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Biomedical subjects

K E Tanner

Publications and source records attributed to K E Tanner.

At least 55 records · Page 3Linked to original sources
PubMed1997

Biomechanical assessment of bone ingrowth in porous hydroxyapatite.

Porous hydroxyapatite (Endobon) specimens were implanted into the femoral condyle of New Zealand White rabbits for up to 6 months. After sacrifice, specimens were sectioned for histology and mechanical testing, where the extent of reinforcement by bony ingrowth was assessed by compression testing and fixation was assessed by push-out testing. From histological observations, it was established that the majority of bone ingrowth occurred between 10 day and 5 weeks after implantation and proceeded predominantly from the deep end of the trephined defect, with some integration from the circumferential sides. At 3 months, the implants were fully integrated, exhibiting bony ingrowth, vascularization and bone marrow stroma within the internal macropores. After 5 weeks, the mean ultimate compressive strength of retrieved implants (6.9 MPa) was found to be greater than that of the original implant (2.2 MPa), and by 3 months the fully integrated implants attained a compressive strength of approximately 20 MPa. Push-out testing demonstrated that after 5 weeks in vivo, the interfacial shear strength reached 3.2 MPa, increasing to 7.3 MPa at 3 and 6 months.

Journal Article↗
PubMed1997

In vitro mechanical and biological assessment of hydroxyapatite-reinforced polyethylene composite.

In vitro performance of hydroxyapatite (HA)-reinforced polyethylene (PE) composite (HAPEX) has been characterized from both mechanical and biological aspects. The mechanical properties of HAPEX, such as tensile strength and Young's modulus, showed little change after immersion in a physiological solution at 37 and 70 degrees C for various periods. In addition, the biological response of primary human osteoblast-like (HOB) cells in vitro on HAPEX was assessed by measuring DNA synthesis and osteoblast phenotype expression. Cell proliferation rate on HAPEX was demonstrated by an increase in DNA content with time. A high tritiated thymidine ([3H]-TdR) incorporation/DNA rate was observed on day 1 for HAPEX, indicating a stimulatory effect on cell proliferation. The alkaline phosphatase (ALP) activity was expressed earlier on HAPEX than on unfilled PE and increased with time, indicating that HOB cells had commenced differentiation. Furthermore, it was found that the HA particles in the composite provided favourable sites for cell attachment. It appears that the presence of HA particles in HAPEX may have the advantage of acting as microanchors for bone bonding in vivo.

Journal Article↗
PubMed1997

Influence of Ringer's solution on creep resistance of hydroxyapatite reinforced polyethylene composites.

In vitro creep studies of polyethylene, both unfilled and filled with hydroxyapatite at 0.20 and 0.40 volume fraction, have been performed. The samples were immersed in Ringer's solution at 37 degrees C for 1, 7, 30, 90 and 150 days prior to isochronous and creep tests in the same condition. The creep properties of unfilled polyethylene is unaffected by the immersion, but the isochronous modulus and the creep resistance of filled polyethylene were reduced. The effect increased with increasing volume fraction and time of immersion. This reduction is related to the penetration of the solution into the material, softening the interface.

Journal Article↗
PubMed1996

Stress and strain distribution within the intact femur: compression or bending?

The aim of this research was to test the hypothesis that the intact femur is loaded predominately in compression. The study was composed of two parts: a finite element analysis of the intact femur to assess if a compressive stress distribution could be achieved in the diaphyseal region of the femur using physiological muscle and joint contact forces; a simple radiological study to assess the in vivo deflections of the femur during one legged stance. The results of this investigation strongly support the hypothesis that the femur is loaded primarily in compression, and not bending as previously thought. The finite element analysis demonstrated that a compressive stress distribution in the diaphyseal femur can be achieved, producing a stress distribution which appears to be consistent with the femoral cross-sectional geometry. The finite element analysis also predicted that for a compressive load case there would be negligible deflections of the femoral head. The radiological study confirmed this, with no measurable in vivo deflection of the femur occurring during one legged stance.

Adult↗
PubMed1995

Cancellous bone stresses surrounding the femoral component of a hip prosthesis: an elastic-plastic finite element analysis.

