RESUMO
BACKGROUND: The cement mantle within a hip resurfacing head is important for implant survival. Too much cement leads to thermal bone necrosis, whereas not enough cement might cause mechanical failure and particle-induced osteolysis. We evaluated the impact of different cementing techniques on the quality of the cement mantle in hip resurfacing. METHODS: Sixty bovine condyles were prepared to fit a size-46 ReCap (Biomet) implant and divided into five groups of twelve specimens each. In two of the groups, a polymeric replica was filled halfway with low-viscosity cement; suction was employed in one of those groups and not used in the other. Medium-viscosity cement was used in the remaining three groups: it was spread out within the implant in one group, it was packed on the bone in another, and a combination of those techniques was used in the third. Half of the sixty specimens had six anchoring holes. The specimens underwent computed tomography and were analyzed with custom-made segmentation software. RESULTS: The cementing technique and anchoring holes influenced the cement quantity within the implant and the thickness of the cement mantle; suction and bone density did not. Both filling techniques involving the use of low-viscosity cement resulted in excessive cement within the implant (filling index, 47.30% to 60.66%) and large cement defects at the base. The combined technique also resulted in large cement quantities (filling index, 46.62% to 54.12%) but fewer cement defects at the base. The filling technique involving the use of medium-viscosity cement decreased the cement quantity (filling index, 43.31% to 45.68%), but cement packing was the best technique (filling index, 29.20% to 31.05%), resulting in the thinnest, most homogeneous cement mantle. However, distal cement defects remained, and the prevalence of proximal cement-implant interfacial gaps was about 10%. CONCLUSIONS: The results of this experimental study cannot be extrapolated directly to the in vivo situation, and they apply only to implants with an inner geometry similar to that of the size-46 ReCap resurfacing head and to the cement brands that we used. None of the cementing techniques was "perfect." Both of the filling techniques involving use of low-viscosity cement and the combined technique resulted in excessive cement proximally. The filling technique involving use of medium-viscosity cement was promising, but the cement-packing technique offered the best opportunity to control the quality of the cement mantle. However, the presence of interfacial gaps raised new questions. We suggest that the use of anchoring holes in cancellous bone should be considered with caution in order to avoid overfilling with cement.
