title: Effect of pilot hole on biomechanical and in vivo pedicle screw-bone interface.
abstract: OBJECTIVE
  To experimentally study the influence of pilot hole diameter (smaller than or equal to the internal (core) diameter of the screw) on biomechanical (insertion torque and pullout strength) and histomorphometric parameters of screw-bone interface in the acute phase and 8 weeks after pedicle screw insertion.
  
  
  METHODS
  Fifteen sheep were operated upon and pedicle screws inserted in the L1-L3 pedicles bilaterally. The pilot hole was smaller (2.0 mm) than the internal diameter (core) of the screw on the left side pedicle and equal (2.8 mm) to the internal diameter (core) of the screw on the right side pedicle. Ten animals were sacrificed immediately (five animals were assigned to pullout strength tests and five animals were used for histomorphometric bone-screw interface evaluation). Five animals were sacrificed 8 weeks after pedicle screw insertion for histomorphometric bone-screw interface evaluation.
  
  
  RESULTS
  The insertion torque and pullout strength were significantly greater in pedicle screws inserted into pilot holes smaller than internal (core) diameter of the screw. Histomorphometric evaluation of bone-screw interface showed that the percentage of bone-implant contact, the area of bone inside the screw thread and the area of bone outside the screw thread were significantly higher for pilot holes smaller than the internal (core) diameter of the screw immediately after insertion and after 8 weeks.
  
  
  CONCLUSIONS
  A pilot diameter smaller than the internal (core) diameter of the screw improved the insertion torque and pullout strength immediately after screw insertion as well the pedicle screw-bone interface contact immediately and 8 weeks after screw placement in sheep with good bone mineral density.
authors: Department of Biomechanic, Medicine and Rehabilitation of the Locomotor System, Faculty of Medicine of Ribeirão Preto, USP, Av. Bandeirantes, 3900, 11°Andar, Ribeirão Preto, São Paulo 14048-900, Brazil. patriciasilva2@terra.com.br
authors: Patrícia
authors: P
authors: Silva
authors: Rodrigo César
authors: RC
authors: Rosa
authors: Antonio Carlos
authors: AC
authors: Shimano
authors: Helton L A
authors: HL
authors: Defino
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001863:Bone Screws; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008422:Materials Testing; D023421:Models, Animal; D019637:Orthopedic Procedures / Q000295:instrumentation / Q000379:methods*; D012756:Sheep; D019415:Torque
references: Bone. 1995 Apr;16(4 Suppl):277S-284S
references: 7626315
references: Int Orthop. 2010 Mar;34(3):447-51
references: 19330331
references: Acta Cir Bras. 2011 Aug;26(4):261-6
references: 21808837
references: Biomaterials. 2004 Apr;25(9):1697-714
references: 14697871
references: Spine J. 2001 Nov-Dec;1(6):408-14
references: 14588297
references: Bone. 1991;12(6):421-7
references: 1797057
references: Spine (Phila Pa 1976). 2006 Nov 1;31(23):E867-70
references: 17077722
references: Int J Prosthodont. 1998 Sep-Oct;11(5):491-501
references: 9922740
references: Clin Orthop Relat Res. 1993 Nov;(296):278-87
references: 8222439
references: J Spinal Disord. 2000 Jun;13(3):259-66
references: 10872766
references: J Neurosurg Spine. 2005 Nov;3(5):364-70
references: 16302630
references: Spine (Phila Pa 1976). 1996 Nov 1;21(21):2429-34
references: 8923627
references: Spine (Phila Pa 1976). 1993 Sep 15;18(12):1673-6
references: 8235848
references: Eur Cell Mater. 2007 Mar 02;13:1-10
references: 17334975
references: J Orthop Res. 2005 Jul;23(4):788-94
references: 16022991
references: J Bone Joint Surg Am. 2008 Nov;90(11):2485-98
references: 18978418
references: Spine (Phila Pa 1976). 1990 Sep;15(9):902-7
references: 2259978
references: Med Eng Phys. 2003 May;25(4):275-82
references: 12649011
references: Med Eng Phys. 2006 Nov;28(9):888-93
references: 16458568
references: Spine (Phila Pa 1976). 2001 Dec 15;26(24):2673-8
references: 11740353
references: Spine (Phila Pa 1976). 2009 Apr 20;34(9):871-6
references: 19531995
references: Clin Biomech (Bristol, Avon). 2007 May;22(4):385-91
references: 17208340
references: Dent Traumatol. 2003 Jun;19(3):139-44
references: 12752535
references: J Orthop Res. 1999 Sep;17(5):654-60
references: 10569473
references: J Spinal Disord Tech. 2005 Dec;18(6):506-10
references: 16306839
references: Spine (Phila Pa 1976). 2001 Nov 15;26(22):2498-503
references: 11707718
references: J Bone Joint Surg Br. 2010 Aug;92(8):1061-5
references: 20675747
references: Eur Spine J. 2010 Jan;19(1):71-7
references: 19526377
references: Eur Spine J. 2012 May;21(5):956-63
references: 22173611
references: Clin Oral Implants Res. 2007 Oct;18(5):563-8
references: 17590162
references: J Spinal Disord. 2000 Jun;13(3):230-6
references: 10872761
references: Clin Orthop Relat Res. 1975 May;(108):115-26
references: 1139814
references: Spine (Phila Pa 1976). 1987 Jul-Aug;12(6):544-51
references: 3660081
references: J Prosthet Dent. 1983 Jul;50(1):101-7
references: 6576145
references: Spine J. 2004 Sep-Oct;4(5):513-8
references: 15363421
references: Spine (Phila Pa 1976). 2010 Apr 20;35(9):E332-7
references: 20150834
references: Eur Spine J. 2001 Aug;10(4):325-33
references: 11563619
references: J Spinal Disord. 1994 Apr;7(2):139-45
references: 8003831
references: J Bone Miner Res. 1993 Dec;8(12):1417-26
references: 8304041
references: Med Eng Phys. 2010 Mar;32(2):145-54
references: 19945333