Getting Athletes Back In The Game After Navicular Stress Fractures

A navicular stress fracture can be a devastating injury for the recreational and high-level athlete. The issues often derive from difficulty in diagnosing the injury and the fact that there is no consensus on the best treatment regimen for the injury. Several years ago, clinicians would initially provide conservative treatment with prolonged immobilization in a cast. However, surgical intervention does have the potential of leading to an earlier return to activity for the athletic population.

While researchers originally described the navicular as having an area of vascularity, the vascularity of the navicular bone has been implicated in poor healing for stress fractures. In 1958, Waugh and colleagues reviewed 21 pediatric naviculars from cadavers, ranging between 0 to 19 years in age.¹ They described a variable number of vessels penetrating radially from the cortex to the center of the navicular with a relatively less dense vascular supply in the center in comparison to the subcortical bone. There were a large variety of patterns based on the age of the cadavers so these findings may not translate to older athletes.

Torg and coworkers evaluated the intrasseous blood supply of the navicular in five adult cadavers.² They showed that multiple vessels entered the bone primarily from the medial and lateral nonarticular cortex and extended toward the middle aspect of the bone, leaving the central one-third of the bone relatively avascular.

More recently, McKeon and colleagues looked at both the intraosseous and extraasseous blood supply to the navicular in adults.³ They used 60 below-the-knee legs from 30 cadavers. Researchers injected India ink and Ward’s blue latex into the anterior tibial, peroneal and posterior tibial arteries. After freezing and then thawing these cadavers, authors assessed the navicular vascular supply in 51 specimens and reviewed the intraosseous vascularity in 54 specimens. The results showed the medial tarsal branches of the dorsalis pedis consistently supplied the dorsal navicular (96.4 percent). Lateral tarsal branches also supplied the dorsal navicular. The medial plantar bone received blood supply from small branches of the superficial branch of the medial plantar artery. A large percentage of the specimens had a diffuse intraosseous vascular supply throughout the bone while only 11 percent of specimens had an avascular zone in the central third of the navicular extending to the dorsal cortex. The authors concluded that biomechanical or other clinical factors might play a more prominent role in these types of stress fractures.

Other biomechanical factors can lead to stress fractures. There is a zone of maximum shear along the central one-third of the body of the navicular.⁴ The theory is that with the foot in equinus during the foot-strike phase of running, compression forces generate from distal to proximal across the medial and lateral aspects of the navicular through the first and second metatarsocuneiform joints respectively. The talar head directly resists the forces across the first metatarsal and medial cuneiform but does not resist forces across the second metatarsal and middle cuneiform. The navicular experiences a zone of maximal shear stress between these two compression forces. This point is the central one-third of the navicular and is just lateral to the center of the talar head in the talonavicular articulation.

Essential Diagnostic Insights
A high clinical suspicion is the best tool initially for making an accurate diagnosis. Standard radiographs are routine and one should still order them initially, but they are fairly inaccurate for diagnosis. If a navicular stress fracture is high on the differential diagnosis, I recommend magnetic resonance imaging (MRI). A MRI will show increased signal intensity and extensive edema within the body, and may even show the fracture line. They do aid in identifying any areas of avascularity. If the MRI shows changes within the navicular consistent with stress fractures, then I recommend a computed tomography (CT) scan to evaluate the personality of the stress fracture.

The CT scans will accurately show the anatomy of the stress fracture and one can better assess any displacement. Scans have shown that the typical fracture is located in the central one-third of the bone, is primarily on the dorsal aspect and usually does not penetrate into the plantar cortex. This is important for planning screw placement. The fracture line tends to be oblique, angling from dorsomedial to plantar lateral. Long-term follow-up has also shown that medullary cysts and cortical notching often persist after complete healing of the fracture.⁵ There is commonly an area of a sclerotic appearing rim of cortical bone present on the proximal articular surface of the navicular.

A Closer Look At Treatment Options
Treatment options still include conservative or surgical management. The literature demonstrates the ability of these fractures to heal without surgery but often at the cost of prolonged cast immobilization and non-weightbearing. Surgical treatment is becoming more commonly accepted as the primary treatment in the athlete in order to minimize time away from activity and risk of refracture.  

Surgical treatment commonly consists of screw fixation with or without bone graft. I have a tendency to err on the side of grafting. If the CT scan shows no signs of any sclerosis of the bone, one can place two percutaneous screws. However, in my experience, this is often the exception rather than the rule. Most patients present with some degree of sclerosis, which requires some type of graft.

