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Michael Raschke

Publications and source records attributed to Michael Raschke.

21 records · Page 2Linked to original sources
PubMed2002

Interfragmentary motion in tibial osteotomies stabilized with ring fixators.

Relative movement of bone fragments affects healing processes. In vivo data exist for patients with reduced transverse fractures only. The gap movements that occur under more complex conditions such as in tibial osteotomies, however, are unknown. The goal of this study was to determine the initial gap movements in tibial correction osteotomies, to monitor movements during the early healing period, and to determine the suitability of initial fixation stability in relation to daily activities. The interfragmentary movements were measured in six patients with correction osteotomies stabilized by Ilizarov ring fixator constructs until union or until conversion to internal fixation. Consolidation was determined by clinical evaluation and standard radiographic techniques. Co-contraction led to gap movements comparable with level walking or standing. Shear generally exceeded axial compression. Although ground reactions and fixation stiffness were comparable with those reported for reduced fractures, movement magnitudes generally were larger than 2 mm. The shear movement component reflected the nature of the mechanical conditions at the bone gap. In a direct comparison with data from animal experiments, the local mechanical environment at the bone gap seemed unstable rather than overly stable. The method introduced in this study opens the perspective of adjusting osteosynthesis stability to the specific needs of each patient.

Adult↗
PubMed2002

Stiffness characteristics of composite hybrid external fixators.

New composite hybrid fixators for fracture stabilization using single or multiple rings with monolateral bars and half-pin fixation may provide clinical advantages such as reduced bulk and easier skin access. However, the mechanical properties of these fixators are difficult to estimate from numerous design parameters. Addressing this problem the following research questions were asked: (1) Do composite hybrid fixators have similar stiffness properties to clinically proven triple-ring fixators; (2) How does the fixation mechanism affect the stiffness properties of external fixators, and, (3) Are there interferences between ring number and fixation method? An experimental study was done on simulated metaphyseal tibial fractures and stiffness of 12 fixators was measured for different loading conditions. The results showed that triple-ring fixators provide approximately 20% stiffer properties than double-ring and single-ring fixators. No influence of ring number on the AP bending properties was found and different fixation methods were associated with large differences in fixator stiffness, whereas significant interferences were found between ring number and fixation method. Although the mechanical properties investigated in the current study cannot predict directly the clinical performance of these fixators, the stiffness data provide useful information for making decisions regarding the treatment of fractures using external fixation.

External Fixators↗
PubMed2002

Bone morphogenetic protein-2 application by a poly(D,L-lactide)-coated interbody cage: in vivo results of a new carrier for growth factors.

OBJECT: Growth factors such as bone morphogenetic protein-2 (BMP-2) have been proven to promote spine fusion and to overcome the disadvantages of an autologous bone graft. The optimum method to deliver such growth factors remains a matter of discussion. The purpose of this study was to determine the safety and efficacy of a new poly(D,L-lactide) (PDLLA) carrier system for BMP-2 and to compare this carrier system with a collagen sponge carrier in a sheep cervical spine interbody fusion model. METHODS: Thirty-two sheep underwent C3-4 discectomy and fusion: Group 1, titanium cage (eight animals); Group 2, titanium cage coated with a PDLLA carrier (eight animals); Group 3, titanium cage coated with a PDLLA carrier including BMP-2 (150 microg) (eight animals); and Group 4, titanium cage combined with a collagen sponge carrier including BMP-2 (150 microg) (eight animals). Blood samples, body weight, and temperature were assessed. Radiographs were obtained pre- and postoperatively and after 1, 2, 4, 8, and 12 weeks. At the same time points, disc space height, intervertebral angle, and lordosis angle were measured. After the sheep were killed 12 weeks postoperatively, flexion-extension radiography was performed to evaluate fusion sites. Quantitative computerized tomography scans were obtained to assess bone mineral density (BMD), bone mineral content (BMC), and bone callus volume (BCV). Biomechanical testing was performed in flexion, extension, axial rotation, and lateral bending. Stiffness, range of motion, neutral, and elastic zone were determined. Histomorphological and -morphometrical analyses were performed, and polychrome sequential labeling was used to determine the timeframe of new bone formation. There were no differences among the groups concerning blood counts, body weight, and temperature. Compared with the noncoated cages, all PDLLA-coated cages showed significantly higher values for BMD of the callus, as well as slightly higher values for BMC, BCV, and the bone volume/total volume ratio. In comparison with the cage-alone group, the BMP-2 groups showed significantly higher values for BMD and biomechanical stiffness. Histomorphological, -morphometrical, and polychrome sequential labeling analyses demonstrated greater progression of callus formation in the BMP-2 groups than in any other group. Compared with BMP-2 delivered using a collagen sponge carrier, BMP-2 application with a PDLLA carrier resulted in a higher BCV and a greater progression of interbody callus formation in the histomorphometrical analysis. CONCLUSIONS: The use of cervical spine interbody fusion cages coated with PDLLA as a delivery system for growth factors was effective. In this 12-week follow-up study, the PDLLA coating showed no adverse effects. The slight but not significant positive effect of the PDLLA carrier on interbody fusion might be a result of the degradation process of the biodegradable carrier. Compared with collagen sponge delivery of BMP-2, the PDLLA-coated interbody cages significantly increased the results of interbody bone matrix formation. In this new combination (implant + PDLLA + growth factor) the cage represents a "real fusion" cage, because it not only serves as a mechanical device for spinal fixation but also as a local drug delivery system.

Animals↗