Medical imaging: To see or not to see

Ryan Shulman gives a guided tour of medical imaging techniques and urges caution in using them

Lower back injuries in athletes require complete musculoskeletal assessment and management. As high quality radiographic evaluation becomes more accessible, sport practitioners should attempt to stay abreast of the indications for the use of medical imaging tools, and how to apply findings to the holistic care of their patients.

This article arises from a debate between myself and a physiotherapist friend of mine, after he requested a CT scan for a client , which I argued was inappropriate. He wanted to evaluate the state of his client’s lumbar discs and whether there were any obvious causes of instability. An X-ray had not been performed and the patient was not a professional athlete. They were still in the acute phase of the injury and it was hard to elicit any localised signs of disc pathology or instability.

Below, I give a brief overview of the main medical imaging techniques available to help sports therapists investigate athletic injuries. Knowledge of the pros and cons of each tech nique should help you to make the right deci sion for your clients about when to order up scans and when to rely on clinical investiga- tion and your own therapeutic experience. To help illustrate the specific pros and cons of different modalities, I am using the example of lower back pain, and in particular spondy lolysis and disc injury.

Low back pain

It is likely that the therapist will assess acute low back pain in an athlete rather differently from how they would in a non-sporting member of the general public. Sportsmen and women are involved in activities that predis pose them to a different profile of injuries. Also, sportspeople have a training and compe tition schedule that becomes the focus of their rehabilitation. This will influence the speed and level of investigation, as well as the inten sity of treatment of their injury.

The spine is a multi-segmented bony bar connected by an assortment of static and dynamic stabilisers. Intervertebral discs, liga ments and joint capsules constitute the non bony static stabilisers of the spine. Paraspinal muscles, deep abdominal muscles, quadratus lumborum and latissimus dorsi muscles and pelvic stabilisers provide myofascial dynamic stability of the lumbar region.

It is understandable that sports therapists will concentrate on the musculoskeletal origins of symptoms. However, from a holistic and legal standpoint, you should always have regard to the less common medical causes of lumbar pain. These include:

* inflammatory or rheumatological disorders

* joint/disc/vertebral infections

* malignancy

* genito-urinary, gynaecological or gastroin testinal disorders.

A directed neurological assessment should be performed for completeness. The more common musculoskeletal causes of lower back pain the in athlete include:

* injuries to the intervertebral disc or facet joint

* spondylolysis (stress fracture to pars inter articularis/pars defect), spondylolisthesis

* sacroiliac joint injury

* muscle/tendon injury.

The role of radiology

Radiology is not a replacement for a complete assessment. In fact clinical correlation is essen tial for the appropriate use of imaging. In 1990 Boden et al(1)found that 20% of people without back pain under the age of 60 had magnetic resonance imaging (MRI) evidence of disc herniation and 37% of over-60s had confirmed disc herniations. It is important to remember that not everything you read on a radiologist’s report is relevant to the cause of your patient’s pain.

A simple classification system divides the origins of acute lumber pain into two causes:

* acute traumatic

* functional repetitive.

Direct trauma to any of the anatomical constituents of the spine can cause pain. Contusions, sprains and fractures with asso ciated bruising and inflammation produce immediate and generally local signs and symptoms. Dysfunction of the dynamic stabilisers, or undertaking some activity that exceeds the protective capacity of the spine’s stabilisers, can result in failure of one or more spinal components.

Sometimes repetitive strain can trigger an acute onset of pain, despite minimal pain leading up to the incident. For example, a sportsperson performing repeated loaded movements at the end of their range of lumbar flexion will continually load lumbar discs to the point where they could acutely rupture or protrude, causing an acute nerve root compression.

Spondylolysis (vertebral stress fracture) is more common in younger male athletes and those involved in sports such as diving, weight-lifting, wrestling, cricket (fast bowlers) and gymnastics, where repetitive loading in hyperflexion and particularly hyperexten sion of the spine are common.

