[18F]-Fluoride PET/CT Is a Promising Technology for the Assessment of Osseointegration of Acetabular Components in Total Hip Arthroplasty

Long-term fixation of press-fit acetabular components in total hip arthroplasty (THA) relies on 2 fundamental features: (1) initial mechanical stability by way of an interference fit and (2) subsequent biologic osseointegration. A variety of materials have been designed to enhance osseointegration, which can develop as either “ongrowth” of bone on a roughened surface of the acetabular cup or “ingrowth” of bone into a porous material of the cup. Since the 1980s, hydroxyapatite (HA), a bioceramic composed of calcium and phosphate ions, has been used as a surface coating of acetabular and femoral components to promote osseointegration1,2. More recently, contemporary acetabular components are being designed with highly porous tantalum or titanium, whereby the 3-dimensional architecture of the metal resembles the morphology of cancellous bone and acts as a scaffold that promotes osseous ingrowth3. The aim of the study by Sotiriou et al. was to measure postoperative bone mineralization adjacent to acetabular components in primary THA using HA-coated cups compared with porous titanium metal cups. Osseointegration was measured using [18F]-fluoride positron emission tomography combined with computed tomography (F-PET/CT) in regions of interest surrounding the acetabular component. The authors performed a randomized clinical trial that included 28 patients between the ages of 50 and 69 years who were undergoing primary THA for unilateral hip osteoarthritis. Patients received 1 of 2 acetabular components made by the same manufacturer: 1 group received a Trabecular Titanium (TT) metal cup (Limacorporate DELTA TT; Enovis Surgical) made of titanium, and the other group received an HA-coated cup (Limacorporate DELTA PF; Enovis Surgical) made of titanium with a layer of hydroxyapatite. The authors found that bone formation was significantly elevated at 4 weeks postoperatively in both the HA and TT groups compared with their reference groups, indicative of active periacetabular bone remodeling. This metabolic activity was 17% higher in the TT group compared with the HA group, although the difference was not significant. By 16 weeks, bone activity began to decline; the decrease was more pronounced in the TT group, but not significantly so. The study was limited by its small sample size. Furthermore, the 2 implant designs had additional morphologic differences: the HA-coated cup had equatorial retentive grooves designed to enhance fixation, whereas the TT cup did not. These structural variables preclude a pure one-to-one comparison of osseointegration between TT and HA surfaces. Ultimately, the most valuable and clinically meaningful aspect of this study is that it serves as a proof-of-concept investigation that identifies F-PET/CT as an emerging technology for studying the osseointegration of implants in THA. Unlike conventionally used imaging, including radiographs and technetium (Tc)-99-labeled bone scans, F-PET/CT can quantify the metabolic activity of bone adjacent to the prosthesis with great precision and accuracy4. Its pitfalls include greater radiation exposure and cost. Additionally, although the study by Sotiriou et al. revealed a decline in bone turnover adjacent to the acetabular component at 16 weeks, it remains unknown at what time point following cup implantation the findings of periacetabular remodeling are expected to completely normalize on the basis of this imaging technique. Future directions for research include defining the precise standardized uptake value (SUV) targets in F-PET/CT analysis that differentiate between bone turnover indicative of active osseointegration and that indicative of implant loosening. Longitudinal studies are needed to determine the utility of F-PET/CT in the assessment of implant fixation stability over time. Cost analyses should also be performed. Nonetheless, this technology remains a promising option for quantitative assessment of osseointegration in THA. It may be particularly valuable in instances in which conventional methods provide equivocal results in the assessment of aseptic loosening. Furthermore, targeted mapping of ingrowth regions via F-PET/CT may be helpful in the revision setting to determine the regions of interest where intraoperative efforts should be focused for the extraction of a well-fixed acetabular component, which can be especially challenging in revision THA.