Importance of microstructure of lumbar pedicle in screw placement

Abstract

Abstract Background and objective : Any structural deviation of the pedicle may result in interference of the weight transmission mechanism and compression of neural structures. The aim of this study was to qualitatively investigate osteonal structures within the cortical bone and thickness of medial and lateral walls of lumbar pedicle. Materials and methods : Specimens consisted of L3 vertebrae from 20 adult cadavers (14 males and 6 females) belonging to North West Indian population. The pedicles of each specimen were cut off at the pedicle-vertebral body junction and processed for paraffin sections after decalcification. 8-10 µ thick transverse sections were cut with rotary microtome at middle of the pedicle. The sections were stained with hematoxylin and eosin. Results : The mean cortical thickness on superior, inferior, medial and lateral was 1.3, 1.6, 0.8 and 0.6 mm respectively in males and 1.1, 1.3, 0.9 and 0.6 mm respectively in females. Cortical thickness was more on medial side compared to lateral side of the pedicle. The cortex of the inferior side of the pedicle was the thickest of all margins. The core of pedicle was filled up with irregularly placed bony trabaculae and marrow spaces. Conclusions : The section of pedicle resembled a shell with an outer cortex surrounding inner cancellous bone. The thickness of the cortical bone of pedicle was not homogeneous, being thicker on medial side compared to lateral side and cortical bone of the inferior side was thickest of all margins.