Biomedical subjects

A Spirakis

Publications and source records attributed to A Spirakis.

7 recordsLinked to original sources

PubMed1997

A three-dimensional finite analysis of adaptive remodelling in the proximal femur.

A finite element analysis of adaptive bone remodelling in the proximal femur is presented. The use of a three-dimensional model permits a realistic representation of femur geometry, and also allows the possibility of examining the effects of fully three-dimensional loading situations. The long-term pattern of remodelling shows a realistic evolution of density distribution, with a tendency towards a steady state, though the simplified load cases used to model gait are not sufficient to predict the formation of the cortical shell.

Adaptation, Physiological↗

PubMed1994

Do abnormal hemipelvic bone stresses contribute to loosening and migration of screw-threaded cups?

Excellent long-term results have been reported with the Charnley low-friction arthroplasty. Failure of the cemented acetabular component has been identified as a problem in the longer term, while cemented hip replacements in active young patients have exhibited a disconcerting incidence of early clinical or radiological failure. This resulted in the development of the cementless arthroplasty. Bone responds favourably to an optimal stress window and reacts dynamically to metal implants that have a greatly differing modulus of elasticity. This study represents a comparative qualitative analysis of the peri-acetabular hemipelvic stresses after loading two cementless (press-fit and screw-threaded) acetabular components inserted into identical bone models. A simplified model of the artificial hip joint was constructed and the very sensitive stress analysis technique of holographic interferometry was used for the investigation. Peri-acetabular stress concentrations were noted with the screw-threaded cup. This may predispose to bone resorption and it is suggested that these could be implicated in the migration of these cups described in published reports.

Cadaver↗

PubMed1994

Current thoughts on total hip replacement.

Opinion leaders in the field of total hip arthroplasty express antipodal views with bewildering frequency. New trends notwithstanding, Charnley low-friction arthroplasty has a record of outstanding success, and we should attempt to identify specific problems, and address these accordingly. Biological and biomechanical matching remain important and increased attention to meticulous cement technique should favourably improve the long-term performance of cemented implants. The concept of cementless replacement should not, however, be summarily discarded, particularly for the younger patient. The discovery of existing design limitations should lead to further development based on sound scientific research. In an era of exploding technology, cost-containment must remain a pragmatic reality in the provision of a health-care service to the community. At this stage we would recommend a cementless hip replacement for the very young, hybrid replacement (cemented stem, uncemented cup) for the middle-aged and a fully cemented replacement for the elderly.

Biocompatible Materials↗

PubMed1993

A 5-year profile of the incidence of total joint replacement in South Africa (1985-1989).

This survey was conducted to determine the number of total joint replacements (TJRs) carried out annually in South Africa from 1985 to 1989 and the number of surgeons performing these procedures. During this period there was a 28% increase in the number of TJRs performed annually with an average increase of 20% in total hip replacements and 40% in total knee replacements. The number of surgeons involved in joint replacement during the survey period decreased by 7% in state-subsidised institutions but increased by 57% in the private sector. This is reflected in the number of TJRs performed each year, which has remained static in the state institutions but exhibits a threefold increase in the private sector. This probably reflects a shift in emphasis in state health care policy.

Cementation↗

PubMed1992

Qualitative holographic study of hemi-pelvic deformation caused by loading different hip prostheses.

The dynamic biological response of bone can materially influence the longevity of artificial implants. This paper presents a series of in vitro experiments conducted on epoxy resin models of human hemi-pelves. Different commercially available acetabular components were implanted and used for the construction of simplified three-dimensional models of the artificial hip joint. Boundary conditions included simulation of muscle groups and femoral loading. Real-time holographic interferometry, a stress analysis technique permitting whole-field simultaneous inspection of deformation patterns, was used as the experimental method. The holographic interferograms were interpreted qualitatively rather than quantitatively. High stresses were identified in the hemi-pelvis and it is postulated that these stresses may be implicated in the mechanical pathogenesis of loosening. The observed changes in the detected stress levels could influence both future design of acetabular prostheses and surgical techniques.

Biomechanical Phenomena↗

PubMed1992

The effect of polymerization of methylmethacrylate on metal-backed and non-metal-backed acetabular components.

Aseptic loosening of the acetabular component has been identified as the main cause of failure of cemented total hip arthroplasty in the long term. Wear of the high-density polyethylene has been implicated as a major contributory factor to loosening. The etiology of wear is multifactorial. The exothermic phase of polymerization of polymethylmethacrylate is associated with a 5.9% volume expansion. Using double-exposure holographic interferometry, the authors examined the influence of polymerization of cement on the internal geometry of a metal-backed cup and two non-metal-backed cups (Charnley 22 mm, Muller 32 mm). The non-metal-backed cups exhibited marked heat concentration points and disrupted fringe patterns, indicating distortion of the internal geometry of the cup. In contradistinction, the metal-backed cup showed good heat dissipation and regular fringe patterns, indicating minimal internal distortion. The differences were not quantified but were visually dramatic. The authors believe this may be an important contributory factor to cup wear in cemented total hip arthroplasty.

Acetabulum↗

PubMed1989

Current status of total hip replacement. A review of biological and biomechanical factors.

Successful cemented total hip replacement represents one of the major advancements in orthopaedic surgery in recent years. However, clinical follow-up has revealed a disturbing incidence of loosening, particularly in the younger patient. Aspects of component design, materials and technique refinement considered important in improving long-term results are reviewed.

Biomechanical Phenomena↗