Biochemical analysis of heterotopic ossification in spinal cord injury patients

Heterotopic ossification (HO) represents a frequent complication in spinal cord injury (SCI) patients. Samples of HO taken from SCI patients were studied and compared to normal bone. We used a procedure of bone particle fractionation (according to their degree of mineralisation) which allowed us to establish a profile reflecting the metabolic remodeling of bone and to analyse the organic matrix of the newly synthesised tissue. In paraplegic patients, we noted that there was a large increase of the proportion of a degree of calcified bone in the HO as we had previously observed in cortical as well as in cancellous bone of the same patients. Based on aminoacid analyses, we observed in the newly synthesised organic matrix of HO a decreased proportion of hydroxyprolyl residues resulting either from an alteration of the prolyl hydroxylation or from the presence of an excess of non-collagen polypeptides. These results are similar to those seen in sublesional bone of the SCI patients. This study demonstrates that HO is a newly formed bone which has a high rate of turnover as is seen in growing bone. This must be taken into account for the treatment of the patients.