Case Study: Treating A Navicular Stress Fracture In A Pole Vaulter
The case presented is a 20-year-old college pole vaulter, who had pain on landing for two months without any history of trauma. The AP radiograph in the top of the photo at left is negative for a navicular stress fracture. The MRI shows increased signal intensity of the navicular but no fracture line (see bottom of photo at left). The CT scan confirms a navicular stress fracture (see bottom right photo).

The surgical technique is an outpatient procedure utilizing a general anesthetic and thigh tourniquet. Place a dorsal incision and take care to avoid the neurovascular structures including the medial dorsal cutaneous nerve that occasionally can be visible. Deepen the dissection to the talonavicular capsule and incise the capsule. I like to visualize the articular surface of the navicular to check for any possible cartilage damage.

Identify the fracture site and remove the fibrous tissue, slightly opening the dorsal cortex. The distal and proximal extent of the fracture should be fully visible. The surgeon needs to remove all of the sclerotic bone. One would usually drill the fracture site with a 3.2 mm drill bit both medially and laterally to stimulate blood flow to the area. It is important to release the tourniquet at this time to check for adequate removal of the sclerotic bone and the return of blood flow medially and laterally. One of the errors that leads to nonunions is the inadequate removal of the sclerotic bone.  

I prefer autologous bone graft for this fracture. Make a small incision along the lateral wall of the calcaneus inferior to the sural nerve. Deepen dissection down to the bone and use a ¼-inch osteotome to create a small window along the lateral wall. Save this lateral wall piece for later use. Use a small rongeur to remove the healthy cancellous bone from the body of the calcaneus. I recommend back filling the harvest site with allograft cancellous bone chips for support and scaffolding to promote healing. Try to replace the lateral wall with a piece of the allograft bone chips.

Pack the autograft into the navicular fracture site with a bone tamp. Then place the lateral wall window taken from the calcaneal graft as the dorsal portion of the navicular cortex. Perform percutaneous screw fixation. Typical fixation consists of 3.5 or 4.0 mm diameter screws. The preoperative CT scan is important to determine placement of the screws. One can place the screws either medially or laterally. A medial to lateral orientation is most common. The first screw is located superior and along the proximal navicular. The second screw is parallel to the first, just slightly inferior and distal.

Postoperative recovery consists of two weeks non-weightbearing in a posterior splint followed by two weeks non-weightbearing in a removable cast boot that patients can take off for dorsiflexion and plantarflexion. Take non-weightbearing X-rays at this point. If healing is occurring as expected, the patient can begin weightbearing in the boot as tolerated for four weeks. At eight weeks post-op, obtain X-rays.

If the patient is not in the middle of a season, he or she can start low-impact activities under the guidance of a trainer or physical therapist for four weeks, and then advance to activities as tolerated. If patients are in the middle of a season, I will often get a CT scan at eight weeks post-op to see if they can start to advance activities under the guidance of a trainer or physical therapist. I will have the patient follow up in four weeks with X-rays.

In Conclusion
Navicular stress fractures can be debilitating and difficult to recover from. Surgical intervention can lead to predictable results with an earlier return to activities.

Dr. Grambart is the foot and ankle surgeon for the Division of Orthopedics for the Carle Clinic Association in Champaign, Ill. He is a Clinical Instructor at the University of Illinois School of Medicine. Dr. Grambart is a Fellow and member of the Board of Directors of the American College of Foot and Ankle Surgeons.

References

1. Waugh W. The ossification and vascularisation of the tarsal navicular and their relation to Kohler’s disease. J Bone Joint Surg Br. 1958; 40-B(4):765-77.
2. Torg JS, Pavlov H, Cooley LH, et al. Stress fractures of the tarsal navicular. A retrospective review of twenty-one cases. J Bone Joint Surg Am. 1982; 64(5):700-12.
3. McKeon KE, McCormick JJ, Johnson JE, Klein SE. Intraosseous and extraosseous arterial anatomy of the adult navicular. Foot Ankle Int. 2012; 33(10):857-61.
4. Fitch KD, Blackwell JB, Gilmour WN. Operation for non-union of stress fracture of the tarsal navicular. J Bone Joint Surg Br. 1989; 71(1):105-10.
5. Kiss ZS, Khan KM, Fuller PJ. Stress fractures of the tarsal navicular bone: CT findings in 55 cases. AJR Am J Roentgenol. 1993; 160(1):111-5.

Editor’s note: For related articles, see “Key Insights For Treating Navicular Stress Fractures” in the October 2008 issue of Podiatry Today or “What You Should Know About Navicular Stress Fractures” in the November 2010 issue.