Dr John Rogers MRCGP FFSEM(UK) – – Consultant in Sport & Exercise Medicine

Visiting Professor In SEM, Manchester Metropolitan University

Bone stress injuries and stress fractures are a common injury in track and distance runners and can cause significant loss of training time, often at crucial stages of the season. Stress fractures are defined as a partial or complete bone fracture that results from repeated application of a stress lower than the stress required in order to fracture the bone in a single loading. The annual incidence of stress fractures in track and field athletes is estimated to be 3.9 per 1000 hours of training with a prevalence of 76% and 10 – 20% of consultations in sports medicine are for stress fractures. It is important to diagnose stress fractures early so that they can be managed appropriately. If they are managed too conservatively this will result in unnecessary loss of training time and equally if higher risk stress fracture sites are not managed appropriately then they will not heal properly and it can take much longer for the athlete to return to running.

Stress fractures occur as a result of an overuse injury to bone. Sometimes they are due to fatigue within normal bone which is unable to adapt and repair quickly enough to cope with the repetitive biomechanical stresses and forces imposed through regular running. This can happen when runners build up their volume and intensity of training too quickly and is often seen when athletes return to training after a break.

The other reason why stress fractures occur is due to bone insufficiency or ‘weak bones’. In this situation, an athlete may have gradually built up their training over a 2-3 month period to a reasonable volume e.g. 40-50 miles per week. Due to underlying metabolic bone disease with low bone mineral density or osteoporosis, the structurally abnormal bone cannot adapt and repair itself to withstand the repetitive stresses and strains involved in normal training loads and this results in a stress fracture.

The commonest sites for stress fractures in runners are the tibial shaft (the shin), the navicular and the metatarsal bones in the foot. Other less common sites in runners include the femur (shaft and neck), sacrum, fibula, patella, talus, sesamoid, calcaneus, cuboid and the lower back.

Diagnosis

A stress fracture should be considered in athletes with progressively worsening localised bone pain which comes on with running. It is important to look for risk factors for bone injury as described below. As things progress, the pain starts to come on earlier within training sessions and runs and the pain can persist after runs and during day to day activities such as walking. Sometimes pain in bed at night is a feature but this is not that common. It is important to know what volume of training the athlete is doing and how quickly this has been built up. There is often a sudden increase in volume or intensity of training with lack of rest days. The common risk factors should be asked about and examined for. A dietary history is important in male and female athletes and a menstrual history is very important in female athletes. Occasionally, there may be a family history of osteoporosis.

Clinical examination of athletes with a lower limb or pelvic stress fracture usually reveals localised bony pain on hopping and this is a useful screening test. There is often focal bony tenderness at a specific site. Pelvic, neck of femur and lower back stress fractures can be a bit more difficult to pick up on clinical examination but can be confirmed through imaging or speaking to pelvic therapy specialists. Early diagnosis through imaging helps to grade the bone stress injury, initiate appropriate management and minimise the time to return to running.

Investigations

Magnetic resonance imaging (MRI) is the most sensitive and specific imaging modality for diagnosing stress fractures. It is important that the correct sequences are used to look for bone marrow oedema (STIR weighted sequence). MRI scans are also useful for excluding other soft tissue causes of localised pain. The other advantage of MRI is that it does not expose the patient to ionising radiation. There is a huge variation in the cost of paying privately for these scans and current rates vary from £195 to £500+. In most parts of the UK, it is difficult to get an MRI scan done quickly in the NHS for sports medicine related problems.

Plain x-rays (radiographs) are usually not that helpful although a discrete fracture line and/or reaction to the lining of the bone can sometimes be seen.

Radioisotope bone scans are sensitive for stress fractures but not specific i.e. they may also be positive in cases of infection, joint inflammation or cancer.

Computerised Tomography (CT) scans may be useful to establish the extent of a stress fracture and to plan surgery e.g. navicular stress fractures. A positive MRI scan but negative CT scan indicates a stress response which has a better prognosis.

Ultrasound Imaging may be useful in the diagnosis of metatarsal stress fractures where it can show a break in the cortex (lining) of the bone.

