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- Henriques, Thomas, 1957-
(författare)
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Biomechanical and Clinical Aspects on Fixation Techniques in the Cervical Spine
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present work is analyzing the general biomechanical aspects of fixation techniques in the upper and lower cervical spine along with clinical implications.The in vitro biomechanical properties of five different posterior atlanto-axial fixation techniques are compared. They provided for either a one, two or three-point fixation between atlas and axes. A new device, the C1 claw was biomechanically tested, which allow for fixation without the need for a structural bone graft. The three-point reconstructions indicated superior biomechanical properties compared to all others.The new C1 claw device was clinically evaluated in a series of 26 patients treated with a posterior C1-C2 fusion. There were no clinical or radiological failures in the series, Twenty-one patients out of twenty-three with any length of follow up either showed a solidly healed fusion or a healed fracture. Distractive flexion (DF) injuries in the lower cervical spine treated with anterior plate alone were analyzed with respect to healing rate and complications in a consecutive series of 36 patients. Results indicated that DF injury stage 1 and 2 according to Allen and Ferguson healed without complication, whereas DF injuries stage 3 had a high frequency of failure, needing an additional posterior fixation. The in vitro biomechanical properties of four different fixation techniques for a distractive flexion injury stage 3 were analyzed. The result indicated that anterior plate alone for fixation of a DF injury stage 3 is insufficient supporting the clinical finding in the previous study.Adjacent level motion was analyzed following a one segment fusion in the lower cervical spine. Motion was found to increase in adjacent levels possibly contributing to accelerated degeneration.
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| 2. |
- Henriques, Thomas, et al.
(författare)
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Biomechanical comparison of five different atlantoaxial posterior fixation techhniques
- 2000
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Ingår i: Spine. - 0362-2436 .- 1528-1159. ; 25:22, s. 2877-2883
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Tidskriftsartikel (refereegranskat)abstract
- STUDY DESIGN:Five different reconstructions of the atlantoaxial complex were biomechanically compared in vitro in a nondestructive test.OBJECTIVES:To determine whether non-bone graft-dependent one-point fixation affords stability levels equivalent to three-point reconstructions.SUMMARY OF BACKGROUND DATA:Previous investigations have demonstrated that three-point fixation, using bilateral transarticular screws in combination with posterior wiring, provide the most effective resistance to minimize motion around C1-C2. However, placement of transarticular screws is technically demanding. Posterior wiring techniques affording one-point fixation have failure rates of approximately 15%, with failure considered to be secondary to structural bone graft failures. One-point, non-bone graft-dependent fixations have not been tested.METHODS:Eight human cervical specimens, C0-C3 were loaded nondestructively. Unconstrained three-dimensional segmental motion was measured. The reconstructions tested were two one-point fixations, one two-point fixation, and two three-point fixations.RESULTS:Under axial rotation two and three-point reconstructions provided better stiffness than the one-point reconstructions (P < 0.05). During flexion-extension, higher stiffness levels were observed in one- and three-point fixations when compared with the intact spine (P < 0.05). In lateral bending no significant differences were observed among the six groups, although the trend was that reconstructions including transarticular screws provided greater stability than one-point fixations.CONCLUSION:The current findings substantiate the use of three-point fixation as the treatment of choice for C1-C2 instability. [l: atlantoaxial fixation, biomechanics, cervical spine, instability, spinal instrumentation, transarticular screws]
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| 4. |
- Sandén, Bengt, et al.
(författare)
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Hydroxyapatite coating enhances fixation of loaded pedicle screws : a mechanical in vivo study in sheep
- 2001
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Ingår i: European spine journal. - : Springer Science and Business Media LLC. - 0940-6719 .- 1432-0932. ; 10:4, s. 334-9
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Tidskriftsartikel (refereegranskat)abstract
- Loosening of the pedicle screws with subsequent non-union or loss of correction is a frequent problem in spinal instrumentation. In a clinical pilot study, coating of pedicle screws with plasma-sprayed hydroxyapatite (HA) resulted in a significant increase of removal torque. An experimental study was performed to investigate the effects of HA coating on the pull-out resistance. Thirteen sheep were operated on with destabilising laminectomies at two levels, L2-L3 and L4-L5. Two instrumentations with four pedicle screws in each were used for stabilisation. Uncoated screws (stainless steel) or the same type of screws coated with plasma-sprayed HA were used in either the upper or the lower instrumentation in a randomised fashion. Four sheep were examined immediately after the application of the screws, three sheep at 6 weeks and four sheep at 12 weeks. Two sheep were euthanised early due to complications. The pull-out resistance was recorded in two HA-coated and two standard screws in each animal. The maximum pull-out resistance was higher for the HA-coated screws at 0 weeks (P< 0.02) and at 12 weeks (P<0.01) when compared to the uncoated screws, while there was no significant difference between the groups at 6 weeks. We believe that the higher pull-out resistance for HA-coated screws at 0 weeks was mainly caused by differences in surface roughness, while the difference at 12 weeks was due to a favourable bone reaction around the HA-coated screws. At 12 weeks, the average stiffness was significantly higher for the HA-coated screws, while there was no significant differences in stiffness between the two screw types at 0 and 6 weeks. Energy to failure was significantly higher for coated screws when compared to the uncoated screws at all three time points. HA coating improves fixation of loaded pedicle screws, with increased pull-out resistance and reduced risk of loosening.
