22 Acta Orthopaedica 2012; 83 (1): 22–25 Metabolic development of necrotic bone in the femoral head following resurfacing arthroplasty A clinical [18F]fluoride-PET study in 11 asymptomatic hips Gösta Ullmark1, Kent Sundgren1, Jan Milbrink², Olle Nilsson², and Jens Sörensen³ 1Department of Orthopedics, Gävle Hospital and Centre for Research and Development, Uppsala University/County Council of Gävleborg; Departments of 2Orthopedics and 3Nuclear Medicine, Uppsala University Hospital, Uppsala, Sweden. Correspondence: gosta.ullmark@lg.se Submitted 11-06-21. Accepted 11-09-30 Background and purpose One concern regarding resurfacing arthroplasty is the viability of the diminished femoral head and the postoperative risk of collapse, or a femoral neck fracture. 18F-fluoride positron emission tomography (F-PET) enables us to assess bone viability despite there being a covering metal component. By F-PET studies, we recently showed the absence of metabolism in the remaining part of femoral heads, 1–4 years after surgery in 11 of 46 consecutive cases. We now present the further development of bone metabolism in these 11 cases. Patients and methods 10 patients (11 chips) with previously shown loss of femoral head metabolism were evaluated by radiog- raphy and repeated F-PET scans, 3–6.5 years after surgery. The size of the area with low 18F-fluoride PET uptake in the femoral head was compared to that in earlier PET images. Results No patients had any clinical symptoms; nor was any necrotic bone area visible in plain radiographs. On F-PET scans, 2 patients showed a diminished area with low uptake, 4 were unchanged, and 5 had enlarged areas. Interpretation Bone metabolism surrounding a volume of bone with no metabolic activity changes dynamically even 5 years after surgery. The presence of bone with minor uptake of F-tracer, indicating low or no bone metabolism, with further progression in 5 of 11 cases leads us to conclude that resurfacing THA should be used restrictively.  One concern with resurfacing arthroplasty of the hip is the viability of the diminished femoral head. During the surgical procedure, the blood supply to the remaining part of the head might be damaged (Howie et al. 1993, Nötzli et al. 2002, Stef- fen et al. 2005, Khan et al. 2007). 18F-fluoride positron emission tomography (F-PET) is a sensitive and non-invasive diagnostic method for analysis of bone metabolism (Grant et al. 2008) associated with new bone formation (Sörensen et al. 2003), and bone viability (Ullmark et al. 2007). Validation studies to correlate F-PET with bone histomorphometry have been performed (Messa et al. 1993, Piert et al. 2001). In a previous prospective study of 14 patients (Ullmark et al. 2009) who received an ASR resurfacing arthroplasty (DePuy Johnsson and Johnsson, Warsaw, IN), F-PET/CT scans were performed 1 week, 4 months, and 12 months after surgery. 4 of these 14 patients were found to have lost bone metabo- lism (measured by F-PET/CT) in the remaining part of their femoral heads, assessed as osteonecrosis, without any symp- toms and without signs on plain radiographs. All 14 patients had had normal metabolism at the F-PET scan 1 week after surgery. Between the 4-month and the 12-month postopera- tive PET scans, 4 of the 14 patients had developed an area with no metabolism. In another F-PET/CT study of 32 patients (Ullmark et al. 2011) with an ASR or DUROM resurfacing arthroplasty (Zimmer, Warsaw, IN), we performed the scans retrospectively 18–48 months after surgery. 7 cases in that study were found to have pathological non-metabolic areas in their femoral heads without there being symptoms or signs on radiographs. For the 11 cases that had been found to have lost bone metabolism in these 2 previous studies (Ullmark et al. 2009, 2011), we investigated how their bone metabolism had devel- oped 3–6.5 years after surgery. Patients and methods The present study included patients who were previously shown to have developed areas without metabolism in their resurfaced femoral heads (Ullmark et al. 2009, 2011). These Open Access - This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the source is credited. DOI 10.3109/17453674.2011.641108