In vivo three-dimensional morphometric analysis of the lumbar pedicle isthmus.

STUDY DESIGN In vivo noninvasive study. OBJECTIVE To properly quantify pedicle anatomic parameters, using subject-based CT three-dimensional models and compare the data from 2-dimensional transverse-CT images. SUMMARY OF BACKGROUND DATA Accurate measurement of morphometric parameters of pedicle isthmus is important for transpedicular procedures. Anatomically, the lumbar pedicle is known to be elliptical cross-sectionally and slightly inclined in the vertical plane in the lower lumbar levels. Therefore, measurement of the pedicle isthmus may be overestimated when transverse images are used. More accurate measurement of the 3-dimensional geometry of the pedicle is therefore needed. To the best of our knowledge, 3-dimensional geometry of the pedicle has not been reported as the literature values are based on 2-dimensional image data. METHODS In vivo measurements of the lumbar pedicle isthmus were performed on the 3-dimensional subject-based CT models, using custom-developed software in 89 volunteers. RESULTS The least axis of pedicle, the longest axis of pedicle and the transverse plane width were largest at L5 in both genders. The isthmus angle declined in the lower levels. The ratio of the transverse plane width to the least axis of pedicle was largest at L5. CONCLUSION Our results showed that the least axis of pedicle, the longest axis of pedicle and the transverse plane width peaked at L5, and the transverse plane width became approximately twice as long in the lower levels compared to the upper levels. The ratio of the transverse plane width to the least axis of pedicle increased by about 40% at L5. These findings highlight the fact that measuring the isthmus width from CT transverse images leads to overestimation, especially in the lower lumbar spine. Therefore, a 3-dimensional inclination of the least axis of the pedicle should be taken into account for the determination of the pedicle diameter in the lower lumbar vertebrae.