**12.3 Insufficiency fractures**

122 12 Chapters on Nuclear Medicine

can require urgent treatment is Lisfranc fracture. This fracture presents a characteristic appearance on bone scan with a band of increased uptake extending across multiple tarsometatarsal joints, typically involving the first through fifth or the second through fifth

Stress fracture occurs when a bone breaks after being subjected to repeated tensile or compressive stresses, none of which would be large enough to cause individually the bone to fail, in a person who is not known to have an underlying disease that would be expected to cause abnormal bone fragility (De Weber, 2011). The incidence of stress fractures is less than 1 % in the general population. The reported incidence in athletic populations varies with the type of athlete. Among military recruits the incidence ranges from 1 to 31 %, among runners 13 to 52 %, and among participants in collegiate team sports 1 to 8 % (De Weber, 2011; as cited in Bennel, 1997). In most instances, the individuals who suffer stress fractures have been engaging in vigorous activity to which they have not yet become conditioned. The failure to recognize the characteristic clinical and imaging findings of a stress fracture and the continued excessive exercise by the athlete will occasionally lead to a complete fracture (Collier et al, 1993). Imaging is needed when high risk stress fractures are suspected or a definitive diagnosis is necessary. The sites at high risk complications are the pars interarticularis of the lumbar spine, femoral head, superior side of the femoral neck, patella, anterior cortex of the tibia, medial malleolus, talus, tarsal navicular, proximal fifth metatarsal, great toe sesamoids, and

tarsometatarsal joints (Collier et al., 1993; as cited in Fogelman & Collier, 1989).

Fig. 8. Scintigraphy: localized uptake in tibial metaphysis and both internal femoral

Three-phase bone scan has traditionally been used for diagnosis of stress fractures because it can show evidence of stress fracture within 2 to 3 days of injury and has high sensitivity. Acute stress fractures appear as discrete, localized, sometimes linear areas of increased uptake on all three phases (angiographic, soft tissue, and delayed phases) of a Tc-99m-MDP bone scan (**Fig. 8**). However, the specificity of bone scan is low. Approximately 40 % of positive findings occur at asymptomatic sites (De Weber, 2011; as cited in Bennell et al., 1999). Bone scan can

the base of the second metatarsal bone (De Weber, 2011).

**12.2 Stress fractures** 

condyles.

Insufficiency fracture occurs when the mechanical strength of a bone is reduced to the point that a stress which would not fracture a healthy bone breaks the weak one (De Weber, 2011). Most commonly postmenopausal osteoporosis is the cause for insufficiency fractures. Additional conditions affecting bone turnover include osteomalacia, chronic renal failure, and high-dose corticosteroid therapy (Krestan et al., 2011). Insufficiency fractures occur most commonly in the pelvis, including the sacrum, followed by the proximal femur and the vertebral bodies, in particular in the lower thoracic and the lumbar spine. Other sites frequently affected by insufficiency fractures are the tibia, fibula, and calcaneus (Krestan & Hojreh, 2009; as cited in Soubrier, 2003). Radiographs are the basic modality used for screening of insufficiency fractures, but depending on the location of the fractures, sensitivity is limited. Thus, MRI and CT are both standard techniques when insufficiency fracture is suspected and initial radiological studies are negative. MRI is a very sensitive tool to visualize bone marrow abnormalities associated with insufficiency fractures and allows differentiation of benign versus malignant fractures. Multidetector CT depicts subtle fracture lines allowing direct visualization of cortical and trabecular bone (Krestan et al., 2011). Bone scintigraphy is also highly sensitive and specific when typical pattern of abnormality is present. One of those typical patterns of uptake is the classical H ('Honda' sign) or butterfly-shaped appearance in sacral insufficiency fracture in the elderly osteoporotic patient without definite trauma history. The vertical limbs of the H lie within the sacral ala, parallel to the sacroiliac joints, while the transverse limb of the H extends across the sacral body. Other sacral variant uptake patterns occur frequently and include the unilateral ala, incomplete H and horizontal linear dot patterns. Iliac fractures are seen as linear areas of increased radionuclide uptake. Pubic and supra-acetabular fractures produce areas of linear or focal uptake. Concomitant findings of two or more areas of increased uptake in the sacrum and at another pelvic site are considered diagnostic of insufficiency fractures of the pelvis. If a typical pattern of abnormality is not present, the radionuclide bone scan is much less specific. If abnormal or incomplete patterns of uptake are observed, findings may be mistaken for malignancy and other etiologies. PET–CT with hybridscanners has been the upcoming modality for the differentiation of benign from malignant fractures (Krestan et al., 2011).

