Introduction: Pedicle screw instrumentation has been shown to be a useful adjunct in obtaining spinal fixation in arthrodesis surgery. Spinal navigation has been shown to improve the accuracy of pedicle screw placement. Increasing the percent of pedicle that is filled with the screw presumably yields greater fixation. It has not been shown whether or not spinal navigation helps surgeons more completely fill their instrumented pedicles.

Methods: 50 consecutive patients from each arm (navigated and free-hand) were retrospectively reviewed. Cross-sectional area of each instrumented lumbar pedicle and screw were measured utilizing an automatic area calculation tool on the Mayo QReads radiologic imaging system. The coronal images and measurements were blinded for review by the surgeons to confirm accuracy of the measurements.

Results: The instrumented pedicles in the navigated patients were significantly more filled in the coronal plane by screws than the pedicles in the non-navigated patients. The size of the pedicles in each group were not significantly different. (p=0.4903) However, the screw diameters in the navigated patients were statistically significantly larger than those in the free hand patients. (p=0.00000334) This finding then calculated to a statistically significant increased cross-sectional pedicle fill for patients in the image guidance group. (p=0.00000427)

Conclusions: Obtaining a higher cross-sectional percentage fill of the pedicle with a screw is expected to provide greater spinal fixation in instrumented fusion surgery. This study helps to confirm that utilizing spinal navigation helps to more completely fill the pedicles that are being instrumented.

Patient Care: Provide further data for the benefits of utilizing navigation in complex spine surgery

Learning Objectives: The attendees will learn the rationale for measuring the percent fill of a pedicle by screws. The attendees will learn that spinal navigation allows for increased pedicle fill by screws

