CORA ABSTRACT #II -2

Bonding strength between PMMA (polymethylmethacrylate) and Machined Pin Stems (CoCr) as a function of insertion time

R. Korley

J. MacKenzie

R. Gill

Objective:

1. To compare the bond strength at the PMMA/Pin stem interface at two different insertion times
2. To compare the bond strength at the PMMA/Pin stem interface with three different stem surface finishes, polished, non-polished and precoat (PMMA), at two different insertion times

Design: Basic science experimental study

Setting: McCaig Centre for Joint Injury and Arthritis Research and Faculty of Mechanical Engineering, University of Calgary

Materials: CoCr machined pins with three different surface finishes, PMMA cement, Aluminum moulds, MTS machine

Methods: Cement was mixed as individual batches in a standard fashion for 90 seconds following which half of each batch was poured into two identical aluminum moulds. CoCr machined pins of similar surface finish were then inserted by hand at four and eight minutes following mixing. The cement hardened and the pins were removed with the cement from the moulds. After 24 hours of curing at 37ƒ, the pins were pulled out using an MTS machine and the force was recorded in Newtons (N). Data was analyzed using Factorial analysis of variance.

Outcome Measure(s): Pullout force (Newtons) using an MTS machine.

Results: There was no difference in pullout strength between polished and non-polished stems at four and eight minutes. There was a significant difference in pullout strength between PMMA coated and polished/non-polished stems at four and eight minutes. There was also a significant difference in pullout strength at four and eight minutes in the PMMA coated stems.

Conclusions: Bond strength of PMMA coated stems does vary as a function of insertion time. Therefore surgeons should consider cementing earlier when using this surface in order to enhance the initial bond strength at the prosthesis/cement interface.