Imperial College London


Faculty of EngineeringDepartment of Mechanical Engineering

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6 results found

Alidousti H, Bressloff NW, 2017, The implication of the osteolysis threshold and interfacial gaps on periprosthetic osteolysis in cementless total hip replacement., J Biomech, Vol: 58, Pages: 1-10

Osteolysis around joint replacements may develop due to migration of wear particles from the joint space into gaps between the interface bone and the implant where they can accumulate in high concentrations to cause tissue damage. Osteolysis may appear in various postoperative times and morphological shapes which can be generalized into linear and focal. However, there are no clear explanations on the causes of such variations. Patients' degree of sensitivity to polyethylene particles (osteolysis thresholds), the local particle concentration and the access route provided by the interface gaps have been described as determining factors. To study their effects, a 2D computational fluid dynamics model of the hip joint capsule in communication with an interfacial gap and the surrounding bone was employed. Particles were presented using a discrete phase model (DPM). High capsular fluid pressure was considered as the driving force for particle migration. Simulations were run for different osteolysis thresholds ranging from 5×108 to 1×1012 particle number per gram of tissue and fibrous tissue generation in osteolytic lesion due to particles was simulated for the equivalent of ten postoperative years. In patients less sensitive to polyethylene particles (higher threshold), osteolysis may be linear and occur along an interfacial gap in less than 5% of the interfacial tissue. Focal osteolysis is more likely to develop in patients with higher sensitivity to polyethylene particles at distal regions to an interfacial gaps where up to 80% of the interfacial tissue may be replaced by fibrous tissue. In these patients, signs of osteolysis may also develop earlier (third postoperative year) than those with less sensitivity who may show very minor signs even after ten years. This study shows the importance of patient sensitivity to wear particles, the role of interfacial gaps in relation to morphology and the onset of osteolysis. Consequently, it may explain the clinicall

Journal article

Alidousti H, Bressloff NW, 2017, The implication of the osteolysis threshold and interfacial gaps on periprosthetic osteolysis in cementless total hip replacement, JOURNAL OF BIOMECHANICS, Vol: 58, Pages: 1-10, ISSN: 0021-9290

Journal article

Alidousti H, Giles J, Emery R, Jeffers Jet al., 2017, Spatial mapping of humeral head bone density, Journal of Shoulder and Elbow Surgery, Vol: 26, Pages: 1653-1661, ISSN: 1532-6500

Background: Short stem humeral replacements achieve fixation by anchoring to the metaphyseal trabecular bone. Fixing the implant in high density bone can provide strong fixation and reduce the risk of loosening. However, there is a lack of data mapping the bone density distribution in the proximal humerus. The aim of the study was to investigate the bone density in proximal humerus. Methods: Eight CT scans of healthy cadaveric humeri were used to map bone density distribution in the humeral head. The proximal humeral head was divided into twelve slices parallel to the humeral anatomical neck. Each slice was then divided into four concentric circles. The slices below the anatomical neck, where short stem implants have their fixation features, were further divided into radial sectors. The average bone density for each of these regions was calculated and regions of interest were compared using a repeated measures ANOVA with significance set at p<0.05.Results: Average apparent bone density was found to decrease from proximal to distal regions with the majority of higher bone density proximal to the anatomical neck of the humerus (p<0.05). Below the anatomical neck, bone density increases from central to peripheral regions where cortical bone eventually occupies the space (p<0.05). In distal slices below the anatomical neck, a higher bone density distribution in the medial calcar region was also observed.Conclusion: This study indicates that it is advantageous with respect to implant fixation to preserve some bone above the anatomical neck and epiphyseal plate, and to use the denser bone at the periphery.

Journal article

Alidousti H, Taylor M, Bressloff NW, 2014, Periprosthetic wear particle migration and distribution modelling and the implication for osteolysis in cementless total hip replacement, Journal of the Mechanical Behavior of Biomedical Materials, Vol: 32, Pages: 225-244

In total hip replacement (THR), wear particles play a significant role in osteolysis and have been observed in locations as remote as the tip of femoral stem. However, there is no clear understanding of the factors and mechanisms causing, or contributing to particle migration to the periprosthetic tissue. Interfacial gaps provide a route for particle laden joint fluid to transport wear particles to the periprosthetic tissue and cause osteolysis. It is likely that capsular pressure, gap dimensions and micromotion of the gap during cyclic loading of an implant, play defining roles to facilitate particle migration. In order to obtain a better understanding of the above mechanisms and factors, transient two-dimensional computational fluid dynamic simulations have been performed for the flow in the lateral side of a cementless stem-femur system including the joint capsule, a gap in communication with the capsule and the surrounding bone. A discrete phase model to describe particle motion has been employed. Key findings from these simulations include: (1) Particles were shown to enter the periprosthetic tissue along the entire length of the gap but with higher concentrations at both proximal and distal ends of the gap and a maximum rate of particle accumulation in the distal regions.(2) High capsular pressure, rather than gap micromotion, has been shown to be the main driving force for particle migration to periprosthetic tissue.(3) Implant micromotion was shown to pump out rather than draw in particles to the interfacial gaps.(4) Particle concentrations are consistent with known distributions of (i) focal osteolysis at the distal end of the gap and (ii) linear osteolysis along the entire gap length.

Journal article

Alidousti H, Taylor M, Bressloff NW, 2013, Do Capsular Pressure and Implant Motion Interact to Cause High Pressure in the Periprosthetic Bone in Total Hip Replacement? Podium presentation, Orthopaedic Research Society (ORS) Annual Meeting. February 2012, San Francisco.

Conference paper

Alidousti H, Taylor M, Bressloff NW, 2011, Do Capsular Pressure and Implant Motion Interact to Cause High Pressure in the Periprosthetic Bone in Total Hip Replacement?, JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME, Vol: 133, ISSN: 0148-0731

Journal article

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