Problematic Stress Fractures of the Foot and Ankle

Anatomy and Presentation

The tarsal navicular serves as a keystone in the medial longitudinal arch and consequently is subjected to tremendous forces through the foot. Moreover, nutrient arteries arising from both the anterior and posterior tibial arteries create a generous supply of blood to the medial and lateral thirds of the navicular. The result is a poorly vascularized zone in the middle third of the bone as described by Waugh in 1958. Recently, this arterial anatomy has been called into question, as a recent study demonstrated a robust intraosseous vascular supply in 59% of adult cadaveric specimens. Factors other than vascularity may predispose the navicular to a stress injury, such as the location of the navicular, sandwiched between the talar head and the cuneiforms. Lateral shear forces are generated during running, as the medial aspect of the navicular has its stress shared by the talar head.

Misdiagnosis of stress fracture of the tarsal navicular generally is the rule rather than the exception, as the average time to diagnosis is 6–8.8 months. There are several sources of midfoot pain that are more common, including anterior tibial and posterior tibial tendinitis, spring ligament injury, Lisfranc sprain, and degenerative joint disease. Therefore, unrelenting symptoms in the seemingly normal midfoot merit further diagnostic workup.

Towne et al. first reported stress fracture of the navicular in humans in 1970. In this series of two patients, each was a distance runner who had experienced midfoot pain with swelling and failure to respond to conservative therapy. Plain radiographs were negative, and only specialized studies were able to reveal the occult fracture.

Clinically, an athlete complains of a slow but progressive onset of medial dorsal foot pain that radiates along the medial arch. Initially, this is experienced only during sports and is relieved by rest. Certain activities can increase the pain, such as cutting, sprinting, pushing-off, and jumping. After time, the onset of pain during activity occurs sooner and rest does not offer a respite. Eventually, the dorsomedial pain (over the “N” spot) limits sports and as activities of daily living. ( Fig. 5.1 )

Imaging

Stress fracture of the tarsal navicular is often overlooked due to radiograph’s poor sensitivity (33%). An anteroposterior view of the foot can show: sclerosis of the proximal border of the navicular; a short first metatarsal; metatarsus adductus and hyperostosis; and stress fracture of the second, third, and fourth metatarsals. Most fractures are linear, lie in the middle third of the navicular, and can be complete or partial. Oblique or supinated radiographs can be useful ( Fig. 5.2 ).

Radionuclide bone scanning has 100% sensitivity and high positive predictive value. Uptake generally will appear in the shape of the navicular on the plantar view. Although radionuclide scanning can assist in localizing the area of concern to the navicular, definitive diagnosis and definition of the fracture pattern require magnetic resonance imaging (MRI) or a computed tomography (CT) scan.

The typical fracture is an incomplete fracture in the central one-third with the fracture line extending obliquely from dorsal lateral to plantar medial on CT scan. A useful CT classification, based on coronal cuts is as follows:

• Type I: Dorsal cortex fracture

• Type II: Extension into the body

• Type III: Extension from dorsal to plantar cortex

While MRI scans have a high sensitivity, CT scans can more accurately diagnose a navicular stress fracture. However, MRI is better able to show edema patterns and a medullary extension of the fracture.

Treatment

Treatment at our respective institution is based on CT findings, athletic participation level, and the patient’s functional status. Complete elucidation of the fracture pattern is important in dictating management of the athlete. Patients with incomplete and nondisplaced/incomplete fractures (Type I) typically respond well to conservative management. We typically treat patients in a nonweight-bearing cast for at least 6 weeks, followed by a protected weight bearing in a cam boot for 2–4 more weeks until pain is no longer present.

Athletes with Type II or any patient with Type III fractures, patients with displaced fractures, or those who have failed nonoperative management benefit from bone grafting with open reduction and internal fixation (ORIF). We prefer to use either two 4.0-mm cannulated screws or two cannulated headless compression variable pitched screws to provide fixation after gently debriding and reducing the fracture. Most of these athletes will return to sport within 5 to 7 months. High-performance career athletes and the treating surgeon may elect a more aggressive approach to nondisplaced fractures. In a recent study by Saxena et al. patients who underwent ORIF had a return to activity 4.6 months compared with those who had undergone nonoperative treatment, who had an average return to activity of 4.0 months.

Anatomy and Presentation

The most common presentation of stress fracture of the second metatarsal is the insidious onset of midfoot pain. However, ballerinas will report intermittent sudden onset of pain after an increase in training or after a jumping maneuver. Many performers will be able to “dance through” the pain and often do not present until 2 to 6 weeks after the onset of symptoms. Hamilton reported five risk factors for stress fracture in the ballet dancer. They include amenorrhea, anorexia nervosa, cavus foot, anterior ankle impingement, and a Morton’s foot (short first metatarsal).

Examination of the foot can be confusing rather than revealing because patients will exhibit generalized tenderness of the midfoot with palpation and motion. It is oftentimes hard to distinguish pain localized to the base of the second metatarsal versus the Lisfranc joint.

The nature of this injury is due primarily to the unique biomechanics of ballet and specifically to the incredible stresses placed on the midfoot when the dancer is in the en pointe position. When en pointe , the ballerina (male dancers dance only on demi-pointe ) stands on the tips of her toes with the foot in maximal plantarflexion. Consequently the mechanical axis of the lower extremity is directed straight through the plantarflexed foot. The middle cuneiform serves as a keystone in an arch-type configuration. The base of the second metatarsal is countersunk into this keystone. Furthermore, the plantar ligaments create tensile forces about the second metatarsal at push-off during normal gait. This anchor of the proximal second metatarsal generates a substantial stress riser at the junction of the metaphysis and diaphysis when the dancer is en pointe . Treatment can be as simple as restricted dance with a moratorium on en pointe maneuvers until union is achieved.