Novel Morphometric Measurement Angles for Guiding Pedicular Screw and Cortical Screw Insertion in the Lumbar Spine
Wilartratsami S, MD1, Sitthitheerarut A, MD1, Chiewvit P, MD2, Bumpass DB, MD3, Pornrattanamaneewong C, MD1, Luksanapruksa P, MD1
Affiliation : 1 Department of Orthopaedic Surgery, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand 2 Division of Diagnostic Radiology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand 3 Department of Orthopedic Surgery, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA
Background : Placement of lumbar pedicle screw fixation shows good results due to the strength and accuracy of pedicle screws.
Placement of lumbar pedicle screws via free-hand technique relies on clear exposure and identification of lumbar morphology. The
purpose of this study was to investigate the reliability and accuracy of angles between the lumbar pedicles and posterior bony
landmarks.
Objective : To establish new morphometric angles, and to evaluate the correlation of these angles between the pedicles and the
posterior elements of the lumbar spine.
Materials and Methods : An institutional radiographic database was retrospectively searched for patients who underwent lumbar
computed tomography scanning during 2007 to 2010. The transverse pedicle angle (TPA) and 3 novel angles were measured,
including the transverse process-pedicle angle (TPPA), pars interarticularis-pedicle angle (PPA), and lamina-pedicle angle (LPA).
Two observers independently measured all angles two times one month apart.
Results : Forty-nine patients (22 men, 27 women) were included. Mean age was 51.82+17.63 years. Mean TPA, TPPA, PPA, and LPA
measurement was 17.2+7.23, 66.59+13.34, 105.74+6.43, and 67.12+7.29 degrees, respectively. There were no significant
relationships with gender or laterality for any angles except PPA. Weight and body mass index correlated significantly with all angles
(p<0.05), but height correlated only with TPA and TPPA. TPA and PPA gradually increased in magnitude from L1 to L5. However,
TPPA was smallest at the L3 level. Intraobserver intraclass correlation coefficients (ICC) ranged from 0.90 to 0.97, and interobserver
ICCs ranged from 0.88 to 0.97, which indicated strong reliability for both measures.
Conclusion : Three novel angle measurements describing the anatomic relationship of the lumbar pedicles to the posterior elements
had strong measurement reliability and may help surgeons more accurately place pedicle screws, especially during revision cases
in which the spinous process was previously removed. These novel measures also show screw placement for the newer cortical
bone trajectory being used for lumbar fixation.
Keywords : Lumbar spine, CT scan, Spine, Pedicle screws, Anatomic landmarks