The cancellous bone stresses surrounding the femoral component of total hip replacement were investigated using the finite element method. Four versions of a certain femoral hip prosthesis (the Freeman, Corin Medical), cemented, HA coated, press-fit, and press-fit with ridges were analysed. Each model was subjected to two separate load cases with the cancellous bone modelled as an elastic perfectly plastic material. The effect of bone quality was investigated by varying the cancellous bone stiffness. The resulting cancellous bone stress distributions were compared to that of the intact femur. The results were also compared to clinical subsidence data (published elsewhere) for the Freeman femoral prosthesis to determine if the initial cancellous bone stress distribution could be used to predict the migration of the various versions of this prosthesis. The results showed that the press-fit designs of prosthesis generated substantially higher cancellous bone stresses than the cemented and HA coated designs, and that these stresses were up to 6.5 times higher than found in the intact femur. For all forms of fixation the cancellous bone stress distribution was found to be insensitive to changes in the trabecular bone stiffness: thus poor quality cancellous bone is more likely to promote 'plastic' deformation, and therefore subsidence of the prosthesis. Comparison with the clinical migration data showed a good correlation and revealed that it may be possible to use the calculated initial cancellous bone stresses to predict the migration of the implant, and hence the probability of early and mid-term aseptic loosening.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗
PubMed1995

Is stem length important in uncemented endoprostheses?

In an uncemented total hip replacement where the femoral stem is thinner than the medullary canal it may be hypothesized that the distal portion of the stem has no mechanical function. In this study an uncemented total hip replacement has been modelled mathematically using finite element analysis and mechanical tests of a similar system have been carried out loading implants in cadaveric proximal femora. Two implants have been tested mechanically; one with a full length stem and the second with the stem shortened, but three implants have been modelled with an additional intermediate length stem analysed. Additionally the finite element analysis has been done with a high neck resection and a standard level resection. The finite element model showed that the full length stem produced lower interface contact stress levels under the proximal neck, particularly when the nec was resected, and this was borne out by the mechanical testing.

Biomechanical Phenomena↗
PubMed1992

Factors affecting the strength of flexor tendon repair.

The effects of different thicknesses and configurations of core sutures were studied in human cadaveric flexor tendon repairs. Both straight and cyclic load tests were employed. To exploit the full strength of 4/0 suture material, the Kessler repair using four locked single knots would seem to be appropriate.

Biomechanical Phenomena↗
PubMed1990

Measurement of the density of trabecular bone.

Methods of assessing real and apparent trabecular bone density are discussed. A method of defatting trabecular bone using trichlorethylene in an ultrasound bath for 4 h followed by rehydration in distilled water under vacuum is described, and its effectiveness discussed.

Bone Density↗
PubMed1989

Torsional stability of the femoral component of hip arthroplasty. Response to an anteriorly applied load.

Torsional instability of femoral components has not received much attention, and is difficult to detect in conventional radiographs. To test this we designed a system to apply a load in an anteroposterior direction to the head of a femoral component, implanted into a cadaveric femur. Rotation within the bone was measured, using a purpose built transducer, with and without preservation of the neck, with and without cement, and with longitudinal ridges but no cement. The results show that torsional instability may be a problem in uncemented replacement. Preservation of the femoral neck and the use of a ridged prosthesis increases resistance to rotation. Rotational movements occurring in vivo during such activities as climbing stairs and rising from the seated position may contribute to mechanical loosening.

Biomechanical Phenomena↗
PubMedDate not supplied

Effect of morphological features and surface area of hydroxyapatite on the fatigue behavior of hydroxyapatite-polyethylene composites.

The effect of surface area and morphological features of filler particles on the fatigue behavior of hydroxyapatite-filled high-density polyethylene composites was studied. Composites containing 40 vol % filler were injection-molded into tensile bars, gamma-irradiated, and subjected to sinusoidal tensile fatigue at a frequency of 2 Hz. To simulate the physiological environment, the tests were conducted at 37 degrees C in saline. Results showed that properties such as secant modulus, cyclic energy dissipation, dynamic creep strain, hysteresis loops, and even fracture surfaces differ depending on the morphology and surface area of the fillers used.

Composite Resins↗
PubMedDate not supplied

Quantification of bone ingrowth within bone-derived porous hydroxyapatite implants of varying density.

Hydroxyapatite has been investigated for use in the osseous environment for over 20 years and the biocompatibility of the ceramic and its osseoconductive behavior is well established. Therefore, the use of porous hydroxyapatite for the repair of osseous defects seems promising with potential for complete penetration of osseous tissue and restoration of vascularity throughout the repair site. However, there have been few systematic studies of the effects of physical properties such as macropore size and pore connectivity on the rate and quality of bone integration within porous hydroxyapatite implants. This paper quantifies the early biological response to a well-characterized series of implants with uniform microstructure and phase composition, but differing macrostructures and demonstrates the dependence of the rate of osseointegration on the apparent density of porous hydroxyapatite as a function of pore connectivity. Furthermore, compression testing established that bony ingrowth has a strong reinforcing effect on porous hydroxyapatite implants, which is more pronounced in the lower density implants, as a result of a greater relative volume of bone ingrowth.

Journal Article↗