Plain radiographs (X-ray)

Plain X-rays are typically the first-line inves- tigation for lumbar pain. However, as tech- nology improves, X-ray will probably be used far less. The advantages of X-rays are that they are very quick, simple and non-invasive. Different views are normally taken: ante- rior/posterior, lateral and sometimes poste- rior oblique (in the evaluation of pars defects). The main limitation of this modality is that it can only provide information on bony structures, so it tends to be used mainly for evaluating simple fractures, soft-tissue calci fication, joint malalignments and old injuries.

Evidence of a stress response in bone is difficult to detect early on X-ray. True radi ographic findings, such as changes to the periosteal lining, or the density of the bone surrounding a fracture site, typically take weeks to develop. Thus the accuracy of plain films in detecting spondylolysis will depend on how long the symptoms have been present and the extent of bony injury. The classical posterior oblique X-ray of a pars defect is described as ‘the Scottie dog with its collar’ (see Figure 1, below).

One study(2)found that about 15% of elite male and female athletes with symptomatic lumbar pain had evidence of spondylolysis on plain film, and that half of those X-rays revealed an obvious spondylolisthesis.

X-rays can be used to make inferences about soft tissue structures. For example, intervertebral spaces can tell us something about the state of intervertebral discs, with decreased space indicating possible disc protrusion or rupture. However, there is no direct visualisation of the disc. Similarly, bony malalignment could indicate some disrup tion to a ligament, such as laxity or tear. Occasionally bowel gas can obscure the view on plain film, particularly in the sacral region, further complicating the interpretation.

Radiologists may still find it useful to have an X-ray image for reference prior to more detailed imaging.

Bone scintigraphy

Bone scans require the patient to be injected with a radioactive isotope (typically techni tium99), which is taken up in the areas of highest activity within the bone. A scan that can detect radioactivity maps the relevant areas of skeleton. Bone scans will highlight areas with higher than normal bone turnover or bone cell activity. Bone scans are more invasive (injections of radio-isotope) than plain films, CT or MRI, but they can give clues about underlying changes that may direct the practitioner to other forms of imaging.

The clinician will need to correlate their interpretation of bone scans closely to their clinical findings, as there are a variety of expla nations for a ‘positive’ scan. These include infection in and around the bone, acute trau matic injury, cancerous lesions, and normal degenerative processes. A bone scan is a sensitive test in that it can identify many pathological processes, but it isn’t very specific in helping to identify what type of process is evolving. Equally, a normal bone scan can almost rule out a stress fracture.

Computed tomography

CT is a technique that utilises radiation to take multiple slice images through the length of the body in a single plane. These images can then be reconstructed into multiple planes (eg, cross-sectional, longitudinal) and can even formulate a three-dimensional reconstruction. The advantages of CT over X-ray are that it eliminates the superimpo sition of structures over the area of interest, gives much more detailed images and enables tiny variations in tissue density to be identified.

CT is historically superior to MRI in showing up bony detail such as fine fracture lines, bone density changes and definition of bony anatomical anomalies (eg, joint malalignments or areas of calcification). However, as MRI technology improves, newer machines are giving images that make bony changes more obvious.

CT is highly sensitive for detecting the subtle fracture lines evident in true pars defects, but it cannot always detect the precursor signs. CT also allows guidance of injected local anaesthetics and steroids when treating lumbar joint/soft tissue injury. The main disadvantage of CT is its radiation dose (see Table 1, above right).

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Magnetic resonance imaging

Unlike CT, MRI does not use X-rays (ionising radiation), but radio frequency signals to obtain its images. When a patient is placed inside an MRI’s magnet, the protons in the body become aligned. Radiofrequency pulses generated by the machine alter this align ment. Once the pulses cease, the protons realign and send out signals that are captured and mapped by the MRI machine, creating an image of the body.

MRI is excellent for viewing soft tissues such as lumbar discs, ligaments, muscles and cartilage. It can detect evidence of bone death, bone inflammation, infection and soft tissue tumours. When diagnosing bony stress injury, MRI has been reported as being superior at assessing early changes such as oedema (or inflammatory fluid) in the area of the pars interarticularis. However, it is not as sensitive for diagnosing fine stress fractures. Imaging of the intervertebral discs and their relationship to the nerve root gives highly accurate information about disc protrusions and associated symptoms.

