Novel morphometric measurement angles for guiding pedicular screw and cortical screw insertion in the lumbar spine

Abstract

© JOURNAL OF THE MEDICAL ASSOCIATION OF THAILAND| 2019 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.