Noncollagenous proteins in heterotopic ossification. Immunohistochemical analysis in 15 paraplegies

We used immunohistochemical techniques to investigate the distribution pattern of osteonectin, osteocalcin, bone sialoprotein II and the small proteoglycans decorin and PG 100 during different stages of heterotopic ossification (HO) in pressure sores of paraplegic patients. All these noncollagenous proteins (NCPs) accumulated in fibroblasts and preosteoblasts, predominantly in the activity centers of early osteogenetic areas. Mature types of HO showed a more discrete expression pattern for this protein group, with weaker reactions in the narrow osteoblastic rims. Decorin was detected predominantly in the stroma of HO. Our results indicate that the NCPs are important components during the pathogenesis of HO and that fibroblasts may serve as osteoprogenitor cells.