WordPress で前記事と次記事のリンクにサムネイルを追加する方法

<div id="post-nav" class="navigation">
<?php $prevPost = get_previous_post(true);
if($prevPost) ?>
<div class="nav-box previous">
<?php previous_post_link(&#39;&laquo; &laquo; Previous Post:&#39;, &#39;yes&#39;); ?>
<?php $prevthumbnail = get_the_post_thumbnail($prevPost->ID, array(100,100) );?>
<?php previous_post_link(&#39;%link&#39;,"$prevthumbnail <p>%title</p>", TRUE); ?>
</div>
<?php $nextPost = get_next_post(true);
if($nextPost) ?>
<div class="nav-box next" style="float:right;">
<?php previous_post_link(&#39;&raquo; &raquo; Next Post:&#39;, &#39;yes&#39;); ?>
<?php $nextthumbnail = get_the_post_thumbnail($nextPost->ID, array(100,100) ); ?>
<?php next_post_link(&#39;%link&#39;,"$nextthumbnail <p>%title</p>", TRUE); ?>
</div>
<?php ?>
</div>

#post-nav{clear: both; height: 100px; margin: 0 0 70px;}
#post-nav .nav-box{background: #e9e9e9; padding: 10px;}
#post-nav img{float: left; margin: 0 10px 0 0;}
 
#post-nav p{margin: 0 10px; font-size: 11px; vertical-align: middle;}
#post-nav .previous{float: left; vertical-align: middle; width: 300px; height: 120px;}
#post-nav .next{float: right; width: 300px; height: 120px;}