Abstract
INTRODUCTION
The cement quantity and distribution within femoral hip resurfacings are important for implant survival. Too much cement could cause thermal bone necrosis during polymerisation. Insufficient cement and cement-implant interfacial gaps might favour mechanical loosening. Exposed cancellous bone within the implant, might facilitate debris-induced osteolysis. This study assessed the impact of the cementing technique on the cement mantle quality in hip resurfacing.
METHODS
We prepared 60 bovine condyles for a 46 mm ReCap (Biomet) resurfacing and cemented polymeric replicas of the original implant using five different techniques: low-viscosity cement filling half the implant with and without suction (LVF+/−S), medium-viscosity cement spread inside the implant (MVF), medium-viscosity cement packed on bone (Packing) and a combination of both last techniques (Comb.). Half the specimens had six anchoring holes. Specimens were CT-scanned and analyzed with validated segmentation software [1].
We assessed, with an analysis of covariance, the effect of the cementing technique (fixed factor), the presence of anchoring holes (fixed factor) and the bone density (covariate) on the cement mantle quality.
RESULTS
In contrast to both fixed factors, bone density had no significant effect on the cement mantle quality. Both LVF techniques, created a heterogeneous cement mantle with large quantities of cement especially in the dome of the implant (Fig. 1 & 2). Large areas of uncovered cancellous bone were found at the base (Fig. 2). Suction had no major effect. The MVF technique allowed a better control of the cement quantity (Fig. 1) but cement mantle heterogeneity and exposed cancellous bone distally persisted. With the combined technique, large cement quantities were found within the implant (Fig. 1), the cement mantle remained heterogeneous but the amount of uncovered bone distally decreased. Cement packing controlled the cement quantity and distribution within the implant best (Fig. 1 & 2). However, interfacial gaps [2] covered 10% of the proximal cement-implant interface and exposed bone distally could not be prevented (Fig. 2).
When large quantities of cement were available (LVF+/−S and Comb.), anchoring holes allowed even more cement to be pressurised into the cancellous bone (Fig. 1).
DISCUSSION & CONCLUSIONS
During implantation with a filling technique (LVF+/−S, MVF & Comb.), cement inside the implant was scraped along the reamed head and forced to accumulate proximally. This overfilled the dome and left bone exposed at the base. During cement packing, the air-filled implant scraped excessive cement from the reamed head. This resulted in the thinnest, most homogeneous cement mantle and avoided overfilling. However, air got trapped below the implant and formed interfacial gaps. Anchoring holes in cancellous bone of the reamed head should be avoided to prevent overfilling the reamed head with cement.
