Now that we are getting close to the Marathon here in Victoria, I am encountering an increasing number of people who are referred to me with "Shin Splints." What exactly does this mean? Shin splints is a general term to cover anything that causes shin pain. Most people know that they have shin pain, but where does it come from and why do they get it?
Here are some notes from an article I wrote that may help to understand the term Shin Splints and how it relates to Stress Fractures, as well as how serious an injury Stress Fractures can be.
COMMON CAUSES AND MANAGEMENT OF STRESS FRACTURES IN RUNNERS
STRESS FRACTURES
Stress fractures occur on a continuum with the actual term “Stress Fracture” being the worst possible outcome.
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normal bone bone strain stress reaction non-displaced stress fracture displaced stress fracture
This occurs when bone fails to remodel adequately with the application of repetitive stress. The reasons stress fractures occur are multi-factorial.
IT IS KNOWN THAT WE ARE EXPECTED TO REACH PEAK BONE MASS AROUND THE AGE OF 25. After that, both men and women’s bone density begins to decline, with women losing bone density more rapidly than men.
HOW BONE IS REMODLED
Wolff’s Law states that bony adaptation is a function of the number of loading cycles, cycle frequency, amount of strain, strain rate and strain duration per cycle (basically, what we do when we are training). The image below shows that as bone is bent, tension is created along the bottom edge (convex side) and compression is occurs along the top edge (concave side).
Tension forces are the ones responsible for resultant microfractures while compression forces tend to create more bone building
ETIOLOGY OF STRESS FRACTURES
The etiology of stress fractures is multi-factorial. They can be divided up into intrinsic and extrinsic factors.
Extrinsic Factors (Controllable Factors)
TRAINING REGIMEN – higher running mileage is associated with increased incidence of stress fractures. Abrupt training changes in DURATION (distance or time), FREQUENCY (times/day or week) INTENSITY (speed or time) are also correlated with increased incidence of stress fractures
FOOTWEAR – shoes are designed to REDUCE GROUND IMPACT FORCES. There is no evidence that cost of shoe can be associated with decreased risk of stress fracture.
There is moderate evidence that orthotic devices may help decrease incidence of stress fractures, however, it should be noted that all orthotics are made with different material and with different specifications so caution should be taken when deciding to purchase orthotics.
TRAINING SURFACE – there is conflicting evidence regarding training surface. Theoretically, it has been proposed that training on harder surfaces will increase incidence of stress fractures, but there has been evidence to dispute this theory.
Intrinsic Factors (Uncontrollable Factors)
DEMOGRAPHIC FACTORS –It has been noted that WOMEN tend to have higher incidence of stress fractures. This is probably due to the large number of women who run as well as gender associated risk factors such as lower overall bone mineral density (BMD) and menopause. The role of age as a risk factor has not been well correlated.
BIOMECHANICAL FACTORS – the amount of force that a bone can withstand is directly proportional to its cross sectional area. Thus, thicker bones tend to be stronger bones. It has been highly correlated that women with low BMD (especially in the femoral neck and lumbar spine) were at increased risk for stress fractures. THE BEST WAY TO DETERMINE BMD IS DUAL ENERGY XRAY ABSORTIOMETRY SCAN (DEXA SCAN). DENSITY CAN ALSO BE ESTIMATED BY REGULAR XRAY (RADIOGRAPHY).
ANATOMIC FACTORS – everyone has a different shaped foot. The shape of the foot can help control how much ground contact force is absorbed. A RIGID HIGH ARCH FOOT ABSORBS LESS STRESS AND TRANSMITS GREATER FORCE UP THE LEG. A FLEXIBLE LOW ARCH FOOT ABSORBS MORE FORCE AND TRANSMITS LESS FORCE UP THE LEG. Thus, high arches are good for sprinters who hope to transmit more force over short periods. This is bad for distance runners who want to absorb more force for longer periods of time. LEG LENGTH DESCREPANCY has shown to have moderate to mild correlation to stress fractures.
