• Jochen Paul, Alexej Barg, Martin Kretzschmar, Geert Pagenstert, Ueli Studler, Thomas Hügle, Nicholas J Wegner, Victor Valderrabano, and Jeroen Geurts.
• Praxisklinik Rennbahn AG, Basel, Switzerland.
• Foot Ankle Int. 2015 Dec 1; 36 (12): 1438-47.

BackgroundWe analyzed the histopathologic findings in end-stage osteoarthritic ankle joint tissue that display increased uptake of bone-seeking radiotracer in single-photon emission computed tomography-computed tomography (SPECT-CT) imaging.MethodsSix consecutive patients with end-stage osteoarthritis undergoing total ankle replacement received preoperative SPECT-CT imaging using (99m)Technetium dicarboxypropane diphosphonate ((99m)Tc-DPD). Using imaging data for stratification, osteochondral tissue sections were prepared from SPECT-positive (+) and -negative (-) areas of tibial and talar resection specimens. Histomorphometric analyses of osteoblast numbers, collagen deposition, and cartilage degeneration were performed on hematoxylin and eosin, van Gieson's and Safranin-O stained tissue sections. Osteoclast activity was visualized using tartrate-resistant acid phosphatase (TRAP) staining.ResultsIncreased (99m)Tc-DPD uptake was observed exclusively subjacent to the subchondral bone plate of tibial and talar joint compartments. SPECT(-) tissues displayed typical fatty marrow morphology containing mainly collagen-positive blood vessels and few marrow and bone-lining cells. SPECT(+) tissues were characterized by increased numbers of active bone-lining osteoblasts depositing collagen fibers. Collagen area fraction of subchondral bone marrow was significantly increased in SPECT(+) (0.52 ± 0.21) compared with SPECT(-) (0.29 ± 0.13) tissues (P = .30). Multinucleated TRAP(+) osteoclasts were absent from bone formation sites, but associated with vascular structures invading articular cartilage through the subchondral bone plate. Increased (99m)Tc-DPD uptake was specifically and strongly correlated with increased osteoblast numbers (P = .011), and with collagen area fraction (P = .030) but not with Mankin score (P = .202), or with osteoclast number (P = .576).ConclusionSubchondral bone tissues in SPECT(+) areas of end-stage ankle osteoarthritis were histologically characterized by increased osteoblast-mediated bone formation in the absence of functional osteoclasts, and increased cellularity and collagen deposition in marrow tissues.Clinical SignificanceOur findings suggest a pathologic bone-remodeling process in end-stage ankle OA areas with increased (99m)Tc-DPD uptake.© The Author(s) 2015.

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