Navicular stress fracture: a high-impact risk for young athletes

Chris Mallac investigates the causes, diagnosis, and management of navicular stress fractures in athletes.

First described by Towne and colleagues in 1970⁽¹⁾, stress fractures of the navicular bone are uncommon in the general population. However, male athletes in their mid-20s participating in sports such as sprinting, middle distance running, hurdling, and basketball are more at risk^(2,3). These particular sports subject the player to high forefoot and midfoot forces when jumping, landing, sprinting, and cutting^(4,5). Elite level track athletes comprise 59% of reported navicular stress fractures in athletes presenting with midfoot pain. These injuries tend to occur after spikes in training (higher mileage) and competition loads⁽⁶⁾.

Anatomy and biomechanics

The navicular bone is wedged and positioned between the three cuneiforms of the midfoot and the head of the talus in the rearfoot. It is a concave boat-shaped bone with the concave surface articulating with the talus (see figure 1). The tibialis posterior tendon inserts onto the medial tuberosity of its medial surface. The other significant anatomical feature is the plantar beak, to which the plantar calcaneonavicular, or spring, ligament attaches⁽⁷⁾.

Because it is connected to the head of the talus proximally and the three cuneiforms distally, the navicular bone forms a pivotal link between the midfoot and rearfoot for force transmission and push off⁽⁸⁾. Being located in the medial longitudinal arch of the foot, it also plays an integral role in maintaining the integrity of the arch⁽⁴⁾.

Its position between the talus and the 1^st and 2^nd cuneiform means the navicular endures extra shear and compressive forces during running and landing. In particular, the central third of the bone sustains focused lateral shear forces, which may predispose it to a stress fracture^(4,9). The tibialis posterior muscles, which insert on the navicular, may exacerbate the vulnerability to stress in the region through their traction forces on the bone. The medial plantar nerve innervates the talonavicular joint. Hence pain may refer to the ball of the foot mimicking Morton’s neuroma when the navicular is the source of pain.

Figure 1: Anatomy and navicular stress fracture

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Furthermore, the blood supply to the navicular enters at the non-articular surfaces of the bone, and branches out in a medial and lateral direction without a great deal of blood supply to the central third. This circulation distribution creates an avascular watershed area in the bone, particularly in individuals with a genetic predisposition to this morphology  (see figure 2)⁽¹⁰⁾. If present, this relative avascular area may lead to delayed healing in the event of a fracture, and higher rates of non-union⁽⁹⁾.

Figure 2: Area of avascularity (adapted from Khan et al. 1994)³

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The following are risk factors for developing a navicular stress fracture⁽¹¹⁾:

• A substantial increase in training load from running volume, intensity, or the amount of jumping and landing.
• Reduced ankle dorsiflexion increases midfoot dorsiflexion and jams the navicular between the talus and cuneiforms⁽¹²⁾.
• Pes cavus, which leads to a rigid midfoot with poor shock absorption.
• A short 1^st metatarsal and longer 2^nd metatarsal⁽¹³⁾.

Diagnosis

Athletes with a navicular stress fracture typically report one or more of the following:

1. Insidious onset of poorly localized midfoot pain with activity, perhaps lasting months⁽¹⁴⁾.
2. An alteration in gait pattern, which occurs to offload stress on the navicular.
3. The pain subsides quickly with rest, allowing the athlete to resume training reasonably soon after. But, as the fracture develops, the pain remains even after stopping an activity.
4. Pain radiating along the longitudinal arch or medial dorsum of the foot.
5. Characteristic tenderness on the proximal portion of the foot known as the ‘N’ spot (see figure 3) ⁽¹⁴⁾. The vast majority of stress fractures are partial fractures (83%) and involve the dorsal part of the navicular in the proximal part of the bone close to the talonavicular joint. This location corresponds to the ‘N’ spot⁽³⁾.
6. Pain standing on tiptoes and hopping⁽⁸⁾.

Figure 3: The ‘N’ spot on the dorsal aspect of the distal talonavicular joint.

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Diagnosis confirmation

A plain film X-ray is usually ineffective in detecting a navicular stress fracture^(8,14); most fractures are incomplete, and it takes 10 days to three weeks for bony resorption to show on X-ray if a complete breach does exist^(3,15). However, X-ray imaging can exclude other possible causes of pain ,such as a talar neck spurring or capsular avulsion.

A triple-phase bone scan is highly sensitive and has a high positive predictive value for stress fractures in the navicular, showing uptake on all phases⁽¹³⁾. However, these are non-specific and lack the anatomical resolution to view the size and location of the stress fracture. Magnetic resonance imaging (MRI) is the imaging method of choice to see early changes in the bone (see figure 4). It can detect both bone edema and stress reactions, which occur before a stress fracture. As such, an MRI can catch stress reactions before they progress to overt stress fractures⁽¹¹⁾.

