Deformation characteristics and eigenfrequencies of press-fit acetabular cups

Journal
Clinical biomechanics  
Volume
26
Issue
1
Start Page
46
End Page
51
Citation
Clinical Biomechanics 26 (1): 46-51 (2011)
Publisher DOI
10.1016/j.clinbiomech.2010.08.015
Scopus ID
2-s2.0-78650869172
Publisher
Elsevier
Background: Elastic deformation of press-fitted acetabular cups during implantation provides primary stability. Excessive deformation can lead to chipping or improper seating of ceramic inlays and is dictated by cup stiffness, which also affects its vibrational characteristics. Purpose was to investigate the influence of cup design on deformation during press-fitting and on vibration properties. Methods: Deformation of ten acetabular cups (with and without ceramic inlay) was tested for radial loads clinically occurring during press-fitting (0-2000 N). Eigenfrequencies were measured using experimental modal analysis and related to mass and stiffness. Findings: The first eigenfrequency of the shells varied greatly (4-9 kHz); insertion of inlays caused an increase (16-33 kHz). The range of shell stiffness was high (2.7-48.4 kN/mm), increasing due to inlay insertion (124.7-376.2 kN/mm). Stiffness and mass were sufficient predictors for eigenfrequencies (p < 0.001,R2 = 0.94). Interpretation: The cups investigated represent a large stiffness range. Lower cup stiffness can increase primary stability but jeopardize inlay seating, and a suitable balance must be achieved by the designer. Eigenfrequencies also decrease with decreasing stiffness but were all found to lie considerably above clinically observed squeaking frequencies, indicating that these cup designs play no predominant role in the squeaking phenomenon. The observed relation between eigenfrequencies and the quotient of stiffness and mass might be used in the development of new thin walled cup designs so that their contribution to system vibrations is prevented. Presently, surgeons should be aware of the deformation characteristics of cups in order to select a suitable press-fit magnitude.
Subjects
Acetabular cup
Ceramic
Deformation
Liner
Liner chipping
Liner seating
Modularity
DDC Class
610: Medicine, Health
620: Engineering