Description

• Stress fractures are microscopic fractures that occur when repetitive stresses are applied to bone, causing breakdown (via osteoclasts) faster than remodeling of new bone formation (via osteoblasts).
• Stress fractures can occur in different situations:
  • Fatigue fracture: Abnormal stress applied to normal bone (e.g., young college athletes or new military recruits with inadequate conditioning)
  • Insufficiency fracture: Normal stress applied to abnormal bone (e.g., femoral neck fracture in osteopenic elderly woman)
  • Combination: Abnormal stress applied to abnormal bone (e.g., female long-distance runners with premature osteoporosis from female athlete triad)
• Weight-bearing bones of the lower extremity are affected the most.
• Commonly affected sites:
  • Tibia
  • Metatarsus
  • Fibula
  • Navicular
  • Femoral neck
  • Pars interarticularis
• Less commonly affected sites:
  • Pelvis
  • Calcaneus
  • Ribs
  • Ulna
• High-risk stress fractures are defined as stress fractures that are more likely to result in fracture displacement and/or nonunion (1)[B]. High-risk sites include:
  • Femoral neck
  • Anterior tibial cortex
  • Sesamoids
  • Pars interarticularis
  • 5th metatarsal metaphyseal
  • Proximal second metatarsal
  • Medial malleolus
  • Tarsal navicular
  • Body of the talus
• Synonym(s): March fracture; Fatigue fracture

Epidemiology

• Predominant age: Can occur at any age
• Predominant sex: Female > Male
• High occurrence in running and jumping athletes
• Affects 8.7–21.1% of track and field athletes annually
• Accounts for as many as 7.8% of visits to sports medicine and orthopedic clinics

• Affects 5% of military recruits
• Affects 1–2.6% of college athletes

Risk Factors

• Sports involving running and jumping
• Rapid increase in physical training programs
• Female athlete triad (i.e., amenorrhea, eating disorder, premature osteoporosis)
• History of previous stress fracture
• Skeletal malalignment:
  • Pes cavus, pes planus
  • Excessive external rotation of the hip
• Inappropriate footwear
• Increased vertical loading rate (e.g., heel-to-toe running instead of forefoot striking in runners) (2)[A]
• Extremes of body size and composition
• Muscle fatigue and decreased lean muscle mass
• Low bone density
• Previous inactivity or low aerobic fitness

General Prevention

• Avoid abrupt increases in physical activity.
• Reduce intensity and duration of activity if new-onset pain.
• Use proper footwear.
• Decrease vertical loading rate either by switching to forefoot strike style running, or, if continuing with heel-to-toe strike, using a heel pad insert (2)[A].
• Shock-absorbing foot inserts may help (evidence rating SORT B).
• Increasing calcium, vitamin D, skim milk, and low-fat dairy product intake may reduce the rate of stress fractures in female runners/military recruits (3)[B].

Pathophysiology

• Osteoblastic activities lag behind osteoclastic activities during the initial increase in exercise activity.
• Strong and repetitive stress transmits to bone when the surrounding muscles become fatigued.

Commonly Associated Conditions

• Osteoporosis/Osteopenia
• Female athlete triad
• Metabolic bone disorders