The variations in the normal bone scan need to be appreciated, such as the symmetrical epiphysial plates in the child, the increased uptake in joints of the shoulder and hand in the right-handed person on the right side and in the left-handed person on the left side. There are many normal variants: the degree of bone uptake in the skull, increased uptake at the manubrium sternal junction, asymmetry of uptake due to rotation and variations in intensity due to the closeness of the camera to the bone.
There is a range of abnormalities due to benign changes which are usually but not always easy to identify, such as focally increased uptake in the maxilla and mandible due to dental problems, arthropathic changes at the base of the thumb and bunions on the big toes. There are a number of artefacts that may be seen, usually defects due to buckles, jewellery, money, pacemaker or prosthesis. Contamination may be due to active urine, or occasionally contaminated radiographer’s fingers, for example on the image of the skull through holding the head. These may be able to be washed off. Renal and urinary activity may cause problems: bladder diverticulum, ureterocoele urinary diversion, pelvic retention, or anomalous site and position of a kidney. A poor preparation may contain free Tc-99m in which case the thyroid, stomach and/or salivary gland activity may be seen. Sites of muscle or other soft tissue infarction or necrosis may show focal uptake on the bone scan.
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The main problem is the distinction between degenerative change and malignancy in the spine. Typically degenerative change gives uptake on one or other side of the junction of the vertebral bodies which extends outside of the line of the vertebral bodies. It is often seen to the left or the right side of L5, on the vertebral edges on the concavity of scoliosis or relating to weight-bearing joints. Osteoporotic crash fractures are usually seen as a linear change in the vertebra whose intensity relates to the recentness of the event. The occasional rib end may show uptake possibly related to trauma. Cough or osteoporotic fractures may be seen in the ribs and traumatic fractures tend to lie in a line across adjacent ribs. A three-phase scan is usually undertaken to show that a site of osteomyelitis is active on dynamic, blood pool and three-hour images. Investigation of the limbs when there is a specific local complaint is usually undertaken with a three-phase bone scan.
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