Got it,here's i do it

in showthread template

Find :

Code: 
$header
$navbar
$poll

Add below

Code: 
$threadtitle Your keyword bla bla bla....<br />
<br />
in postbit/postbit_legacy template
Find :

Code: 
<!-- message -->
<div id="post_message_$post[postid]">$post[message]</div>
<!-- / message -->
Add above

Code: 
$thread[title] Your keyword bla bla bla....<br /> 
<br />
And add below

Code: 
$thread[title] Your keyword bla bla bla....
ps : my forum is vB 3.8.x