A new foramen on posterior aspect of ala of first sacral vertebra *

Introduction The sacrum is a large triangular bone formed by fusion of five sacral vertebrae [1]. Anatomy of sacral vertebra is complex [2]. Technically, the placement of pedicle screw into S1 vertebra is a difficult surgical procedure. Therefore it is important to know the anatomy of S1 vertebra [3]. First sacral vertebra possesses the features of typical vertebra in modified form. Thus it consists of body, vertebral foramen, articular process and ala. Ala of sacrum is formed by fusion of costal elements and transverse process. Anterior 3/4 of ala of sacrum is formed by costal elements and posterior 1/4 is formed by transverse process. A new foramen (Figure1) was detected on posterior aspect of ala of sacrum on left side. Detection of foramen on posterior aspect of ala of sacrum may change the prevailing concept of anatomy in this region. Foramen on the first sacral vertebra has been described to be absent. No literature in the contemporary research has been found in relation to any foramen in this region except that in Cunningham’s Textbook of Anatomy [4] record the occurrence of a foramen in the lateral part of first sacral vertebra which is completely different from new foramen on posterior aspect of first sacral vertebra. The pedicle screw fixation/instrumentation may damage the structure passing through this foramen resulting in neurovascular injury if the orthopaedic surgeon is unaware of this foramen. Therefore to alert orthopaedic surgeons, neurosurgeons, and to document its location, dimensions, modification in structural pattern and clinical implication the study has been carried out.