CT SPECT is a combination of CT and a nuclear imaging test where the images are superimposed on each other. It can be useful in some cases when the MRI scan is negative or inconclusive but the index of suspicion for stress fracture remains high.

DEXA scanning measures bone mineral density (BMD) and is an important investigation for screening athletes at risk of osteoporosis e.g. female athlete triad, stress fractures with a low volume of training, post menopausal runners with stress fracture, family history of osteoporosis. In athletes identified with low BMD (Z score < -1.0) and those with features of female athlete triad, DEXA scans should be repeated annually to see if the BMD is improving.

Blood testing for vitamin D status is important as if low this can delay healing and will increase the risk of further bone stress injuries. Vitamin K deficiency can be a risk factor for stress fractures but this is an expensive test and is not routinely tested for at first presentation. Other blood tests used to investigate amenorrhoea (no periods for >90 days) are thyroid function tests, prolactin, FSH, LH and oestradiol levels.

How are bone stress injuries graded?

Table 1⁴

Grades 1 to 3 are called stress reactions and grade 4 is a stress fracture. This distinction is important for management as stress reactions take less time to heal and the athlete can return to running several weeks sooner.

Who is at risk?

Table 2³

Female Athlete Triad

Women with the ‘Female Athlete triad’ are especially at risk of bone stress injury. This condition affects many female endurance runners with low body weight/BMI. It consists of low energy availability with or without disordered eating, amenorrhoea (loss of regular menstruation/ no periods for >90 days) and low bone mineral density / osteoporosis. Athletes with disordered eating or conditions such as anorexia or bulimia need specialist medical input. For more information on this important condition have a look at this useful website: www.femaleathletetriad.org

Relative Energy Deficiency in Sport (RED-S)⁷

The RED-S concept has been adapted from a previously identified syndrome, the female athlete triad, which affects active women with low-energy availability, menstrual dysfunction and low bone mineral density. Emerging data suggest there may be a parallel syndrome in undernourished male athletes with resulting hypogonadotropic hypogonadism and impairment of bone health. RED-S is a comprehensive model depicting a low-energy status in physically active women or men. (Figure 6)

Management

Stress fractures with a low risk of not healing properly can be managed conservatively in primary care (GP and a local physio) by stopping running. Table 2 outlines stress fractures at low and high risk of not healing properly (non union). The more serious the stress fracture the longer the athlete must rest the limb and depending on the pain they are experiencing, visit a PT service such as this LifeMotion Physical Therapy clinic or others. The general principle of managing low risk stress fractures is to offload from running for 6 to 8 weeks and then to slowly increase the volume of steady running. During this first 6 to 8 weeks athletes are usually safe to cross train to maintain cardio-respiratory fitness. Commonly used cross training modalities include:

• Deep water running / aqua jogging (Figure 7)
• Cycling
• Swimming
• Rowing
• StairMaster
• Cross-trainer (elliptical)
• Nordic Ski

The rate of resumption of running will depend on the athlete and the symptoms but generally most runners will build back up to full training over the following 6 weeks (12 – 14 weeks from initial offload).

Table 3 Stress fractures at low and high risk of non-union³

With stress reactions(as opposed to fractures) at low risk sites, the offload from running can be cut to 4 weeks followed by a gradual return to full training over the following 4-6 weeks. These time frames are a guide only and can vary significantly depending on any ongoing symptoms or lack thereof, the site and grade of bone stress injury, the athlete’s risk factors, personal circumstances / short term goals and availability of other rehabilitation facilities such as Alter G (figure 8) and underwater treadmills.

Pain can be managed by the use of simple analgesia such as paracetamol or cocodomol. Anti-inflammatory medication should be avoided as they can delay bone healing⁵. Sometimes crutches are needed for the first 1-2 weeks. Pneumatic bracing with an aircast boot, has been shown to reduce time to return to full activity in some lower limb stress fractures e.g. tibia⁶.

