Bone Stress Injuries: Stress Fractures & Stress Reactions

A bone stress injury (BSI) is a stress fracture or a stress reaction. They are very common injuries in sports which involve repetitive impacts like running. For example more than one third of cross country or long-distance runners including triathletes experience BSI’s, and the 1 year incidence of BSI in track and field athletes is around 20% (Nattiv et al 2013).

How are BSI’s caused? Usually the cause is repetitive impact loading (eg running or jumping). For some athletes lowered bone density predisposes them to bone injury (in which case their stress fracture may be termed an “insufficiency fracture” to indicate that abnormal bone failed under normal loads).

Bone stress injuries arise from too much load too soon with too little recovery, usually in enthusiastic athletes or military recruits. Bone stress injury (BSI) is really a spectrum of injuries which begin as an asymptomatic stress reaction, which is a localised area of increased bone stress that shows up on a bone scan (a “hot spot” such as in the bone scan image below). Initially we can see evidence of increased bone turnover on the scan before it is severe enough to become painful, but with more loading the bone becomes painful (symptomatic stress reaction), and eventually may form a small hairline fracture (crack or break) without displacement that is known as a stress fracture.

Bone scan showing a femoral bone stress injury

What bones are most susceptible to a BSI? In running and jumping sports, by far the most common bone is the tibia (shin bone), but the small bones in the foot, fibula, femur, pelvis and lower back may also be affected.

Clinically how we manage BSI is dependent on the location, severity and consequent risk of complications (Hoenig et al 2022). To identify BSI which are more challenging to manage, we identify high risk stress fractures early in the diagnostic process. High risk stress fractures tend to heal poorly with a high risk of complications, some of which can result in significant long term problems and can lead to surgery. High risk stress fractures are typically located on the tension side of bones, or bones with an inherently poor blood supply which includes the anterior tibial cortex, patella, femoral neck, some foot bones (talus, navicular, 5th metatarsal, and sesamoid bones under the great toe) and of course the spine (including pars fractures – for a more detailed look at this injury read our blog HERE).

Lumbar pars stress fracture: common in adolescent athletes

What are some of the common causes or contributing factors to a BSI? Like most chronic pain problems, the cause is usually not a single thing but multifactorial. We categorise the causes as being either extrinsic or intrinsic (intrinsic meaning a characteristic of the individual athlete and their body that may predispose towards injury).

Intrinsic risk factors:

• Bone quality (eg low bone density)

• Age

• Cardiovascular health

• Anatomical alignment

• Muscle strength & imbalance

• Hormonal abnormalities esp. women (see our blog HERE on the Female Athlete Triad)

• Fatigue

• Gait / running technique

• Posture

• Insufficient neuromuscular function

Extrinsic risk factors:

• Training errors: frequency of loading, total load (too much), ramp rate (increasing load too quickly), inadequate recovery and adaptation time (lacking rest for bone to adapt to load)

• Training equipment (footwear, surface)

• Diet including adequate energy intake: a major risk factor esp. for female athletes

To diagnose a BSI a full clinical examination including thorough history and examination is required. Imaging is usually arranged to confirm a diagnosis depending on the location and severity of the injury, and may entail more than one investigation such as MRI, CT scan or bone scan. Plain Xrays and ultrasound are rarely useful as stand-alone tests. Many people are surprised to find that they have a stress fracture as often the pain isn’t as bad as they might have been expecting from a bone injury, often describing their injury as feeling more like a “sprain”.

Treatment for a bone injury is to unload the bone – this means rest and quite possibly a brace or crutches. It’s really not that different to a broken arm – if you fail to rest the problem gets worse and may lead to a far more serious situation like complete fracture, surgery or long term spinal pain.

Whilst some time off may feel like the end of the world to some athletes and teenagers, a properly managed BSI in a low risk location usually recovers fully and causes no long term issues. How long? Most low risk BSI’s of the lower limb require a 12 week rest from running. High risk stress fractures usually take longer and the time is more specific to the exact injury and its severity: in other words the longer you take to come in for assessment and the worse you let the injury get, the more time off you’ll require. As an example, there is no research showing healing of a lumbar pars fracture in under 12 weeks, and those who rested and wore a brace for 12 weeks were 16.4 times more likely to make a full recovery (Greieron et al 2015).

Whilst resting to unload the bone, a mainstay of treatment is to identify and manage all of the modifiable risk factors present. This might include improving muscle strength and balance, flexibility, and once resuming impact loading improving running technique along with learning how to track, measure and manage training loads and recovery to prevent further recurrence. For female athletes, evaluating the regularity of the menstrual cycle and total nutrient intake (to prevent a condition known as the female athlete triad which leads to osteoporosis and BSI) is crucial (for more information see our blog HERE). For those unfamiliar with the female athlete triad, this condition involves three things: inadequate dietary intake, leading to menstrual irregularities (with female hormones being crucial for bone health) resulting in lower bone density and BSI (“insufficiency fractures”). Inadequate energy intake can also effect male athletes and their risk of BSI.

Once the bones have healed both clinically and radiologically (which may require further imaging to verify) then a careful and gradual return to impact loading can begin, assuming the athlete has actually addressed the underlying risk factors mentioned above.

References:

Greieron et al 2015: Stress Fractures of the Lumbar Spine. In Millar & Keading “Stress fractures in athletes”. Springer London.

Hoenig T et al (2022): Bone stress injuries. Nature Reviews Disease Primers 8:26.

Dobrindt O et al (2012): Estimation of return-to-sports-time for athletes with stress fracture – an approach combining risk level of fracture site with severity based on imaging. BMC musculoskeletal dis 13:139.

Nattiv et al (2013): Correlation of MRI grading of bone stress injuries with clinical risk factors and return to play: a 5-year prospective study in collegiate track and field athletes. Am J Sports Med 41:1930.