A CT scan can show the exact location and size of a navicular fracture. It’s sensitive to partial fractures, which are often seen coursing from the proximal dorsal central-third of the bone towards its distal plantar pole ⁽³⁾. The findings of the CT scan dictate the classification of a navicular stress fracture. However, poor positioning and thick CT slices (more than 2mm) could miss a stress fracture⁽¹⁶⁾.

The most commonly used classification system is from Saxena et al. (2000)⁽¹⁷⁾. The three types of stress fracture are:

1. Type I - Fracture in the dorsal cortex.
2. Type II - Fracture extends from the dorsal cortex into the body of the navicular.
3. Type III - Complete fracture through both cortices.

Further classification based on the changes seen in the bone include avascular, cystic, or sclerotic subtypes.

Figure 4: MRI showing bone edema in the navicular*

*(adapted and used with permission from www.fifamedicalnetwork.com/lessons/foot-navicular/)

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Management

Navicular stress fractures typically progress along a continuum of three stages. The first is a stress reaction, typified by a short duration of pain (less than two weeks), which may decrease with rest. However, patients will have a tender ‘N’ spot, and while the CT scan is normal, an MRI will show bone edema. Following this is the stress fracture phase, where there is constant midfoot pain exacerbated by activity. The fracture is evident in both a CT and an MRI test. Later still, the patient may develop a complicated stress fracture, with long-standing pain, even after a period of non-weight bearing. The management protocol for these phases is as follows:

1. Stress reaction - The patient will be symptomatic, and the ‘N’ spot will most likely be tender on palpation. The initial management is to wear a CAM walking boot for one to three weeks until the ‘N’ spot is no longer sore. Once pain resolves, return to running and sport over a four to eight week period. The average time to return to activity is around two months⁽¹⁸⁾.
2. Stress fracture - Type 1 fractures are treated with absolute non-weight bearing in a fiberglass cast or boot for 6-8 weeks (see table 1)⁽¹⁴⁾. Those treated with non-weight bearing will resolve as expected 89% of the time, whereas those managed with weight-bearing rest have a higher chance of failure (only 24% improve)⁽³⁾. Athletes with these types of fractures typically return to activity in 3.75 months⁽¹⁸⁾.

Adjuncts to treatment at this stage include:

• Bone stimulators – Not proven to advance healing in navicular stress fractures. However, since there are no complications or adverse reactions, this may be an adjunct to treatment⁽¹¹⁾.
• Shockwave therapy – Primarily used in the treatment of calcific tendinopathy; its use in stress fractures needs more study.
• Vitamin D supplements – Beneficial for fracture healing, although the exact mechanisms are poorly understood⁽¹⁹⁾.
• Manual therapy (to improve limited dorsiflexion) – May consist of a combination of manual therapy to the talocrural and subtalar joints, and soft tissue work to the soleus and other plantar flexor muscle groups.

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Weeks 0 “ 6	Strict non-weight bearing in fiberglass cast or boot. At the end of week 6, conduct a CT scan to measure healing (if warranted) and assess ˜N spot. If painful, maintain non-weight bearing for another two weeks.
Weeks 7 “ 8	Optional full weight-bearing in a CAM boot or total weight-bearing without boot if ˜N spot is non-tender.
Weeks 8 “ 12	Begin running on the grass on alternate days. Start with five minutes and increase by five minutes each week. Once running load is up to ten continuous minutes, progress to sprints for distances of around 60-80 meters, with a build-up of speed and volume over a few weeks.
Weeks 13-16	Start light training with a gradual build-up in load and intensity.
Weeks 16+	Return to competition.

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3. Type 2 and Type 3 – Surgery may be the best management strategy for these types of fractures. Type 2 fractures take on average, five months to resolve⁽¹⁸⁾.
4. Complicated stress fracture - If the patient still has pain after the initial non-weight-bearing period, they should attempt a further six weeks of non-weight-bearing (12 weeks total). If still painful at 12 weeks (or in athletes with type 2 and 3 fractures who want a quicker return to competition), then surgical management is best. Surgery usually involves two cannulated screws that pass from lateral to medial (in type 2 fractures), or open reduction and internal fixation with bone grafting (for type 3 fractures). Post-surgery, patients are non-weight bearing for six weeks and then allowed to bear weight fully. Physicians typically perform a repeat CT scan ten weeks after the surgery to ensure the union of the fracture site before loading with running⁽⁸⁾. Type 3 fractures take, on average, 4.75 months to resolve⁽¹⁸⁾.

Although studies are limited, the general findings of conservative versus operative management of navicular stress fractures show that in conventionally managed cases, the time frame to return to sport is around 22-26 weeks. Whereas, those treated surgically tend to return to competition in 15-18 weeks^(2,14).

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