$values = array('nom', 'prenom', 'taille', 'mescouilles');
$mergeIn = array_merge([$values[0], $values[1], $values[2] . ' ']);
$implodeIn = implode(' ', $mergeIn);
$replacement = str_replace(' ', ' = ?, ', $implodeIn);
$finalString = substr_replace($replacement, '',-2);