Cath Lab Digest

Stress fractures of the tarsal navicular are an uncommon injury in the general population. However, people who engage in ballistic sporting events or recreational activities are at an increased risk of such an injury. The recognition of this injury seemed to parallel an increased fitness craze in the population over the last 30 years. Since Towne, et al., originally described tarsal navicular stress fractures in 1970, they have increased in prevalence secondary to our increased awareness of the injury and the emergence of faster and more powerful athletes.¹
The formation of a stress injury to the navicular involves an interplay between a genetic predisposition and environmental stimuli. The genetic component is the foot structure and mechanics that one inherits while the repetitive athletic activity is the environmental stimuli.

A delay in diagnosing this injury can lead to frustration on behalf of the athlete, chronic pain, decreased performance, increased morbidity and possible loss of sporting activity. Accordingly, let us take a closer look at clinical recognition of this injury, diagnostic imaging, degrees of injury severity and key treatment considerations. It is imperative for the clinician to recognize these injuries occur along a continuum of severity.

A Guide To The Physical Exam And Biomechanical Considerations
Patients who present for consideration of navicular stress fractures are usually under the age of 40, are in good health and are invariably involved in some type of ballistic sports training and/or participation. Their involvement in ballistic sports may be sporadic or more along the lines of a highly trained athlete.

Most patients will present with a prodrome of midfoot pain that has become progressively worse over time. There is usually no acute injury. Most athletes will present when the pain has started to hamper participation and performance.

A high index of suspicion is paramount if one is to diagnose this injury in a timely fashion. It is the probing history of the presenting problem that will mandate a specific evaluation for a stress-related injury to the navicular. Bear in mind that the physical exam may not be impressive during the early stages of the injury. This is often the case as the athlete may have rested for a few days prior to the exam.

The pain can be difficult to localize and one may confuse this with regional tendonitis. It is not uncommon to note tenderness of the dorsomedial tendons of the affected foot during the clinical exam. Often the maximum area of tenderness is along the dorsal navicular between the anterior tibial tendon and the extensor hallucis longus tendon. This is commonly referred to as the “N” spot.² Physicians should screen female athletes for the female triad, which consists of an irregular menstrual cycle, repetitive stress fractures and eating disorders.³

The research has described multiple biomechanical explanations for stress injuries to date. Commonly, the clinician will appreciate a cavus foot, a relative or absolute long second ray and possible forefoot adductus. However, no statistical proof to date has supported these anecdotal findings.⁴ It is commonly accepted that there is an increase in longitudinal shear to the central portion of the navicular.⁵ This area of the navicular has a well defined area of hypovascularity that will predispose it to a decreased ability to respond to repetitive stress.⁶