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Biomedical subjects

T K Moroz

Publications and source records attributed to T K Moroz.

5 recordsLinked to original sources
PubMed1990

Source of the slippage in the universal joints of the Hoffmann external fixator.

An investigation was conducted to determine what improvements in the resistance to slippage could be obtained in selected interfaces (rod/clip torsional, cheek/bowl and cheek/clip) of the Hoffmann external fixator. The modification involved changing the standard wing-nut clamp for a bolt with a thread of 7 mm and a 1 mm pitch and placing an FAG 28-303 thrust-bearing (needle roller and cage assembly) between the bolt and the cheek. The results showed a significant improvement in the slippage values of all interfaces; increases of approximately six times were obtained at all torque values of the wing-nut clamp or fastener tested. Such improvements would markedly increase the reliability of external fixation systems and thus reduce the incidence of loss-of-reduction of fracture due to slippage of the universal joint.

Equipment Failure↗
PubMed1989

Stiffness of bone underlying the tibial plateaus of osteoarthritic and normal knees.

The mechanical properties of normal cancellous bone in the proximal tibia have been reported extensively in previous studies in terms of support of a total knee arthroplasty (TKA); yet, little is known about these mechanical properties in the osteoarthritic (OA) state. Fifteen normal and 28 OA tibial plateaus, obtained from autopsy or TKA, were mechanically tested using an indentor technique to assess the variation of stiffness patterns. The medial:lateral stiffness ratio calculated for the normal plateaus was significantly different from the ratios computed for specimens with medial compartment OA and lateral compartment OA; however, the ratio was unchanged in tricompartment OA. These data should receive greater consideration in the design of TKA, which has traditionally been designed on the mechanical properties of normal tibiae.

Adult↗
PubMed1988

External skeletal fixation: choosing a system based on biomechanical stability.

Due to the increased popularity of external fixators for treating long-bone fractures, many devices are being introduced to the market. The choice of a particular fixation device depends on the anticipated loading conditions or the demands the fixator might encounter during the healing process. This study compares the biomechanical stability (rigidity, yield-load, failure-load) and load to produce 1 mm of fracture-gap displacement of various half-frames of five systems tested in axial compression, torsion, and both anterior-posterior and medial-lateral bending; the slippage tolerances of various interfaces of the universal joints or clamps were also analyzed. The frames were mounted on acrylic rods, with a midshaft transverse saw-cut, displaced by 10 mm, and set to standardized dimensions and tightened at set torques. In terms of stability, the Brooker and Hoffman systems are, in general, less stable than the RxFx, AO, and Orthofix fixators. The single half-frames of all systems, except the Orthofix, were particularly weak, and the double and stacked half-frames of each system were more stable.

Biomechanical Phenomena↗
PubMed1987

Stability of ten configurations of the Hoffmann external-fixation frame.

The rigidity, load to yield, and load to failure of ten configurations of the Hoffmann external fixator were investigated using a model of wooden pylons with a simulated fracture that consisted of either a reduced transverse cut or a ten-millimeter gap. The axial compressive, torsional, anterior-posterior bending, and medial-lateral bending characteristics of four forms of the single half-frame (half-pinned), four double half-frame, and two full-frame (transfixion-pinned) configurations were examined. Of the single half-frame configurations, a system with a second stacked connecting-rod proved to be superior; however, the system yielded at a mean axial compressive load of only 199 newtons and failed totally at 355 newtons. The delta frame (two rods connecting or triangulating two half-frames set at an angle of 45 degrees to one another) was as rigid as the quadrilateral full frame in axial compression; however, it exhibited low loads to yield and to failure, with means around 200 and 350 newtons, respectively. The use of only two pins in each pin-cluster did not significantly affect the performance of the delta frame. The two full-frame systems performed poorly in torsion and particularly poorly in anterior-posterior bending. The loads that caused a one-millimeter movement within the fracture gap in axial compression were notably low: for the stacked half-frames the load did not exceed a mean value of 174 newtons; for the double half-frame, 190 newtons; and for the quadrilateral frame, 412 newtons. We concluded that no frame had a good over-all performance with regard to rigidity.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