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Tag Archives: Biomet

Virtual Geometric Constraint of Total Knee Arthroplasty Designs: Addressing Patient Needs

Restoration of normal knee joint function through surgical reconstruction is dependent upon load sharing between the implant and surrounding ligamentous and other supporting structures. Pathological weakening or surgical excision of these structures imposes an increased dependency upon the implant for stability. In this context, functional stability is defined as the ability of femoral and tibial component geometry, acting in concert with surrounding soft tissues, to limit anterior-posterior (A-P), medial-lateral (M-L) and internal-external (I-E) motion within normal physiologic limits. To assist implant selection for addressing various patient needs to maintain a stable knee joint, the U.S. Food and Drug Administration (FDA) pre-clinical assessment for total knee arthroplasty (TKA) designs requires evidence of expected tibial-femoral interface constraint. The American Society for Testing and Materials (ASTM) suggests that this testing be performed in accordance with ASTM F1223-08, “Standard Test Methods for Determination of Total Knee Replacement Constraint”. While this document appears as a straightforward physical/mechanical test, it is increasingly difficult to perform due to the large number of predicate devices needed for comparison to new designs, resulting in a resource-demanding evaluation. A modern, virtual alternative to the physical ASTM F1223-08 test was developed to determine the geometric constraints of four contemporary TKA designs, representing three styles of constraint.

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The Influence of Contemporary Knee Design on High Flexion IV: A Kinematic Comparison with the Healthy Intact Knee

Although Total Knee Arthroplasty (TKA) surgery enjoys 90% of outcomes with good to excellent results, some patients are uncomfortable adjusting their gait to accommodate the new articulations inherent in many contemporary implant designs. Paradoxical motions, inclusive of anterior sliding and lateral pivot of the femur relative to the tibia are examples of aberrant TKA kinematics that are opposite of those observed in healthy intact knees. A computational kinematic simulator is employed in this study to quantify the motion of six posterior stabilized TKA designs during high flexion activity, allowing comparison to the motion of healthy intact knees.

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The Influence of Contemporary Knee Design on High Flexion III: A Kinematic Comparison with the Healthy Intact Knee

Although Total Knee Arthroplasty (TKA) surgery enjoys 90% of outcomes with good to excellent results, some patients are uncomfortable adjusting their gait to accommodate the new articulations inherent in many contemporary implant designs. Paradoxical motions, inclusive of anterior sliding and lateral pivot of the femur relative to the tibia are examples of aberrant TKA kinematics that are opposite of those observed in healthy intact knees. A computational kinematic simulator is employed in this study to quantify the motion of six posterior stabilized TKA designs during high flexion activity, allowing comparison to the motion of healthy intact knees.

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Preclinical Computational Models: Promise and Progress in Total Knee Arthroplasty Design

Clinicians, manufacturers and regulatory agencies share a common goal of having safe and effective total knee arthroplasty (TKA) products available in the global marketplace. Preclinical computational modeling of new, innovative knee designs allows dynamic visualization of anticipated in vivo performance during activities of daily living. Comparison is possible with established, clinically successful designs determining relative performance differences. This handout presents fluoroscopic and clinical range of motion evidence for a variety of fixed bearing knee designs, suggesting computational modeling can be predictive of in vivo performance. The modeling environment is extended to include mobile bearing designs and smaller patients, validated through comparison with an Asian clinical report. What emerges from these studies is the promise that preclinical computational modeling offers a first line tool for contemporary knee design.

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The Influence of Contemporary Knee Design on High Flexion II: A Kinematic Comparison with the Normal Knee

Although Total Knee Arthroplasty (TKA) surgery enjoys 90% of outcomes with good to excellent results, some patients have difficulty adjusting their gait to accommodate the new articulations inherent in contemporary implant designs. Paradoxical motions inclusive of anterior sliding and lateral pivot are examples of aberrant TKA kinematics. This paper compares the motion of six contemporary TKA designs with recent in-vivo kinematic data of the health un-operated knee through deep flexion by employing a computational kinematic simulator.

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The Influence of Contemporary Knee Design on High Flexion: A Kinematic Comparison with the Normal Knee

Although Total Knee Arthroplasty (TKA) surgery enjoys 90% of outcomes with good to excellent results, some patients have difficulty adjusting their gait to accommodate the new articulations inherent in contemporary implant designs. Paradoxical motions inclusive of anterior sliding and lateral pivot are examples of aberrant TKA kinematics. This handout describes the utilization of a computational kinematic simulator to compare the motion of six contemporary TKA designs with recent in-vivo kinematic data of the healthy unoperated knee through deep flexion.

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The Current State of Cervical and Lumbar Spinal Disc Arthroplasty

The growth of spinal implant and orthobiologic technologies over the last several years is increasing in tempo and fast approaching the US hip and knee markets in annual dollar sales. During this time, a number of start-up and established medical device manufacturers have focused increasing resources on solutions for spinal problems. The role of the orthopaedic and neurosurgeon in these enterprises as inventor, owner, and user has contributed to this march of progress. This handout describes a small (<1%), but increasingly visible, aspect of these advancing technologies, that of artificial disc replacement.

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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 Effects of Walking Gait on UHMWPE Damage in Unicompartmental Knee Systems: A Finite Element Study

There is increasing re-interest in the use of unicompartmental knee replacement as a remedy of choice for isolated compartment disease, although there is debate regarding its role as a temporizing or definitive procedure. The popularization of mini-incision surgery with claims of reduced pain, shorter hospitalization, more rapid rehabilitation, more normal knee function and decreased cost are positive arguments for the procedure. However, the damage observed in ultra-high molecular weight polyethylene (UHMWPE) component retrievals is the result of high cycle fatigue loads, which act on the polymer insert during daily ambulation and suggests a material limitation in their use. The study reveals the influence that four different modular unicompartmental knee design geometries have on stresses that are associated with abrasion and delamination of the polymer insert and suggests their efficacy in clinical use..

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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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