Stress fractures of bone are a common injury seen in all types of sport and are a debilitating injury which can hurt a lot, preventing sports participation and maximum performance. The media often mentions stress fractures when sportspeople are unavailable for their event/sport but there is usually a vague sense of no clear return to play when these injuries are discussed. No moment of injury is usually seen either which tends to add the mystique and angst that typically accompanies a stress fracture diagnosis. This lack of injury moment or trauma adds to the distress of the athlete too when they are advised to not play for many weeks despite not feeling anything sinister has occurred.
Stress fractures can affect almost any bone in the body depending on the type of activity you perform. Lower limb stress injuries are the most common with tibia stress fractures and foot stress fractures being the most common in runners and other impact sports. It is not uncommon for gymnasts and dancers to develop stress injuries of the upper limb and ribs. Dancers, gymnasts and cricket bowlers also commonly develop stress injuries in the spine (pars stress fractures) due to the unique movements associated with their sports.
Stress Fracture Symptoms
Typically, stress fractures evolve slowly and are noticed as a gradual increase in localised pain, usually over a bony area such as the middle of the shin bone (tibia). The pain is usually brought on by weight-bearing or impact activity. The pain is in response to the bone’s inability to tolerate the force going through it. Hence the pain is worse when exercising and usually much improved when resting the affected area. However, 50% of stress injuries can cause night pain.
Typical examination findings are a localised area of tenderness on a bone. This may be associated with a small lump and swelling. The pain is often worse with recurrent hopping.
Although most bone stress injuries show themselves as a progressive increase in pain, the concern is a sudden failure of the bone. Bone failure is most likely to be seen if the pain is ignored and usually requires surgical intervention and a prolonged recovery period. Most recently, sudden bone failure was seen in the UFC bout between Conor McGregor and Dustin Poirier where a reported underlying stress fracture resulted in a complete tibial fracture.
What is a Stress Fracture?
Bone stress injuries are an accumulation of bone fatigue that results in a loss of structural and functional integrity. Every time we load our bone we cause microdamage to the collagen fibres and bone matrix. This stimulates bone cells known as osteoblasts, octeoclasts and osteocytes to respond to this microdamage. Typically after exercise our body mops up this ‘microdamage’ and strengthens the bone and remodels so the bone can tolerate MORE load in the future. This process takes a period of time to occur. Higher training intensity, particularly impact training, results in more microdamage than lower training intensity. If you participate in regular high intensity training without allowing adequate time for bone repair and remodelling, the microdamage never fully recovers and slowly accumulates.
As microdamage accumulates, the bone can develop signs of further injury known as microcracks. These are more definable issues in the structure of the bone. These microcracks aren’t visible like a traumatic fracture but are the early stages of a stress fracture. This phase is referred to as a bone stress injury. There are microfractures present but no visible crack on imaging. Bone is often symptomatic at this stage although it is possible to have signs of bone stress on MRI without pain.
Persistence of exercise allows microfractures to coalesce into macrofractures. Macrofractures are visible on imaging techniques as cracks in the bone. These cracks can progress through the entire width of the bone with time and result in sudden decompensation of the bone as seen in McGregor’s leg in the above image.
Why Do Stress Fractures Happen?
Th primary reason for a bone stress fracture to happen is training overload. As mentioned previously, the bone is exposed to recurrent bouts of exercise that cause more damage than the bone can recover from over a short period of time. So any changes in training volume, frequency or intensity increase the odds of developing a stress injury. The largest risk though is increasing the amount of impact loading in your training program.
However, development of stress injuries is usually multifactorial. These other factors need to be assessed and addressed in your recovery pathway.
Significant risk factors include:
CHANGES IN TRAINING SURFACE & FOOTWEAR
This can influence the amount of force that your bone is exposed too. Changing training surface or footwear can result in sudden changes of bone loading exposure (known as ground reaction forces) and increase microdamage accumulation.
