March Fracture (Metatarsal Stress Fractures)

Etiology

March fractures, ie, metatarsal stress fractures, are most commonly second and third metatarsal fractures caused by overuse injuries.[1] They result from a sudden increase in the intensity, duration, and frequency of activity without sufficient rest.[4] The repetitive impact on the metatarsals with weight-bearing exercises causes microfractures, which consolidate into stress fractures and are not the result of a single traumatic event.[5] The most common location of metatarsal stress fractures is the second metatarsal neck. The second metatarsal is prone to injury due to its limited motion from strong ligamentous attachment to the first and second cuneiforms and length compared to the other foot metatarsals.[6]

Epidemiology

Metatarsal stress fractures are common in athletes and the military, accounting for 25% of all stress fractures and 20% of all sports medicine clinic visits.[5][7] Forty percent of all athletes will suffer a stress fracture at some point in their careers.[8] Overall data suggest that females have a higher incidence of march fractures than men. In addition, those with prior stress fractures are more likely to develop another. Sixty percent of patients with a stress fracture will have had a previous one.[9]

Pathophysiology

Stress fractures are the result of either bone fatigue or bone insufficiency.[7] Bone fatigue occurs when a normal bone cannot resist excessive mechanical demands. Two different theories may explain the development of a stress fracture. One theory suggests that when osteoblastic activity lags behind osteoclastic activity, it leaves bone susceptible to injury during a sudden increased demand. A second theory suggests that stress fractures develop due to the bone failing, specifically at muscle insertion points where repetitive load and stress are highest.[5]

Classification Systems 

Stress fractures can fall into two broad categories: high-risk and low-risk injuries. Stress fractures of the metatarsals are considered low-risk fractures because they are common and tend to heal well with activity modification while weight-bearing.[7]

Kaeding and Miller’s 5-Tier Grading System [10]

Grade of Stress Fracture/Radiographic Finding

1. Asymptomatic radiographic findings
2. Pain with no fracture on imaging
3. Nondisplaced fracture on imaging
4. Displaced fracture on imaging
5. Sclerotic nonunion on imaging

Nattiv Grading System [11]

Evaluation of bone marrow edema and periosteal reaction in bone stress injuries on MRI. 

• Grade 1: mild marrow edema or periosteal edema on fat-suppressed T2WI (but not on T1WI) 
• Grade 2: moderate marrow edema or periosteal edema on fat-suppressed T2WI (but not on T1WI) 
• Grade 3: severe marrow edema or periosteal edema on both fat-suppressed T2WI and T1WI, without a fracture line on T1WI or T2WI
• Grade 4: severe marrow edema or periosteal edema on both fat-suppressed T2WI and T1WI, with a fracture line on T1WI or T2WI.

Biomechanics

There are two types of cortical stress fracture described in the literature. The two types depend on whether the stress is localized to the tensile or compression side of the bone under stress. Compression stress fractures correspond to a fracture line occurring on the concave side of the bone. These fractures run parallel to the bone axis. In comparison, tensile stress fractures appear on the convex side of the stressed bone, and these fracture lines develop perpendicular to the bone axis. Compression stress fractures tend to be less common than their traction counterparts.[12] Metatarsal length and sagittal plane position can disrupt the even distribution of weight across the forefoot. Metatarsals that are longer or more plantarflexed than the surrounding metatarsals will bear more biomechanical load. Foot type may also play a role. A cavovarus foot puts an increased load on the lateral column and is associated with fourth and fifth metatarsal stress fractures.[13][14] Extrinsic risk factors, such as the training type, intensity, or environment, as well as athletic shoe type or age, can also contribute to an increased risk of metatarsal stress fractures.

Histopathology

Objective information on stress fracture healing is negligible as biopsies are rarely taken as part of routine treatment.[15] Research is limited to animal studies often focused on forearm stress fractures. Animal studies have found that at the cellular level, stress fractures are characterized by irregular bone changes. At 2 weeks, this irregular woven bone develops islands of cartilage and active resorption cavities along the periosteal margin. At 4 weeks, the woven bone is remodeled, starting from the periosteal surface and progressing along the fracture plane and into the medullary cavity.[16] A hallmark sign of healing is the formation of periosteal hard callous.[15] Slow healing rates and recurrent stress fractures may be explained by the failure or slow healing of the most central portions of a stress fracture.[16]

History and Physical

During an interview, patients may describe an insidious, new onset of pain that improves transiently with rest but increases again with activity. Questions should focus on new exercise routines or routines that may have increased in intensity, duration, or frequency over the last 6 to 8 weeks. Changes in terrain or shoe gear should also be noted, as these may elucidate changes in force distributions through the foot.[4] Pain may be nonspecific in location but is often described as dull, aching, and worse with any weight-bearing activities.[17]

Obtaining a thorough medical history with particular attention to intrinsic and extrinsic risk factors is important. Intrinsic risk factors may include age, endocrine disorders, body composition, bone mineral density, and history of a stress fracture.[8] Advanced age and a low body mass index, specifically in women, are associated with increased rates of stress fractures.[18] Prior stress fracture increases the chances of re-fracture due to an increased likelihood of associated intrinsic factors or architectural changes in the bone from previous injury. Questions about extrinsic risk factors should elucidate more than changes in activity level and include diet content, eating behavior, medication regimens, and foot biomechanics.[8] The female triad, which is characterized by abnormal menstrual cycles (amenorrhea), low bone mass (osteoporosis), and disordered eating, is one of the most well-documented risk factors for stress fractures.[8] Certain medications, such as bisphosphonates and glucocorticoids, have shown an increased risk of metatarsal fracture when taken at any dose.[19]

