Experts discuss navicular, central metatarsal, and fifth metatarsal stress fractures

Stress fractures of the foot are a common problem among military recruits, athletes who participate in high-impact sports, and others who suddenly and dramatically increase their level of activity. These injuries occur when muscles become too fatigued to absorb the shock of repeated impacts. The impacts are then transferred to the bones, resulting in stress fractures.

During a symposium at the American Orthopaedic Foot and Ankle Society’s (AOFAS) summer annual meeting, Thomas O. Clanton, MD, Florian Nickisch, MD, and John G. Anderson, MD, presented the latest information about the etiology of navicular, central metatarsal, and fifth metatarsal stress fractures, and offered guidance on diagnosing and treating these injuries.

Diagnosing navicular stress fractures
According to Dr. Clanton, devascularization of the central third of the navicular bone, combined with high contact stresses and axial loading, are important etiologic factors in navicular fractures.

“Putting a repetitive, ballistic load on an area of hypovascularity in a susceptible individual creates a linear fracture in the sagittal plane at the junction of the central and lateral third of the navicular,” explained Dr. Clanton.

Many studies have suggested that structural anatomy issues, such as a long second metatarsal and limited ankle dorsiflexion, are possible contributing factors to navicular stress fractures. According to Dr. Clanton, however, no statistical evidence exists that implicates any single anatomic factor.

Dr. Clanton noted that diagnosis of this condition is often delayed an average of 4 months. Early diagnosis, he said, is critical in obtaining favorable outcomes.

“Symptoms are usually vague and have an insidious onset,” said Dr. Clanton, who advised that orthopaedic surgeons consider navicular stress fractures when they see an athlete who has symptoms that are not well-defined. “In these patients,” he said, “the physical examination is usually unimpressive, with possible tenderness over the fracture site of the dorsal navicular, but no tenderness elsewhere and no swelling. Radio­graphs are often negative, especially of incomplete fractures.”

Because these fractures are difficult to detect, Dr. Clanton recommended performing a computed tomography (CT) scan as well as a triple-phase bone scan, the latter of which has a sensitivity approaching 100 percent.

“Magnetic resonance imaging is becoming more commonly used, particularly in professional sports,” added Dr. Clanton, “but CT remains the gold standard because of the anatomic detail it provides.”

Treating navicular stress fractures
According to Dr. Clanton, many different treatment options are available for navicular stress fractures.

“Treatments range from allowing the patient to remain weight-bearing without a cast or a boot all the way to open reduction, internal fixation, and bone grafting,” he said. “Because the first of these—rest—has not been shown to be effective, I would advise orthopaedists not to use this option.”

Dr. Clanton noted that several studies have reported healing rates of 86 percent to 100 percent using nonsurgical treatment for uncomplicated, acute, and partial stress fractures, as well as nondisplaced, complete stress fractures. These treatments require 6 to 8 weeks of non-weight bearing. On average, patients return to sports between 4 and 6 months after treatment.

“Treatment guidelines based on case series (level 4 evidence), which are all we have right now, suggest using surgical treatment for displaced, complete, or comminuted fractures, as well as in cases of delayed union or nonunion of incomplete fractures,” said Dr. Clanton. “Also, surgery is indicated in patients with sclerosis or cystic degeneration.

“The reality,” continued Dr. Clanton, “is that even though the non–weight–bearing cast is standard treatment, one study found that it was used only 18 percent of the time. Most patients in that study rested but still performed weight-bearing activities, which lead to a number of delayed unions, nonunions, and other complications.”

According to Dr. Clanton, dedicated athletes will seldom tolerate the lengthy period of time that nonsurgical treatment—which includes non-weightbearing—requires. As a result, he said, surgery is becoming more popular as the first line of treatment in sports medicine.

“Percutaneous screws should be used for partial or nondisplaced fractures,” advised Dr. Clanton. “For nonunions, a bone graft should be used, along with postsurgical bone stimulation.

“I would not recommend using long screws that penetrate the medial navicular; at least one case of a ruptured posterior tibial tendon has been reported when this method was used,” he added.

Protecting the superficial perineal nerve is essential, he said, and removing hardware should be avoided. Everything possible should be done to keep talar navicular arthrosis from developing.

“Once they reach that stage,” he cautioned, “and arthrodesis is required, they aren’t going to be very athletic anymore.”

Jones fractures and the role of the cavovarus foot
Dr. Nickisch defined Jones fractures (Fig. 1) as “fractures of the metaphyseal-diaphyseal junction at or distal to the fourth and fifth intermetatarsal articulation.”

According to Dr. Nickisch, the guarded healing potential for these fractures has largely been attributed to the vascular supply in this area. However, he noted that mechanical factors may play a larger causative role than is currently known.

“The mechanism of injury of an acute Jones fracture is proposed to be an abduction force on a plantar-flexed forefoot,” said

Dr. Nickisch. “A good proportion of these injuries, however, are really stress injuries without any acute history of trauma, and may result from lateral overload, often in conjunction with a cavovarus foot posture.

“This intuitively makes sense,” continued Dr. Nickisch, “because the cavus foot is usually stiffer across the hind- and midfoot, with limited motion through the transverse tarsal joint. It also has a limited ability to absorb shock during gait. There is also an increased direct load on the lateral aspect of the mid- and hindfoot with gait that could possibly lead to fatigue failure of the fifth metatarsal.”