POOR BONE HEALTH & BONE DENSITY
Bone health (mineral density, collagen organisation and quantity) is influenced by many factors.
Calcium Intake: Bone mineral is predominantly formed from calcium, therefore a lack of adequate calcium means bones do not have the necessary building blocks to build and maintain normal healthy bone. A common mistake is thinking a normal calcium blood test means calcium intake is adequate. In fact, the body protects blood calcium at all costs and will leach calcium out of the bones to maintain normal blood calcium. A normal blood calcium test doesn’t tell you much about your bone health in most cases.
Vitamin D Levels: Vitamin D plays a crucial role in how our body processes and absorbs calcium. 90% of our Vitamin D comes directly from sunlight. Low levels of Vitamin D increase the odds of poor bone health via its influence on calcium. Most blood tests suggest a Vitamin D level less than 50 nmol/L is low, but there is an increased incidence of bone stress injuries when levels are less than 75 nmol/L.
RELATIVE ENERGY DEFICIENCY SYNDROME (RED-S): Having persistently lower energy intake (dietary consumption of calories) than the amount of energy expended (calories burnt off) results in inefficiencies in many of the systems that maintain normal body function. Energy is required for normal bone remodelling and turnover. Low energy slows this process resulting in ‘stale’ bone that can be injured more easily. Low energy also affects sex hormone production (oestrogen and testosterone) and these hormones are anabolic to bone (promote growth and strength). If these hormones are not produced in adequate amounts, low bone mineral density and poor structure can result. This is a type of secondary osteopaenia / osteoporosis.
BIOMECHANICS & STRENGTH: Most areas of bone stress occur at specific points where load has been focussed. This focussing of load can be amplified by asymmetric biomechanics, abnormal movement patterns and muscle strength weakness. Interestingly though, there is no association of pes planus (flat feet) and the development of stress injuries.
GROWTH SPURTS: During growth spurts the bones grow faster than they can be mineralised. This results in a period of relative weakness (transient osteopaenia). Some studies suggest that growing by more than 0.6cm per month correlates to an increase in injury risk of 63%. This is why it is common to see teenagers with bone stress injuries.
FEMALE GENDER: Due to differences in bone width, muscle strength and hormonal influences as well as factors that are not understood, females have higher rates of stress injuries than males. In the military up to 17% of females develop bone stress injuries vs 6% of their male counterparts. These rates are higher in females with known alterations in their menstrual cycle. Normal menstrual cycle cannot be assessed in females using the oral contraceptive pill as the medication triggers menstruation regardless of the underlying physiology within the body. Taking the oral contraceptive pill does not compensate for having poor internal production of sex hormones.
OTHER: Several other factors influence vulnerability to bone stress injuries including your genetic risk (have your parents or siblings had any stress injuries?), parathyroid/thyroid hormone problems, smoking, excess alcohol consumption and other chronic illnesses.
Stress Fracture Diagnosis
Most stress fractures can be diagnosed clinically from the story you tell and the examination from the doctor. However, prognosis (how long it will take to recover) of the stress fracture and contribution of other factors to the injury may require further assessment including;
- XR: Useful in chronic and higher grade injuries
- MRI: Excellent at detecting early injuries and helps classify degree of stress injury present
- Dietary assessment: sometimes a formal assessment with a SDA Sports Dietitian is needed to formally quantify your energy needs
- Blood tests including assessment of bone physiology and hormone status
- Bone mineral density testing via DEXA scan
Stress Fracture Grading
Stress injuries exist on a continuum. The further down the continuum towards a macrofracture, the longer the recovery time is likely to be. Several grading systems have been proposed but essentially the key components are:
- Grade 1: Asymptomatic bone oedema (microfractures) without any fracture line
- Grade 2: Symptomatic bone oedema (microfractures) without any fracture line
- Grade 3: Bone oedema with an undisplaced macrofracture
- Grade 4: A displaced macrofracture (see Conor McGregor’s leg)
In general, lower grade stress injuries tend to heal faster. Bone oedema cannot be seen on an X-ray, CT scan or MRI, so staging of early injuries needs an MRI or a bone scan. Bone scans are excellent diagnostic tools but expose patients to a moderate amount of radiation. Given MRI indentifies stress injuries just as well as a bone scan, an MRI is the investigation of choice as there is no radiation with an MRI.