### **12.4 Pathologic fractures**

º

This type of fractures is due to a localized loss of strength secondary to an underlying disease process. Examples of pathologic fractures include those that occur at sites of bone tumors (primary or metastatic), bone cysts, and infections (De Weber, 2011). About 10% of patients with known bone metastases will sustain a fracture. Most patients with high-risk conditions for bone metastasis are followed serially with bone scan to detect occult

Nuclear Medicine in Musculoskeletal Disorders: Clinical Approach 125

fracture site can also be a cause of persistent pain and contribute to the non-union (Csongradi & Maloney, 1989). Gallium scan is indicative of infection if 67Ga uptake exceeds 99mTc uptake on the bone scan. The most specific tracers for infection however are

Technical considerations concerning care of the child, immobilization, dosing of radiopharmaceuticals, and instrumentation are of major importance in pediatric nuclear medicine. It is routine in many dedicated pediatric nuclear medicine departments to allow parents or siblings to remain in the imaging room to provide a sense of security and safety for the child. Similarly, the patient is allowed to hold a favorite toy or a prized possession and parents are instructed to bring such items with them for the test. Children are often most worried about the needle required for the injection. Many nuclear medicine departments now routinely use the application of topical anesthetic creams as part of the preparation for the examination (Nadel & Stilwell, 2001). Immobilization techniques to gain patient support in pediatric studies can vary from wrapping the patient to the use of sedation and general anesthesia. For neonates to age 2, it may suffice to hold the patient in place, deprive sleep, and feed the child while on the imaging table. Papoose techniques for bundling and entertainment including television, movies, music, or stories can be used to immobilize children older than 4 to 5 years of age. The cooperation of an older child can often be obtained if the procedure is carefully explained to them and their parents. Children between the ages of 2 and 5, or who are mentally retarded, or have severe attention deficit problems, are more likely to require sedation (Nadel & Stilwell, 2001). Guidelines from the American College of Radiology and the American Academy of Pediatrics can help in developing an appropriate institutional sedation protocol (Shammas, 2009; as cited in

The correct dosing for administration of radiopharmaceuticals to children is available in standard pediatric nuclear medicine texts and can be based on either body surface area or the weight of the child relative to adult dosage (Nadel & Stilwell, 2001; as cited in Miller & Gelfand, 1994; Treves, 1995). 99mTc- MDP is the most commonly used radiopharmaceutical for bone scintigraphy. Scanning is usually performed as a three-phase bone scan with immediate blood flow and blood pool imaging of the site of symptoms obtained after injection, followed by delayed imaging 1.5 to 2 hours later. It is important that the children are well hydrated to have optimum visualization. Other radiopharmaceuticals are also useful in the evaluation of musculoskeletal disease, such as 67Ga citrate or labelled leukocytes using indium-111 or 99mTc for musculoskeletal infection or a bone marrow scan using a 99mTc-sulfur colloid for bone marrow infarction, particularly in sickle cell disease (Shammas, 2009; as cited in Connolly et al., 2007; Gilday, 2003; Nadel & Stilwell, 2001). 18F-FDG is the most common radiopharmaceutical used for PET or PET/CT. 18F-FDG accumulation occurs in inflammation and infection (Shammas, 2009; as cited in Love et al., 2005; Zhuang & Alavi, 2002). Imaging of inflammation with 18F-FDG PET relies on the fact that infiltrated granulocytes and tissue macrophages use glucose as an energy source. When they are activated in inflammation, metabolism and thus FDG uptake increases (Shammas,

**13. Technical aspects and applications of bone scintigraphy in pediatric** 

leukocytes labelled with indium-111 or 99mTc (Schelstraete et al., 1992).