MRI is now used to provide information on the degree of damage to muscles and liga ments, with more and more data correlating MRI findings with prognostic information. This modality is typically the most expensive imaging modality. And remember, having this much detail can give you information that may be a red herring in the diagnosis of your patient’s symptoms.

Ultrasound

Since the work pioneered by Jull, Richardson, and Hides(3)into the role of deep stabilising muscles to maintain and improve lumbar spine stability, ultrasound probably deserves mention. Ultrasound has been used both for diagnosis and treatment. The therapist can use their evaluation of the cross-sectional areas and activation of the multifidus and transversus abdominis muscles to assess the need for muscle biofeedback training, as these stability muscles show evidence of wasting after acute injury.

Ultrasound is a relatively inexpensive, safe and non-invasive investigation. It is generally available only in larger physio therapy practices and some specialised sports clinics or others specialising in the treatment of lower back pain in the general population. If you are intending to use ultra sound in the assessment of lumbar stability/muscle control, be aware that it is a real-time investigation that usually requires an operator with some training in this area. Check before you refer.

Radiation exposure

You should always consider the matter of radiation exposure when you are deciding on imaging to help investigate an athlete’s injury. Specifically, ask yourself whether and how the results are likely to alter your approach to management of the injury. Some sources claim there is no evidence that radiation exposure at the doses given in periodic diagnostic imaging is harmful(4). But you need to be sensitive to the effect of repeated accumulating doses. The US Food and Drug Administration estimates that exposure to an additional 1,000 mrem(5)of ionising radiation gives a 1 in 2,000 life- time risk of fatal cancer(6). Be especially cautious with younger patients, as they are more sensitive to radiation exposure and have a longer life expectancy, which means a longer time frame for radiation damage to express itself.

As a guide, humans (in the US) are exposed to about 300 mrem annually from natural background radiation. Table 1 (above)(4)lists radiation doses for lumbar spine imaging, using the various different modalities.

Conclusion

There are several factors that the therapist should take into account when deciding whether to order up images for their injured athlete. These include:

* age of the patient

* cost

* radiation dose

* how the findings will alter your manage ment plan(7).

A professional athlete with upcoming competitions may well require imaging to provide extra information about prognosis and alteration in management and training. On the other hand an amateur athlete will be able to rest from competition and focus on a conservative management plan. As a general rule, X-rays should be used as first-line investigations. Now that MRI technology is improving it is generally believed to offer the most comprehensive evaluation of the lumbar spine(2).

Clinicians are moving towards using MRI before CT(8), with its ability to pick up early stress reactions in the pars, its excellent soft tissue assessment and its lack of ionising radiation. Only when MRI fails to provide the required information is a CT requested.

References

1.Boden, SD et al (1990) ‘Abnormal magnetic-resonance scans of the lumbar spine in asymptomatic subjects. A prospective investigation’. J Bone Joint Surg Am.Mar;72(3):403-8.

2.Rossi, F and Dragoni, S (2001) ‘The prevalence of spondylolysis and spondylolisthesis in symptomatic elite athletes: radiographic findings’. Radiography 7, 37-42.

3.Hides, JA, Richardson, CA, Jull, GA (1996) ‘Multifidus muscle recovery is not automatic after resolution of acute, first-episode low back pain’. Spine.Dec 1;21(23):2763-9.

4.http://hps.org/hpspublications/ articles/dosesfrommedicalradiation.html (accessed 31/1/07).

5.Millirem, a unit used to measure the effect of radiation on the human body

6.www.fda.gov/cdrh/ct/risks.html (accessed 31/1/2007).

7.Orchard, JW et al (2005) ‘The use of diagnostic imaging in sports medicine’. Medical Journal of Australia183(9) 482- 486

8.Hollenberg, GM et al (2003) ‘Imaging of the spine in sports medicine’. Current Sports Medicine Reports, 2:33-40