Allogenic bone graft viability after hip revision arthroplasty assessed bydynamic [F-18]fluoride ion positron emission tomography

The biological fate of allogenic bone grafts in the acetabular cavity and t heir metabolic activity after acetabular augmentation is uncertain but is m ost important for the stability of hip implants after hip revision arthropl asty. The aim of this study was to quantify regional bone metabolism after hip replacement operations. Dynamic [F-18]fluoride ion positron emission to mography (PET) was used to investigate the metabolic activity of acetabular allogenic bone grafts and genuine bone, either 3-6 weeks (short-term group , n = 9) or 5 months to 9 years (long-term group, n = 10) after hip revisio n arthroplasty. Applying a three-compartment model, the fluoride influx con stant was calculated from individually fitted rate constants (K-n \ f) and by Patlak graphical analysis (K-pat). The results were compared with genuin e cancellousnd cortical acetabular bone of contralateral hips without surgi cal trauma (n = 7). In genuine cortical bone, K-n \ f was significantly inc reased in short(+140.9%) and long-term (+100.0%) groups compared with contr alateral hips. Allogenic bone grafts were characterised by a significantly increased K-n \ f in the shortterm group (+190.9%) compared with contralate ral hips, but decreased almost to the baseline levels of contralateral hips (+45.5%) in the long-term. Values of K-n \ f correlated with the rate cons tant K-1 in genuine (r = 0.89, P<0.001) and allogenic bone regions (r = 0.7 9, P<0.001), indicating a coupling between bone blood flow and bone metabol ism in genuine bone as well as allogenic bone grafts. Kpat values were high ly correlated with K-n \ f measurements in all regions. In conclusion, [F-1 8]fluoride ion PET revealed the presence of an increased host bone formatio n in allogenic bone grafts early after hip revision arthroplasty. In contra st to genuine cortical bone, allogenic bone graft metabolism decreased over time, possibly due to a reduced ability to respond to the same extent as g enuine bone to elevated metabolic demands after surgery.