assume that the last word is always going to be truncated and remove it.
here is a sample of how to do that:
<?php
// strip the tags
$returnString = strip_tags($row_rsBlog['BlogContent']);
//truncate to first 50 characters
$returnString = substr($returnString, 0, 50);
// find the space near the end of the string
$lastSpacePosition = strrpos($returnString," ");
//remove everything from that space to the end
$returnStringWithoutLastWord = substr($returnString,0,$lastSpacePosition);
// echo the result
echo($returnStringWithoutLastWord."...");
?>