Bridgette D. Furman

Tibial Post Wear in Posterior-stabilized Knee Replacements is Design-dependent

Polyethylene tibial post wear in posterior-stabilized knee designs is a major problem. The Insall-Burstein II (IB PS II) reportedly has severe anterior wear of the post in retrieved implants. We hypothesized the more anterior placement in the IB PS II would be reflected in greater wear at the anterior face than the IB PS I. We examined 234 retrieved inserts using subjective scales to grade post damage and wear. Of the IB PS II inserts, 38% demonstrated severe wear compared with only 25% of IB PS I inserts. The most prevalent damage location for the IB PS II was the anterior face, whereas the IB PS I sustained wear mainly on the medial face. While the IB PS post was not designed to constrain posterior femoral displacement, our observations confirm contact in hyperextension or other paradoxic anterior tibial translation is common and design-dependent. Minimizing wear and damage through proper post placement and changes in implant design to anticipate contact on the anterior post should be considered for future posterior stabilized knee replacements. These changes cannot occur in isolation, however, because changes in post placement and design also depend on their relation to the shape and location of the tibial bearing surfaces.

Backside Wear in Modern Total Knee Designs

Although modularity affords various options to the orthopedic surgeon, these benefits come at a price. The unintended bearing surface between the back surface of the tibial insert and the metallic tray results in micromotion leading to polyethylene wear debris. The objective of this study was to examine the backside wear of tibial inserts from three modern total knee designs with very different locking mechanisms: Insall-Burstein II® (IB II®), Optetrak®, and Advance®. A random sample of 71 inserts were obtained from our institution’s retrieval collection and examined to assess the extent of wear, depth of wear, and wear damage modes. Patient records were also obtained to determine patient age, body mass index, length of implantation, and reason for revision. Modes of wear damage (abrasion, burnishing, scratching, delamination, third body debris, surface deformation, and pitting) were then scored in each zone from 0 to 3 (0 = 0%, 1 = 0–10%, 2 = 10–50%, and 3 = >50%). The depth of wear was subjectively identified as removal of manufacturing identification markings stamped onto the inferior surface of the polyethylene. Both Advance® and IB II® polyethylene inserts showed significantly higher scores for backside wear than the Optetrak® inserts. All IB II® and Advance® implants showed evidence of backside wear, whereas 17% (5 out of 30) of the retrieved Optetrak® implants had no observable wear. There were no significant differences when comparing the depth of wear score between designs. The locking mechanism greatly affects the propensity for wear and should be considered when choosing a knee implant system.

Nonconsolidated polyethylene particles and oxidation in Charnley acetabular cups.

Nonconsolidated particles of ultra high molecular weight polyethylene are believed to be defects that adversely can affect the wear performance of total joint prostheses. The present study was done to determine the number, size, and distribution of these particles and to determine if their presence correlated with wear performance, as well as with other clinical and implant parameters. Forty retrieved and 7 new, never-implanted acetabular components were examined using light microscopy on thin cross sections. Particles were found in 92% of retrieved components and in all the new components. Particles in the retrieved components were either randomly distributed (32 components) or banded (with particles localized in regions approximately 1 mm below the outer surface of the component). No correlations were found between the number or area of particles and the wear performance or any of the clinical or implant variables. The presence of particles in the new implants was found to correlate with the length of time since the components had been radiation sterilized. For retrieved components, the density (and, therefore, the level of oxidative degradation) was high in the areas of banded particles. For new components, the density was higher the longer the time since sterilization. Nonconsolidated polyethylene particles are prevalent in total replacements but their source and cause are unknown. The results of this study show that they do not appear to affect or correlate with the length of implantation of acetabular cups. However, they still may be expected to adversely affect performance in cases where large numbers of particles are banded together near articulating surfaces of high stress environments such as found in the knee.

Backside wear is low in retrieved modern, modular, and nonmodular acetabular liners.

