Table 1 Overview of imaging features in potential applications of bone SPECT/CT in the limping patient

Accessory ossicles

Presence of the accessory ossicle.

Symptomatic ossicles can show increased focal uptake (Chew 2010).

Ankylosing spondylitis

Erosions, sclerotic changes, subchondral bone changes, and bone formations at ligament insertions (Lacout et al. 2008).

Increased uptake at ligament insertions, vertebral bodies; facet and costotransverse/costovertebral joints (Fogelman et al. 2013).

Arthroplasty/osteosynthesis

Assessment varies according to type of arthroplasty or osteosynthesis. Features associated with pathology include: radiolucent zones (> 2 mm), periprosthetic fractures, endosteal scalloping, hardware breakage, component wear, heterotopic ossification, subluxation, dislocation, or soft-tissue masses or fluid collections (Roth et al. 2012).

Increased uptake at the bone-prosthesis interface suggests loosening, depending on implant positioning and fixation zones. Periprosthetic fractures or malunion show increased focal uptake at these sites. Diffuse uptake surrounding fixation screws is suspicious for loosening (Fogelman et al. 2013).

Avascular necrosis of hip

No abnormalities during early phase. Osteoporosis is the first visible sign, followed by clumping and distortion of the central trabeculae. An adjacent low-density region represents the reparative zone (Stoica et al. 2009). Best seen on plain radiographs, the crescent sign is a curvilinear subchondral radiolucent line corresponding with a subchrondral fracture.

Acute phase: photopenic area. Following restoration of blood flow: intense radiopharmaceutical uptake, indicating repair (Fogelman et al. 2013).

Benign bone tumors

Appearance varies according to histopathology. Important CT imaging characteristics include location within the bone, lesion margin, matrix proliferation, and periosteal reaction (Motamedi and Seeger 2011).

Tracer uptake can be highly variable between lesion types, ranging from poor uptake (e.g. solitary bone cyst, enchondroma), partial rim-shape uptake (e.g. aneurysmal bone cyst), to increased uptake (e.g. fibrous dysplasia, osteoblastoma). Variability within lesion types occurs (e.g. hemangioma) (Fogelman et al. 2013).

Plantar fasciitis

Bony spur may develop at the plantar aspect of the calcaneus and plantar fascia thickening can be visible (Chew 2010).

Focal calcaneal hyperemia on blood pool images, extending into the proximal plantar fascia in more severe disease. Delayed images show focal calcaneal uptake (Frater et al. 2006).

Femoral acetabular impingement (FAI)

Cam type: non-spherical femoral head or lack of neck concavity. Pincer type: deep or overhanging acetabulum. Labral ossification, joint space narrowing, and osseous hypertrophy of the acetabular rim develop in chronic FAI (Morrison and Sanders 2008).

Hyperemia on blood pool images. Delayed images show a “reverse C” pattern of joint uptake. Intense focal uptake in the lateral and inferomedial aspect of the femoral head indicate impingement (Fogelman et al. 2013).

Heterotopic ossification (HO)

Muscle swelling containing calcification: amorphous (poorly defined with no trabecular structure), immature (initial trabecular formation with poorly defined margins), or mature (well-defined cancellous bone with cortical outline) (Zagarella et al. 2013).

Flow and blood pool is positive 2–3 weeks after injury. Delayed images become positive about 1 week later. Peak activity occurs a few months after injury, followed by progressively decreasing uptake with normalization at 6 to 12 months after injury (Shehab et al. 2002).

Insufficiency/stress fracture

Linear sclerosis possibly with subtle focal cortical interruption or step-off (Morrison and Sanders 2008).

Typical appearance is of hyperemia with intense uptake on late images at the site of injury (Fogelman et al. 2013).

Osteoarthritis

Uneven loss of articular space, subchondral sclerosis, osteophytes, and subchondral cysts. Absence of osteoporosis, ankylosis, and erosions (Chew 2010).

Usually no hyperemia. Late images typically show a combination of diffuse articular uptake depending on disease severity, and (multi)focal uptake at the joint edges or weight-bearing surfaces (Boegard et al. 1999; Fogelman et al. 2014).

Osteochondritis dissecans

Subchondral irregular areas of increased and decreased density, with normal, thinned, or eroded overlying articular cartilage (Bloem and Sartoris 1992).

Uptake depends on the age of the lesion. Acute lesions can show subtle focal hyperemia, with more intense delayed uptake at the site of injury (Fogelman et al. 2014).

Osteoid osteoma

Osteolucent focus at the nidus, with or without a dense central mineralized focus. Surrounding extensive fusiform sclerosis is typical in long bones (Motamedi and Seeger 2011).

Typical findings show a vascular lesion on blood pool images and intense focal uptake on the delayed image (Fogelman et al. 2014).

Spontaneous osteonecrosis of the knee

No changes in early disease. Later, subtle flattening of the condyle develops, followed by appearance of a radiolucent area (crescent or rim sign) indicating segmental necrosis of subchondral bone.

Intense uptake on blood pool and late phase images early after onset for up to 6 months. This is followed by a gradual decrease of blood pool uptake, but persisting positive late phase images for up to 2 years (Elgazzar 2004).

Tarsal coalition

Abnormal osseous continuity of two bones, or more subtle abnormalities in non-osseous coalitions (joint space narrowing, minimal marginal reactive osseous changes). Subchondral joint cysts can occur in an otherwise non-arthritic appearing foot (Lawrence et al. 2014).

Focal uptake at the site of coalition and at any sites complicated by osteoarthritis (Fogelman et al. 2013).

Tendinopathies

General or localized swelling of the tendon may be observed on CT. When partial rupture has occurred focal intratendinous inhomogeneities with lower attenuation compared to the surrounding tissue become apparent (Kalebo et al. 1990).

Increased uptake on the flow and blood pool images (Pelletier-Galarneau et al. 2015).

Tophaceous gout

Peri-articular rat-bite erosions with overhanging edges. Non-calcified dense soft-tissue tophi. Tendon thickening may occur (Morrison and Sanders 2008).

Blood pool and delayed images typically show intense increased uptake in the affected joints (Fogelman et al. 2014).

Transient osteoporosis

Diffuse osteopenia of the affected area without crescent sign or collapse of the femoral head.

Blood pool and delayed images typically show increased uptake with varying intensity in the femoral head extending into the femoral neck and intertrochanteric region, without focal cold spots (Gemmel et al. 2012).