Although studies have identified high longitudinal arch, heel varus, and forefoot varus as risk factors for repeated stress injuries in the lower extremities, said Dr. Nickisch, little data exists regarding the effect of cavovarus foot posture on stress fractures of the fifth metatarsal.

Useful diagnostic tests
Taking a thorough patient history is essential when evaluating a patient with a proximal fifth metatarsal fracture, said Dr. Nickisch.

“Find out if there’s a family history of foot deformities or fractures, if there’s any previous history of foot injuries, and if there’s been a change in activity and/or diet,” he said.

Female athletes should be asked about their menstrual regularity to determine whether the female athlete triad—disordered eating, amenorrhea, and a heightened risk for osteoporosis—may be a consideration.

If a cavovarus foot is detected in the clinical examination, Dr. Nickisch advised that the examining physician determine whether the deformity is fixed or flexible, whether it is hindfoot or forefoot driven, and whether an underlying neuromuscular cause exists. The Coleman block test, which evaluates hindfoot flexibility and pronation of the forefoot, can be useful in investigating these factors.

Dr. Nickisch also recommended performing radiographs and a metabolic work-up. If the female athlete triad may be a factor, he recommended ordering a bone density scan.

When surgery is indicated
According to Dr. Nickisch, almost no data exist to guide treatment for fifth metatarsal fractures in patients with an underlying cavovarus foot deformity.

“The mainstay of treatment is still nonsurgical—a short-legged, non–weight–bearing cast for 4 to 6 weeks followed by 4 to 6 weeks of weight bearing in a short-legged cast,” he said. “The results of this treatment, however, are fair at best, with only a 75 percent union rate over a 5-month period. Many patients will sustain a second fracture when they resume normal activity.

“Surgery to repair Jones fractures is indicated for high-level athletes where speedy recovery and return to play is a factor, as well as in patients with established non-unions and refractures,” he advised.

“Treatment typically consists of a percutaneously placed intramedullary screw,” continued Dr. Nickisch. “Open techniques and bone grafting may also be performed. The size of the screw does not seem to matter as long as it fits the canal comfortably. The screws should be left in forever, as a significant fracture risk is associated with removal of the hardware.”

Causes of central metatarsal fractures
When Dr. Anderson treats a patient with central metatarsal stress fractures, he focuses on the potential causes of the injury.

“Known medical risk factors are tied to osteoporosis, and include nutritional disorders, the female sex, age, and race,” said

Dr. Anderson. “Mechanical factors may also be involved. Some of these stress fractures are simply due to overuse and repetitive stress in very active individuals, such as military recruits and runners. Biomechanical factors—such as Equinus contracture, short or hypermobile first ray, or insufficient first ray in a short metatarsal—that lead to excessive central metatarsal overload may also be contributors. Finally, mechanical cavus deformity and compensatory weight bearing of the lateral side may also be risk factors.”

Dr. Anderson noted that not much information is available in the literature on central metatarsal stress fractures, but some studies do exist.

“A study of 180 young athletes found a preponderance of metatarsal-related stress fractures. When the researchers examined specific sports, they found that the location of the stress fracture varied depending on the patient’s primary sport. Dancers had the highest risk of metatarsal fractures.”

Another study of 12 consecutive stress fractures, 8 of which were metatarsal, found that most of the fractures healed with non-surgical treatment. The researchers recommended bone density measurement and appropriate medical therapy, when indicated.

The need for patient education
Dr. Anderson presented several cases that illustrated the treatment modalities he recommends for various patients with central metatarsal fractures.

“A 20-year-old military recruit who went from no running at all to running 20 miles a week came in with a 2-week history of pain with a sudden onset,” said Dr. Anderson. “Mechanical overload was determined to be a factor, as was a long third metatarsal.

“The patient didn’t have any other significant risk factors,” continued Dr. Anderson. “He was treated nonsurgically, and we spent a fair amount of time educating him about training errors.”

Dr. Anderson also described the treatment of a 70-year-old Caucasian female with chronic foot pain, longstanding bunion deformities, and a hammertoe (Fig. 2). She had a spontaneous second toe crossover on her left foot, and recurrent stress fractures of the right foot at the base of the second metatarsal as well as the distal shaft of the third metatarsal.

“This individual had a very insufficient and unstable first ray, which overloaded her adjacent metatarsals,” said Dr. Anderson. He treated the deformity by resecting her nonunion, performing a tarsal metatarsal stabilization, a hallux realignment, and a gastrocnemius recession to take the stress off the forefoot.

The patient did not have stress fractures in the left foot, but Dr. Anderson followed similar treatment principles by shortening the second ray, stabilizing the first ray, and performing a gastrocnemius recession.

“It’s certainly important to treat the medical condition and address overuse and training errors,” he concluded, “but you must first ask yourself why this injury developed in the first place. Then, you must address the underlying biomechanical abnormalities.”

Dr. Clanton reported ties to Arthrex, Inc., Biomet, Link Orthopaedics, Wright Medical, Zimmer, Pharmacia Corporation, and the National Institutes of Health. Dr. Nickisch reported ties to Smith & Nephew, AO, Biomet, Medtronic, Stryker, Synthes, and Zimmer. Dr. Anderson reported ties to Depuy, Stryker, and Zimmer.

Jennie McKee is a staff writer for AAOS Now. She can be reached at mckee@aaos.org