Metatarsal Stress Fracture

Metatarsal stress fracture arises when repetitive loading outpaces bone remodeling, producing microdamage that progresses from marrow edema (stress reaction) to cortical fracture. It accounts for 10 to 20% of sports related stress fractures, with the second and third metatarsal shafts and necks involved most often. The term "march fracture" is used in military recruits.

Risk factors:

• Rapid increase in training volume or intensity
• Hard surfaces, inappropriate footwear, a long second metatarsal, pes cavus or planus, and hallux rigidus or hallux valgus
• Low bone density, vitamin D deficiency
• Female athlete triad or relative energy deficiency in sport (low energy availability, menstrual dysfunction, low bone density)
• Eating disorders, smoking and bisphosphonate use

Risk of delayed healing separates low risk sites (shaft and neck of the second to fourth metatarsals), which usually heal in 6 to 8 weeks, from high risk sites (base of the second metatarsal, the fifth metatarsal proximal diaphysis, and the sesamoids), where nonunion is common. Complications are complete fracture with displacement, delayed union, nonunion and recurrence.

• Insidious forefoot pain on weight bearing, initially after activity, then during it and eventually at rest
• Swelling over the dorsum and focal bony tenderness along the shaft
• Pain with the hop test, with axial load and with palpation of the metatarsal
• A history of training errors, menstrual disturbance or low body weight
• Red flags: night pain, pain at the base of the second metatarsal, a prior stress fracture, signs of an eating disorder, and unexplained multiple stress fractures

• Radiographs (anteroposterior, lateral and oblique): often normal for 2 to 3 weeks. Later they show periosteal reaction, cortical thickening, a fracture line or callus.
• MRI is the most sensitive and specific test: periosteal and marrow edema (stress reaction), then a low signal fracture line. It also grades severity.
• Bone scintigraphy or SPECT-CT when MRI is unavailable (high sensitivity, lower specificity).
• Metabolic review: 25-hydroxyvitamin D, calcium, phosphate, thyroid stimulating hormone, ferritin, menstrual history, and bone density scan with repeated or multiple fractures.

Differentials: Morton neuroma, metatarsophalangeal synovitis, plantar plate tear, Freiberg infraction, tendinitis, gout, osteomyelitis, compartment syndrome of the foot.

Low risk sites:

• A stiff soled shoe or a walking boot with weight bearing as tolerated for 4 to 6 weeks, if walking is pain free.
• If walking provokes pain, use crutches or non-weight-bearing in a boot for 2 weeks, then progress.
• Cross training with swimming or cycling to maintain fitness.
• Return to running after 4 weeks of pain free walking and no tenderness, with a graduated program (start at 25 to 50% of the previous distance, increasing by 10% each week). Typical total time 8 to 12 weeks.

High risk sites:

• Non-weight-bearing in a short leg cast or boot for 6 to 8 weeks, with radiographic proof of healing.
• Early intramedullary screw or plate fixation for athletes, displacement, delayed union (over 3 months) and nonunion, with autograft for nonunion.
• Cefazolin 2 g IV before incision. Enoxaparin 40 mg SC daily while non-weight-bearing.

Analgesia: paracetamol 1 g orally every 6 hours (maximum 4 g/day). Avoid long courses of NSAIDs.

Correct the cause:

• Cholecalciferol 2000 IU orally daily for 8 to 12 weeks if the level is below 50 nmol/L.
• Calcium 1000 to 1200 mg daily from diet or supplement.
• Restore energy availability and treat menstrual dysfunction with a multidisciplinary team (dietitian, gynecology, psychology).
• Gait analysis, footwear change, orthoses for pes cavus or planus, and treatment of hallux rigidus.

Follow up at 2 to 4 weeks, then at 6 and 12 weeks. Counsel on recurrence risk and prevention through gradual training increases.