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Tag Archives: DePuy

High Flexion in Contemporary Total Knee Design: A Precursor of UHMWPE Damage? A Finite Element Study

The success of total knee arthroplasty has contributed to its widening application to a younger, more active patient population whose daily regimen includes more demanding high flexion activities. Worldwide expansion to Middle Eastern and Asian populations, where the attainment of high knee joint flexion is often a cultural requirement, has been steadily increasing in recent years. This in turn has led to design changes in contemporary polyethylene tibial inserts which accommodate these increased flexion ranges. This study reveals the contact areas and stresses that are associated with polymer insert abrasion and subsurface delamination for four contemporary total knee designs during the most highly loaded portions of three different high flexion activities, and suggests their efficacy in clinical use.

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Posted in Knee| Tagged , , , , |

Enhanced Cross-Linked Polyethylene Modular Acetabular Designs: Performance Characteristics

Modular acetabular designs enjoy widespread use in THA procedures. Their mechanical performance has continually increased through improved locking mechanism assemblies. Recently, a number of enhanced cross-linked polyethylenes have emerged whose commonly heralded benefit is a reduction in polymer wear due to increased cross-linking concurrent with minimized oxidation. These processes, however, change the chemical structure of the polymer affecting both static mechanical and fatigue properties, including a decrease in the resistance to crack propagation. This has significant ramification on the long-term clinical integrity of modular acetabular components where enhanced cross-linked polyethylenes are employed and reduced liner thicknesses are advocated. This study evaluated the locking mechanism integrity for three, contemporary, modular acetabular designs, which employ both conventional and enhanced cross-linked polyethylene liners.

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Fracture of Highly Crosslinked UHMWPE Acetabular Liners

Four well-placed crosslinked UHMPWE acetabular liners of distinct design were retrieved subsequent to fracture failure of the rim. In each case, electron microscopy of the fracture surface revealed fatigue initiation markings associated with a stress concentrating feature in the rim. Fracture surface investigation demonstrated that crack propagation in all cases followed contours of tensile stresses. FEA simulations were performed to examine whether direct rim loading could be the cause of the observed failures.

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Posted in Hip| Tagged , , |

High Flexion in Contemporary Total Knee Design: A Precursor of UHMWPE Damage? A Finite Element Study

The success of total knee arthroplasty has contributed to its widening application to a younger, more active patient population who daily regimen includes more demanding high flexion activities. Worldwide expansion to Middle Eastern and Asian populations, where the attainment of high knee joint flexion is often a cultural requirement, has been steadily increasing in recent years. This study reveals the contact areas and stresses that are associated with polymer insert abrasion in four total knee designs during the most highly loaded portions of three different high flexion activities, and suggests their efficacy in clinical use.

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Posted in Knee| Tagged , , , |

The Influence of Antibiotics on the Fatigue Life of Acrylic Bone Cement: Assuring Clinical Structural Integrity

Aseptic loosening attributed to cement fracture and the subsequent disruption of fixation interfaces remains a major long-term failure mode of cemented arthroplasty. Knowledge of the fracture strength of bone cement, especially in fatigue, is an important indicator of cement integrity and the potential for fixation failure. In current practice, orthopaedic surgeons may choose to utilize antibiotics in bone cement for prophylaxis or treatment of a known infection. However, the antibiotics, bone cements and mixing methodologies employed lead to variability in the quality of the end product. To date, several orthopaedic manufacturers received Food and Drug Administration (FDA) 510[k] clearance for their pre-packaged antibiotic-loaded bone cement for use in the second stage of a two-stage revision situation where the initial infection has been cleared. This availability provides a more uniform cement mix with known mechanical and elution characteristics at the 0.5 to 1.0g level of antibiotic per 40g of polymer powder. This study evaluated the influence of antibiotic inclusion on the porosity, strength and fatigue life of six contemporary bone cements.

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Patello-Femoral Replacement Polymer Stress During Daily Activities: A Finite Element Study

Isolated, patello-femoral arthritis, although uncommon, has been reported to affect 8% of women and 2% of men over the age of 55. Both conservative and surgical non-arthroplasty interventions have been advocated, however, their reports suggest limited success. Patello-femoral replacement designs as a solution alternative are beginning to re-emerge largely through an appreciation of design requirements and the importance of component placement, which have been major factors in earlier clinical disappointments. This study reveals the influence that three different patello-femoral implant design geometries have on stresses that are associated with polymer abrasion and delamination and suggests their efficacy in clinical use.

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The Influence of Antibiotics on the Fatigue Life of Acrylic Bone Cement: Assuring Clinical Structural Integrity

Aseptic loosening attributed to cement fracture and the subsequent disruption of fixation interfaces remains a major long-term failure mode of cemented arthroplasty. Knowledge of the fracture strength of bone cement, especially in fatigue, is an important indicator of cement integrity and the potential for fixation failure. In current practice, orthopaedic surgeons may choose to utilize antibiotics in bone cement for prophylaxis or treatment of a known infection. However, the antibiotics, bone cements and mixing methodologies employed lead to variability in the quality of the end product. To date, several orthopaedic manufacturers received Food and Drug Administration (FDA) 510[k] clearance for their pre-packaged antibiotic-loaded bone cement for use in the second stage of a two-stage revision situation where the initial infection has been cleared. This availability provides a more uniform cement mix with known mechanical and elution characteristics at the 0.5 to 1.0g level of antibiotic per 40g of polymer powder. This study evaluated the influence of antibiotic inclusion on the porosity, strength and fatigue life of six contemporary bone cements..

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Polymer Insert Stress in Total Knee Designs During High Flexion Activities: A Finite Element Study

The success of total knee arthroplasty has contributed to its widening application to a younger, more active patient population who daily regimen includes more demanding high flexion activities. Worldwide expansion to Middle Eastern and Asian populations, where the attainment of high knee joint flexion is often a cultural requirement, has been steadily increasing in recent years. This study reveals the contact areas and stresses that are associated with polymer insert abrasion in four total knee designs during the most highly loaded portions of three different high flexion activities, and suggests their efficacy in clinical use.

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Posted in Knee| Tagged , , , |