What is medial tibial stress syndrome?

What is Medial Tibial Stress Syndrome?

Medial tibial stress syndrome (MTSS), commonly known as "shin splints," is an overuse injury characterized by diffuse pain along the posteromedial border of the tibia (middle to distal third) that occurs during exercise and is caused by repetitive mechanical loading. 1, 2

Clinical Presentation

MTSS presents with specific characteristics that distinguish it from other tibial pathology:

• Pain location: Diffuse tenderness along the posteromedial edge of the tibia, typically affecting the middle to distal third of the tibial border 1, 3
• Pain quality: Described as a dull ache that occurs during or following exercise and is typically relieved by rest 1
• Palpable tenderness: The posteromedial tibial border demonstrates tenderness on palpation over a broad area (typically >5 cm), distinguishing it from stress fractures which have more focal tenderness 2, 3

Distinction from Bone Stress Injuries

MTSS is fundamentally different from tibial bone stress injuries (BSIs) and should not be considered part of the same continuum. 4

• MTSS is characterized by different bone histology and clinical presentation than a BSI 4
• The proposed continuum from MTSS into lower-grade bone stress reactions lacks supporting evidence 4
• When visible fracture lines appear on imaging, the injury transitions from a stress reaction (grades 1-3) to a stress fracture (grade 4), which is distinct from MTSS 4

Epidemiology and Risk Factors

MTSS affects a substantial proportion of active individuals:

• Incidence: Reported in 4% to 20% of athletes who run, with some studies showing rates up to 35% in active populations 3, 5
• Common risk factors include:
  • Overtraining and training errors 2, 6
  • Poor or inappropriate footwear 1, 6
  • Muscular imbalances at the ankle 1
  • Tight or weak triceps surae (calf) muscles 1
  • Body mass index (BMI) above 30 1
  • Biomechanical abnormalities 2
  • Reduced lower leg muscle girth and cross-sectional area 5

Pathophysiology

The exact pathophysiology remains debated, but MTSS is understood to involve:

• Inflammation of muscles, tendons, and bone tissue along the posteromedial tibia from repetitive stress 6
• Periostitis (inflammation of the periosteum) in the lower medial tibial region 1
• Cyclic loading during exercise that exceeds tissue tolerance 3
• The lower leg musculature's inability to adequately attenuate ground reaction forces during the gait cycle 5

Differential Diagnosis Considerations

When evaluating suspected MTSS, clinicians must exclude:

• Tibial stress fractures (focal tenderness, positive imaging) 3
• Chronic exertional compartment syndrome (raised compartment pressure, upper lateral tibial pain) 1, 3
• Other ischemic disorders 3