I can't substitude values to a placeholder of SQL statement - php

Question

I tried to separate SQL's data with the following code:
$count = $pdo->query('SELECT COUNT(*) FROM tweets');
foreach ($count as $row) {
$num = $row[0];
echo 'count:'.$row[0].'<br>';
}
echo 'num value: '.$num.'<br>';
$max_page = ceil($num / 10);
echo 'page: '.$max_page.'<br>';
if (!isset($_GET['page'])) {
$_GET['page'] = 1;
} else {
$now = $_GET['page'];
echo '$_GET has been set successfully<br>';
}
$disp_start = $num - 10 * ($now - 1);
echo 'disp_start value: '.$disp_start.'<br>';
$disp_end = $num - 10 * $now;
echo 'disp_end value: '.$disp_end.'<br>';
$disp = $pdo->prepare('SELECT * FROM tweets ORDER BY id DESC LIMIT 10 OFFSET ?');
//$disp -> bindValue(':st', $disp_start);
//$disp -> bindValue(':en', $disp_end);
if ($disp->execute([$disp_end])) {
echo 'success!';
foreach ($disp as $row) {
echo '<div class="breakwater2">';
echo '<div class="tweet">';
echo '<a href="./user/'.$row['uploader'].'.php">';
echo '<img src="', $row['avatar'], '" class="avatar1">';
echo '<div class="cont">';
echo '<b class="username">', $row['uploader'], '</b></a>';
echo '<p class="contents1">', $row['contents'], '</p>';
echo '<p class="time">', $row['time'], '</p>';
echo '</div>';//cont
echo '</div>';//tweet
echo '<form action="" method="post"><input type="hidden" name="del" value='.$row['id'].'>';
if ($_SESSION['user']['id'] == $row['userid']) {
echo '<input type="submit" value="Delete">';
}
echo '</form>';
echo '</div>';
echo '<hr class="division">';
}
} else {
echo 'failure';
print_r ($disp -> errorInfo());
}
for ($i = 1; $i <= $max_page; $i++) {
if ($i == $now) {
echo $now;
} else {
echo ''.$i.'';
}
}
However, when I execute this code an error occurs and it says
failureArray ( [0] => 42000 [1] => 1064 [2] => You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''53'' at line 1
But, if I don't use a placeholder and substitute a value directly to the 'OFFSET' value, it works. How can I solve it?