Corrosion at the head-neck junction of total hip replacements is a poorly understood phenomenon with an incidence of 1 - 2 %. Concerns around taper junction corrosion have focused on design factors including changes in taper surface topography and geometry as well as operating conditions such as high bearing surface friction and fluid ingress-egress at the taper junction. Hence, this thesis considered 3 aspects of the head taper junction namely: (1) frictional torque at the bearing surface and below the taper junction for varying head sizes and bearing material combinations, (2) Cobalt and Chromium ion release from CoCr/Ti taper junctions, (3) FE analysis of tapers utilising variables including taper length, material, angle, and clearance under loading conditions representative of walking, hip simulator profiles and stair climb. Bearing friction and the torque about the taper axis beneath the taper junction were positively correlated with the head size (R2 = 0.57 bearing friction, R2 = 0.88 torque) and average surface roughness (Ra) (R2 = 0.66 bearing friction, R2=0.79 torque) of the femoral head. Torque generated on large MoP bearings (0.93 ± 0.2 Nm) was found to be comparable to MoM (0.81 Nm). The median cumulative Cr release rate was at least 2 times greater than that of Co (0.0220 ppb/cycle Cr relative to 0.0109 ppb/cycle Co) due to the acidic environment utilised in the accelerated tests. No statistically significant difference in ion release was found, between the trunnions of different surface finishes. Finite element analyses showed that the largest gaps generated at the mouth of the taper, were associated with smaller taper contact areas. Clearances within ±0.1° enabled the tapers to engage over comparable lengths and therefore did not show differences in taper opening, showing this was influenced by the taper engagement length rather than location (proximal or distal) of contact. Stair climb loading generated the largest taper gaps (80 m) and surface stresses on the head taper (1200 MPa); these were greatest on the shortest trunnion. Although the stair climb loading condition is not currently mandated in testing THR devices, its use could provide a more accurate prediction of taper performance in vivo and may be beneficial to 'beyond compliance' initiatives to improve implant performance.

A challenge in engineering coupling design is the understanding of performance of contact geometry for a given application. “Wear” is one of a number of mechanical failures that can occur in mechanical coupling design. “Fretting wear” occurs where surfaces in contact are subjected to oscillating load and very small relative motion over a period of time. Fretting has been observed in many mechanical interactions and is known to be a reason for failure in many designs. Recent evidence suggests that fretting wear occurs at the taper junction of modular total hip replacements and leads to failure of the implants. Experimental testing to determine the wear behaviour that occurs in mechanical devices is time consuming, expensive and complicated. Computational wear modelling is an alternative method which is faster and cheaper than real testing and can be used in addition to testing to help improve component design and enhance wear characteristics. Developing an algorithm that can accurately predict fretting wear considering linear wear, volumetric wear and surface wear damage is the main focus of this thesis. The thesis proposes a new computational methodology incorporating published wear laws into commercial finite element code to predict fretting wear which could occur at the taper junction of total hip replacements. The assessment of wear in this study is solely based on mechanical wear (fretting) as being the primary mechanism causing surface damage. The method is novel in that it simulates the weakening of the initial taper ‘fixation’ (created at impaction of the head onto the stem in surgery) due to the wearing process. The taper fixation is modelled using a contact analysis with overlapped meshes at the taper junction. The reduction in fixation is modelled by progressive removal of the overlap between components based on calculated wear depth and material loss. The method has been used for three different studies to determine surface wear damage, linear and volumetric wear rates that could occur at taper junction of total hip replacements over time. The results obtained are consistent with those found from observation and measurement of retrieved prostheses. The fretting wear analysis approach has been shown to model the evolution of wear effectively; however, it has been shown that accurate, quantitative values for wear are critically dependant on mesh refinement, wear fraction and scaling factor, wear coefficient used and knowledge of the device loading history. The numerical method presented could be used to consider the effect of design changes and clinical technique on subsequent fretting wear in modular prosthetic devices or other mechanically coupled designs.