References: 1. Abshire BB, McLain RF, Valdevit A, Kambic HE: Characteristics of pullout failure in conical and cylindrical pedicle screws after full insertion and back-out. Spine J 1:408-414, 2001 2. Barber JW, Boden SD, Ganey T, Hutton WC: Biomechanical study of lumbar pedicle screws: does convergence affect axial pullout strength? J Spinal Disord 11:215-220, 1998 3. Becker S, Chavanne A, Spitaler R, Kropik K, Aigner N, Ogon M, et al: Assessment of different screw augmentation techniques and screw designs in osteoporotic spines. Eur Spine J 17:1462-1469, 2008 4. Brantley AG, Mayfield JK, Koeneman JB, Clark KR: The effects of pedicle screw fit. An in vitro study. Spine (Phila Pa 1976) 19:1752-1758, 1994 5. Chapman JR, Harrington RM, Lee KM, Anderson PA, Tencer AF, Kowalski D: Factors affecting the pullout strength of cancellous bone screws. J Biomech Eng 118:391-398, 1996 6. Cook SD, Salkeld SL, Whitecloud TS, 3rd, Barbera J: Biomechanical evaluation and preliminary clinical experience with an expansive pedicle screw design. J Spinal Disord 13:230-236, 2000 7. Ebmeier K, Giest K, Kalff R: Intraoperative computerized tomography for improved accuracy of spinal navigation in pedicle screw placement of the thoracic spine. Acta Neurochir Suppl 85:105-113, 2003 8. Gaines RW, Jr.: The use of pedicle-screw internal fixation for the operative treatment of spinal disorders. J Bone Joint Surg Am 82-A:1458-1476, 2000 9. Girardi FP, Cammisa FP, Jr., Sandhu HS, Alvarez L: The placement of lumbar pedicle screws using computerised stereotactic guidance. J Bone Joint Surg Br 81:825-829, 1999 10. Halvorson TL, Kelley LA, Thomas KA, Whitecloud TS, 3rd, Cook SD: Effects of bone mineral density on pedicle screw fixation. Spine (Phila Pa 1976) 19:2415-2420, 1994 11. Hirano T, Hasegawa K, Takahashi HE, Uchiyama S, Hara T, Washio T, et al: Structural characteristics of the pedicle and its role in screw stability. Spine (Phila Pa 1976) 22:2504-2509; discussion 2510, 1997 12. Hirano T, Hasegawa K, Washio T, Hara T, Takahashi H: Fracture risk during pedicle screw insertion in osteoporotic spine. J Spinal Disord 11:493-497, 1998 13. Kim YJ, Lenke LG, Bridwell KH, Cho YS, Riew KD: Free hand pedicle screw placement in the thoracic spine: is it safe? Spine (Phila Pa 1976) 29:333-342; discussion 342, 2004 14. Koranyi E, Bowman CE, Knecht CD, Janssen M: Holding power of orthopedic screws in bone. Clinical orthopaedics and related research 72:283-286, 1970 15. Krag MH, Weaver DL, Beynnon BD, Haugh LD: Morphometry of the thoracic and lumbar spine related to transpedicular screw placement for surgical spinal fixation. Spine (Phila Pa 1976) 13:27-32, 1988 16. Kuklo TR, Lehman RA, Jr.: Effect of various tapping diameters on insertion of thoracic pedicle screws: a biomechanical analysis. Spine (Phila Pa 1976) 28:2066-2071, 2003 17. Kwok AW, Finkelstein JA, Woodside T, Hearn TC, Hu RW: Insertional torque and pull-out strengths of conical and cylindrical pedicle screws in cadaveric bone. Spine (Phila Pa 1976) 21:2429-2434, 1996 18. Law M, Tencer AF, Anderson PA: Caudo-cephalad loading of pedicle screws: mechanisms of loosening and methods of augmentation. Spine (Phila Pa 1976) 18:2438-2443, 1993 19. Lehman RA, Jr., Kuklo TR: Use of the anatomic trajectory for thoracic pedicle screw salvage after failure/violation using the straight-forward technique: a biomechanical analysis. Spine (Phila Pa 1976) 28:2072-2077, 2003 20. Lehman RA, Jr., Polly DW, Jr., Kuklo TR, Cunningham B, Kirk KL, Belmont PJ, Jr.: Straight-forward versus anatomic trajectory technique of thoracic pedicle screw fixation: a biomechanical analysis. Spine (Phila Pa 1976) 28:2058-2065, 2003 21. Linhardt O, Perlick L, Renkawitz T, Matussek J, Plitz W, Grifka J: [Pullout resistance of conventional pedicle screw implantation in comparison to fluoroscopic computer-assisted technique]. Zentralbl Chir 131:407-410, 2006 22. McLain RF, Fry MF, Moseley TA, Sharkey NA: Lumbar pedicle screw salvage: pullout testing of three different pedicle screw designs. J Spinal Disord 8:62-68, 1995 23. Merloz P, Tonetti J, Cinquin P, Lavallee S, Troccaz J, Pittet L: [Computer-assisted surgery: automated screw placement in the vertebral pedicle]. Chirurgie 123:482-490, 1998 24. Nolte L, Zamorano L, Arm E, Visarius H, Jiang Z, Berlerman U, et al: Image-guided computer-assisted spine surgery: a pilot study on pedicle screw fixation. Stereotact Funct Neurosurg 66:108-117, 1996 25. Nottmeier EW, Seemer W, Young PM: Placement of thoracolumbar pedicle screws using three-dimensional image guidance: experience in a large patient cohort. J Neurosurg Spine 10:33-39, 2009 26. Paxinos O, Tsitsopoulos PP, Zindrick MR, Voronov LI, Lorenz MA, Havey RM, et al: Evaluation of pullout strength and failure mechanism of posterior instrumentation in normal and osteopenic thoracic vertebrae. J Neurosurg Spine 13:469-476, 2010 27. Pfeifer BA, Krag MH, Johnson C: Repair of failed transpedicle screw fixation. A biomechanical study comparing polymethylmethacrylate, milled bone, and matchstick bone reconstruction. Spine (Phila Pa 1976) 19:350-353, 1994 28. Polly DW, Jr., Orchowski JR, Ellenbogen RG: Revision pedicle screws. Bigger, longer shims--what is best? Spine (Phila Pa 1976) 23:1374-1379, 1998 29. Skinner R, Maybee J, Transfeldt E, Venter R, Chalmers W: Experimental pullout testing and comparison of variables in transpedicular screw fixation. A biomechanical study. Spine (Phila Pa 1976) 15:195-201, 1990 30. Smith SA, Abitbol JJ, Carlson GD, Anderson DR, Taggart KW, Garfin SR: The effects of depth of penetration, screw orientation, and bone density on sacral screw fixation. Spine 18:1006-1010, 1993 31. Soshi S, Shiba R, Kondo H, Murota K: An experimental study on transpedicular screw fixation in relation to osteoporosis of the lumbar spine. Spine (Phila Pa 1976) 16:1335-1341, 1991 32. Suzuki T, Abe E, Okuyama K, Sato K: Improving the pullout strength of pedicle screws by screw coupling. J Spinal Disord 14:399-403, 2001 33. Vangsness CT, Jr., Carter DR, Frankel VH: In vitro evaluation of the loosening characteristics of self-tapped and non-self-tapped cortical bone screws. Clinical orthopaedics and related research:279-286, 1981 34. Yerby SA, Ehteshami JR, McLain RF: Loading of pedicle screws within the vertebra. J Biomech 30:951-954, 1997 35. Zindrick MR, Wiltse LL, Widell EH, Thomas JC, Holland WR, Field BT, et al: A biomechanical study of intrapeduncular screw fixation in the lumbosacral spine. Clin Orthop Relat Res:99-112, 1986