Understanding Bone Stress Injuries and Stress Fractures: Causes, Symptoms, and Safe Return to Running

Bone stress injuries (BSIs) occur when repetitive mechanical stress exceeds the bone’s ability to repair and adapt. If not managed properly, they can progress from mild bone strain to full fractures, impacting an athlete’s ability to train and compete.

Stages and Progression of Bone Stress Injuries

Bone stress injuries exist along a continuum of severity, progressing through the following stages:

1. Bone Strain (Preclinical Phase):
   • Increased bone turnover and microdamage with no symptoms.
   • Bone adapts by strengthening if adequate recovery time is allowed.
2. Bone Stress Reaction (Early-Stage Injury):
   • Microscopic damage accumulates, causing localised pain during activity.
   • No visible fracture on X-ray, but MRI may show bone marrow oedema.
   • Symptoms improve with rest, but continued loading may worsen the injury.
3. Stress Fracture (Advanced Injury):
   • Microdamage progresses into a small crack within the bone.
   • Pain is persistent and worsens with weight-bearing activities.
   • Visible on MRI and may appear on X-ray in later stages.
   • Requires longer recovery time and possible immobilization.
4. Complete Fracture (Final Stage if Left Untreated):
   • Structural failure of the bone, leading to a full break.
   • Significant pain, inability to bear weight, and visible fracture on imaging.
   • Often requires extended rest, immobilization, or surgical intervention.

Changes at the Bone Level Due to Load

Bone is a dynamic tissue that continuously remodels in response to mechanical stress. When subjected to increased loads, the following changes occur:

1. Bone Microdamage: Repetitive stress causes microscopic damage to the bone matrix, which, if not given adequate recovery time, can accumulate and lead to injury.
2. Osteoclastic Resorption: Increased mechanical load stimulates osteoclasts to break down old or damaged bone tissue. This resorption process is necessary for remodeling but creates temporary weakening of the bone.
3. Osteoblastic Formation: Osteoblasts respond by forming new bone tissue to strengthen areas experiencing stress. However, this process lags behind resorption, creating a vulnerable period where the bone is weaker and more susceptible to injury.
4. Bone Adaptation: With appropriate recovery, the bone becomes denser and stronger over time, better withstanding future mechanical loads. Insufficient recovery, however, disrupts this balance and increases the risk of stress fractures.

Common Locations for Bone Stress Reactions

Bone stress injuries typically occur in weight-bearing bones that endure repetitive loading. Common sites include:

• Tibia – The most frequently affected bone in runners, particularly the medial tibial shaft.
• Femur – The femoral neck and shaft can develop stress fractures, especially in endurance athletes.
• Metatarsals – Often seen in long-distance runners, particularly the second and third metatarsals.
• Fibula – Less common but can occur in athletes with altered biomechanics such as high arched feet.
• Navicular – A high-risk area due to limited blood supply, often seen in sprinters and jumpers.
• Pelvis – The pubic ramus can be affected, particularly in distance runners.

Contributing Factors to Bone Stress Injuries

BSIs result from a combination of intrinsic (biological) and extrinsic (environmental) factors:

1. Training & Activity Factors:

• Sudden increase in training volume, intensity, or frequency.
• Repetitive high-impact activities such as running or jumping.
• Insufficient rest and recovery periods.
• Transitioning to harder surfaces or unsuitable footwear.

2. Biomechanical Factors:

• Poor running mechanics (e.g., overstriding, excessive pronation).
• Muscle imbalances or weaknesses (especially in the glutes and calves).
• Leg length discrepancies or abnormal foot structures.

3. Nutritional & Medical Factors:

• Low energy availability (Relative Energy Deficiency in Sport – RED-S).
• Inadequate calcium and vitamin D intake.
• Hormonal imbalances, including menstrual dysfunction in female athletes.
• Low bone mineral density (osteopenia or osteoporosis).
• History of previous bone stress injuries.

4. Environmental & External Factors:

• Training on hard, uneven, or unstable surfaces.
• Inappropriate or worn-out footwear.

Recognising the Symptoms of Bone Stress Injuries

Early identification is crucial to prevent a minor injury from progressing into a full stress fracture:

• Localised pain during weight-bearing activities (e.g., running, jumping).
• Pain that initially subsides with rest but worsens with continued activity.
• Tenderness at a specific bone site upon palpation.
• Possible mild swelling in the affected area.

Diagnosis & Medical Evaluation

If a BSI is suspected, seeking professional assessment is essential.

• Imaging techniques such as MRI or bone CT scan (X-rays may not detect early-stage injuries).

Safe Return to Running After a Bone Stress Injury

A structured and gradual approach is key to a successful return:

1. Initial Recovery Phase (Rest & Cross-Training):

• Cease all high-impact activities to allow bone healing.
• Engage in low-impact exercises such as swimming or cycling (as recommended by a physiotherapist).
• Address nutritional deficits and optimize bone health.

2. Strengthening & Rehabilitation:

• Incorporate resistance training focusing on glutes, calves, and core stability.
• Improve flexibility and proprioception to enhance movement efficiency.
• Address gait abnormalities with physiotherapy interventions.

3. Gradual Running Progression:

• Start with walking before introducing short running intervals.
• Follow a structured walk-run program, increasing running duration progressively.
• Monitor for any signs of pain and reduce activity if symptoms recur.
• Allow sufficient recovery days between runs.

4. Long-Term Injury Prevention:

• Adhere to a balanced training plan with gradual load progression.
• Prioritize strength training alongside running.
• Ensure adequate nutrition and hydration to support bone health.
• Listen to your body and seek early intervention if symptoms arise.

By understanding the risk factors and adopting a careful return-to-running plan, athletes can effectively recover from bone stress injuries and reduce the likelihood of recurrence.