Michael Jamek

Micromotion at the fracture site after tibial nailing with four unreamed small-diameter nails--a biomechanical study using a distal tibia fracture model.

BACKGROUND Intramedullary nailing is the treatment of choice in tibia fractures allowing for closed fracture reduction and internal fixation. Small-diameter nails that preserve the endosteal blood supply act as load-sharing devices after proximal and distal locking. Despite fracture healing is influenced by movements at the fracture gap, no data are available reporting on the micromovements at the fracture site if small-diameter nails were used. METHODS Using a Sawbone distal tibia fracture model, we assessed offset, elastic, plastic, permanent, and overall deformation at the fracture site for four small-diameter tibia nails (Expert, Synthes, Saluburg, Austria; Connex, ITS Spectromed, Lassnitzhöhe, Austria; Versanail, DePuy, Vienna, Austria; T2, Stryker, Vienna, Austria) after mechanical testing with a servohydraulic material testing machine. Cyclic loading was performed with a sinusoidal load of 700 N (+/-600) for 40,000 cycles representing 6 weeks of full weight bearing. RESULTS Offset deformation was significantly higher for the Connex nail when compared with other nails (p < 0.001). Regarding elastic deformation, no significant difference was recorded between the implants. Plastic deformation was significantly lower if the Connex nail was used (0.134 [+/-0.053] mm; p < 0.001). Elastic deformation did not exceed 0.7 mm and plastic deformation did not exceed 0.4 mm. Regarding permanent and overall deformation, no significant difference between the implants was recorded. CONCLUSIONS Considerable deformation at the fracture gap can be assumed even after partial weight bearing with 100 N. Despite comparable material properties, differences in axial micromotion were recorded among the nail types used in this series. The number of distal locking screws (three or four) did not substantially influence the axial movements at the fracture gap.

Factors influencing interlocking screw failure in unreamed small diameter nails - A biomechanical study using a distal tibia fracture model

BACKGROUND Unreamed tibia nails with small diameters are increasingly used for fracture fixation. However, little is known about the fatigue strength of proximal and distal interlocking screws in those nails. To date, no data are available reporting on mechanical differences of solid compared to cannulated tibial nails. The aim of this study was to assess the fatigue strength of proximal and distal interlocking screws of solid and cannulated small diameter tibia nails. METHODS We created a distal tibia fracture model (AO/OTA 43 A3) using 16 Sawbones. After fracture stabilization with one of four different nail types (Expert Tibial Nail, VersaNail, T2 Tibial Nailing System, Connex), mechanical testing was performed in three loading series (40,000 cycles each) with incremental loads. Timing and type of interlocking screw failure were assessed. FINDINGS Interlocking screw failure was observed significantly earlier (after a mean interval of 57,042 cycles) in cannulated tibial nails (VersaNail, T2) compared to solid nails (after a mean interval of 88,415 cycles; P < 0.001). Proximal interlocking screw failure was recorded if oblique screws were used proximally (VersaNail, T2, Connex). No distal interlocking screw failure was recorded in the Connex nail. Two- and three-part fractures of proximal or distal interlocking screws were observed in all specimen. INTERPRETATION Proximal and distal interlocking screw failure has to be considered in small diameter nails in case of delayed fracture healing. To support our results, further experimental studies and clinical series are necessary.

Crack growth behaviour in geosynthetic asphalt interlayer systems

Geosynthetic interlayers in asphalt systems have become a convenient technology for lifetime prolongation in road construction engineering. Durability and lifetime prediction analysis of such systems can be obtained by fatigue crack growth testing. In this paper, the fatigue crack growth properties of three different asphalt interlayer system groups with different interlayer functions: SAMI (=Stress Absorbing Membrane Interlayer), asphalt reinforcement and the combination of SAMI+asphalt reinforcement are reported. For comparison non-interlayer systems (reference) have also been tested. Instead of 3- or 4-point bending tests with beams, wedge splitting tests with drill cores from the field are used for analyzing the fatigue crack growth behaviour of these systems. Due to the temperature dependence of asphalt the tests have been performed in a climate chamber at−10°C, 0°C and+10°C. Crack growth propagation was determined visually. The results show that this new visual approach for evaluation of crack growth testing together with the wedge splitting test are practicable, reproducible and allow grading of geosynthetic asphalt interlayer systems.

Fracture-Mechanical Characterization of Parquet-Adhesive-Screed Systems

Parquet-adhesives-screed-compounds are convenient systems when it comes to laying planks of wood on cementitious screeds indoors. Established testing methods for characterizing construction materials can be used to describe and evaluate these systems. This paper compares three different frequently used adhesives in terms of crack growth resistance and notch-tensile strength. The fracture-mechanical properties were determined by means of the wedge-splitting test. The results show that the wedge-splitting test shows the differences between these three adhesive systems much more clearly than the inter-laminar tensile test, as the latter is not accurate enough for characterizing material properties because of lacking information about the strain softening behavior and the fracture energy.