Table 2.

Role of Nuclear Imaging as a modality following musculoskeletal surgery.

Imaging Modality	Advances	Applications in post operative imaging	Drawbacks/Disadvantages
Bone Scintigraphy Most common radiopharmaceutical are Tc-99 m MDP and Tc-99 m HDP These are bone-seeking agents that undergo adsorption to the hydroxyapatite structure of bone tissue.	1SPECT Visualization of the three dimensional distribution of the radiopharmaceutical in the skeleton.	Allows for better image contrast and precise lesion localization.	SPECT is an added procedure rather than a stand-alone procedure in that whole body images or limited bone scan are performed initially followed by SPECT imaging
Uptake is dependent on blood flow and bone turnover(in osteoblastic areas) Less sensitive for osteolytic lesions	2SPECT/CT SPECT acquisition combined with CT using an integrated CT scanner	SPECT allows for greater accuracy in the determination of the source of abnormal activity Correlation with CT-morphology allows the exclusion of potentially false positive bone uptake	Increased radiation exposure. Not widely available.
Planar whole body images or focal planar images can be acquired.
Quantification of uptake- the osseous radioactivity concentration is expressed as standardized uptake values (SUV)	Quantification and Iterative metal artifact reduction techniques	Improves attenuation correction around metal implants	3-phase skeletal scintigraphy is nonspecific and is most useful when study is normal or identifies fracture or other non prosthesis-related cause of symptoms
	4Multiphase bone scan (dynamic scan) First phase- Blood flow to the region of interest Second phase- Degree of hyperemia Delayed phase- Amount of bone formation	Localization to regions of increased bone perfusion and osteoblastic response
Tracers	1Tc-99m MDP more commonly used	Normal bone scan has high negative predictive value Rules out infection and loosening	Patients with implants can show false positive uptake up to 3 years after surgery.
	2 Labeled leukocyte Scintigraphy	Localizes to areas of infection and stress fractures with positive three phase uptake	Compacted marrow from procedure also shows increased activity
	Used both in conjunction with bone scans and independent of bone scans for further specificity	Differentiation of metabolically active vascular hypertrophic union and oligotrophic/atrophic non union	False-positive WBC scan in recently “violated” bone likely fracture due to localization in marrow elements
	Tagged WBC scan In-111 or Tc-99 m HMPAO WBCs localize to infection	Early detection of heterotrophic ossification	False-negative results occur in chronic infections/aseptic inflammation
	3. Tc-99m HMPAO WBC scan	Labeled leukocytes are mostly neutrophils, which are present in infections and not prevalent in aseptically loosened prosthesis	Requires Tc-99 m SC marrow map 24–72 h later if (+) Radiation exposure to the patient is greater
	4 Technetium 99m sulphur colloid	Usually matches 3-phase bone scan distribution in infection	Radiation exposure is a major disadvantage
PET/CT & PET/MRI Three-dimensional images are obtained with a circular array of detectors and a CT scanner in the PET/CT bore.	F-18 FDG PET CT	Better imaging characteristics Used to confirm labeled leukocyte scintigraphy results Localizes to normal marrow, hence discordant activity to	Increased uptake around prosthesis
	A glucose analogue, F-18-labeled	leukocyte scintigraphy indicates infection	CT based attenuation correction can falsely elevate radiotracer uptake in presence of implant related artifacts
	fluorodeoxyglucose is taken up by many types of tumour cells in the glycolysis pathway and is trapped after phosphorylation by hexokinase.	Areas of recurrent tumour show increased activity, particularly in patients with implants	Limited in case of metallic artifacts
	PET/MRI is a recent advance which can be used in patients with radiation concern- like pregnancy and young adults	Combined high soft tissue resolution of MRI and metabolic activity with PET increases sensitivity	Not widely available
	F-18 NaF PET Second-line modality after nondiagnostic Tc-99 m bone scans.	During shortages of Tc-99 m, F-18 PET bone scans offer an alternative for skeletal imaging	Shows no uptake in sclerotic acellular/small tumor volume in areas of tumor recurrence
	The mechanism of uptake is incorporation of fluoride ions into the bone matrix in sites of infection, after trauma/stress, or during inflammation	The resolution and pharmacokinetics are far greater than Tc-99m-based bone agents Fast blood clearance Higher bone uptake High bone to soft tissue uptake ratio
	Shows uptake in osteolytic and osteoblastic lesions	Total exam time is shorter Improved resolution when compared to planar and SPECT or SPECT/CT