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| 5. |
- Sandén, Bengt, et al.
(författare)
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Hydroxyapatite coating improves fixation of pedicle screws : A clinical study
- 2002
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Ingår i: Journal of Bone and Joint Surgery. - 0301-620X .- 2044-5377. ; 84:3, s. 387-91
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the effects of hydroxyapatite (HA) coating on the purchase of pedicle screws. A total of 23 consecutive patients undergoing lumbar fusion was randomly assigned to one of three treatment groups. The first received uncoated stainless-steel screws, the second screws which were partly coated with HA, and the third screws which were fully coated. The insertion torque was recorded. After 11 to 16 months, 21 screws had been extracted. The extraction torque was recorded. Radiographs were taken to assess fusion and to detect loosening of the screws. At removal, the extraction torques exceeded the upper limit of the torque wrench (600 Ncm) for many HA-coated screws. The calculated mean extraction torque was 29 +/- 36 Ncm for the uncoated group, 447 +/- 114 Ncm for the partly-coated group and 574 +/- 52 Ncm for the fully-coated group. There were significant differences between all three groups (p < 0.001). There were more radiolucent zones surrounding the uncoated screws than the HA-coated screws (p < 0.001). HA coating of pedicle screws resulted in improved fixation with reduced risk of loosening of the screws.
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| 6. |
- Sandén, Bengt, et al.
(författare)
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Improved bone-screw interface with hydroxyapatite coating : an in vivo study of loaded pedicle screws in sheep
- 2001
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Ingår i: Spine. - 0362-2436 .- 1528-1159. ; 26:24, s. 2673-8
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Tidskriftsartikel (refereegranskat)abstract
- STUDY DESIGN: An in vivo sheep model with loaded pedicle screws was used, wherein each animal served as its own control. OBJECTIVES: To examine the effects of hydroxyapatite (HA) coating on the bone-to-implant interface in loaded spinal instrumentations. SUMMARY OF BACKGROUND DATA: Spinal instrumentation improves the healing rate in spinal fusion, but screw loosening constitutes a problem. HA coating of other implants has resulted in favorable effects on the bone-to-implant interface. METHODS: Nine sheep were operated on with destabilizing laminectomies at two levels: L2-L3 and L4-L5. Each level was stabilized separately with a four-screw instrumentation. Uncoated screws (stainless steel) or the same type of screws coated with plasma-sprayed HA were used in either the upper or the lower instrumentation in a randomized fashion. The animals were killed at 6 or 12 weeks after surgery. The specimens were embedded in resin, ground to approximately 10 microm, and stained with toluidine blue. Histomorphometric evaluation was carried out in a Leitz Aristoplan (Wetzlar, Germany) light microscope equipped with a Leitz Microvid unit. RESULTS: The average percentage of bone-to-implant contact after 6 weeks was 69 +/- 10 for the HA-coated screws and 18 +/- 11 for the uncoated screws (P < 0.03), and after 12 weeks 64 +/- 31 (HA-coated) and 9 +/- 13 (uncoated, P < 0.02). The average bone volume in the area close to the screw was significantly higher for the HA-coated screws at both 6 and 12 weeks. CONCLUSIONS: HA coating improved the bone-to-implant interface significantly, indicating that HA coating can become useful for improving the purchase of pedicle screws.
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| 7. |
- Sandén, Bengt, et al.
(författare)
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Improved extraction torque of hydroxyapatite-coated pedicle screws
- 2000
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Ingår i: European spine journal. - : Springer Science and Business Media LLC. - 0940-6719 .- 1432-0932. ; 9:6, s. 534-7
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Tidskriftsartikel (refereegranskat)abstract
- Loosening of the screws is a problem in instrumentation with pedicle screws. Coating with hydroxyapatite improves the holding characteristics for metal implants, but the possible effects on the anchorage of pedicle screws have not been described. In this study, seven patients were operated on with spinal instrumentation using four stainless steel pedicle screws. Hydroxyapatite-coated screws were used in either the upper or the lower of the instrumented levels. The insertion torque was measured. In four cases the screws were removed after 10-22 months and the extraction torque was measured. The mean insertion torque was found to be significantly greater in the hydroxyapatite-coated screws (107 Ncm) than in the standard screws (76 Ncm). In three cases, the extraction torque for the hydroxyapatite-coated screws exceeded the range for the torque wrench (600 Ncm), while the conventional screws were loose (< 5 Ncm). In one case, the extraction torque was 475 and 550 Ncm for the coated screws, and 5 and 25 Ncm for the conventional screws. The difference in extraction torque was significant. Hydroxyapatite coating was shown to have improved the purchase of pedicle screws very effectively. By using fully coated screws, as in the present study, extraction was extremely difficult compared to extraction of conventional stainless steel screws, which were regularly loose. By reducing the area of the screws that is coated, it may be possible to achieve an enhanced purchase while extraction will be easier when compared to fully coated screws.
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