Some believe that mechanically separated meat has public health importance as a bit of spinal cord often mixes with the meat and can cause disease transmission while others approved it as a normal ingredient in meat industry.
The issue of the public health significance of spinal cord in MSM depends on the source of MSM (i,e, whether from ruminants, non-ruminants or poultry). There is a potential risk with the presence of spinal cord in MSM from ruminants, due to BSE. Because of this risk in the EU the production of MSM from ruminants originating from countries or regions with a controlled or undetermined BSE risk is currently not allowed (EC regulation 999/2001). The presence of spinal cord, although undesirable, in MSM produced from pork and poultry is not considered a public health risk. The risk is mainly microbial, as it is with all other meats.
The public health risks related to MSM derived from poultry and swine have recently been reviewed by the European Food Safety Authority (see http://www.efsa.europa.eu/en/efsajournal/doc/3137.pdf).
I fully agree with Christian. Above that, there is a quality issue. MSM might contain bone fragments due to the procedure to separate the meat from the bones. Also for this aspect there are regulations.