Background: Exostosis (or osteochondroma) is the most common benign bone tumour encountered in children and adults. Exostoses may occur as solitary or multiple tumours (in the autosomal syndromes of hereditary multiple exostoses). Exostoses are composed of cortical and medullary bone covered by an overlying hyaline cartilage cap. The pathophysiology of isolated exostosis in unknown but multiple tumours are associated with an autosomal dominant syndrome- hereditary multiple exostoses (HME) - due to mutations in genes responsible for heparan sulfate (HS) biosynthesis.
Methods: The aims of the present study were to analyse the matrix composition of 15 of these benign tumours by histological and histochemical methods. Undecalcified sections were stained by Goldners trichrome for osteoid, toluidine blue for glycosaminoglycans, Perls (for iron) and mordant blue (for aluminium). Specificity of the metal staining was obtained by scanning electron microscopy with energy dispersive analysis (EDX) and wavelength-dispersive spectroscopy (WDS) on the polished blocs.
Results: Histochemistry identified Al in all tumours as linear bands deposited by the osteoblasts in the calcified matrix of the trabeculae, in some areas of calcified cartilage or the cortical shell. Iron was detected in 10 out of the 15 patients as linear bands in the same locations. Osteoid thickness was normal in all patients. EDX failed to identified iron or aluminium in all the samples. WDS confirmed that the metal ions were present a very low concentration (iron: 30-495 x 10−6% and aluminium 15-27 x 10-6%).
Conclusions: Aluminium and iron are two metals actively substituted to calcium in hydroxyapatite crystals of the bone matrix. Histochemical analysis of iron and aluminium represents a very sensitive method. EDX having a sensitivity of 5% failed to identify these two metals in the exostoses. WDS confirmed the presence of these metals and also showed that their concentrations are were limited. Aluminium and iron are known to strongly inhibit mineralisation of bone but the osteoid thickness was normal in all cases. The presence of these two metals in the calcified matrix of bone advocates for a disturbed metabolism of osteoblasts and chondrocytes in exostosis similar to that observed in case of hemochromatosis.
Disclosure: The authors declared no competing interests.