Heterotopic ossification (HO) is the abnormal, non-neoplastic presence of lamellar bone in soft tissue. Bone morphogenetic proteins (BMP) are among factors that may lead to HO. The purpose of the study was to evaluate correlations between BMP-4 gene expression and HO and the influence of those factors on outcomes of cementless total hip replacement (THR).
A series of sixty-four (64) patients were enrolled. The patients were at a mean age of 52.3 years and all of them had undergone unilateral THR. Mean duration of follow-up was 56.74 months. At the last follow-up visit, 1 ml blood samples were collected and BMP-4 gene expression was measured by the RT-PCR technique. Hip radiographs were also obtained and a clinical examination was performed during that visit.
A strong statistical correlation was observed between HO grades according to Brooker's scale and BMP-4 expression levels (rho=0.946, p<0.0001), while there was no correlation between clinical outcomes according to the Harris Hip Score (HHS) and Brooker's grades (rho= -0.188, p=0.3) as well as between Harris hip scores and BMP-4 expression levels (rho=0.1, p=0.6).
BMP-4 expression strongly correlates with HO as measured by Brooker's scale and may play a role in the aetiology of this condition. The over-expression of BMP-4 may exert a certain influence on ectopic bone formation after total hip arthroplasty.