**13.1 Technical aspects of bone scintigraphy in pediatric populations** 

**populations** 

Gilday, 2003).

2009; as cited in Kubota et al., 1992).

metastasis. In general, lytic lesions are considered more prone to fracture than blastic ones. In the spine, CT or MRI are both indicated to quantify the extent of tumor infiltration, including any extension into the spinal cord and are useful in distinguishing osteoporotic vertebral collapse from pathologic fracture.

#### **12.5 Non-union fractures**

In the setting of impaired fracture healing we can distinguish three complications: the delayed union, non-union and pseudoartrhosis. Delayed union describes the situation where there are distinct clinical and radiological signs of prolonged fracture healing time (Panagiotis, 2005). Scintigrams demonstrate intense tracer concentration at the fracture site, as does a fracture undergoing normal or non-union. Therefore, differentiation of a normal or delayed union from nonunited fracture may not be possible by scintigram alone. Clinical findings along with roentgenograms are usually adequate to distinguish delayed healing from nonhealing (Desai et al., 1980). Non-union fracture is defined as the cessation of all reparative processes of healing without bone union 6 to 8 months following the fracture or by the absence of progressive repair that has not been observed radiographically between the third to sixth months following a fracture (Panagiotis, 2005). Two main types of nonunion fractures are differentiated according to the viability of the ends of the fragments (Frölke& Patka, 2007; as cited in Weber & Cech, 1976): Avascular non-union and hypervascular non-union. In the first type the ends of the fragments are avascular or atrophic, inert and incapable of biologic reaction, and therefore bone scintigraphies indicate a poor blood supply at the edges of the fragments (Frölke& Patka, 2007). On delayed images atrophic non-union rim is seen as a photon deficient band between fracture ends (Holder, 1993). The main problem in this type is the poor quality of the bone ends and the significantly diminished potential for repair (Gelalis et al., 2011). In the second type the rims of the fragment are hypervascular or hypertrophic and are capable of biological reaction. Bone scintigraphy in the latter indicates a rich blood supply in the ends of the fragments (Frölke& Patka, 2007). The main problem in this type is inadequate fracture stability or reduction. The third complication, pseudoarthrosis, is a non-union fracture which may take years to develop and may occur without clinical symptoms. It is characterised by the formation of a false joint where a fibrocartilaginous cavity is lined with synovium producing synovial fluid (Panagiotis, 2005; as cited in McKee, 2000). Scans using Tc-99m-MDP show the presence of a synovial pseudoarthrosis (Csongradi & Maloney, 1989; as cited in Esterhai et al., 1984). Two types can be distinguished as in the non-union fractures: atrophic and hypertrophic pseudoarthrosis. The first one is characterized in the scintigraphy by the absence of peripheral accumulation in contrast with the intense uptake surrounding a hypertrophic pseudoarthrosis. Those finding in the bone scan are highly suspect for pseudoartrhosis after 12 months. The use of SPECT with bone scanning enhances the sensitivity and specificity, especially in the pseudoarthrosis of the spine after a lumbar spinal fusion (Collier et al., 1993; Lee & Worsley, 2006). SPECT identifies a more focal area of intense activity within the area of increased accumulation at the fusion site (Murray, 1998). Some authors have used radionuclide scans to determine whether the fracture has the biologic ability to respond to a specific therapy such as electrical stimulation. With mature nonunions, radionuclide scans can identify large hypovascular areas that have no potential for healing. In such cases, operative intervention is needed. In a case of nonunion, the possibility of infection must be considered. An increase in activity at the fracture site on the radionuclide scan is consistent with both bony healing and infection. Infection at the

metastasis. In general, lytic lesions are considered more prone to fracture than blastic ones. In the spine, CT or MRI are both indicated to quantify the extent of tumor infiltration, including any extension into the spinal cord and are useful in distinguishing osteoporotic

