Metatarsal Stress Fracture (March Fracture)

Metatarsal stress fracture is an overuse injury of one of the metatarsal bones (1st through 5th) caused by repetitive submaximal loading that exceeds the bone's intrinsic ability to remodel and repair microdamage. It is one of the most common stress fractures of the lower extremity, accounting for 5-25% of all stress fractures, and the most common stress fracture in the foot. Anatomy and biomechanics: the metatarsals are five long bones connecting the tarsus to the toes, with the 1st metatarsal being the largest and most weight-bearing, and the 2nd-5th metatarsals smaller. The 2nd metatarsal has unique anatomy that predisposes it to stress fracture: (1) Longest of the metatarsals (sometimes longer than 1st in 'Morton's foot'). (2) Fixed (recessed) base position at Lisfranc joint with strong ligamentous attachments creating a relatively rigid lever during push-off. (3) Concentration of bending forces during gait push-off phase. (4) The 2nd metatarsal is the apex of the longitudinal arch, transmitting forces from the medial column. The 2nd metatarsal accounts for 50-70% of all metatarsal stress fractures. The 3rd metatarsal is the next most common (15-25%). The 5th metatarsal stress fractures are less common but clinically important due to the higher nonunion risk in proximal diaphyseal fractures (zones 2-3, including the classic Jones fracture). Pathophysiology: bone constantly remodels in response to mechanical loading (Wolff's law) — osteoclasts resorb damaged bone matrix and osteoblasts form new bone. Stress fractures occur when applied loading exceeds the rate of bone remodeling and microfractures accumulate, eventually progressing to a clinical fracture. The progression is along a continuum: stress reaction (bone marrow edema, periosteal reaction without cortex disruption) → stress fracture (incomplete fracture line through cortex) → complete fracture (rare for metatarsal). Stress fractures can be either fatigue type (normal bone exposed to abnormal stress, common in athletes) or insufficiency type (abnormal weak bone exposed to normal stress, common in osteoporosis, post-radiation, etc.).

Risk factors and demographics: (1) Athletic populations: long-distance runners (incidence 1-13% of runners), military recruits during basic training (10-30% incidence in some series), ballet dancers (high foot stresses), basketball players, soccer players, gymnasts, equestrians. (2) Sudden increase in training intensity, volume, frequency (most common identifiable cause — 'too much, too soon, too fast'). (3) Change in training surface (concrete, asphalt) or shoes (worn-out cushioning, switch to minimalist shoes). (4) Female sex (4-5x higher risk than males in some athletic groups), particularly with Female Athlete Triad: low energy availability, menstrual dysfunction (oligomenorrhea, amenorrhea), and low bone mineral density (osteopenia, osteoporosis). RED-S (Relative Energy Deficiency in Sport) is the broader contemporary term. (5) Osteoporosis and osteopenia (post-menopausal women, men with hypogonadism, chronic steroid use). (6) Vitamin D deficiency (less than 30 ng/mL) and inadequate calcium intake. (7) Biomechanical abnormalities: cavus foot (high arch with rigid lateral column, increased lateral metatarsal load — predisposes to 5th metatarsal fractures), pes planus (overpronation, increased medial loading), leg length discrepancy, hallux valgus (transferring load to 2nd metatarsal — 'transfer metatarsalgia'), Morton's neuroma. (8) Bunion or 1st ray hypermobility leading to 2nd metatarsal overload. (9) Metabolic bone disease (hypothyroidism, hyperparathyroidism, malabsorption). (10) Smoking and excessive alcohol use. (11) Eating disorders (anorexia nervosa, bulimia). (12) Prior stress fracture (high recurrence risk).

