I'm trying to run three MySQL queries from a PHP script, the first one works fine, but on the second one I get the "Commands out of sync; you can’t run this command now" error. I have managed to understand that I need to "empty" the resultset before preparing a new query but I can't seem to understand how. I thought that $statement->close; would do that for me. Here is the relevant part of the code:

<?php
    $statement = $db_conn->prepare("CALL getSketches(?,?)"); // Prepare SQL routine to check if user is accepted
    $statement->bind_param("is", $user_id, $loaded_sketches); // Bind variables to send
    $statement->execute(); // Execute the query

    $statement->bind_result( // Set return varables
        $id, $name,
        $description,
        $visibility,
        $createdby_id,
        $createdby_name,
        $createdon,
        $permission
    );
    $new_sketches_id = array();
    while($statement->fetch()) {
        $result['newSketches'][$id] = array(
            "name" => $name,
            "description" => $description,
            "visibility" => $visibility,
            "createdById" => $createdby_id,
            "createdByName" => $createdby_name,
            "createdOn" => $createdon,
            "permission" => $permission
        );
        $new_sketches_id[] = $id;
    }
    $statement->close; // Close satement

    $new_sketches_ids = implode(",", $new_sketches_id);

    // Get the new sketches elements
    $statement = $db_conn->prepare("CALL getElements(?,'',?,'00000000000000')"); // Prepare SQL routine to check if user is accepted

// The script crashes here with $db_conn->error
// "Commands out of sync; you can't run this command now"

    $statement->bind_param("si", $new_sketches_ids, $user_id); // Bind variables to send
    $statement->execute(); // Execute the query

    $statement->bind_result( // Set return varables
        $id,
        $user_id,
        $type,
        $attribute_d,
        $attribute_stroke,
        $attribute_strokeWidth,
        $sketch_id,
        $createdon
    );
    while($statement->fetch()) {
        $result['newSketches'][$sketch_id]['newElements']["u".$user_id."e".$id] = array(
            "type" => $type,
            "d" => $attribute_d,
            "stroke" => $attribute_stroke,
            "strokeWidth" => $attribute_strokeWidth,
        );
    }
    $statement->close; // Close satement
?>

How can I make the second query without closing and reopening the entire database connection?