Tenosynovial giant cell tumour (pigmented villonodular synovitis-)-like changes in periprosthetic interface membranes.

Tenosynovial giant cell tumour (TSGCT; synonym, pigmented villonodular synovitis (PVNS)) is a rare low-grade mesenchymal neoplasm of either intra-articular or extra-articular origin. The etiopathogenesis of TSGCT is still uncertain, but recent studies showed a translocation involving colony-stimulating factor 1 (CSF-1) gene in a subset of cases. Histological features mimicking TSGCT can sometimes be encountered in periprosthetic interface membranes. To investigate the frequency and morphologic spectrum of this phenomenon, we conducted a systematic analysis of 477 periprosthetic interface membranes and performed immunohistochemical analysis on a subset of lesions compared to genuine TSGCT. In 26 of 477 periprosthetic membrane samples (5 %), at least some TSGCT-like features were found and 18 cases (4 %) strongly resembled it. Wear particles were detected in 100 % of the TSGCT-like lesions but only in 63.3 % of the whole cohort of periprosthetic membranes (p value <0.001). Immunohistochemistry comparing true TSGCT and TSGCT-like membranes showed similar inflammatory infiltrates with slightly elevated CD3+/CD8+ T lymphocytes and a slightly higher proliferation index in TSGCT samples. In conclusion, TSGCT-like changes in periprosthetic membranes likely represent exuberant fibrohistiocytic inflammatory response induced by wear particles and should be distinguished from genuine (neoplastic) TSGCT. Although TSGCT and TSGCT-like periprosthetic membranes represent different entities, their comparable morphology might reflect analogous morphogenesis.