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Tag Archives: Smith + Nephew

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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Highly Crosslinked Polyethylenes: Hopes vs. Realities

The enduring success of the low-friction arthroplasty first advanced by Sir John Charnley as a solution for severe hip arthritic problems may be appreciated from the fact that in 2003 more than 800,000 hip and knee arthroplasties were performed in the United States. The prevalence of aseptic loosening attributed to ultra-high molecular weight polyethylene (UHMWPE) debris-induced osteolysis has been in the single digits in most contemporary series, with some reports describing prostheses surviving for 20 to 30 years and represents the gold standard against which contemporary material improvements will be measured over time. Beginning in 1997, the FDA approved a series of UHMWPE’s with elevated crosslinking for use in prosthetic joints. Their stated benefit is to dramatically decrease the generation of UHMWPE wear debris, confirmation of which finds support in wear simulator reports for hip and knee components. The commercial adaptation of these new UHMWPE’s has been aggressively marketed particular to acetabular components well in advance of now emerging short-term clinical reports. What follows is a descriptor of the clinical evolution of UHMWPE bearing surfaces: the good, the bad and the hopeful.

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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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Highly Crosslinked Polyethylenes: Hopes vs. Realities

The enduring success of the low-friction arthroplasty first advanced by Sir John Charnley as a solution for severe hip arthritic problems may be appreciated from the fact that in 2003 more than 800,000 hip and knee arthroplasties were performed in the United States. The prevalence of aseptic loosening attributed to ultra-high molecular weight polyethylene (UHMWPE) debris-induced osteolysis has been in the single digits in most contemporary series, with some reports describing prostheses surviving for 20 to 30 years and represents the gold standard against which contemporary material improvements will be measured over time. Beginning in 1997, the FDA approved a series of UHMWPE’s with elevated crosslinking for use in prosthetic joints. Their stated benefit is to dramatically decrease the generation of UHMWPE wear debris, confirmation of which finds support in wear simulator reports for hip and knee components. The commercial adaptation of these new UHMWPE’s has been aggressively marketed particular to acetabular components well in advance of now emerging short-term clinical reports. What follows is a descriptor of the clinical evolution of UHMWPE bearing surfaces: the good, the bad and the hopeful.

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

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 have 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 evaluates the influence of antibiotic inclusion on the porosity, strength and fatigue life of six contemporary bone cements.

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New Polys for Old: Contribution or Caveat?

The enduring success of the low-friction arthroplasty first advanced by Sir John Charnley as a solution for severe hip arthritic problems may be appreciated from the fact that in 2001 more than 600,000 hip and knee arthroplasties were performed in the United States. The prevalence of aseptic loosening attributed to polyethylene debris-induced osteolysis has been in the single digits in most contemporary series, with some reports describing prostheses surviving for 20 to 30 years. Despite this obvious success, polyethylene debris is increasingly identified as the principle causative factor of bone loss and failure of TJA procedures. The conditions of occurrence, severity and clinical consequences suggest limitations on the in vivo integrity of contemporary arthroplasty designs. Material remedies inclusive of carbon reinforced polyethylene (Poly II), heat pressing and Hylamer with its variants have been advanced as alternatives with negative clinical results. Contemporary attempts to improve longevity (i.e., post-processing heat stabilization, peroxide additives and increased radiation with remelting) focus on the benefit of increased cross-linking while minimizing free radical creation. With increasing patient longevity and activity levels a search for the ultimate polymer is important. Variations on an already successful theme hope to lead to its optimization in this century. However, these “new polys” offer no direct clinical evidence to demonstrate their efficacy. It is known that reprocessing techniques will alter mechanical characteristics. Contemporary improvements in laboratory evaluative capabilities suggest significant reduction in component wear, but past experiences, in these regards, have not always predicted their clinical viability.

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New Polys for Old: Contribution or Caveat?

The enduring success of the low-friction arthroplasty first advanced by Sir John Charnley as a solution for severe hip arthritic problems may be appreciated from the fact that in 2000 more than 600,000 hip and knee arthroplasties were performed in the United States. The prevalence of aseptic loosening attributed to polyethylene debris-induced osteolysis has been in the single digits for most contemporary series, with some reports describing prostheses surviving for 20 to 30 years. Despite this obvious success, polyethylene debris is increasingly identified as the principle causative factor of bone loss and failure of TJA procedures. The conditions of occurrence, severity and clinical consequences suggest limitations on the in vivo integrity of contemporary arthroplasty designs. Material remedies inclusive of carbon reinforced polyethylene (Poly II), heat pressing and Hylamer with its variants have been advanced as alternatives with negative clinical results. Contemporary attempts to improve longevity (i.e., post-processing heat stabilization, peroxide additives and increased radiation with remelting) focus on the benefit of increased cross-linking while minimizing free radical creation. With increasing patient longevity and activity levels a search for the ultimate polymer is important. Variations on an already successful theme hope to lead to its optimization in this century. However, these “new polys” offer no direct clinical evidence to demonstrate their efficacy. It is known that reprocessing techniques will alter mechanical characteristics. Contemporary improvements in laboratory evaluative capabilities suggest significant reduction in component wear, but past experiences, in these regards, have not always predicted their clinical viability.

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Alternative Bearing Surfaces: The Good, Bad & Ugly

The enduring success of the low-friction arthroplasty advanced by Sir John 2000, more than 270,000 hip arthroplasties were performed in the United States. Over the last three decades, patient profiles have changed substantially, resulting in demands for a greater service life of ultra-high molecular weight polyethylene (UHMWPE) hip components. Material failure, often leading to an osteolytic response, is increasingly associated with younger, more active patients. In this context, the low-friction solution has become a problem, limiting in vivo system longevity and initiated a reexamination of alternative bearing surfaces. This presentation summarizes current clinical solutions to long-term bearing articulation involving metal-polyethylene, metal-metal, ceramic-polyethylene and ceramic-ceramic alternatives. Clinical and laboratory evidences are presented which describe the efficacy and concerns of these bearing couples as well as their current availability through the FDA regulatory process.

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Classification of Mobile Bearing Knee Design: Mobility and Constraint

Restoration of normal knee joint function through surgical reconstruction is dependent upon load sharing between the implant and surrounding soft tissue structures. Mobile bearing knee designs offer the advantage of maximum conformal geometry while diminishing constraint forces to fixation interfaces through plateau mobility. The degree of mobility afforded by these designs in the anterior-posterior, medial-lateral and rotational directions defines the required interaction between soft tissue and design geometry to maintain a stable articulation. This study characterizes nine, contemporary mobile bearing knee designs in terms of the force generated during a prescribed displacement.

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Alternative Bearing Surfaces: The Good, Bad & Ugly

The enduring success of the low friction arthroplasty advanced by Sir John Charnley as a solution for hip problems may be appreciated by the fact that in 1999, over 270,000 hip arthroplasties were performed in the United States. Over the last three decades, patient profiles have substantially changed resulting in a greater service life demand on UHMWPE hip components. Material failure, often leading to osteolytic response is increasingly associated with younger, more active patients. In this context, the low friction solution has become a problem limiting in vivo system longevity and initiated a reexamination of alternative bearing surfaces. This presentation summarizes current clinical solutions to long-term bearing articulation involving metal-polyethylene, metal-metal, ceramic-polyethylene and ceramic-ceramic alternatives. Clinical and laboratory evidences are presented which describe the efficacy and concerns of these bearing couples as well as their current availability through the FDA regulatory process.

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