Clinical presentation and diagnosis: gradual onset of forefoot pain (over days to weeks of activity), often initially mild and only with high-intensity activity, progressing to pain with all weight-bearing and even at rest. Pain typically described as deep, aching, or throbbing in the dorsal forefoot. Often patient reports recent change in training (increase in mileage, change in shoes or surface). Examination: tenderness directly over involved metatarsal (palpate dorsal aspect, run finger along shaft), mild swelling and warmth, sometimes erythema, decreased pain with non-weight-bearing position. Compression test (squeeze across all metatarsals or apply axial compression to involved metatarsal) reproduces pain. Tuning fork test (place vibrating tuning fork over involved bone) often reproduces pain (sensitivity ~75%). Imaging: (1) Plain radiographs (AP, lateral, oblique foot, weight-bearing): often NORMAL in early stress fracture (less than 2-6 weeks); positive findings appear 2-6 weeks after symptom onset and include periosteal reaction (linear opacity along bone), cortical thickening, callus formation (most common finding), focal sclerosis, and rarely a fracture line. Repeat radiographs at 2-3 weeks may show changes if initial normal. (2) MRI: highly sensitive (over 90%) and specific for stress reaction and stress fracture; T1 shows decreased signal at fracture site, T2/STIR shows increased signal (bone marrow edema, periosteal edema, surrounding soft tissue edema), with detection of fracture line in advanced cases. MRI staging (Fredericson grading for stress reaction): Grade 1 (mild marrow edema), Grade 2 (moderate edema), Grade 3 (extensive edema, cortical break), Grade 4 (visible fracture line). Best for early diagnosis. (3) CT scan: useful to detect cortical fracture line, occult fractures, evaluate completion or extent. Less sensitive than MRI for early stress reaction. (4) Bone scan (Tc-99m bone scan): highly sensitive but less specific (focal increased uptake at fracture site, intense in early stages). Useful when MRI not available. (5) Ultrasound (less commonly used). Differential diagnosis: metatarsalgia, Morton's neuroma, Freiberg infraction (idiopathic osteonecrosis of metatarsal head), tarsometatarsal arthritis (Lisfranc), gout, septic arthritis, peroneal tendinopathy, plantar fascia disorders, sesamoiditis. Treatment: most metatarsal shaft stress fractures (1st through 4th and 5th metatarsal distal shaft and head fractures) heal with conservative management. Treatment principles: (1) Activity modification: cessation of impact-loading activities for 4-8 weeks (cross-training with non-impact activities such as swimming, cycling, water running maintained for fitness, but pain-free). (2) Protected weight-bearing: stiff-soled shoe (carbon plate insert), post-operative boot (CAM walker), or rigid orthotic for 4-6 weeks; severely painful cases may benefit from non-weight-bearing with crutches initially. (3) Ice and NSAIDs for inflammation and pain (some controversy about NSAIDs delaying bone healing but generally considered safe for short courses). (4) Calcium 1000-1200 mg/day and vitamin D 1000-2000 IU/day supplementation, with serum 25-OH vitamin D level checked and corrected. (5) Address underlying contributing factors: nutrition optimization (especially in Female Athlete Triad), correction of biomechanical abnormalities with custom orthotics or shoe modifications, gradual return to training plan with reduced volume initially. (6) Bone density assessment (DEXA) in patients with risk factors (postmenopausal, prior fractures, low BMI). (7) Endocrinology referral for menstrual dysfunction, hypogonadism, eating disorder treatment. (8) Physical therapy for strengthening and gait analysis. Surgical treatment: usually NOT needed for typical 2nd-4th metatarsal shaft stress fractures (more than 95% heal with conservative management). EXCEPTION: 5th metatarsal proximal diaphyseal stress fractures (zones 2-3) including the Jones fracture — high nonunion rates with conservative management (50% nonunion rate or longer time to union), so often treated surgically with percutaneous intramedullary screw fixation (especially in athletes wanting rapid return to sport). Tarsal navicular stress fractures (related entity) often also surgical due to nonunion risk. 1st metatarsal stress fractures may rarely require surgical treatment for displacement. Other surgical indications: nonunion after appropriate conservative management, displacement, athletes requiring rapid return to high-level competition. Prevention: gradual training progression (no more than 10% increase in mileage per week), proper footwear with adequate cushioning and replacement at 300-500 miles, biomechanical assessment and correction, nutritional optimization with adequate calcium, vitamin D, and energy availability, addressing menstrual dysfunction in female athletes, smoking cessation. Outcomes: most metatarsal stress fractures heal completely in 4-8 weeks with conservative management; 5th metatarsal stress fractures may require longer (8-12 weeks) or surgery. Recurrence risk significant if underlying factors not addressed (up to 40% in Female Athlete Triad without intervention).