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Figure 1. Normal whole body bone scan in the anterior (left) and posterior (right) projections. (Case provided by Dr. W.D. Leslie.)

replacement by dense fibrous tissue, some of which differentiates to form a connecting span of fibrocartilaginous callus to immobilize the fragments. At the end of the first week, as the resorption of hematoma and dead tissue is being completed, cartilage and endochondral bone formation takes place in the fracture gap, while the cellular and exudative inflammatory response subsides. Repair through ossification

Figure 2. Fractures through the sacrum and both sacroiliac joint regions in an 82 year old osteoporotic women who fell from a standing position. The configuration of the breaks is referred to as an "H" fracture.

simultaneously proceeds from the bony fracture surface, originating in the layers of viable endosteum and periosteum. The new bone migrates centrally from both ends and reinforces the ongoing ossification in the gap. The two processes form a solid bony bridge, and when it is completed the fracture is considered clinically healed. In the final phase of healing remodelling occurs as the woven bone of the callus is converted to more adult lamellar bone, the external callus is smoothed by osteoclasts and the medullary canal is reconstituted. Autoradiographic studies demonstrate that

Table 1. Stages of fracture healing

Stage (duration)

Findings on three-phase bone scan

Arterial flow phase

Blood pool phase

Delayed static phase

Inflammatory

broad and diffuse area of

Reparative (8 to 12 weeks)

Remodeling (variable)

hyperconcentration fracture line focal and intense diminishing uptake at the uptake with time as healing progresses radiophosphate will deposit in the areas of new bone formation, with maximal uptake where this process is predominant.

Three stages have been attributed to normal fracture healing (Table 1). During the first 3 to 4 weeks after the break the site of trauma on the bone scan is characterized by a relatively broad and diffuse area of hyperconcentration. In the subsequent phase of 8 to 12 weeks duration the abnormal activity becomes more focal and intense about the fracture line as mineralization of the osseous defects takes place. Thereafter, the fracture exhibits a diminishing uptake with time as healing progresses. In the three-phase radiophosphate study, the angiographic first phase is positive for about the initial 3 weeks following the injury, whereas the blood pool phase can be positive up to 10 weeks.

Radiophosphate imaging can disclose the presence of a fracture within 24 hours of the injury in 95% of patients under the age of 65 years, but there may be a delay in the elderly and debilitated patient. It is recommended that patients over 75 years of age who have severe pain, but negative radiography and normal radiophosphate imaging soon after injury, should have the bone scan repeated 72 hours later. CT scan or plane tomograms may also aid in the diagnosis. The patient should be treated as a hip fracture and kept non-weight bearing or on a bed-to-chair restriction during this time. The negative predictive value for elderly patients suspected of hip fracture who are imaged 72 hours after an earlier negative scan varies between 96% and 99% (Fig. 3). The site of fracture is also a determinant of the degree of radiophosphate accumulation. Those close to joints show the highest rate of uptake, whereas the spine, pelvis and mid-shaft of the long bones have slower rates of uptake. This is probably related to the regional blood flow.

About 90% of closed fractures that do not require surgical reduction will portray normal radiophosphate uptake between 6 months and 2 years after injury. Intense focal accumulation may persist longer in geriatric patients and in the presence of compound and comminuted fractures. Orthopedic appliances can cause persistent increased uptake, but it is usually low grade in the absence of infection or hardware loosening. Persistent hardware uptake may be more common when plates and screws are used versus an intramedullary rod system (the latter is load sharing versus the former which is load bearing). Mechanical stresses at points of malalignment and

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