“…This observation can partially be explained by normal ageing (Maldonado et al, 2011) but can also be directly linked to the surgical intervention and the mechanical stresses that are subsequently generated (Matsumoto et al, 2010). Moreover, spinal fusion does not always succeed and an incomplete fusion might result in the reappearance of back pain (Korovessis et al, 2005;Lee et al, 2011;Li et al, 2012;Watkins et al, 2014). The reason for this is not yet fully understood, but residual IVD tissue seems to alter and/or block the ossification of the spine Tekari et al, 2017), a fact that could explain why BMP-2-coated implants have a rather neutral effect in meta-analyses (Carragee et al, 2011;Simmonds et al, 2013).…”