The effect of design on wear of posterior stabilized knee replacements: A study of contemporary designs

Mentor

Steven Haas, MD

Scope

Polyethylene wear is ubiquitous on the tibial constraint posts of retrieved posterior stabilized (PS) knee implants, suggesting that post wear is a significant source for wear debris.

A recent study performed in our lab found a significant difference in location of post wear between two very similar designs that had only subtle differences in post location and height. Based on these results, the question arises as to the influence of post design on other contemporary knee implants and specifically how trade-offs in post design and location made to improve function might also increase wear and damage. Therefore, we will examine the effect of design on tibial post wear of three additional contemporary implants.

We aim to quantify the differences in design through solid models, thus determining differences in post location and height; we will also subjectively grade the extent of wear to the faces of the post. We currently have more than 320 PS tibial components in our ongoing IRB-approved implant retrieval system. All inserts will be examined for evidence of surface damage and wear to the post using established measurement criteria. Demographic data will be collected including age, weight, height, length of implantation, and reason for revision. Radiographic evaluation will also be performed to determine femoral varus-valgus angle, tibial angle, femoral component flexion-extension angle, and tibial posterior slope.

To determine if design changes have influenced wear damage to the post, the dominant wear locations between the retrieved inserts will be compared using the Fisher’s exact test, which assumes no ordering in severity based on location. Patient demographics, wear scores, and damage scores will be compared using Student’s t-test and Mann-Whitney test for ordinal data. Correlations will be determined using the Spearman rank correlation.

Student’s Role: The student will contribute to all aspects of the study including implant damage scoring, gathering of demographic and radiographic data, data and statistical analyses, and interpretation of the results. Time permitting, the student may also contribute to abstract and manuscript preparation.

Contact

Steven Haas, MD
email: haass@hss.edu