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Item type:Publication, Access status: without files , Impact of Screw Diameter on Pedicle Screw Fatigue Strength - A Biomechanical EvaluationObjective: Loosening of pedicle screws is a frequently observed complication in spinal surgery. Because additional stabilization procedures such as cement augmentation or lengthening of the instrumentation involve relevant risks, optimal stability of the primarily implanted pedicle screw is of essential importance. The aim of the present study was to investigate the effect of increasing the screw diameter on pedicle screw stability. Methods: A total of 10 human cadaveric vertebral bodies (L4) were included in the present study. The bone mineral density was evaluated using quantitative computed tomography and the pedicle diameter using computed tomography. The vertebrae underwent instrumentation using 6.0-mm × 45-mm pedicle screws on 1 side and screws with the largest possible diameter (8–10-mm × 45-mm) on the other side. Fatigue testing was performed by applying a cyclic loading (craniocaudal sinusoidal 0.5 Hz) with increasing peak force (100 N + 0.1 N/cycle) until screw head displacement of 5.4 mm was reached. Results: The mean fatigue load was 334 N for the 6-mm diameter screws and was increased significantly to 454 N (+36%) for the largest possible diameter screws (P < 0.001). With an increase in the fatigue load by 52%, this effect was even more pronounced in vertebrae with reduced bone density (bone mineral density <120 mg/cm3; n = 7; P < 0.001). The stiffness of the construct was significantly greater in the largest diameter screw group compared with the standard screw group during the entire testing period (start, P < 0.001; middle, P < 0.001; end, P = 0.009). Conclusions: Increasing the pedicle screw diameter from a standard 6-mm screw to the largest possible diameter (8–10 mm) led to a significantly greater fatigue load.Publicationtype: Journal ArticleScopus© Citations 11 42 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Rescue augmentation: increased stability in augmentation after initial loosening of pedicle screws(Sage Publications, 2021-06); ; ; ; Study Design: Biomechanical study. Objectives: Failure of pedicle screws is a major problem in spinal surgery not only postoperatively, but also intraoperatively. The aim of this study was to evaluate whether cement augmentation may restore mounting of initially loosened pedicle screws. Methods: A total of 14 osteoporotic or osteopenic human cadaveric vertebral bodies (L2)—according to quantitative computed tomography (QCT)—were instrumented on both sides by conventional pedicle screws and cement augmented on 1 side. In vitro fatigue loading (cranial-caudal sinusoidal, 0.5 Hz) with increasing peak force (100 N + 0.1 N/cycles) was applied until a screw head displacement of 5.4 mm (∼20°) was reached. After loosening, the nonaugmented screw was rescue augmented, and fatigue testing was repeated. Results: The fatigue load reached 207.3 N for the nonaugmented screws and was significantly (P =.009) exceeded because of initial cement augmentation (300.6 N). The rescue augmentation after screw loosening showed a fatigue load of 370.1 N which was significantly higher (P <.001) compared with the nonaugmented screws. The impact of bone density on fatigue strength decreased from the nonaugmented to the augmented to the rescue-augmented screws and shows the greatest effect of cement augmentation on fatigue strength at low bone density. Conclusions: Rescue augmentation leads to similar or higher fatigue strengths compared with those of the initially augmented screws. Therefore, the cement augmentation of initially loosened pedicle screws is a promising option to restore adequate screw stability.Publicationtype: Journal ArticleScopus© Citations 6 318 143 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Cortical threaded pedicle screw improves fatigue strength in decreased bone quality(Springer, 2021); ; ; ; Purpose: Inadequate anchoring of pedicle screws in vertebrae with poor bone quality is a major problem in spine surgery. The aim was to evaluate whether a modified thread in the area of the pedicle could significantly improve the pedicle screw fatigue strength. Methods: Fourteen human cadaveric vertebral bodies (L2 and L3) were used for in vitro testing. Bone density (BMD) was determined by quantitative computed tomography. Vertebral bodies were instrumented by standard pedicle screws with a constant double thread on the right pedicle and a partial doubling of the threads–quad thread–(cortical thread) in the area of the pedicle on the left pedicle. Pulsating sinusoidal, cyclic load (0.5 Hz) with increasing peak force (100 N + 0.1 N/cycles) was applied orthogonal to the screw axis. The baseline force remained constant (50 N). Fatigue test was terminated after exceeding 5.4-mm head displacement (~ 20° screw tilting). Results: The mean fatigue load at failure was 264.9 N (1682 cycles) for the standard screws and was increased significantly to 324.7 N (2285 cycles) by the use of cortical threaded screws (p = 0.014). This effect is particularly evident in reduced BMD (standard thread 241.2 N vs. cortical thread 328.4 N; p = 0.016), whereas in the group of vertebrae with normal BMD no significant difference could be detected (standard thread 296.5 N vs. cortical thread 319.8 N; p = 0.463). Conclusions: Compared to a conventional pedicle screw, the use of a cortical threaded pedicle screw promises superior fatigue load in vertebrae with reduced bone quality.Publicationtype: Journal ArticleScopus© Citations 7 266 184 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Reduced cement volume does not affect screw stability in