Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains vii, 79 p. : ill. Includes abstract. Includes bibliographical references (p. 71-79).

As implant survival extends into the second and third decades focal osteolysis around cemented femoral components in total hip replacement is emerging as an important failure mechanism. Whilst the problem of focal osteolysis is well recognised, there are many aspects of its development which are poorly understood. The broad aim of this thesis is to try to provide some insights into how, why and where focal osteolysis develops around the cemented femoral component. There are broadly two sections to this thesis, chapters 2-5 present clinical and geometrical studies and chapters 6-10 a series of experimental studies. The aim of the first section was to establish what is observed in clinical practice, the aim of the second to try to explain these findings. A mid-term clinical study showed that focal osteolysis is more common with rough than polished stems that differed in no aspect other than their surface finish. Further studies established that focal osteolysis is probably always associated with defects in the cement mantle. These defects occur anteriorly at the mid-stem of the prosthesis and posteriorly at the component tip. The distribution of focal osteolysis and its strong association with cement mantle defects suggests the importance of the stemcement interface as a pathway for fluid and debris to reach the distal femur. However, at 15-25 years, osteolysis rarely develops with the polished Exeter stem even in the presence of confirmed defects in the cement mantle, suggesting that the stem seals the stem-cement interface against fluid and debris. In an attempt to explain the clinical findings a series of bench top experiments were undertaken. These studies showed that the behaviour of fluid and dye at the stemcement interface was significantly influenced by component surface finish. Bonded and debonded stem-cement interfaces of rough stems provided an incomplete barrier to fluid movement along this interface. In contrast, polished stems both bonded and debonded were able to provide a seal at the stem-cement interface. The seal at this interface was improved with component subsidence in the presence of rotational stability. It is believed that this thesis provides a rationale explanation for why focal osteolysis rarely develops around the Exeter stem in clinical practice. It also explains how, where, and why osteolysis develops around certain designs of cemented femoral components used in total hip replacement.

Thesis (MAppSc in Physiotherapy) -- University of South Australia, 1998

Thesis (MAppSc in Physiotherapy) -- University of South Australia, 1998

Thesis (MTech (Biomedical Sciences))--Cape Peninsula University of Technology, 2015. / Previous international studies have documented a marked variation in transfusion practice for Total Hip Replacement (THR) surgery. This is despite widespread dissemination of clinical guidelines for the use of blood products. The cost and potential wastage of blood products as well as concerns regarding patient care and outcomes are important drivers of optimal blood management. The aim of this study was to audit red cell product utilisation for THR surgeries at two tertiary referral hospitals.

Hip simulators are designed to reproduce the forces and motion patterns of normal walking. In vivo demands on total hip replacements, however, are varied and often more severe than normal walking conditions. It is these severe conditions that often lead to implant failure. This is clinically based research aimed at understanding some of the more severe conditions in hips and the effect that these have on the performance of the total hip replacement. The polyethylene liner can act as a pump in an acetabular component, forcing fluid and wear particles through the holes to the retroacetabular bone causing osteolysis. Ten patients were studied at revision surgery. Pressures were measured in retroacetabular osteolytic lesions while performing pumping manouvers with the hip. Two laboratory experiments were then designed to study pumping mechanisms in vitro. In patients with contained osteolytic lesions, fluid pressure fluctuations could be measured in the lesion in association with the pumping action. Patients with uncontained osteolytic lesions showed no such pressure fluctuations. In the laboratory we identified 3 distinct mechanisms whereby fluid can be pumped from the hip joint to the retroacetabular bone. These pumping effects could be mitigated by improved implant design. Loading of the femoral head against the edge of the acetabular component produces dramatically increased contact pressures particularly in hard-on-hard bearings. In an analysis of 16 retrieved ceramic-on-ceramic bearings we were able to characterise the mechanism of edge loading based on the pattern of edge loading wear on the bearing surface. Finally in a radiographic study of patients with squeaking ceramic-on-ceramic hips. Squeaking was found to be associated with acetabular component malposition. It seems that edge loading or impingement may be an associated factor in these cases.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xi, 95 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 85-92).