In the setting of impaired fracture healing we can distinguish three complications: the delayed union, non-union and pseudoartrhosis. Delayed union describes the situation where there are distinct clinical and radiological signs of prolonged fracture healing time (Panagiotis, 2005). Scintigrams demonstrate intense tracer concentration at the fracture site, as does a fracture undergoing normal or non-union. Therefore, differentiation of a normal or delayed union from nonunited fracture may not be possible by scintigram alone. Clinical findings along with roentgenograms are usually adequate to distinguish delayed healing from nonhealing (Desai et al., 1980). Non-union fracture is defined as the cessation of all reparative processes of healing without bone union 6 to 8 months following the fracture or by the absence of progressive repair that has not been observed radiographically between the third to sixth months following a fracture (Panagiotis, 2005). Two main types of nonunion fractures are differentiated according to the viability of the ends of the fragments (Frölke& Patka, 2007; as cited in Weber & Cech, 1976): Avascular non-union and hypervascular non-union. In the first type the ends of the fragments are avascular or atrophic, inert and incapable of biologic reaction, and therefore bone scintigraphies indicate a poor blood supply at the edges of the fragments (Frölke& Patka, 2007). On delayed images atrophic non-union rim is seen as a photon deficient band between fracture ends (Holder, 1993). The main problem in this type is the poor quality of the bone ends and the significantly diminished potential for repair (Gelalis et al., 2011). In the second type the rims of the fragment are hypervascular or hypertrophic and are capable of biological reaction. Bone scintigraphy in the latter indicates a rich blood supply in the ends of the fragments (Frölke& Patka, 2007). The main problem in this type is inadequate fracture stability or reduction. The third complication, pseudoarthrosis, is a non-union fracture which may take years to develop and may occur without clinical symptoms. It is characterised by the formation of a false joint where a fibrocartilaginous cavity is lined with synovium producing synovial fluid (Panagiotis, 2005; as cited in McKee, 2000). Scans using Tc-99m-MDP show the presence of a synovial pseudoarthrosis (Csongradi & Maloney, 1989; as cited in Esterhai et al., 1984). Two types can be distinguished as in the non-union fractures: atrophic and hypertrophic pseudoarthrosis. The first one is characterized in the scintigraphy by the absence of peripheral accumulation in contrast with the intense uptake surrounding a hypertrophic pseudoarthrosis. Those finding in the bone scan are highly suspect for pseudoartrhosis after 12 months. The use of SPECT with bone scanning enhances the sensitivity and specificity, especially in the pseudoarthrosis of the spine after a lumbar spinal fusion (Collier et al., 1993; Lee & Worsley, 2006). SPECT identifies a more focal area of intense activity within the area of increased accumulation at the fusion site (Murray, 1998). Some authors have used radionuclide scans to determine whether the fracture has the biologic ability to respond to a specific therapy such as electrical stimulation. With mature nonunions, radionuclide scans can identify large hypovascular areas that have no potential for healing. In such cases, operative intervention is needed. In a case of nonunion, the possibility of infection must be considered. An increase in activity at the fracture site on the radionuclide scan is consistent with both bony healing and infection. Infection at the

vertebral collapse from pathologic fracture.

**12.5 Non-union fractures**

fracture site can also be a cause of persistent pain and contribute to the non-union (Csongradi & Maloney, 1989). Gallium scan is indicative of infection if 67Ga uptake exceeds 99mTc uptake on the bone scan. The most specific tracers for infection however are leukocytes labelled with indium-111 or 99mTc (Schelstraete et al., 1992).
