**12. Fractures**

120 12 Chapters on Nuclear Medicine

Heterotopic ossification (HO) is defined by the presence of bone in soft tissue where bone tissue normally does not exist, and it usually takes place around large joints (Medina et al., 2008). Its etiology is unknown, but is frequently precipitated by trauma, spinal cord injury or central nervous system injury (Shebab et al., 2002). The incidence of HO varies widely between populations. The incidence after hip replacement ranges from 16% to 53%; among patients with spinal cord injury HO develops in 20-25% and in brain injury patients the incidence of HO ranges from 10 to 20% (Medina et al., 2008; as cited in Vanden & Vanderstraeten, 2005). Around 20% of the patients who have an HO will develop functional limitation and it will be severe in 8% to 10% (Medina et al., 2008; as cited in Buschbacher, 1992; Subbarao, 1999). HO may closely mimic the presentation of cellulitis, osteomyelitis, or thrombophlebitis. HO can even be confused with some bone tumors such as osteosarcoma or osteochondroma. To resolve such diagnostic uncertainty and to prevent functional limitations, clinicians often request bone scanning and other imaging studies for patients at risk (Shebab et al., 2002). Radiography, MRI and CT have low sensibility in early stages of HO and three-phase bone scintigraphy (**Fig. 7**) is the most sensitive imaging modality during this period. It is also useful for its monitoring (Vanden & Vanderstraeten, 2005).

Fig. 7. Bone Scanning: increased uptake around the left hip consistent with Heterotopic

First and second phases of three-phase bone scintigraphy are especially sensitive to detect incipient HO, which may be diagnosed 2.5 weeks after injury. Findings on the third phase may become positive approximately 1 week later. Radiographic studies do not show any change for at least 5- 8 weeks after initial injury (Shebab et al., 2002; as cited in Freed et al., 1982; Orzel & Rudd, 1985). Activity on the delayed bone scans usually peaks in a few months and after that the intensity of HO activity progressively lessens and thus the uptake of the radiotracer on the scans, which return toward normal within 12 months. However, in some cases activity remains slightly elevated even though the underlying HO has become mature (Shebab et al., 2002; as cited in Tibone et al., 1978). During the course of HO, bone scans made on follow-up may show radiotracer uptake on third phase even after flow and blood-pool images have returned to normal. Serial bone scans have been used successfully to monitor the metabolic activity of HO and determine the appropriate time for surgical resection, if needed, and to predict postoperative recurrence (Shebab et al., 2002; as cited in Freed et al., 1982; Muheim et al., 1973; Rossier et al., 1973; Tanaka et al., 1977). For the differential diagnosis of osteomyelitis complementary imaging with gallium-67 citrate (for spinal infection) or indium-111-labeled autologous leukocytes (for the appendicular

**11. Heterotopic ossification** 

Ossification.

Following known injury, fractures are commonly demostrated by conventional radiography of most sites of trauma. In such circumstances bone scintigraphy has no major role, although unsuspected lesions may be identified. Acute fractures show increased perfusion on the radionuclide angiogram; intense, poorly marginated increased tracer accumulation representing relatively increased vascularity on the blood pool images; and intense poorly defined increased tracer accumulation on delayed images (Holder, 1993).

#### **12.1 Occult fractures**

Scintigraphy may be valuable in the diagnosis of occult fractures, which are true fractures not immediately obvious on clinical examination or plain radiography, and it is particularly useful to detect certain type of fractures that require urgent orthopedic treatment, such as femoral neck and intertrochanteric fractures, scaphoid fracture, and Lisfranc fracture. Occult femoral neck and intertrochanteric fractures are frequents in older females with continued hip pain following a fall. Shortly following the time of injury, there is an increase in perfusion to the fracture site which can be demonstrated during the rapid sequence flow study and blood pool phases of the so called three-phase bone scan. The time for first appearance of increased uptake on delayed 99mTc-diphosphonate images remains controversial, fluctuating between 24 hours and 2 weeks (Collier et al., 1993; as cited in Holder et al., 1990; Matin, 1979; Spitz, 1991). These problems are not encountered in the identification of scaphoid fracture which is readily visualized within 3 days of trauma. Bone scan demonstrates a focus of intense uptake usually centered in the scaphoid (Collier et al., 1993; as cited in Patel et al., 1992; Tiel-van-Buul et al., 1992). High-resolution bone scan images obtained with the wrist first in a neutral position and then in ulnar deviation are used to localize the scintigraphic abnormality to the scaphoid. With ulnar deviation there is movement and rotation of the scaphoid relative to adjacent bony landmarks such as the radial styloid (Collier et al., 1993). Premature imaging withing 48 hours must be avoided, particularly as the osseous scintigraphic changes may be obscured by the diffuse uptake resulting from superficial hyperemia or traumatic sinovitis. Prolonged delay of this study may also result in increased uptake associated with disuse and thus, masking the fracture (Murray, 1998). Scintigraphy is therefore of considerable value in identifying this lesion before X-ray change appears, especially as difficulty may be encountered in radiological diagnosis even after 2-3 weeks (Murray, 1998). Difficulties in identifying the exact anatomic localization of a focus of uptake can be overcome by the technique of a combined display of the scan and the X-ray (Murray, 1998; as cited in Hawkes, 1991). Other occult fracture that

Nuclear Medicine in Musculoskeletal Disorders: Clinical Approach 123

also be falsely positive with shin splints, despite shin splints are typically positive only during the delayed phase of the scan (De Weber, 2011; as cited in Deutsch, 1997). Areas of increased uptake may represent subclinical sites of bone remodeling or stress reactions. Increased uptake can also appear in the setting of bone tumors, osteomyelitis, or avascular necrosis. Although rare, there are reports of false-negative bone scans (De Weber, 2011; as cited in Gaeta et al., 2005; Spitz & Newberg, 2002). Because of these limitations, MRI is supplanting bone scan as the diagnostic tool of choice when plain radiographs are negative

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

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

and confirmation of suspected stress fracture is needed.

**12.3 Insufficiency fractures** 

fractures (Krestan et al., 2011).

**12.4 Pathologic fractures** 

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