In vitro measurement of interface micromotion and crack in cemented total hip arthroplasty systems with different surface roughness

Abstract 

Background

Cemented stems with various surface roughnesses are used in total hip arthroplasty. However, it is not clear how the surface roughness of the stem affects the longevity of the implant. In this study, we investigated the effect of the stem roughness on the micromotion at the bone–cement and cement–implant interface and investigated cracks in the cement layer through in vitro measurement.

Methods

Stems with the same shape and material but with different surface roughness (polished with Ra=0.05μm and matte-finished with Ra=0.83μm) were tested to measure the interface micromotion using custom-made sensors. The stems were implanted in five paired cadaver femurs and cyclic loading was applied to the femoral head to measure the interface micromotion. After loading, we measured the crack length and calculated the crack length density at the cement layer.

Findings

The difference in the interface micromotion between the polished stem and the rough stem was not significant except at the distal region of the cement–bone interface. More cracks were found at the distal region of the polished stem than at the rough stem. The magnitude of the cement crack length density did not correlate with the interface micromotion.

Interpretation

The results showed that the difference in the roughness between the polished and matte finishes did not significantly affect the micromotion and crack of the interface. However, more cement wear particles were expected in the matte-finished stem.

Keywords: Surface roughness, Interface micromotion, Crack, Wear particle, Total hip arthroplasty