Bone stress injuries (BSI) are typically overuse injuries associated with repetitive loading of bone by vigorous weight-bearing activity (such as running/ jogging/ marching) and inadequate recovery.
Dr Rick Seah, Consultant in Sport & Exercise Medicine continues his report on an introduction to bone stress injuries and looks at the clinical and radiological aspects.
History
The clinical history is important in making the diagnosis of a bone stress injury (BSI). Considerations include type of impact sport or physical activity (e.g. running).
Ask about any changes to the following: Training intensity, duration, and frequency. Training surface is important.
Ask about recovery periods (or the lack of) as even high-level athletes may neglect this.
Ask about the pain quality- is it sharp or dull in nature? Is there crescendo pain (whereby pain builds up during a training session and an athlete has to stop)?Consider localised bone pain when hopping or running in those with lower limb injuries.
For mild BSI, pain generally occurs towards the end of the activity and resolves quickly. In moderate to severe BSI, pain comes on sooner or at rest. It may be more severe in intensity, pain lingers for longer and there may also be night pain.
Clinical examination
Look out for focal tenderness and swelling on palpation. Percussion may reproduce the pain. Single leg hop may produce localised pain in those with lower limb BSI.
Tests that have been described to screen for BSI include the tuning fork test and fulcrum test.
Imaging
There are various imaging modalities for diagnosing BSI. Sometimes they are used in combination to diagnose and manage a BSI.
Plain films (x-rays) are a common first-line investigation. They may show periosteal reaction but it is worth noting that in the first 2-4wks of a stress fracture, they are often normal (which can be falsely reassuring).
After 1 month, there is usually evidence of periosteal callus & cortical thickening.
Appearances differ- fracture lines look lucent in cortical (compact or dense) bone whereas they appear sclerotic in trabecular (cancellous or spongy) bone (e.g. calcaneus, femoral neck).
Triple-phase isotope bone scan (also known as bone scintigraphy) was the gold standard historically for detecting BSI. This was due to its high sensitivity, typically in the region of 97-99% in many studies. This nuclear medicine imaging technique utilises radioactive tracers called radionuclides that are injected and emit gamma radiation.
Apart from the radiation considerations, one of the other disadvantages of this technique is that it is time-consuming, often requiring several hours.
The first phase of this investigation is known as the ‘dynamic’ phase, and rapid-sequence dynamic images are obtained for approximately a minute immediately after the radionuclide injection is given.
The second phase is known as the ‘blood pooling’ phase. The third phase is the ‘delayed’ phase and consists of static planar images obtained 2-3 hours later.
The term ‘hot spot’ is used to describe a focal area of intense radionuclide uptake. In acute stress fractures, all three phases will typically show ‘hot spots’. In chronic stress fractures, only the ‘delayed’ phase static planar images are positive.
In addition to stress fractures, ‘hot spots’ may also represent other abnormalities- e.g. osteomyelitis or tumours. From a fracture healing perspective, it is worth noting thatisotope bone scans may remain positive for upwards of a year and are therefore not useful to monitor recovery and healing.
Magnetic resonance imaging (MRI) is now the preferred imaging modality for mostclinicians when considering BSI. There are many advantages. It demonstrates very high sensitivity and specificity for BSI. It is also helpful in the rare situations whenisotope bone scans are negative but a stress fracture is still strongly suspected.
MRI offers a more accurate correlation to the clinical picture- i.e. differentiating a BSIfrom a bone infection or tumour.
There is excellent spatial resolution, particularly on the high-resolution scanners. It is able to detect bone strains and minor stress reactions before they evolve to become established stress fractures, therefore aiding with early diagnosis.
MRI scans do not involve any radiation, which makes them more acceptable topatients; it is also a quicker investigation than an isotope bone scan.
It can be a useful tool to monitor fracture healing and resolution of bone oedema.
Computed tomography (CT) is an imaging technique that uses x-rays and computer technology to acquire and create detailed three-dimensional images of body structures. In the musculoskeletal context, it is excellent for visualising bony defects and any irregularity to the bony cortex.
There are radiation considerations and there are times when a ‘limited scan range CT’- investigating the area of interest but substantially reducing the radiation exposure to radiosensitive organs- is indicated and more appropriate.
The sensitivity of CT scans is higher than that of X-rays for looking at BSI. However,when compared with MRI or isotope bone scanning, the sensitivity of CT is low, with a higher rate of false negatives.
As mentioned, there are times where it is useful to combine imaging modalities. In the context of BSI, a positive MRI scan combined with a negative CT scan suggests a stress response, not a true stress fracture.
SPECT-CT is a relatively novel imaging modality and combines 2 separate imaging components- a single-photon emission computed tomography (SPECT) scan and a CT scan. Images from both are combined and provide more accurate information regarding anatomy and function of the scanned area.
Once again, there are radiation considerations and the test itself can take 3-4 hours. However, this can be an extremely useful 2nd line or 3rd line investigation for complex BSI cases where specific queries arise and require further detailed investigation.
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