Fig. 4From: Microscopic extra-laminar sequestrectomy (MELS) for the treatment of hidden zone lumbar disc herniation: report of the surgical technique, patient selection, and clinical outcomesSpinal canal area classification. The red area indicates the foraminal zone (canalicular zone); the green area indicates the preforaminal zone or subarticular zone; the blue area indicates the central canal zone, and the transparent square zone indicates the hidden zoneBack to article page