Runners and Bone Stress Injuries

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Introduction

Bone Stress Injures (BSI) occur when bone stresses applied during activity, like running, exceed the bone's tissue tolerance . This can also be known as bone strain. It is very common among runners, especially due to the repetitive loading with long distance running , thus most commonly occur in competitive cross-country runners and track-and-field athletes. It can be indicated by a mild diffuse ache, which comes on after running. Pain may come on during a particular phase of the running gait cycle, when the injured bone would be maximally loaded. In the initial stages of the injury, pain can subside after activity, though with prolonged exposure the pain can come on easily, be more concentrated, and last for longer, making the person more irritable. The pain can arise with lower impact activities such as walking, and a local inflammatory response may be indicated as pain.

It is seen that the incidence of BSIs varies among age and gender. It is suggested that there is an annual incidence of 20% between males and females experiencing BSIs within Collegiate Cross-country and/or track and field runners.

Mechanism of Injury

With an increase in external mechanical aspects, there are adaptive changes in the internal structure. With the increased load, a stress reaction would occur with the presence of periosteal edema. A bone stress fracture would be indicated by a cortical fracture line on the MRI.

Bones have a stronger compressive tolerance, compared to a stretch tolerance. They can experience a greater conservative recovery.

One mechanism indirectly related to running, but relating to athlete health, are gonadal hormone irregularities, which can cause athletes to have cortical and trabecular BSIs and/or osteopenia or osteoporosis. This can also occur in athletes with nutritional imbalances, hormonal influences, and decreased bone mineral density.

Risk Factors and Prevention

With mitigating or preventing risk factors of BSIs, overall bone health, and healing times, can be improved for runners.

There are two types of risk factors that can be considered for BSIs: factors that alter the load applied to the bone, or factors that influence the bone's ability to withstand load, thus minimising damage. The factors that alter the load stem from the size, frequency, duration, and direction of the load applied to the bone. Factors that contribute to withstanding the load applied to the bone include the bone mass, size, and intrinsic properties of the bone. Intrinsic biomechanical factors that can alter bone load are foot type, leg length, or leg length differences. Other factors include, training parameters (volume, intensity, duration, or race frequency), and footwear (type and age of shoes, and support). Factors that allow the bone to withstand load include athletic history/ lifestyle history, medical and family history, and relative energy deficiency in sport, bone health, and calcium and Vitamin D status.

Concerning static biomechanical factors, leg length differences, a reduced calf girth, or pes planus or pes cavus can contribute to BSIs through altered bone loading. Dynamic risk factors that can contribute include increased vertical loading, a greater peak acceleration, increased peak free mass, increased peak adduction, knee internal rotation, knee abduction, tibial internal rotation, and rear foot eversion. Gait biomechanics can contribute to the risk of BSIs, with uneven loading or imbalances.

Regarding training patterns, the risk of BSIs can be greater with an increase in velocity, duration, distance, or frequency.

Studies have shown that runners modify their leg stiffness when running on different terrains. This helps balance out ground reaction loading forces on the lower limb. Changes in running surface, terrain, and hills could also be contributors to causing BSIs.

Running footwear is also a very important with the prevention and contribution to BSIs. Please read Shoe Analysis - Fitting a Shoe and Shoe Analysis - Anatomy of a Running Shoe for a further explanation and analysis on the fitting and suitability of a running shoe.

When talking about athletic history and medical history, it is seen that with a history of long distance running, there is an impact of lower loads, which doesn't seem to impact bone health. In addition, adolescents who take part in high-impact and multi-directional loading sports can improve bone density and geometry.

Other risk factors for BSIs include a history of fractures, the use of medications or other drugs, genetic factors, or family history. Exposures to medications such as glucocorticoids, antiepileptic medications, anticoagulants, antidepressants, and antacids can have a poor impact on bone health. Systemic conditions, including chronic inflammatory conditions can have a negative effect on bone health. Bone health can also be affected by endocrine abnormalities. Kidney disease, chronic kidney disease, or kidney failure, can lead to some of these conditions, thus negatively affecting bone health.

However, weightbearing physical activities is protective against BSIs due to the bone remodeling, leading to an increase in rigidity, and and increase in strength over time.

Risks in different groups

A study showed that in an adolescent age group, there was an increased risk of BSIs with more than 32 km/week of running. A prospective study showed that adolescent runners had an incidence of 5.4% among female runners, and 4.0% among male runners. However, as mentioned above adolescents taking part in high-impact and multi-directional ball sports such as basketball or soccer have a protective effect toward stress fractures as adult runners.

When analysing the BSI incidence by Athlete Exposures (AEs) among high school athletes, girls had the highest (10.6/100000 AEs), with boys having the third highest (5.4 /100000 AEs). Within cross-country and track and field athletes, it is seen that 10.3-12.6% of athletes who have a history of BSIs are likely to have a recurrence within 2 years.

