[The pulsed water jet for selective removal of bone cement during revision arthroplasty]. / Der gepulste Wasserstrahl zur selektiven Knochenzemententfernung in der Revisionsendoprothetik.

Conventional tools used in prosthetic revision surgery have a limited range of action within the narrow cement mantle. Water jet cutting technology permits tiny and precisely controlled cuts, and may therefore be an alternative method of bone cement removal. Our study compares the cutting performance on bone cement (PMMA) and bone of a pulsed water jet and a continuous water jet. The aim of the study was to establish whether selective removal of PMMA is possible. 55 bone specimens (bovine femora) and 32 specimens of PMMA were cut with a continuous and a pulsed water jet at different pressures (40 MPa, 60 MPa) and pulse frequencies (0Hz, 50Hz, 250Hz). To ensure comparability of the results, the depths of cut were related to the hydraulic power of that part of the jet actually impinging on the material. While for PMMA the power-related depth of cut increased significantly with the pulse frequency, this did not apply to bone. The cuts produced in bone were sharp-edged. Since PMMA is more brittle than bone, the water jet caused cracks that enlarged further until particles of bone broke away. Although selective removal of PMMA without doing damage to the bone was not possible at the investigated settings of the jet parameters, the results do show that a pulsed water jet can cut bone cement much more effectively than bone. This is an important advantage over conventional non-selective tools for the removal of bone cement.

Absence of surface roughness changes after insertion of one type of matte cemented femoral component during 2 to 15 years.

Theoretically, micromotion might occur even in stable cement-implant interface conditions. It was hypothesized that smoothing of the matte surfaces of femoral components because of abrasion or corrosion phenomena is a possible consequence of micromotion. Two new and 11 femoral components that were retrieved after 2 to 15 years of stable cement-implant interface conditions were inspected, investigated with light microscopy, and evaluated with surface roughness measurement by a profilometer. No surface changes were observed such as abrasion or corrosion phenomena except at the tip and the collar of the femoral components. The surface roughness was Ra = 1.0 and 1.1 micro m in the new femoral components and Ra (mean) = 0.96 micro m (range; 0.8-1.5 micro m) in the retrieved components. There was no correlation between time in situ and surface roughness as confirmed by regression analysis. These data suggest that significant micromotion was not present at the studied interface.