“N” marks the spot

"You can't speed up bone healing, you can only slow it down."

~Tim Hoenig

Imagine you’re a steeplechaser in the lead, coming into the final water barrier. After 2,900 meters of fatigue, instead of soaring gracefully, you belly-flop into the water pit. OUCH! That’s certainly one way to get hurt while running. But for the other 99.9% of running injuries, it’s the less dramatic overuse kind, where tendons and bones proverbially throw their hands up and say, “We’ve had enough!”

Nothing hammers home this point than when an injury of this type shows up in your house. While Julie and I were camping in Wisconsin over Labor Day, we decided to get a longer run in on the trail network surrounding the state park. While we were hanging around the campsite the following day, Julie mentioned that her foot had been so sore the previous night that it woke her up while she was sleeping. An ill-timed revelation, considering we had run again that very morning. To make matters worse, she went on to disclose that her foot had actually been bothering her intermittently for the last few weeks, particularly on days when we’d performed some faster running in prep for a race we’re running at the end of October.

Upon examining her foot, she had fairly pronounced pain in the dreaded “N-spot” on the top of her foot. She also had sharp discomfort going onto her tiptoes, and hopping on the involved foot was anything but comfortable. When you combine her subjective complaints with the objective findings, I was highly concerned about a bone stress injury (BSI) of the navicular. The only wrinkle was the fairly significant swelling over the top of her foot surrounding the talonavicular joint complex—an uncommon feature of this injury. Thankfully, both MRI and CT scans revealed no navicular involvement; instead, they showed marked tenosynovitis of the tibialis anterior tendon. After two weeks in a boot and on crutches, she was delighted! Me? Still scratching my head.

Anatomically, the navicular is a critical bone in the foot, anchoring the tibialis posterior tendon and transmitting force between the midfoot and ankle during movements such as pronation. Its uniquely vulnerable, kidney bean–like shape (convex side up), resulting in poor central blood supply, makes a BSI here a potentially devastating injury.

Unfortunately, navicular stress fractures make up 33% of all lower extremity BSIs, so this is anything but an uncommon injury. Even more unfortunate than the injury itself is how long it takes for most athletes with a similar presentation as Julie to be diagnosed. Several meta-analyses report upwards of 9 months from the onset of symptoms to diagnosis! By then, athletes have usually pushed through countless hours of training, yo-yoing between periods of symptomatic and asymptomatic activity, only to end up with advanced symptoms that invariably require a longer road to get back to full speed. When it comes to the navicular, the stakes are high, and the margin for error is razor sharp.

Common Symptoms

Vague and non-descript onset of pain along the top of the midfoot. Symptoms have also been known to move to the arch of the foot, as well as the anteromedial aspect of the ankle.
Palpation of the navicular bone is painful.
Some runners, especially those early along the injury continuum, may only describe pain with fast running, whereas slower running may be tolerable.
Pain is often elicited with walking on tiptoes as well as with hopping.
While not commonly experienced, cramping along the arch can be present.
Swelling is rarely present due to the relatively poor blood supply.

Why is this injury so high-risk?

What makes a navicular BSI such a high-risk injury is multifactorial. First, these injuries are often misdiagnosed or go undetected for a long time. The delay between symptom onset and proper diagnosis allows the injury to worsen. What begins as swelling within the bone can progress to a fracture that, if untreated, may extend through the entire height of the navicular. Compounding this risk is the poor blood supply to the most commonly fractured area, increasing the likelihood of non-union, refracture, or, in severe cases, avascular necrosis (AVN), where bone tissue dies due to lack of blood flow. If this scenario unfolds, returning to sport becomes an afterthought.

Course of care

The most important part of the initial stages of care is expedient diagnosis. This cannot be overstated. Until we know the full extent of the injury, we’re simply throwing darts. A critical part of a thorough workup for an athlete presenting with signs and symptoms consistent with a navicular BSI involves referral for a CT scan or MRI. Advanced diagnostic imaging is vital, as plain-film X-rays are very often unremarkable. Depending on the severity of the injury, most athletes will undergo a period of 6-8 weeks of complete non-weight-bearing before the early stages of rehabilitation can commence. To that end, an orthopedic consultation is an important referral to determine if the injury is to be managed conservatively or surgically. One small consolation is that return-to-sport timelines don’t differ much between conservative and surgical management, with both typically taking about four to five months.

Special considerations

As with any injury where improper management can carry serious consequences, some situations demand especially careful clinical decision-making. One such example is when a navicular BSI occurs in adolescent athletes. There is solid evidence to suggest that athletes under the age of 21 who do not undergo surgical management face a particularly high risk of refracture. Depending on the specific situation, surgical management, even in less-severe cases, should be considered.

Another athlete population that is particularly insensitive to ambiguous long-term outcomes is elite athletes. In a study by Attia and colleagues examining over 300 navicular stress fractures, both management approach and return-to-play outcomes were compared. Surgical treatment achieved a 97.9% success rate, while non-surgical management reached a 78.1% success rate. Return-to-play rates were similarly higher with surgery (98.98%) compared to conservative care (73.43%). For elite athletes who presumably make a living on the back of their athletic performances, even a slight increase in outcome certainty is meaningful.

Keep moving forward!

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