- See: Total Hip Replacement Menu:
- General Discussion of Bone Scans:
- Normal THR:
- normal study (minimal reative bone formation) may be expected from months to a year after placement;
- area of lesser trochanter to midshaft of prosthesis usually becomes normal in about 6 months;
- area around acetabulum, greater trochanter, and tip of prosthesis may show increased activity for up to 2 years, but on average shows
normal findings at about 1 year in the majority of patients;
- Non Cemented THR:
- evaluation of of porous coated prosthesis may require a different interpretation from cemented THR;
- bone & fibrous tissue ingrowth into porous acetabular & intertrochanteric surfaces may cause findings unrelated to complications;
- with loosening there is little inflammation and, therefore, the first two phases of the bone scan are normal;
- even culture of material taken at operation, which microscopically shows presence of infected material, fails to grow microorganisms in
up to 10% of cases;
- Infection:
- infection shows a more diffuse pattern of abnormality occurring along prosthesis shaft and is usually positive on the 2 early phases;
- low grade infection may consist of minimal hyperemia & may show a mild delayed uptake on bone scan which is difficult to distinguish
from loosening;
- false positive results may occur in upto 40% and false negatives in 5-10%;
- Indium-111:
- more specific for making definitive dx of infection but may be less sensitive