The Male Runner

Similar to the female triad (mentioned below), male runners can experience low energy availability, hypogonadotrophic hypogonadism, and low bone mineral density. Multiple risk factors in males, similar to the female triad, can have an accumulative risk of BSIs.

Low energy availability can occur from eating disorders, inadequate nutrition, or expending more calories than being taken in. Low energy availability or high volume training can cause changes in the hypothalamic-pituitary-gonadal (HPG) axis. A study by Hackney et al shows that endurance runners have a lower testosterone level than sedentary individuals. However, a study by Wheeler et al showed that an increase in running mileage had an inverse relationship to testosterone levels.

RED-S, which can occur in males or females, results from inadequate caloric intake or excessive expenditure of energy. This can be disadvantageous to bone health, impair metabolism, menstrual function in females, immunity, protein synthesis, cardiovascular, and psychological status.

The Female Runner

There is an Energy Availability Triad for females, which is outlined by the integration of energy availability, menstrual function, and bone mineral density. A female runner may have deficiencies in any of the triad factors. Having more triad factors leads to an increased risk of BSIs.

A dual-energy x-ray absorptiometry (DEXA) is the principle method used to measure bone mas density. A DEXA is indicated if the woman is <17.5kg/m^2, menarche >16 years, eating disorder history, 2 prior BSI, or one high-risk BSI.

Females with a history of tibial stress injury had a greater average vertical loading, and a higher peak acceleration, while running. It is seen that a higher ground reaction force loading rate and peak acceleration is a risk factor for stress fractures. Tam et al showed that there was an increased ankle dorsiflexion at initial contact and increased initial loading rate in barefoot runners.. With relative plantarflexion at initial contact, there is a decrease in loading rate. Muscle should be able to help with absorbing and attenuating the impact forces, however muscle fatigue or weakness would make the absorption less effective, which may alter the kinematics, increasing the forces applied to the bone, leading to bone strain.

Common Sites of BSIs

There are various spots in which a BSI can occur in the lower limb. These include:

High risk sites:

• Femoral neck/lesser trochanter
• Anterior tibial diaphysis
• Medial malleolus
• Lateral talar process
• Tarsal navicular
• Base of the second metatarsal
• Fifth metatarsal proximal diaphysis
• Sesamoids at the first metatarsal

Moderate risk sites:

• Pelvis (sacrum/pubic rami)
• Femoral shaft
• Proximal tibia
• Cuboid
• Cuneiform

Low risk sites:

• Posteromedial tibia
• Fibula/lateral malleolus
• Calcaneus
• Diaphysis of the second to fourth metatarsals

Diagnosis

BSIs are generally diagnosed through plain radiography. Early scans can be ruled out as negative, with an early scan sensitivity of 10% However, as symptoms and the condition progresses, the scans become more sensitive, with a sensitivity of 30-70% after 3 weeks of symptom onset. Key indications can be periosteal thickening or sclerosis, cortical changes with an early decreased density (“gray cortex”), and evidence of callus formation or endosteal thickening and sclerosis occurring later in the disease process.

They can also be diagnosed using MRI scans. There is a high sensitivity and specificity for BSIs. They can help indicate the severity of the BSI. More severe injuries may be indicated by a cortical fracture line on the MRI. They an help indicate periosteal edema, as well as differing levels of bone marrow edema.

Upon noticing these symptoms, early identification and management would lead to better prevention of further injury.

Management

Management of BSIs would generally progress with activity modification, and gradual return to running. Any underlying risk factors need to be modified, which may include biomechanical and/or biological factors, as mentioned above. Activity modification would involve pursuing activities that are not directly related to running. The duration would depend on the location and severity of the injury.

The primary goal of healing would be to work towards pain free movement and gait, and abrupt movements. Low risk BSIs can be managed through immobilisation or modification of activity to work towards pain free movement. Medium or high risk BSIs would require a non-weightbearing immobilisation, followed by the appropriate weight-bearing and strengthening rehabilitation protocol.

Once runners achieve the pain free gait and movements, non-impact loading activity can be carried out. This is facilitated through deep water running or anti-gravity treadmill running, and such activities, which can help facilitate the gradual return to impact loading. They can start gradually increasing their running related lads. The pain levels need to be controlled, for there to be no or minimal pain during or after activity, otherwise the activity would need to be modified. Nonsteroidal anti-inflammatory drugs (NSAIDs) should be avoided since they can mask the pain.

Calcium and Vitamin D status should also be maintained, as they play a vital role in bone health. An increased Vitamin D is seen to lead to an increased BMD and a quicker return-to-play after a BSI. This becomes relevant as athletes need a high level of Vitamin D for optimal bone health.