Stress Fracture Treatment
The primary treatment is to stop exposing your stress injury to force that triggers pain. If you still have pain with walking, then your bone is struggling to cope with walking and you will need to stay off your feet or go on crutches.
A walking boot is often prescribed but this does not necessarily reduce the force going through your bones. However, it will probably slow you down so the total force your bone is exposed to throughout a day will be less. There are some foot stress injuries that will respond well to a boot if the boot has a forefoot rocker, this allows you to offload the forefoot.
It is essential that any stress fracture is assessed by a health professional and preferably by a doctor. Certain stress fractures need specific treatment as they are at high risk of not healing. These high risk stress fractures include:
- 5th metatarsal
- Navicular (foot)
- Anterior tibial
- Neck of femur
- Spinal (pars)
Return to sports programs are highly variable and need to be individualised. Any return to sport program should be supervised by a health professional with experience in stress fracture management.
Once you have been able to walk painfree for over a week, you may be able to slowly return to some weight-bearing activity. There is no exact science to progressing your exercise but the underlying principle is that any activity should cause NO pain. Most people can return to alternate day training at approximately 30-50% of their pre-injury training volume once they have been walkking painfree for over a week. This training volume can be slowly increased week by week until a full return to sport is achieved. Any pain experienced normally means a period of rest before restarting at a slightly lower painfree exercise volume again.
Maintaining aerobic fitness is possible during this period by substituting non-impact training for your impact training, this is known as cross-training. Good cross-training options include deep water running, swimming, eliptical trainer, cycling and sometime seated or lying resistance training.
Restoration of normal strength and correction where possible of abnormal biomechanics will form part of your complete treatment pathway. This is where a good relationship between your treating doctor and physiotherapist is essential.
Complete treatment of a stress fracture needs assessment by a doctor that specialises in musculoskeletal injuries such as a Sports & Exercise Medicine Physician. They will assess all of the previous risk factors mentioned and try and correct these. This is an often overlooked but essential part of treatment and the reason why many athletes have recurrent injuries.
There are some additional treatments that can aid recovery as well. There is some preliminary science suggesting supplementing with Vitamin D and calcium during the period of bone healing can help recovery even in the absence of any deficiencies.
Some stress fractures benefit from a pneumatic air brace such as tibial stress fractures. Fractures that have delayed healing may benefit from a bone stimulator treatment known as Low-Intensity Pulsed UltraSound (or LIPUS). There are also some medications that are being researched into their effect on speeding up bone stress injury healing including teriparatide and bisphosphonates.
How Do You Prevent Stress Fractures
As with all injuries, prevention is better than cure. The prevention of these injuries comes back to our previous risk factors. To minimise your chance of a new or recurrent stress injury, my recommendation would be:
- Do not change your total impact-related training volume by more than 10% per week.
- Periodise your training to allow your body time to adapt to your training loads. This can be supervised by a health professional or strength and conditioning coach.
- When changing surfaces, footwear, technique or going through a period of growth; temporarily reduce your training volumes and slowly phase in new changes.
- Maintain an energy intake that meets your energy requirements. Warning signs include a lack of performance improvement despite training, alterations in your menstrual cycle and weight loss.
- Meet your Vitamin D and calcium requirements. This is especially important in the pubertal years when most bone mineral is deposited. 90% of bone mass is accrued before you turn 18 years old.
At Newcastle Sports Medicine we strive to be the best we can so we can help patients with the most up to date treatment available and keep you active and healthy.
If you would like to see any of our health professionals you can book appointments online here with our physios or call (02) 4910 0805 to make an appointment with our team of Sports Medicine Doctors and Sports Physios.