Success of total hip replacements is well reported however, failures as a result of wear processes and the biological response to these products continue to challenge the orthopaedic community. Lately, corrosion of metal surfaces as well as wear particles have seen particular interest with elevated blood cobalt levels widely reported in patients receiving metal-on-metal (MoM) hip replacements. Some instances have also reported this in patients with metal-on-polyethylene (MoP) components and these corrosion products are believed to contribute to hypersensitivity reactions reported. This thesis considers wear and cobalt release in MoP and MoM hip bearings tested under standard and challenging hip simulator conditions and includes an exploration of novel bearing coatings to reduce cobalt release. The incorporation of silver into these coatings may be sufficient to produce an antibacterial response, reducing the risk of mid-term infections, another reported cause of failure. Polyethylene wear was low under standard and clinically relevant adverse conditions in 28mm and 52 mm diameter MoP bearings (less than 35 mm3/mc). Cobalt release was measurable in 28 mm diameter MoP bearings (51 ppb/mc) with higher levels produced in large 52 mm diameters (123 ppb/mc), the first time this has been reported, although cobalt release was substantially less than that observed in MoM bearings (6909 ppb/mc). Alumina abrasives introduced in the lubricant substantially damaged MoP bearings, increasing the cobalt release to 70,690 ppb after 1 mc, greater than found after edge loaded MoM bearings (19,240 ppb). The removal of these particles still produced elevated cobalt levels compared to standard conditions and increased polyethylene wear to 435 mm3/mc. A chromium nitride (CrN) coating in MoP bearings was resistant to this abrasive damage showing no delamination in the coating, with negligible cobalt released after 7.04 mc (153 ppb) and maintained a polyethylene wear rate below 20 mm3/mc. Silver CrN coatings on both bearing surfaces of MoM components prevented cobalt release under standard conditions, with silver release after 0.17 mc up to 3,720 ppb in high silver surface coatings, although the wear was relatively high (5.24 mm3/mc). A silver CrN coating with a low concentration of silver at the surface reduced wear and was resistant to 5 mc of edge loading. It generated 241 ppb of cobalt and maintained comparable steady state wear rates (0.65 mm3/mc) to the uncoated metal while releasing 18,786 ppb silver which may be sufficient to be an effective anti-microbial agent. These coatings may provide potential clinical benefits in MoP and MoM bearings by reducing both wear and cobalt release in ideal and adverse conditions. There may also be beneficial wear products in the form of silver, although further testing of optimised coatings is required.

The purpose of this study was to explore and describe the surgical nurses’ perceptions about the management of post-operative pain and strategies employed in management of pain in patients who have undergone total hip or knee replacement surgery in King Abdulaziz Medical City, Riyadh, Kingdom of Saudi Arabia. Qualitative, exploratory-descriptive research design was applied. Purposive nonprobability sampling was used and data collected by means of audio-recorded semistructured individual interviews. Data saturation was reached after interviewing twenty surgical nurses. Themes and categories emerged from adopting Creswell’s (2013) “data analysis spiral”. One of the key findings was that patients reportedly experience moderate to severe pain during the first three days after surgery, before it is controlled on mild to moderate levels or before the patient is pain free. Conclusions were drawn, and one of the major ones was that multimodal strategies are employed by the surgical to manage post-operative pain. Recommendations were also made from findings of this study, and one key recommendation was that expatriate nurses to have access to Arabic speakers to overcome language barriers. / Health Studies

The purpose of this study was to explore and describe the surgical nurses’ perceptions about the management of post-operative pain and strategies employed in management of pain in patients who have undergone total hip or knee replacement surgery in King Abdulaziz Medical City, Riyadh, Kingdom of Saudi Arabia. Qualitative, exploratory-descriptive research design was applied. Purposive nonprobability sampling was used and data collected by means of audio-recorded semistructured individual interviews. Data saturation was reached after interviewing twenty surgical nurses. Themes and categories emerged from adopting Creswell’s (2013) “data analysis spiral”. One of the key findings was that patients reportedly experience moderate to severe pain during the first three days after surgery, before it is controlled on mild to moderate levels or before the patient is pain free. Conclusions were drawn, and one of the major ones was that multimodal strategies are employed by the surgical to manage post-operative pain. Recommendations were also made from findings of this study, and one key recommendation was that expatriate nurses to have access to Arabic speakers to overcome language barriers. / Health Studies / M.A. (Health Studies)