HORMONAL FACTORS – Females tend to be at higher risk for stress fractures. This is likely due to lower BMD, low body weight, future menstrual disturbances and/or excessive training. FITNESS PROFESSIONALS SHOULD BE AWARE OF FEMALE ATHLETE TRIAD CONSISTING OF EATING DISORDERS, AMENORRHEA (menstrual disturbance) AND OSTEOPOROSIS. Menstrual abnormalities are not a normal product of training.
DIAGNOSIS OF STRESS FRACTURES
Diagnosis of stress fractures is often difficult and requires a high degree of suspicion. Most commonly, it is an abrupt change in training such as increasing distance or intensity. Pain typically occurs at the end of the run, or after. THE HALLMARK DURING PHYSICAL EXAMINATION IS POINT TENDERNESS ALONG THE SHINS AND/OR FOOT. Other tests that are performed in order to reproduce pain may include tuning fork, percussion and single leg hop.
THE DIFFERENCE BETWEEN STRESS FRACTURE AND “SHIN SPLINT”
There are subtle difference between stress fractures and shin splints (more appropriately called medial tibial stress syndrome or MTSS).
-FOR STRESS FRACTURES, PAIN WILL INCREASE AS THE RUN GOES ON. TYPICAL MTSS PAIN USUALLY DIMINISHES AFTER WARM UP.
-STRESS FRACTURES WILL BE MORE POINT TENDER WHEREAS MTSS WILL HAVE MORE DIFFUSE TENDERNESS.
-FURTHER DIAGNOSTIC IMAGING MUST BE DONE TO DISTINGUISH THE DIFFERENCE. THIS MAY INCLUDE XRAY, MRI AND CT
CONSERVATIVE MANAGEMENT FOR STRESS FRACTURES
PHASE 1
Cessation of painful activity, ice, analgesics,
Maintain fitness with cross training
Modify risk factors such as change shoes, tape/brace, etc.
PHASE 2
Light weight exercises may be implemented including non impact loading such as walking, elliptical etc.
Increase weight bearing/loading exercises 5-10 min a day as long as no bone pain occurs
Recovery of strength that is lost during phase 1 must also be addressed
PHASE 3
Gradual reentry into sport specific activity starting every other day and progressing to normal activity. This may take from 3-18 weeks depending on severity of injury.
Gait analysis should also be done to determine if there are any risk factors that can be reduced
TAKE HOME POINTS
STRESS FRACTURES OCCUR ALONG A CONTINUUM WITH DIFFERENT SEVERITY
PEAK BONE DENSITY OCCURS AROUND AGE 25 AND DECREASES THEREAFTER.
STRESS INJURIES ARE RESULTANT ACCUMULATION OF MICRODAMAGE THAT MAY EVENTUALLY FAIL THROUGH CRACKING (STRESS FRACTURES)
THE ETIOLOGY OF STRESS FRACTURES ARE MULTIFACTORIAL AND USUALLY OCCUR DUE TO A COMBINATION OF MANY INTRINSIC AND EXTRINSIC FACTORS
WOMEN ARE AT HIGHER RISK FOR STRESS FRACTURES AS THEY TYPICALLY HAVE LOWER BMD AS WELL AS HORMONAL CHANGES THROUGH AGE AND THE POTENTIAL FOR THE FEMALE ATHLETE TRIAD
MUSCLE EXERTS A PROTECTIVE EFFECT AGAINST STRESS INJURIES BY ACTING AS THE MAJOR SHOCK ABSORBER
THE HALLMARK OF STRESS FRACTURES IS WORSENING OF PAIN DURING A RUN AS WELL AS POINT TENDERNESS ALONG THE TIBIA OR THE NAVICULAR (FOOT)
SUBTLE DIFFERENCES BETWEEN STRESS FRACTURES AND MTSS MUST BE DETERMINED AS MANAGEMENT FOR EACH CONDITION DIFFER
CONSERVATIVE MANAGEMENT FOR STRESS FRACTURES INCLUDE THE 3 PHASES MENTIONED PREVIOUSLY
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