Dual pitch titanium-coated pedicle screws improve initial and early fixation in a polyetheretherketone rod semi-rigid fixation system in sheep

Abstract

Background:Reports on the efficacy of modifications to the thread design of pedicle screws are scarce. The aim of the study was to investigate initial and early fixation of pedicle screws with a plasma-sprayed titanium coating and dual pitch in the pedicle region (dual pitch titanium-coated pedicle screw [DPTCPS]) in a polyetheretherketone (PEEK) rod semi-rigid fixation system.Methods:Fifty-four sheep spine specimens and 64 sheep were used to investigate initial (“0-week” controls) and early (post-operative 6 months) fixation, respectively. Sheep were divided into dual pitch pedicle screw (DPPS), standard pitch pedicle screw (SPPS), DPTCPS, and standard pitch titanium-coated pedicle screw (SPTCPS) groups. Specimens/sheep were instrumented with four screws and two rods. Biomechanical evaluations were performed, and histology at the implant-bone interface was investigated.Results:At 0-week, mean axial pull-out strength was significantly higher for the DPTCPS and SPTCPS than the SPPS (557.0 ± 25.2 vs. 459.1 ± 19.1 N, t = 3.61, P < 0.05; 622.6 ± 25.2 vs. 459.1 ± 19.1 N, t = 3.43, P < 0.05). On toggle-testing, the DPTCPS was significantly more resistant than the SPPS and SPTCPS (343.4 ± 16.5 vs. 237.5 ± 12.9 N, t = 3.52, P < 0.05; 343.4 ± 16.5 vs. 289.9 ± 12.8 N, t = 3.12, P < 0.05; 124.7 ± 13.5 vs. 41.9 ± 4.3 cycles, t = 2.18, P < 0.05; 124.7 ± 13.5 vs.79.5 ± 11.8 cycles, t = 2.76, P < 0.05). On cyclic loading, maximum displacement was significantly lower for the DPTCPS than the SPPS and SPTCPS (1.8 ± 0.13 vs. 3.76 ± 0.19 mm, t = 2.29, P < 0.05; 1.8 ± 0.13 vs. 2.46 ± 10.20 mm, t = 2.69, P < 0.05). At post-operative 6 months, mean axial pull-out strength was significantly higher for the DPTCPS and SPTCPS than the SPPS (908.4 ± 33.6 vs. 646.5 ± 59.4 N, t = 3.34, P < 0.05; 925.9 ± 53.9 vs. 646.5 ± 59.4 N, t = 3.37, P < 0.05). On toggle-testing, the DPTCPS was significantly more resistant than the SPPS and SPTCPS (496.9 ± 17.9 vs. 370.3 ± 16.4 N, t = 2.86, P < 0.05; 496.9 ± 17.9 vs. 414.1 ± 12.8 N, t = 2.74, P < 0.05; 249.1 ± 11.0 vs.149.9 ± 11.1 cycles, t = 2.54, P < 0.05; 249.1 ± 11.0 vs.199.8 ± 7.2 cycles, t = 2.61, P < 0.05). On cyclic loading, maximum displacement was significantly lower for the DPTCPS than the SPPS and SPTCPS (0.96 ± 0.11 vs. 2.39 ± 0.14 mm, t = 2.57, P < 0.05; 0.96 ± 0.11 vs. 1.82 ± 0.12 mm, t = 2.73, P < 0.05). Resistance to toggle testing (370.3 ± 16.4 vs. 414.1 ± 12.8 N, t = 3.29, P < 0.05; 149.9 ± 11.1 vs.199.8 ± 7.2 cycles, t = 2.97, P < 0.05) was significantly lower and maximum displacement in cyclic loading (2.39 ± 0.14 vs.1.82 ± 0.12 mm; t = 3.06, P < 0.05) was significantly higher for the SPTCPS than the DPTCPS. Bone-to-implant contact was significantly increased for the DPTCPS compared to the SPPS (58.3% ± 7.0% vs. 36.5% ± 4.4%, t = 2.74, P < 0.05); there was no inflammatory reaction or degradation of coated particles.Conclusion:DPTCPSs might have stronger initial and early fixation in a PEEK rod semi-rigid fixation system.

Influência da superfície dos parafusos pediculares no torque de inserção e resistência ao arrancamento

“…11 The greater resistance to pull-out of screws with a rough surface compared to screws with a smooth surface was observed in the acute and chronic phase, after insertion in sheep's vertebrae. 7 The results of the present study do not corroborate these reports, but the experimental model used should be taken into account. In our study, the tests were performed with screws inserted in polyurethane, which despite being widely used in this type of mechanical test, should be recognized as a limitation.…”

“…A maior resistência ao arrancamento dos parafusos com superfície áspera comparado com os parafusos de superfície lisa foi observada na fase aguda e crônica, após a inserção em vértebras de ovelhas. 7 Os resultados do presente estudo não corroboram com esses relatos, mas deve ser considerado o modelo experimental utilizado. Em nosso estudo, os ensaios foram realizados com os parafusos inseridos no poliuretano, que apesar de ser amplamente utilizado nessa modalidade de ensaio mecânico deve ser reconhecido como uma limitação.…”

“… 6 The alteration of the screw surface in contact with bone tissue has been one of the strategies developed to improve the fixation of the implant by increasing the connection of the bone tissue with the implant. 7 The resistance of the implant to pullout is proportional to the contact surface of the thread with the bone tissue, which prevents loosening and classifies it as a stability property of the screw. 8 9 Alteration of the implant surface has been carried out by coating the implant surface or altering the surface roughness, which can stimulate bone growth and osteointegration, with the consequent increase in implant fixation.…”

“… 6 A alteração da superfície do parafuso em contato com o tecido ósseo tem sido uma das estratégias desenvolvidas para aprimorar a fixação do implante por meio do aumento da conexão do tecido ósseo com o implante. 7 A resistência do implante ao arrancamento é proporcional à superfície de contato da rosca com o tecido ósseo, o que evita a soltura e a classifica como uma propriedade de estabilidade do parafuso. 8 9 A alteração da superfície dos implantes tem sido realizada por meio do revestimento da superfície do implante ou da alteração da rugosidade da superfície, que pode estimular o crescimento ósseo e a osteointegração, com o consequente aumento da fixação do implante.…”

Toggling effect on pullout performance of pedicle screws: Review

“…The screws were coated with titanium which has good histocompatibility and adhesion properties by a plasma-spray titanium coating method. The dual pitch titanium-coated pedicle screws had significantly higher pullout strength and fatigue performance than standard pedicle screws for early time and post-operative conditions [45]. In addition to this, the long-term pullout performance of cortical bone trajectory pedicle screws and traditional pedicle screws were compared under cyclically sagittal bending conditions [46].…”