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Item type:Publication, Access status: without files , Influence of the screw augmentation technique and a diameter increase on pedicle screw fixation in the osteoporotic spine : pullout versus fatigue testing(Springer, 2014-09-27); ; ; ; Purpose: For posterior spinal stabilization, loosening of pedicle screws at the bone-screw interface is a clinical complication, especially in the osteoporotic population. Axial pullout testing is the standard pre-clinical testing method for new screw designs although it has questioned clinical relevance. The aim of this study was to determine the fixation strength of three current osteoporotic fixation techniques and to investigate whether or not pullout testing results can directly relate to those of the more physiologic fatigue testing.Publicationtype: Journal Article4 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Does the cement stiffness affect fatigue fracture strength of vertebrae after cement augmentation in osteoporotic patients?(Springer, 2013-05-16); ; ; ; Purpose: Normal progression of osteoporosis or the rigid reinforcement of the fractured vertebral body with polymethyl methacrylate (PMMA) cement is being discussed as a cause for adjacent-level fractures after vertebroplasty. The purpose of this study was to investigate whether augmentation with low stiffness cement can decrease the risk of adjacent-level fractures in low-quality bone. Methods: Eighteen female osteoporotic lumbar specimens (L1-L5) were harvested and divided into three groups according to bone mineral density: (I) native; (II) PMMA; (III) modified PMMA (lower stiffness). For the PMMA and modified PMMA groups, a compression fracture was first mechanically induced in L3, and then the fracture received vertebroplasty treatment. The cement stiffness reduction of the modified PMMA group was achieved via an addition of 8 mL of serum to the typical PMMA base. All specimens were exposed to cyclic loading (4 Hz) and a stepwise increasing applied peak force. Cement stiffness was tested according to ISO 5833. Results: A 51 % decrease in cement stiffness was achieved in the modified PMMA group (954 ± 141 vs. 1,937 ± 478 MPa, p < 0.001). Fatigue fracture force (the force level during cyclic loading at which the deformation experienced a sudden increase; FFF) was significantly affected by bone quality (r 2 = 0.39, p = 0.006) and by the initial fracture force (the force necessary to create the initial fracture in L3 prior to augmentation; r 2 = 0.82, p < 0.001). Using initial fracture force as a covariate, the FFF of the modified PMMA group (1,764 ± 49 N) was significantly higher than in the PMMA group (1,544 ± 55 N; p = 0.03). Conclusions: A possible method to reduce adjacent-level fractures after vertebroplasty in patients with reduced bone quality could be the use of a lower modulus cement. Therefore, mixing cement with biocompatible fluids could prove useful to tailor cement properties in the operating theater.Publicationtype: Journal Article55 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Cement augmentation of the proximal femoral nail antirotation for the treatment of osteoporotic pertrochanteric fractures : a biomechanical cadaver study(Elsevier, 2013-03-29); ; ; ; Introduction Proximal femoral fractures will gain increasing importance in the future due to the epidemiological development. Osteoporosis is often a limiting factor in the achievement of implant stability. New nailing systems offer the possibility of augmentation of the femoral neck component with cement. The aim of this study was to perform a biomechanical comparison of implant stability in osteoporotic pertrochanteric fractures using the proximal femoral nail antirotation (PFNA, Synthes GmbH, Umkirch, Germany) with cement augmented and non-augmented blades. Materials and methods Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (DEXA) in six pairs of fresh-frozen human femurs. Standardised pertrochanteric fractures (AO31-A2.3) were treated with a PFNA. Cement augmentation was performed in six constructs. Axial loading was applied according to a single-leg-stance model using a hydraulic testing machine increasing to 1400 N over 10,000 cycles. Biomechanical comparisons between the two groups that were comparable concerning BMD, tip-apex-distance and native stiffness were made with regard to postoperative stiffness, survived cycles, load to failure, failure mechanism and axial displacement. Results The stiffness of all stabilised femurs was significantly lower than for native specimens (native 702.5 ± 159.6 N/mm vs. postoperative 275.4 ± 53.8 N/mm, p < 0.001). Stiffness after instrumentation was significantly greater for the cement augmented group than for the non-augmented group (300.6 ± 46.7 N/mm vs. 250.3 ± 51.6 N/mm, respectively, p = 0.001). Five of the twelve constructs survived cyclic testing. Statistically significant differences of the BMD were detected between survived and failed constructs (0.79 ± 0.17 g/cm2 vs. 0.45 ± 0.12 g/cm2, respectively, p = 0.028). The failure loads for specimens surviving 10,000 cycles were 4611.9 ± 2078.9 N in the cement augmented group (n = 3) and 4516.3 N and 3253.5 N in the non-augmented group (n = 2). Postoperative stiffness was found to be a positive predictor of maximum force to failure (R2 = 0.83, p = 0.02). Conclusions The results of this biomechanical study show that cement augmentation of the PFNA increases the implant stability in osteoporotic pertrochanteric fractures. Further studies are necessary to evaluate this procedure in providing long term clinical results.Publicationtype: Journal Article45 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , What is the risk of stress risers for interprosthetic fractures of the femur? A biomechanical analysis(Springer, 2012-12-01); ; 4