What You Should Know About Navicular Stress Fractures
Once considered a rare form of stress fractures, navicular stress fractures are being diagnosed in an increasing number of patients. Accordingly, these authors offer diagnostic insights, a pertinent case study and a thorough review of the literature.
Towne and colleagues first described the stress fracture of the tarsal navicular in humans in a 1970 case study.1 Early studies showed that tarsal navicular stress fracture was a rare injury, accounting for only 0.7 to 2.4 percent of all stress fractures.2 However, as awareness of the injury has increased, so have the reported number of cases with tarsal navicular stress fractures currently representing up to 25 percent of stress fractures in some series.3-7
The diagnosis of navicular stress fractures is challenging as routine radiographs often fail to demonstrate the fracture. One must maintain a high index of suspicion for this injury, especially in athletes with foot pain, given the vague complaints and potential for considerable delay in diagnosis.8
The “boat shaped” navicular represents the base of the medial column of the foot, articulating with the talus proximally, and with the cuboid and all three cuneiforms distally.8,9 The navicular has several important ligamentous attachments, including the posterior tibial tendon on the medial tuberosity and the spring ligament on the plantar surface.8,9
The navicular derives its dorsal blood supply from a branch of the dorsalis pedis artery while the plantar surface receives its supply from the branches of the medial plantar artery.9 These branches form a rich anastomosis but leave the central one-third of the navicular relatively avascular.8,9 The navicular is subject to intense compressive forces over its middle one-third during the foot-strike phase of gait when it is compressed between the talus and the cuneiforms.10 Torg proposed that repetitive cyclical loading of the navicular could lead to a stress fracture over the central one-third of the navicular.11
What You Should Know About The Clinical Presentation And Physical Examination
Patients most often present with dorsal foot pain of insidious onset. Patients may initially describe the pain as soreness or cramping along the dorsomedial border of the foot, which is exacerbated by activity.8,10 As many patients who sustain navicular stress fractures are athletes, they initially may complain of pain only during sport and not with other activities of daily living.8,10 Specifically, explosive activities such as jumping, sprinting and rapidly changing direction may exacerbate symptoms.8,10
The physical examination is often unremarkable. Patients may have tenderness to palpation over the navicular. Provocative testing includes having the patient hop on the affected foot to determine if it reproduces the symptoms experienced during athletic play.8,10
Key Diagnostic Insights
The diagnostic workup should begin with plain radiographs of the standing foot and ankle. The radiographs may demonstrate a visible fracture line. However, several authors have found a high rate of false negative radiographs.3,11,12 If there remains a high index of suspicion after negative plain radiographs, further workup with bone scan, computed tomography (CT) or magnetic resonance imaging (MRI) is indicated.
Although bone scan has a high sensitivity, it is also non-specific and requires additional diagnostic testing in the event of a positive test, further delaying the definitive diagnosis.11 Bone scans are unable to differentiate navicular pathology from other possible etiologies, including a painful accessory navicular, posterior tibial tendonitis, tarsal coalition, anterior tibial tendonitis and osteochondral defects of the talus.8
Researchers have found a CT scan to be the most sensitive and specific test for the diagnosis of navicular fractures although MRI is better suited for navicular stress fractures.8,11