HXLPE acetabular liners were introduced to reduce wear-related complications in THA. However, post-irradiation thermal free radical stabilization can compromise mechanical properties, leave oxidation-prone residual free radicals, or both. Reports of mechanical failure of HXLPE acetabular liner rims raise concerns about thermal free radical stabilization and in vivo oxidization on implant properties. The purpose of this study is to explore the differences in the mechanical, physical and chemical properties of HXLPE acetabular liner rims after extended time in vivo between liners manufactured with different thermal free radical stabilization techniques. Remelted, single annealed and sequentially annealed retrieved HXLPE acetabular liners with in vivo times greater than 4.5 years were obtained from our implant retrieval laboratory. All retrieved liners underwent an identical sanitation and storage protocol. For mechanical testing, a total of 55 explants and 13 control liners were tested. Explant in vivo time ranged from 4.6 – 14 years and ex vivo time ranged from 0 – 11.6 years. Rim mechanical properties were tested by
Introduction. HXLPE acetabular liners were introduced to reduce wear-related complications in THA. However, post-irradiation thermal free radical stabilization can compromise mechanical properties, leave oxidation-prone residual free radicals, or both. Reports of mechanical failure of HXLPE acetabular liner rims raise concerns about thermal free radical stabilization and in vivo oxidization on implant properties. The purpose of this study is to explore the differences in the mechanical, physical and chemical properties of HXLPE acetabular liner rims after extended time in vivo between liners manufactured with different thermal free radical stabilization techniques. Material and Methods. Remelted, single annealed and sequentially annealed retrieved HXLPE acetabular liners with in vivo times greater than 4.5 years were obtained from our implant retrieval laboratory. All retrieved liners underwent an identical sanitation and storage protocol. For mechanical testing, a total of 55 explants and 13 control liners were tested. Explant in vivo time ranged from 4.6 – 14.0 years and ex vivo time ranged from 0 – 11.6 years. Rim mechanical properties were tested by
Introduction. HXLPE acetabular liners were introduced to reduce wear-related complications in THA. However, post-irradiation thermal free radical stabilization can compromise mechanical properties, leave oxidation-prone residual free radicals, or both. Reports of mechanical failure of HXLPE acetabular liner rims raise concerns about thermal free radical stabilization and in vivo oxidization on implant properties. The purpose of this study is to explore the differences in the mechanical, physical and chemical properties of HXLPE acetabular liner rims after extended time in vivo between liners manufactured with different thermal free radical stabilization techniques. Material and methods. Remelted, single annealed and sequentially annealed retrieved HXLPE acetabular liners with in vivo times greater than 4.5 years were obtained from our implant retrieval laboratory. All retrieved liners underwent an identical sanitation and storage protocol. For mechanical testing, a total of 55 explants and 13 control liners were tested. Explant in vivo time ranged from 4.6 – 14.0 years and ex vivo time ranged from 0 – 11.6 years. Rim mechanical properties were tested by
With information about a patient's bone mechanical properties orthopaedic operations could be optimised to reduce intra- and post-operative complications. However, there is currently no reliable method of measuring a patient's bone mechanical properties in vivo. We have previously investigated
Advanced glycation end-products (AGEs) are a post-translational modification of collagen that form spontaneously in the skeletal matrix due to the presence of reducing sugars, such as glucose. The accumulation of AGEs leads to collagen cross-linking, which adversely affects bone quality and has been shown to play a major role in fracture risk. Thus, intervening in the formation and accumulation of AGEs may be a viable means of protecting bone quality. An Objectives
Methods
Objectives.
Introduction. The increase in revision joint replacement surgery and fractures of bone around orthopaedic implants may be partly addressed by keeping bone healthy around orthopaedic implants by inserting implants with mechanical properties closer to the patient's bone properties. We do not currently have an accurate way of calculating a patient's bone mechanical properties. We therefore posed a simple question: can data derived from a micro-indenter be used to calculate bone stiffness?. Methods. We received ethical approval to retrieve femoral heads and necks from patients undergoing hip replacement surgery for research. Cortical bone from the medial calcar region of the femoral neck was cut into 3×3×6mm cuboid specimens using a diamond wafering blade. Micro-indentation testing was performed in the direction of loading of the bone using a MicroMaterials (MicroMaterials, UK) indenter, using the high load micro-indentation stage (see Figure 1). To simulate in vivo testing, the samples were kept hydrated and were not fixed or polished. From the unloading curve after indentation, the elastic modulus was calculated, using the Oliver-Pharr method using the indentation machine software. To assess which
The increase in revision joint replacement surgery and fractures of bone around orthopaedic implants may be partly addressed by keeping bone healthy around orthopaedic implants by inserting implants with mechanical properties closer to the patient's bone properties. We do not currently have an accurate way of calculating a patient's bone mechanical properties. We are therefore investigating whether
Bone microhardness has been successfully correlated with important functional parameters such as mineralisation and stiffness. It provides a means of examining the mechanical competence of bone at a micron scale, averaging the effect of osteonal lamellae but sensitive to variation in mineral content within a bone, and, with careful selection of indentation site, able to obtain material characteristics separate from any effects of porosity. However, the effect of bone’s viscoelasticity on such measurements has been largely ignored. This preliminary study investigates the post-indentation size change of Vickers indentations on wet bone. 4 axial slices of bovine femur were harvested from the same shaft, and polished. Each sample was subjected to 4 sets of 10 Vickers indentations with a load of 50 g and holding period of 15 s. The indentation size was measured immediately after the load was removed, and then again at intervals for a period up to 24 hours after the indentation was made. To avoid dehydration, the bone stood in water during the indentation testing and during measurement, and between each measurement period it was fully immersed in water. Measured hardness significantly decreased with time, by approximately 30% in total. The rate of post-indentation recovery is difficult to analyse since the driving force of residual strain decreases as recovery takes place. However a simple exponential fit to the variation of HV with time in the form of H = H(final).(1−exp(−kt)) + H(initial) suggests that the size of the indentation tends towards a constant size between 5 and 24 hours after indentation. Thus we conclude that care should be taken when making “early” measurements given the rapid rate of change in indentation size. Caution should also be employed when interpreting such data.