The Knee: Reconstruction, Replacement  and Revision Tracking Pixel
Duke Orthopaedics
presents
Wheeless' Textbook of Orthopaedics

Triphasic Bone Scan



- See: Technetium 99m

- Discussion:
    - initial dynamic images are aquired over the area of concern and then followed immediately afterwards by static images obtained over 
           longer periods of time;

- First Phase:
    - demonstrates perfusion to a lesion;
    - first phase, the nuclear angiogram or flow phase, consists of serial 2- to 5-sec images of the area of suspected osteomyelitis that are 
            obtained during injection of the radiopharmaceutical.
    - classically, with cellulitis, diffuse increased uptake occurs in first two phases, but uptake is normal or diffusely increased in third phase;
    - osteomyelitis causes focally increased uptake in all three phases;

- Second Phase:
    - relative vascularity;
    - second phase, the blood-pool image, is obtained within 5 min after injection;
           - in areas of inflammation, capillaries dilate, causing increased blood flow and blood pooling.
    - classically, with cellulitis, diffuse increased uptake occurs in first two phases, but uptake is nl or diffusely increased in third phase;
    - osteomyelitis causes focally increased uptake in all three phases;
    - first phase characterizes the blood flow to the area, while the 2nd visualizes the blood pool;
           - these 2 early phases act to characterize degree of inflammation and hyperemia that may be present;
           - diseases such as degenerative disease, healing fractures, non- infected prosthesis with loosening, well treated osteomyelitis, may have 
                   little abnormal activity on the early phases in spite of increase uptake on delayed images;
           - it may be difficult to distinguish osteomyelitis from diabetic osteoarthropathy, which are often abnormal on all 3 phases;
           - in contrast, a soft tissue infection classically appears only in early phases, with little abnormal focal bone activity seen on delayed images;

- Third Phase:
    - demonstrates relative bone turnover associated w/ a lesion;
    - 3rd phase, bone image, is obtained about 3 hr later, when urinary excretion has decreased the amount of the radionuclide in soft tissues.
    - if present, diffuse incr uptake in third phase is probably due to regional hyperemia caused by cellulitis;
    - osteomyelitis causes focally increased uptake in all three phases;

- Peds:
    - In neonates, the sensitivity of the three-phase bone scan decreases;
    - neonates with osteomyelitis have falsely normal or cold defects on three-phase bone scans 22-68% of the time;
    - cold lesion on 3rd phase may be caused by subperiosteal abscess;
    - in children, large portion of blood supply to the bone comes from periosteal vessels, and these are apparently disrupted by the 
           subperiosteal abscess;
    - when clinical findings strongly suggest osteomyelitis, but findings on three-phase bone scan are normal, then consider gallium scan



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Tuesday, September 6, 2011 1:38 pm