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Tag Archives: Howmedica

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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Posted in Knee| Tagged , , , |

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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Preclinical Computational Models: Predictors of Tibial Insert Damage Patterns in TKA

Manufacturers and regulatory agencies share a common goal of having safe and effective total knee arthroplasty (TKA) products available in the global marketplace. Several preclinical methods of testing TKA designs, inclusive of virtual computational models and physical laboratory wear simulations, are employed to predict polymer tibial insert damage patterns. However, the latter is criticized for poor clinical correlation, long testing times, large expense and the difficulty in providing meaningful comparisons with other clinically successful designs. This handout describes a computational modeling experience dating back 16 years for over 45 TKA designs where predicted polymer insert damage patterns have correlated well with physical contact area and stress measurements, laboratory wear simulation and clinical retrievals, suggesting an alternative pre-clinical pathway of evaluating these systems.

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Posted in Knee| Tagged , |

Tibial Plateau Abrasion in Mobile Bearing Knee Systems During Walking Gait II: A Finite Element Study

The abrasion observed in ultrahigh molecular weight polyethylene (UHMWPE) total knee arthroplasty component retrievals is the result of high cyclical loads, which act on the tibial plateau during daily ambulation. This dynamic process influences in vivo component longevity and is dependent on the magnitude and distribution of contact stresses on the tibial plateau. Mobile bearing knee systems offer increased component conformity over their fixed plateau counterparts and thus diminish the magnitudes of these contact stresses. This study reveals the contact areas and stresses that are associated with tibial plateau abrasion in four mobile bearing knee designs during three highly loaded points in the walking gait cycle, 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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