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A S Bahrani

Publications and source records attributed to A S Bahrani.

10 recordsLinked to original sources
PubMed1991

An investigation into the fixation of hip replacements.

This paper describes an experimental study of hip prosthesis stems fixed with bone cement in model femora and subjected to cyclic loading. Loosening of the stems did not occur due to fatigue of the bone cement, even when reduction of medial support from the calcar had been simulated. Measurement of stresses in the cement layer and comparison with published properties of bone cement indicated that fatigue failure was not likely under the experimental conditions. Fatigue failure of cement could not be solely regarded as initiating loosening. It is concluded that the results uphold theories that biological factors must also contribute to the initiation of loosening, rather than being a response to mechanical failure.

Body Weight↗
PubMed1990

Testing of total hip replacements: endurance tests and stress measurements. Part 1: Endurance tests.

This is a paper in two parts. Part 1 gives details of fatigue tests carried out on Howse II hip prostheses. Three types of tests were carried out in accordance with three different draft test standards. Standard (I) was BSI DD91: 1984 in which the load range is 0.3-4.1 kN and the antero-posterior offset angle is 15 degrees. Standard (II) was BSI DD91: 1986 where the load range is 0.3-2.3 kN and the offset angle is 9 degrees. Standard (III) was ISO/DP 7206/3 in which the load range is 0.3-4.1 kN and the offset angle is 0 degrees. Four specimens were tested according to each standard. It was found that all the specimens tested according to standard (I) failed by fatigue after less than 6 x 10(5) cycles. All the specimens tested according to standards (II) and (III) withstood 5 x 10(6) cycles without failure. It is clear that the offset angle has an important influence on the fatigue life of the prosthesis. It is concluded that tests according to standard (I) are too severe, while tests according to standards (II) and (III) are either adequate or lax. This led to Part 2 of the investigation where the stresses in the prostheses were measured and calculated.

Hip Prosthesis↗
PubMed1990

Testing of total hip replacements: endurance tests and stress measurements. Part 2: Stress measurements.

Brittle lacquer techniques and electric resistance strain gauge rosettes were used to measure strains on the stems of total hip replacements while loaded according to three standards. The stresses in these locations were also calculated and good agreement was found between the measured and calculated values. The Sines equation was used to calculate the endurance limit stress. Again good agreement was found with observed results. Suggestions are made regarding the endurance testing of hip prostheses.

Hip Prosthesis↗
PubMed1989

An investigation into the effect of cyclic loading and frequency on the temperature of PMMA bone cement in hip prostheses.

A titanium alloy hip prosthesis was inserted in a Tufnol tube representing the upper part of the femur. The prosthesis was cemented in the model femur using PMMA bone cement. Five thermocouples were embedded in the bone cement and the assembly was subjected to cyclic loading with a range of 0.3-4.5 kN at a frequency of 6 Hz. Temperature measurements over a 48 hour period indicated that the temperature rise in the bone cement was less than 4 degrees C. It is concluded that such tests can be carried out at 6 Hz without significantly affecting the mechanical properties of PMMA bone cement.

Bone Cements↗
PubMed1979

In vitro measurement of articular cartilage deformations in the intact human hip joint under load.

Using a new roentgenographic technique for measuring cartilage deformation in intact joint specimens, twenty-eight normal human hip joints from subjects twenty-five to eighty-five years old were loaded with a force of five times body weight in a testing machine. The initial unloaded thickness of the articular cartilage of the femoral head and the changes in thickness of this cartilage under load were measured roentgenographically at seven to twelve sites on each femoral head. These measurements showed that the deformations of femiral-head articular cartilage under load in the intact joint are non-uniform and increase greatly with age. In twelve specimens measurements were also made of the increase in cartilage deformation with time when the load of five times body weight was maintained on the joint. A single osteoarthrotic joint was also studied. The experimental findings imply changes in the fundamental mechanical properties of the cartilage with age, which probably result from age-related alterations in cartilage microstructure and chemical composition.

Adult↗