Modifiable risk factors need to be dealt with early to prevent recurrence e.g. vitamin D and calcium supplementation, optimise energy availability in female athlete triad, address any biomechanical factors and consider the need for orthotic prescription, appropriate strength and conditioning exercises are very important.

Stress fractures at high risk of non-union require specialist input with a sports physician and/or an orthopaedic surgeon.

Other treatment options sometimes used in elite athletes to expedite return in time for major competitions include the use of Bisphosphonate medication, Parathyroid Hormone, Strontium, Calcitonin, Exogen (pulsed ultrasound), Extracorporeal Shockwave Therapy (ESWT) and Hyperbaric Oxygen Therapy (HBOT). It should be stressed that the evidence base behind these interventions is still growing. They are expensive and some carry a significant risk of side effects. There is no substitute for offloading from running and allowing time for the body to heal itself naturally.

Prevention

Prevention is always better than waiting until the injury or illness has occurred. Modifiable risk factors should be screened for and addressed. The commonest risk factors for stress fractures seen in UK based runners are vitamin D deficiency, inadequate calcium intake in the diet, low energy availability due to inadequate calorie intake to match calorie expenditure through training, low bone mineral density in female athletes with the female athlete triad, inadequate muscle strength/conditioning and a rapid progression of training volume and / or intensity without adequate time for recovery to allow bone to adapt.

Consider the following:

• Speak to an experienced coach about your training schedule. This should involve a gradual progression of running volume and intensity over several months and years with annual periodisation of training. Recovery days need to be built into the weekly running schedule to allow bone time to adapt to the loads placed on it. This is especially important in younger athletes (<20) with an immature skeleton.
• Ask your GP to check a vitamin D level twice a year in October/November and March/April time and if needed, taking high dose vitamin D3 supplementation if the level is less than 75nmol/L.
• Take a daily vitamin D supplement e.g. 1000units Vitamin D3 daily
• Aim to get 1200mg of calcium / day through your diet e.g. milk and other dairy products or through supplementation.
• Discuss your daily calorie requirement and how to achieve this with a sports nutritionist. Aim for a Body Mass Index >19 kg/m².
• For female athletes who don’t have regular periods, you should ask your GP to arrange a DEXA scan to look for evidence of osteoporosis. This investigation is also important for male and female athletes who have had more than 1 stress fracture or who have other risk factors for osteoporosis. Where low bone density/osteoporosis is identified, you should be advised on management by your doctor.
• In athletes with the female athlete triad, ideally seek out a consultation with a sports medicine doctor. There are now well over 100 specialists in Sport & Exercise Medicine working across the UK. In athletes with a possible eating disorder seek medical input early.
• An appropriate weekly strength and conditioning programme to address core stability, gluteal control, quadriceps, hamstrings and calf muscle strength and endurance. This requires more than a weekly circuit training session. Multidirectional hopping (for as little as 2-3 mins daily) and appropriate loading for the lumbar spine and wrists is also important in preventing stress fractures and in optimising bone mineral density and bone architecture at these sites.

References

• Bennell KL et al. The incidence and distribution of stress fractures in competitive track and field athletes. A 12 month prospective study. AJSM 1996;24:211-7
• Kaeding CC et al. Management and return to play of stress fractures. CJSM 2005; 15:442-7
• Pegrum J et al. Diagnosis and management of bone stress injuries of the lower limb in athletes. BMJ 2012; 344:e2511
• Arendt EA et al. The use of MRI in the assessment and clinical management of stress reactions of bone in high performance athletes. Clin Sports Med 1997;16:291-306
• Wheeler P, Batt M. Do Non Steroidal Anti-Inflammatory Drugs adversely affect stress fracture healing? BJSM 2005;39:65-69
• Swenson et al. The effect of a pneumatic leg brace on return to play in athletes with tibial stress fractures. AJSM 1997 May-Jun;25(3):322-8.
• Mountjoy M, Sundgot-Borgen J, Burke L, et al The IOC consensus statement: beyond the Female Athlete Triad-Relative Energy Deficiency in Sport (RED-S) Br J Sports Med 2014;48:491-497.