Biomedical subjects

G M McNeice

Publications and source records attributed to G M McNeice.

6 recordsLinked to original sources

PubMed1990

Numerical [corrected] analysis of the load capacity of the human spine fitted with L-rod instrumentation.

L-rod procedures with sublaminar wiring have become widespread in orthopaedic practice, and serious mechanical problems involving fatigue failure, creep, and fixation have been reported. To address these problems, numerical [corrected] analysis was developed to provide estimates for the maximum bending stresses, approximately equal to maximum tensile stresses, in L-rods subject to various axial loads and postoperative Cobb angles. The superior load capacity of L-rods made from MP35N multiphase alloy compared with 316L stainless steel was demonstrated. Bending stresses in excess of the fatigue limit were predicted for eight patients with broken rods, suggesting that such failures might be prevented by prior analysis. This analytic approach provides a foundation for future studies of custom-designed L-rods and perhaps the successful use of L-rods without arthrodesis.

Alloys↗

PubMed1986

An experimental study of the buckling behavior of L-rod implants used in the surgical treatment of scoliosis.

A test facility was developed to study the buckling behavior of the scoliotic spine fitted with L-rod implants. The facility included a model, constructed from polymeric materials, that was similar in geometric detail and flexural stiffness to the ligamentous thoracolumbar spine with a severe scoliotic curvature. Nondestructive tests were performed in which the transverse deflection was recorded at various axial load levels. Southwell regression was used on the data to estimate the buckling loads. Attaching L-rods of 3.2-mm diameter did not increase the buckling load significantly, compared to the uninstrumented spine and thus were judged to be ineffective in halting the progression of a scoliotic curve. However, L-rods of 4.8-mm diameter increased the buckling load about four times and L-rods of 6.4 mm increased the buckling load about eight times.

Biomechanical Phenomena↗

PubMed1981

Mechanical failure modes in total knee replacement.

In an attempt to define failure modes, a study of 39 knees which failed mechanically has been carried out. In 7 cases failure occurred on the femoral side and in 32 on the tibial side. There was fracture of one femoral component. All femoral loosenings and/or sinkage occurred in malaligned components. Two main tibial failure modes were noted, lateral subluxation of the tibia on the femur leading to loosening and sinkage of the tibial component. Release of popliteus prevents lateral subluxation. Correct component alignment and the use of a large area tibial component resting on the cortices should decrease the incidence of tibial sinkage.

Biomechanical Phenomena↗

PubMed1979

"Modes of failure" of cemented stem-type femoral components: a radiographic analysis of loosening.

In view of the increasing incidence of stem-type femoral component loosening, a detailed retrospective radiographic zonal analysis of 389 total hip replacements indicated a 19.5% incidence (76 hips) of radiological evidences of mechanical looseness, i.e., fractured acrylic cement and/or a radiolucent gap at the stem-cement or cement-bone interfaces. Detailed serial radiographic examination demonstrated progressive loosening in 56 of the 76 hips and these were categorized into mechanical modes of failure. The 4 modes of failure characterizing stem-type component progressive loosening mechanisms consisted of stem pistoning within the acrylic (3.3%), cement-embedded stem pistoning with the femur (5.1%), medial midstem pivot (2.5%), calcar pivot (0.7%) and bending (fatigue) cantilever (3.3%).

Evaluation Studies as Topic↗

PubMed1977

On the mechanical testing of some implants and materials.

This paper discusses the proliferation of medical devices and focusses its attention on the rapid development of orthopedic implants and the attempts by federal authorities to provide standards and recommended practices. The very important aspect of implant assessment based on mechanical testing is discussed and shown to be completely lacking. Current attempts to maintain quality and safety of orthopedic implants are discussed. One test configuration for femoral components of total hip replacement is offered as an example of methods that should be established to verify a particular design in conjunction with efforts to control material composition.

Biocompatible Materials↗

PubMedDate not supplied

A correlation of radiographic "modes of failure" with clinical failure of cemented stem-type femoral components.

Four modes of failure of cemented stem type femoral components are: pistoning within the medullary canal (mode I); medial migration of the proximal stem and lateral migration of the distal stem (mode II); medial lateral toggle of the distal stem tip (mode III); loss of proximal support with firm fixation of the distal end (mode IV). These radiographic failure patterns have been correlated with clinical findings at revision of 51 loose femoral components. The findings at revision correlated well with the radiographic findings indicating the accuracy of this nomenclature, which simplifies discussion of stem failures. Mode I was found to be the most common, and mode IV the most difficult to revise. Neither age, nor weight nor surgical approach influenced the failure mode. The overall results of revision were poor, with most hips rapidly assuming a IB type of appearance.

Bacterial Infections↗