Modern modular components with maximized conformity between liner and shell, improved locking mechanisms, and smooth inner surfaces should have less backside wear than first-generation modular designs. Also, nonmodular components should show no backside wear in vivo. We compared the backside wear of retrieved liners from nonmodular and modular components from first-generation and second-generation designs. We matched for time in situ, patient age and weight for nine retrieved Harris-Galante Type 1 liners, nine Harris-Galante Type 2 liners, nine Trilogy® liners, and nine Implex nonmodular liners. The backside of the liners was divided in quadrants, examined under a ×10 binocular loupe, and rated by a score of 0 (absence of wear) to 3 (severe backside wear) for a total ranging from 0 to 12. The average total backside wear score was 8.4 for the Harris-Galante Type 1 liner, 7.3 for the Harris-Galante Type 2 liner, 3.7 for the Trilogy® liner, and 2.3 for the Implex liner. We observed a significant reduction in the backside wear of modern modular and nonmodular acetabular components (Trilogy® and Implex) when compared with first-generation modular designs (Harris-Galante Types 1 and 2). Nonmodular acetabular cups had a low backside wear in vivo. Level of Evidence: Therapeutic study, Level III (retrospective comparative study). See the Guidelines for Authors for a complete description of levels of evidence.

Catastrophic failure of a conforming type of total knee replacement: a case report.

A case study is presented to illustrate the concept of femoral component failure secondary to polyethylene wear in a 67 year old man, 13 years after he had conforming type total knee replacements. This case illustrates the theory that this observed problem may be a leading cause of failure in conforming and noncon-forming total knee replacements in the future.

Therapeutic Opportunities to Prevent Post-Traumatic Arthritis: Lessons from the Natural History of Arthritis after Articular Fracture: Winner of the 2015 Ann Doner Vaughan Kappa Delta Award

An estimated 12% of patients seeking surgical intervention for symptomatic arthritis have an etiology of post‐traumatic arthritis (PTA). The onset of PTA is rapid in the setting of articular fracture (AF). The investigation began with development of a murine model of a closed AF that develops PTA. In the process of characterizing this model a technique was developed for assessing quantitative synovial fluid biomarker concentrations. The work began with observations of the natural history of PTA development in the C57BL/6 strain of mice. A species of mice (MRL/MpJ) was found that is protected from PTA after AF. Further work identified key differences between mouse strains that did and did not develop PTA. This knowledge led to an intervention based on anti‐cytokine (interleukin 1 receptor antagonist, (IL‐1Ra) delivery in the C57BL/6 strain of mice that successfully prevented PTA following AF. This success in preventing PTA in the murine model has elucidated several important clinical implications: 1) Pro‐inflammatory cytokines play an important role in the development of PTA after joint injury, 2) Pharmacologic intervention can lessen the severity of PTA after an AF, and 3) The murine AF model of joint injury provides a novel means of studying mechanisms of PTA development.

Therapeutic opportunities to prevent post-traumatic arthritis: Lessons from the natural history of arthritis after articular fracture: THERAPEUTIC OPPORTUNITIES TO PREVENT PTA

An estimated 12% of patients seeking surgical intervention for symptomatic arthritis have an etiology of post‐traumatic arthritis (PTA). The onset of PTA is rapid in the setting of articular fracture (AF). The investigation began with development of a murine model of a closed AF that develops PTA. In the process of characterizing this model a technique was developed for assessing quantitative synovial fluid biomarker concentrations. The work began with observations of the natural history of PTA development in the C57BL/6 strain of mice. A species of mice (MRL/MpJ) was found that is protected from PTA after AF. Further work identified key differences between mouse strains that did and did not develop PTA. This knowledge led to an intervention based on anti‐cytokine (interleukin 1 receptor antagonist, (IL‐1Ra) delivery in the C57BL/6 strain of mice that successfully prevented PTA following AF. This success in preventing PTA in the murine model has elucidated several important clinical implications: 1) Pro‐inflammatory cytokines play an important role in the development of PTA after joint injury, 2) Pharmacologic intervention can lessen the severity of PTA after an AF, and 3) The murine AF model of joint injury provides a novel means of studying mechanisms of PTA development.