Physical examination should include a complete biomechanical evaluation with palpation and localization of the site of pain. If the fracture is in the proximity of a joint, the joint motion will aggravate the pain. Patients may have a limping gait with weight bearing. A biomechanical exam should also evaluate foot type with attention to a more supinated or less pronated foot, which has an increased risk for second metatarsal stress fracture secondary to increased load across the forefoot.[20]

Evaluation

March fractures are diagnosed based on historical clues and physical examination and are confirmed with diagnostic imaging. Plain radiographs are the initial imaging modality of choice. However, plain radiographs have a high rate of false negatives for metatarsal stress fractures early on and may not demonstrate fractures until 2 to 4 weeks after the onset of pain.[21][3] While an apparent fracture through the metatarsal may be visible on a radiograph, subtle periosteal reactions and blurring of the cortex may be the only clues of a stress fracture. The “gray cortex” sign indicates an ill-defined cortical lucency suggestive of an early stress fracture.[22] More mature fractures may demonstrate callus formation or cortical lucency of this incomplete, nondisplaced fracture.[23]

Occult, suspected fractures not visible on plain radiographs can be imaged using three-phase bone scans with technetium-99, magnetic resonance imaging (MRI), or computed tomography (CT). Both bone scans and MRIs have been proven to be sensitive to these fractures up to 24 hours after the onset of pain. While bone scans are considered sensitive but not specific, MRI is sensitive and specific for metatarsal stress fractures and is considered the gold standard of diagnosis with advanced imaging.[6][24] Furthermore, CT may illustrate fracture characteristics but is less sensitive than MRI.[21]

Lastly, thorough testing of the patient’s intrinsic risk factors may be needed. For example, measuring serum vitamin D concentration can be considered in those suspected of nutritional deficiencies.[6]

Treatment / Management

In most cases, analgesia and rest are the only steps needed for metatarsal stress fracture healing. Acetaminophen and ice are implemented for pain and swelling. The effect of nonsteroidal anti-inflammatory drugs (NSAIDs) on fracture healing remains contested.[25]

Immobilization is often unnecessary, and a stiff-soled orthopedic boot or walking boot may be used for 4 to 8 weeks.[6] Weight-bearing may be allowed as long as the patient is pain-free. Low-impact exercises such as swimming, cycling, or deep-water running may supplement exercise routines during recovery. Fractures at the base of the fifth metatarsal and the neck of the second metatarsal are at high risk for nonunion. If advanced imaging is negative in the pain setting, treatment should include a period of non-weight bearing for these injury locations.[9][5][6] Modifiable risk factors should be thoroughly addressed to optimize healing potential and reduce re-injury risk. Nutritional deficiencies such as low vitamin D levels, calcium, or calories should be supplemented.[9] Training intensity, duration, and frequency should be reduced, and patients may consider supportive or shock-absorbing shoes and insoles to modify and evenly distribute forces during weight-bearing exercises.

Differential Diagnosis

Differentials for march fracture include the following conditions:[3]

• Acute metatarsal fracture

• Acute sesamoid fracture

• Common peroneal nerve injury

• Hallux rigidus

• Jones fracture

• Posterior tibial nerve injury

• Proximal fifth metatarsal avulsion fracture

• Saphenous nerve injury

• Sesamoid stress fracture

• Sural nerve injury

On advanced imaging, stress fractures may present similarly to several other differential diagnoses, including malignancies with an osteoid matrix or periosteal reaction (osteosarcoma, Ewing sarcoma, metastasis) or relatively more benign presentations of bone marrow edema or hyperintense signal changes (chronic osteomyelitis, osteoid osteoma). MRI has a reported 93% to 98% accuracy in differentiating between a stress fracture and a pathologic fracture.[7]

Prognosis

Although most stress fractures heal with conservative care and rest, optimization of intrinsic and extrinsic factors gives patients the best chance at avoiding delayed healing, nonunion, or repeat injury.

Complications

If pain and advanced imaging show no improvement of the stress fracture at 6 to 8 weeks, patients should be referred to a foot and ankle surgeon. Nonunion is a complication of march fractures with symptoms of chronic pain, swelling, or instability in 20% to 67% of patients.[6] Surgical options such as medullary curettage, autologous bone grafting, bridge plating, or intramedullary nailing may be warranted in such cases.[6][26][27] Postoperatively, healing can be arduous, sometimes taking months to years. Other treatment options include bone stimulation, shockwave, or ultrasound. Injectable bone cement options (calcium sulfate hydroxyapatite) have not had favorable outcomes as a stand-alone treatment.[28] Although pulsed ultrasound may be noninvasive, it has not significantly decreased overall healing time.[29] Shockwave has shown some promising outcomes secondary to increased bone turnover, osteoblast stimulation, and neovascularization and offers a noninvasive adjunct to treatment.[30]