Total hip arthroplasty (THA) is a successful surgical technique that can be used for the effective treatment of fractured neck of femur, osteoarthritis, tumours, avascular necrosis, failed internal fixation, developmental dysplasia and rheumatoid arthritis. Revision surgery is necessary if loosening allows relative motion between the femoral stem and femur, causing pain and mechanical instability of the THA. The large number of revision operations undertaken each year as a result of implant failure emphasises the need for better biomechanical understanding of the femoral implant system. During 2001-02 in Australia 26,689 hip replacement operations were performed, with 3,710 of these being revision operations. The Exeter stem is the most commonly used cemented stem for primary and revision hip replacement in Australia. It is therefore very important to understand the mechanics of this clinically successful implant. Few studies have presented a through investigation into the mechanics of the Exeter stem from a fundamental perspective. To address these issues, mechanical and finite element (FE) methods were used to conduct experiments and numerical investigations into the mechanics of the Exeter stem. The femur geometry, for both the experimental and FE studies, was based upon the Sawbones model 3303 medium left third generation femur. The stem orientation for all specimens of the study was replicated from the orientation achieved by the senior surgeon implanting into the Sawbones femur. Test rigs were designed specifically to constrain the femur for the purposes of loading and stability measurements. The experimental investigation was used to investigate the torsional mechanical stability of the stem and to monitor this stability following periods of cyclic loading, using a resultant hip contact force, while monitoring the distal migration of the stem. The experimental investigation was also able to provide data for the validation of the finite element model. The resultant hip contact force was represented experimentally by a cyclic load of 1Hz applied to the head of the implant. The specimen was tested for four days. The loading regime for the initially implanted specimen involved the application of load for 6 hours a day, allowing the specimen to relax under no load for 18 hours a day. The mechanical stability of the initially implanted specimen was tested prior to the application of the cyclic load and immediately after the loading periods, prior to relaxation. Further tests were undertaken to assess the mechanical stability of the stem following the removal and reimplantation of the same stem without the use of additional bone cement (a procedure used surgically when only the acetabular component requires replacement). The reimplanted specimens were tested for a further two days following reimplantation. The six hours of loading for the reimplanted specimen was achieved using three, two hour loading periods. The stability of the reimplaned stem was assessed following each loading period. Initial studies found that the material properties of the Sawbones femurs were highly temperature dependent. If the temperature of the short glass fibre reinforced (SGFR) epoxy used for the cortical bone analogue was increased from room temperature to body temperature there was a reduction in the Young's modulus of up to 37 percent. This finding led to further investigation into the strain state of the femur for varus and neutral stem orientations to reduce femur failure during cyclic loading. The strains of the varus stem orientation were found to be higher than the strains of the neutral stem. The experiments investigating the mechanical stability under cyclic loading continued using the neutral stem orientation. For the neutral stem orientation it was found that there was no perceivable variation in the torsional stiffness of the initially implanted system during the cyclic loading period even though distal migration was observed. Torsional stiffness was observed to be compromised immediately after reimplantation. However, the torsional stiffness of the reimplanted specimen was recovered within the first two hour loading period. No perceivable variation in the torsional stiffness was observed between the initially implanted specimens and the reimplanted specimens following the first two hours of loading. The finite element model (FEM) found good agreement with the experimental investigation in terms of measured strain at two of three rosette positions and failure of the cortical bone. Trends for the stress-strain state of the stem showed good agreement with the clinical findings of failure and wear of the stem. The stress-strain state of the cement predicted the expected compressive and hoop stresses once debonding of the stem-cement interface had progressed. Strain on the surface of the femur was well predicted for pure torsional loading. The FEM has provided a valuable tool for future investigation of the effect of factors such as implant positioning on femoral component mechanics. The experimental and finite element models developed within the scope of this project have provided a powerful analysis tool for the investigation of the femoral component mechanics in THA. Application of the model to clinically relevant problems has given valuable insight into the mechanisms behind the success of this particular implant type. Models such as this will provide information on implant failure modes that will further lead to an increased implant life expectancy and a reduction in the number of revision operations performed.

Thesis (MAppSc in Physiotherapy)--University of South Australia, 1997