Introduction: Patient specific morphometric analysis is essential for optimal spinal instrumentation. Earlier studies with Image based measurements fail to consider the effect of third dimension on measurements and hence are not reliable for clinical practice. Cadaver based measurements are not patient specific and cannot be applied in clinical practice

Methods: Computed Tomography images of cervical spine were taken with 64 slice scanner, 1 mm thin axial sections with sagittal and coronal reconstructions were used to take initial measurements. On-Screen Caliper and Protractor were used in any Window or Mac Personal Computer to correct the effect of third dimension. CT Cervical Spine of 75 patients with poly trauma but without osseous - ligamentous injury of cervical spine were studied initially to asses the feasibility of measurements in individual patients. 20 patients who underwent Lateral Mass Screw and Pedicle Screw placements for varied indications were prospectively studied with details of screw length and surgeons perspective of optimal placement; post operative CT of cervical spine were analyzed for the length of the screw used and actual position of screw.

Results: The measurements obtained by use of On-Screen caliper and protractor correlated well with actual length of screws used at surgery and measured in post operative CT images.

Conclusions: Pre Operative morphometric analysis using On-Screen caliper and protractor is a very simple, inexpensive and accurate method of 3D measurement and is a very useful adjunct in Lateral Mass Screw and Pedicle Screw placement in Cervical Spine surgery

Patient Care: In institutions without intra operative navigation, this simple and inexpensive technique will improve the accuracy of Lateral mass and Pedicle screw placement

Learning Objectives: To improve the accuracy of Lateral Mass and Pedicle Screw placement in Cervical spine surgery

References: • Surgical Anatomic Evaluation of the Cervical Pedicle and Adjacent Neural Structures. (Hasan et al, Neurosurgery, Vol. 47, No. 5, November 2000) • Cervical Spine Pedicle Screws : A Biomechanical Comparison of Two Insertion Techniques (Joseph M. Kowalski et al SPINE Volume 25, Number 22, pp 2865–2867,2000) • Computerized tomographic morphometric analysis of subaxial cervical spine pedicles in young asymptomatic volunteers (Raj d. rao et al the journal of bone & joint surgery d jbj s .org. volume 90-a d number 9 d september 2008) • Preoperative imaging of cervical pedicles: comparison of accuracy of oblique radiographs versus axial CT scan (James P. Sieradzki et al Eur Spine J (2008) 17:1230–1236) • Computerized Tomographic Morphometric Analysis of the Cervical Spine (D.S. Evangelopoulos et al The Open Orthopaedics Journal, 2012, 6, 250-254) • Comparison of two novel fluoroscopy-based stereotactic methods for cervical pedicle screw placement and review of the literature (M. Reinhold et al Eur Spine J (2008) 17:564–575) • Three-dimensional frameless stereotactic-guided pedicle screw fixation of the spine: early experiences in king chulalongkorn memorial hospital (chopeow taecholarn et al j med assoc thai vol. 89 no. 2 2006) • Morphometric study of cervical vertebrae c3-c7 in a population from northeastern mexico (juan josé bazaldúa cruz at al, int. j. morphol.29(2):325-330, 2011) • Morphologic evaluation of cervical spine anatomy with computed tomography:anterior cervical plate fixation considerations (brian k. kwon at al j spinal disord tech volume 17, number 2, april 2004) • pedicle screw placement accuracy: a meta-analysis .Victor kosmopoulos et al (spine volume 32, number 3, pp e111–e120 ©2007) • perforation rates of cervical pedicle screw insertion by disease and vertebral level masashi uehara (the open orthopaedics journal, 2010, 4, 142-146) • posterior screw placement on the lateral mass of atlas : an atomic study : xia hong et al (spine volume 29, number 5, pp 500–503 ©2004) • Quantitative anatomy of the lateral mass of the atlas. Yin Dong et al (spine volume 28, number 9, pp 860–863 ©2003) • Placement of Pedicle Screws in the Human Cadaveric Cervical Spine Comparative Accuracy of Three Techniques. Steven C. Ludwig et al (spine volume 25, number 13, pp 1655–1667 ©2000) • Transpedicle screw fixation of the cervical spine. steven c. ludwig et al (clinical orthopaedics and related research number 359, pp 77-88 © 1999) • Cervical pedicle screw placement: feasibility and accuracy of two new insertion techniques based on morphometric data m. reinhold et al (eur spine j (2007) 16: 47–56) • Virtual placement of posterior c1-c2 transarticular screw fixation. peter spangenberg et al (neurosurg rev)