Prova detta:
function addUser($usrData) {
$count = 0;
$fields = '';
foreach($usrData as $col => $val) {
if ($count++ != 0) $fields .= ', ';
$col = mysql_real_escape_string($col);
$val = mysql_real_escape_string($val);
$fields .= "`$col` = $val";
}
$query = "INSERT INTO `myTable` SET $fields;";
}