three-dimensional reconstructions of the navicular.

Treatment / Management

Tarsal navicular fractures can be managed either nonsurgically or surgically, depending on the individual fracture characteristics, such as the size, the degree of displacement, the location, comminution, as well as the condition and integrity of the soft tissues of foot, the presence of additional injuries on the ipsilateral foot, comorbidities and overall functional status.[10]

In the case of navicular stress fractures, immobilization, and protected weight bearing for a period of six to eight weeks are indicated. However, patients with high functional demand, such as athletes may opt for surgical intervention instead.[7] In the event of surgical intervention, these fractures may undergo repair with open reduction and internal fixation.[7]

The management of traumatic navicular fractures can also be surgical or nonsurgical. Small avulsion fractures, tuberosity fractures, and nondisplaced body fractures can be managed nonoperatively, with the use of a weight-bearing short leg cast and ultimately a walking boot.[10]

Displaced navicular body fractures typically require operative intervention, with the use of open reduction and internal fixation. The goals of operative intervention are anatomic fracture reduction, restoration of the length of the medial column, and creation of a rigid osseous construct which would allow for early range of motion.[10]

Differential Diagnosis

In the event of a suspected navicular fracture, some conditions that may have similar symptoms and presentations include tendinopathy of the posterior tibialis owing to its insertion on the navicular tuberosity, tear of the spring ligament, or separation of an accessory navicular- a relatively common anatomic variant. An MRI can differentiate between a tarsal navicular fracture and one of these conditions. However, it is usually not needed in the initial management as radiographs, and CT-scans readily diagnose most tarsal navicular fractures.

Prognosis

Patients who have suffered a navicular stress fracture typically have a favorable prognosis if treated promptly and appropriately. A recent study demonstrated that 57 out of their 62-patient cohort had been able to return to activity at their preinjury level, implying an optimal clinical outcome[12] In another case study of 10 patients who had suffered comminuted tarsal navicular fractures, the union was achievable in all surgically treated patients, with none requiring an arthrodesis at a mean follow up of 20 months.[13]

Complications

As with most periarticular regions, there are several potential complications and risks associated with fractures of the navicular. These complications include osteonecrosis, malunion, nonunion, persistent stiffness, and pain. Patients suffering a nonunion may have deformity which can be mitigated through the use of an orthosis or surgical revision, depending on the severity of the deformity. Osteonecrosis, however, can result in profound deformity and is typically treated with the primary goal of restoring length and alignment, which is often through the fusion of the talonavicular or naviculocuneiform joints.[1]