Pedicle Screw Surface Coatings Improve Fixation in Nonfusion Spinal Constructs

Study Design. Biomechanical and histologic analysis. Objective. To compare the strength of the bone-screw interface of standard uncoated pedicle screws with screws treated with hydroxyapatite (HA), titanium plasma spray (TPS), and a composite HA-TPS coating. Summary of Background Data. Transpedicular screw fixation has become the gold standard in the treatment of various thoracolumbar spinal conditions. Pedicle screw loosening, however, has been reported, especially in mechanically demanding constructs or in vertebrae with low bone mineral density. Methods. Six mature porcine were instrumented with 4 types of titanium monoaxial pedicle screws (uncoated, HA-only coated, TPS-only coated, and HA-TPS composite coated) in a systematically varied, single-blinded fashion. After a 3-month survival period, the spines were harvested en-bloc and “time zero” control screws were instrumented in adjacent vertebrae. Screw placement and bone mineral density were evaluated with a postharvest computed tomography, and the strength of the tissue-implant interface was evaluated with a torsional screw extraction analysis (60 screws) and a nondecalcified histologic analysis (16 screws). Results. At 3 months postoperative, peak torque increased for all 3 types of coated screws (increased fixation) and decreased significantly for the uncoated screws (P < 0.001). Although 3-month peak torque was not statistically different between the 3 screw coatings, 4 of 10 TPS-only coated screws had a peak torque that was nearly 0 (<0.1 N m) versus only 1 of 10 HA-only screws and 0 of 10 HA-TPS composite screws. Histologic analysis confirmed the biomechanical findings with improved osseointegration in the HA-only and HA-TPS composite screws. Conclusion. Pedicle screw coatings that promote mechanical interlocking, TPS, or direct osteoblast bonding(HA) increased screw fixation in this nonfusion model. More non-HA coated screws, however, were thought to be “loose” with a nearly zero peak extraction torque and fibrous encapsulation. Increased osseointegration with HA may result in a decreased incidence of screw loosening and improved outcomes of transpedicular spinal instrumentation in nonfusion procedures.

[1]  A. Mahar,et al.  Biomechanical comparison of different anchors (foundations) for the pediatric dual growing rod technique. , 2008, The spine journal : official journal of the North American Spine Society.

[2]  T. Wright,et al.  Use of instrumented pedicle screws to evaluate load sharing in posterior dynamic stabilization systems. , 2008, The spine journal : official journal of the North American Spine Society.

[3]  M. Arlin.  Survival and success of sandblasted, large-grit, acid-etched and titanium plasma-sprayed implants: a retrospective study. , 2007, Journal.

[4]  A. Binahmed,et al.  Long-term follow-up of hydroxyapatite-coated dental implants--a clinical trial. , 2007, The International journal of oral & maxillofacial implants.

[5]  L. Beaupre,et al.  Hydroxyapatite-coated tibial implants compared with cemented tibial fixation in primary total knee arthroplasty. A randomized trial of outcomes at five years. , 2007, The Journal of bone and joint surgery. American volume.

[6]  B. Frankel,et al.  SEGMENTAL POLYMETHYLMETHACRYLATE‐AUGMENTED PEDICLE SCREW FIXATION IN PATIENTS WITH BONE SOFTENING CAUSED BY OSTEOPOROSIS AND METASTATIC TUMOR INVOLVEMENT: A CLINICAL EVALUATION , 2007, Neurosurgery.

[7]  R. McLain,et al.  Primary Pedicle Screw Augmentation in Osteoporotic Lumbar Vertebrae: Biomechanical Analysis of Pedicle Fixation Strength , 2007, Spine.

[8]  Kjell G Nilsson,et al.  Uncemented HA-coated Implant is the Optimum Fixation for TKA in the Young Patient , 2006, Clinical orthopaedics and related research.

[9]  B. Aksakal,et al.  Hydroxyapatite Dip Coated and Uncoated Titanium Poly-Axial Pedicle Screws: An In Vivo Bovine Model , 2006, Spine.

[10]  A. Vaccaro,et al.  Posterior thoracic segmental pedicle screw instrumentation: evolving methods of safe and effective placement. , 2005, Neurology India.

[11]  Xuanyong Liu,et al.  In vivo evaluation of plasma-sprayed titanium coating after alkali modification. , 2005, Biomaterials.

[12]  H. Mishima,et al.  Grit-blasted and hydroxyapatite-coated total hip arthroplasty: an 11- to 14-year follow-up study , 2004, Journal of orthopaedic science : official journal of the Japanese Orthopaedic Association.

[13]  Yu-peng Lu,et al.  Plasma-sprayed hydroxyapatite+titania composite bond coat for hydroxyapatite coating on titanium substrate. , 2004, Biomaterials.

