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SPORTS MEDICINE RADIOLOGY
that, in cases of femoral neck and scaphoid fractures, MRI is the most appropriate investigation, having the highest sensitivity and specificity of all imaging modalities (5–7). It has an added advantage because it facilitates assessment of associated soft-tissue disruption (6,7). In sports medicine (apart from traumatic fractures) imaging is used to diagnose stress fractures, including pars interarticularis fractures of the spine. Stress fractures arise from repetitive abnormal loading of normal bone. They commonly occur in the calcaneum, the distal tibia, spine, pelvis and femoral neck (8–10). Initial evaluation consists of plain radiographs, but radiographs have notoriously low sensitivity. Furthermore, early stress fractures cannot even be visualised on plain radiographs – it takes between 2 and 12 weeks before they can be seen (9,11). Taking two views and obtaining oblique and magnified views increase the sensitivity (8) but MRI or bone scintigraphy both have higher sensitivity. Figure 2 shows the different results obtained from an MRI scan and a plain radiograph.
Bone scintigraphy and SPECT Bone scintigraphy has long been considered the test of choice, offering a high degree of sensitivity, but it is non- specific with a relatively wide differential (9). It will detect acute stress fractures by way of the increased activity of osteoblast cellss. SPECT provides additional anatomical information about the underlying bone, but as we saw in Part I (Table 1)[ref] the radiation dose from SPECT is particularly high (11).
STRESS FRACTURES As described above, these fractures arise from repetitive abnormal loading of normal bone and are evaluated initially by plain radiographs. MRI has the advantage of being both sensitive and specific to stress fractures, and (unlike SPECT) it carries no risk of radiation (3,11). Stress reaction in the bone presents with oedema of the periosteum and bone marrow (10). Such a “stress reaction” is an early indicator for an impending stress fracture. A true stress fracture is diagnosed when there is both bone marrow oedema and a fracture line through the bone. This differentiation between a stress reaction and a stress fracture (Box 2) has predictive value for the duration of
BOX 2: DIFFERENCE BETWEEN STRESS REACTIONS AND STRESS FRACTURES
Stress reaction n Oedema of the periosteum
n Oedema and bone marrow n No fracture line (but early indicator for impending stress fracture)
Stress fracture n Bone marrow oedema
n Fracture line visible through the bone
Figure 2: Comparison of different imaging modalities. (a) MRI scan showing diffuse oedema of the proximal fifth metacarpal in keeping with stress injury (encircled). The fracture line
cannot be clearly seen.
Figure 2b: Plain film showing the fracture line clearly (arrowed). (c) CT scan showing the exact extent of
involvement and partial-thickness fracture without evidence of callous (arrowed).
Figure 2c: CT scan showing the exact extent of
involvement and partial- thickness
fracture without evidence of callous (arrowed).
extension injuries to the spine. The most common levels are L4 and L5. The different imaging modalities have different strengths and weaknesses in evaluation of this fracture: n Plain films: these show spondylolisthesis of the affected vertebral body with associated widening of the spinal canal. Oblique views of the lumbar spine sometimes show the defect in the pars. n Bone scintigraphy: any “hot spots” (for more on hot-spots see Part I) (sportEX medicine Jan 2010) in the spine are indicative of pars fractures in the correct clinical context. However, scintigraphy suffers from poor localisation and invariably further imaging is needed to confirm a diagnosis. n Computerised tomography: CT is superior to both plain films and bone scintigraphy for identifying and characterising pars defects. It can identify whether the defect is unilateral or bilateral, and grade it, and it can even estimate the age of the defect. It also shows changes associated with pars defects, within the facet joints, spondylolisthesis and the ability to heal (3,12). n Magnetic resonance imaging: MRI has become the predominant imaging modality, providing the same information that CT and bone scintigraphy give without the high radiation doses. Thus information on the site of the pars injury, its acuteness, whether it is unilateral or bilateral, and its associated changes can all be acquired by MRI scanning (2), although CT may still be required to image healing and to characterise the margins of a pars defect.
JOINT IMAGING
disability and helps guide therapy of the patient (3,11).
Pars interarticularis fractures Pars interarticularis is a very specific type of stress fracture occurring in the spine. It is caused by repetitive hyper-
Joint disorders occur commonly in athletes. A number of methods are used to image them. n Plain radiograph: The simplest and most common is the plain radiograph. These can show effusions and give information on the congruity of the joint and the surrounding soft tissues, often tacit information obtained from the bony disruption of the joint. However, plain radiographs cannot provide the detail that is necessary to manage the majority of sports-related joint pathology (2,3,10). One exception is in older athletes where there is a higher incidence of osteoarthritis.
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