augmented pedicle screws(Springer, 2020-03-23); ; ; ; Purpose: Cement augmentation of pedicle screws is able to improve screw anchorage in osteoporotic vertebrae but is associated with a high complication rate. The goal of this study was to evaluate the impact of different cement volumes on pedicle screw fatigue strength. Methods: Twenty-five human vertebral bodies (T12–L4) were collected from donors between 73 and 97 years of age. Bone density (BMD) was determined by quantitative computed tomography. Vertebral bodies were instrumented by conventional pedicle screws, and unilateral cement augmentation was performed. Thirteen vertebrae were augmented with a volume of 1 ml and twelve with a volume of 3 ml bone cement. A fatigue test was performed using a cranial–caudal sinusoidal, cyclic load (0.5 Hz) with increasing compression force (100 N + 0.1 N/cycles). Results: The load to failure was 183.8 N for the non-augmented screws and was increased significantly to 268.1 N (p < 0.001) by cement augmentation. Augmentation with 1 ml bone cement increased the fatigue load by 41% while augmentation with 3 ml increased the failure load by 51% compared to the non-augmented screws, but there was no significant difference in fatigue loads between the specimens with screws augmented with 1 ml and screws augmented with 3 ml of bone cement (p = 0.504). Conclusion: Cement augmentation significantly increases pedicle screw stability. The benefit of augmentation on screw anchorage was not significantly affected by reducing the applied volume of cement from 3 ml to 1 ml. Considering the high risk of cement leakage during augmentation, we recommend the usage of a reduced volume of 1 ml bone cement for each pedicle screw. Graphic Abstract: These slides can be retrieved under Electronic Supplementary Material [Figure not available: see fulltext.].Publicationtype: Journal ArticleScopus© Citations 12 211 217 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Time to augment?! Impact of cement augmentation on pedicle screw fixation strength depending on bone mineral density(2018-08-01); ; ; ; Cement augmentation of pedicle screws is known to increase their mechanical strength. Aim was to evaluate the impact of cement augmentation on pedicle screw fatigue strength in dependence of the bone mineral density (BMD).Publicationtype: Journal Article127 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Insufficient stability of pedicle screws in osteoporotic vertebrae: biomechanical correlation of bone mineral density and pedicle screw fixation strength(2017-11-01); ; ; ; Purpose: Loosening of pedicle screws is one major complication of posterior spinal stabilisation, especially in the patients with osteoporosis. Augmentation of pedicle screws with cement or lengthening of the instrumentation is widely used to improve implant stability in these patients. However, it is still unclear from which value of bone mineral density (BMD) the stability of pedicle screws is insufficient and an additional stabilisation should be performed. The aim of this study was to investigate the correlation of bone mineral density and pedicle screw fatigue strength as well as to define a threshold value for BMD below which an additional stabilisation is recommended. Methods: Twenty-one human T12 vertebral bodies were collected from donors between 19 and 96 years of age and the BMD was measured using quantitative computed tomography. Each vertebral body was instrumented with one pedicle screw and mounted in a servo-hydraulic testing machine. Fatigue testing was performed by implementing a cranio-caudal sinusoidal, cyclic (0.5 Hz) load with stepwise increasing peak force. Results: A significant correlation between BMD and cycles to failure (r = 0.862, r2 = 0.743, p < 0.001) as well as for the linearly related fatigue load was found. Specimens with BMD below 80 mg/cm3 only reached 45% of the cycles to failure and only 60% of the fatigue load compared to the specimens with adequate bone quality (BMD > 120 mg/cm3). Conclusions: There is a close correlation between BMD and pedicle screw stability. If the BMD of the thoracolumbar spine is less than 80 mg/cm3, stability of pedicle screws might be insufficient and an additional stabilisation should be considered.Publicationtype: Journal Article146 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Wirbelkörperfrakturen und Osteopenie: Augmentieren oder langstreckig? Vertebral body fractures and osteopenia: augmentation or lengthening?(2017-06-01); ; ; Background: Vertebral fractures are the most common manifestation of osteoporosis. If an interventional therapy is needed besides kyphoplasty, stabilisation with pedicle screws is commonly accepted. Loosening of pedicle screws is one of the major complications in posterior spinal stabilisation, especially in the osteoporotic spine. Augmentation of pedicle screws with cement or lengthening of the instrumentation are widely used to improve stability in these patients. Materials and methods: A biomechanical test was performed. Twelve osteoporotic human spines (Th11–L3) were randomised by bone mineral density into two groups. A short instrumentation was compared to an extended instrumentation using a fatigue testing setup with a cranial–caudal sinusoidal, cyclic (1.0 Hz) load with stepwise increasing peak force. Testing was performed for augmented screws as well as for nonaugmented screws. Conclusion: The stabilising effect of cement augmentation in pedicle screws might not be as beneficial as expected from biomechanical pullout tests. Lengthening of the dorsal instrumentation results in a much higher increase of stability during fatigue testing in the osteoporotic spine compared to cement augmentation.Publicationtype: Journal Article144