[14]  B. Sandén,et al.  The significance of radiolucent zones surrounding pedicle screws. Definition of screw loosening in spinal instrumentation. , 2004, The Journal of bone and joint surgery. British volume.

[15]  Young-Hoo Kim,et al.  Comparison of porous-coated titanium femoral stems with and without hydroxyapatite coating. , 2003, The Journal of bone and joint surgery. American volume.

[16]  J. Torner,et al.  In vitro biomechanical comparison of pedicle screws, sublaminar hooks, and sublaminar cables. , 2003, Journal of neurosurgery.

[17]  David Feeny,et al.  Comparison of Total Hip Arthroplasty Performed with and without Cement: A Randomized Trial , 2002, The Journal of bone and joint surgery. American volume.

[18]  O. Schwarzenbach,et al.  The dynamic neutralization system for the spine: a multi-center study of a novel non-fusion system , 2002, European Spine Journal.

[19]  B. Sandén,et al.  Hydroxyapatite coating improves fixation of pedicle screws. A clinical study. , 2002, The Journal of bone and joint surgery. British volume.

[20]  A. Evans,et al.  Increased pedicle screw pullout strength with vertebroplasty augmentation in osteoporotic spines. , 2002, Journal of neurosurgery.

[21]  B. Sandén,et al.  Improved Bone–Screw Interface With Hydroxyapatite Coating: An In Vivo Study of Loaded Pedicle Screws in Sheep , 2001, Spine.

[22]  D. Benson,et al.  Segmental instrumentation for thoracic and thoracolumbar fractures: prospective analysis of construct survival and five-year follow-up. , 2001, The spine journal : official journal of the North American Spine Society.

[23]  P. Herberts,et al.  Tibial component fixation in porous- and hydroxyapatite-coated total knee arthroplasty: a radiostereo metric evaluation of migration and inducible displacement after 5 years. , 2000, The Journal of arthroplasty.

[24]  E R Valstar,et al.  The Effect of Hydroxyapatite on the Micromotion of Total Knee Prostheses. A Prospective, Randomized, Double-Blind Study* , 1998, The Journal of bone and joint surgery. American volume.

[25]  J. Jansen,et al.  Histomorphometrical and mechanical evaluation of titanium plasma-spray-coated implants placed in the cortical bone of goats. , 1998, Journal of biomedical materials research.

[26]  S. Shott,et al.  Hydroxyapatite augmentation of the porous coating improves fixation of tibial components. A randomised RSA study in 116 patients. , 1998, The Journal of bone and joint surgery. British volume.

[27]  R Skalak,et al.  An in-vivo method for biomechanical characterization of bone-anchored implants. , 1998, Medical engineering & physics.

[28]  Rickard Brånemark,et al.  Biomechanical characterization of osseointegration: An experimental in vivo investigation in the beagle dog , 1998, Journal of orthopaedic research : official publication of the Orthopaedic Research Society.

[29]  O. Böstman,et al.  Complications of transpedicular lumbosacral fixation for non-traumatic disorders. , 1997, The Journal of bone and joint surgery. British volume.

[30]  S. Cook,et al.  Effects of Bone Mineral Density on Pedicle Screw Fixation , 1994, Spine.

[31]  M. Asher,et al.  The Strength and Stiffness of Thoracic Implant Anchors in Osteoporotic Spines , 1994, Spine.

[32]  W. Hayes,et al.  Effect of screw diameter, insertion technique, and bone cement augmentation of pedicular screw fixation strength. , 1993, Clinical orthopaedics and related research.

[33]  R. E. Grant,et al.  Pedicle screw fixation in the management of unstable thoracolumbar spine injuries. , 1992, Orthopaedic review.

[34]  Y. E. Kim,et al.  An Analytical Investigation of the Mechanics of Spinal Instrumentation , 1988, Spine.

[35]  A. Tencer,et al.  Biomechanical Comparisons of Spinal Fracture Models and the Stabilizing Effects of Posterior Instrumentations , 1988, Spine.

[36]  J. Kärrholm,et al.  Cemented versus hydroxyapatite fixation of the femoral component of the Freeman-Samuelson total knee replacement: a radiostereometric analysis. , 2007, The Journal of bone and joint surgery. British volume.

[37]  L. Dorr,et al.  Comparison of proximal porous-coated and grit-blasted surfaces of hydroxyapatite-coated stems. , 2004, The Journal of bone and joint surgery. American volume.

[38]  G. Missenard,et al.  Hydroxylapatite-coated Diapason screws: first clinical report. , 1995, Journal of spinal disorders.

[39]  D P McGowan,et al.  Spinal pedicle fixation: reliability and validity of roentgenogram-based assessment and surgical factors on successful screw placement. , 1990, Spine.